Merge bitcoindevkit/bdk#1530: chore: fix clippy lints

8bf8c7d080194872188e1ab7a6f14c06b121e371 chore: fix clippy lints (Jose Storopoli)

Pull request description:

  ### Description

  Fix some clippy CI lints

  ### Notes to the reviewers

  More caught by the Nix CI in #1320.

  ### Changelog notice

  chore: clippy lints

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [ ] I've added tests for the new feature
  * [ ] I've added docs for the new feature

  #### Bugfixes:

  * [ ] This pull request breaks the existing API
  * [ ] I've added tests to reproduce the issue which are now passing
  * [ ] I'm linking the issue being fixed by this PR

ACKs for top commit:
  notmandatory:
    ACK 8bf8c7d080194872188e1ab7a6f14c06b121e371

Tree-SHA512: 6b53cb739e506d79106a2f42aa2b8fa28ef226543fbbf100225f10ed82257f6fd0218f09c0f1291803fbc9c1c88e32ba1c7e02fe3f601ccc9dc5be8a6efea6e1

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,26 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: 'bug'
+assignees: ''
+
+---
+
+**Describe the bug**  
+<!-- A clear and concise description of what the bug is. -->
+
+**To Reproduce**  
+<!-- Steps or code to reproduce the behavior. -->
+
+**Expected behavior**  
+<!-- A clear and concise description of what you expected to happen. -->
+
+**Build environment**  
+ - BDK tag/commit: <!-- e.g. v0.13.0, 3a07614 --> 
+ - OS+version: <!-- e.g. ubuntu 20.04.01, macOS 12.0.1, windows -->  
+ - Rust/Cargo version: <!-- e.g. 1.56.0 --> 
+ - Rust/Cargo target: <!-- e.g. x86_64-apple-darwin, x86_64-unknown-linux-gnu, etc. -->  
+
+**Additional context**  
+<!-- Add any other context about the problem here. --> 

.github/ISSUE_TEMPLATE/enhancement_request.md

@@ -0,0 +1,17 @@
+---
+name: Enhancement request
+about: Request a new feature or change to an existing feature
+title: ''
+labels: 'enhancement'
+assignees: ''
+
+---
+
+**Describe the enhancement**  
+<!-- A clear and concise description of what you would like added or changed. -->
+
+**Use case**  
+<!-- Tell us how you or others will use this new feature or change to an existing feature. --> 
+
+**Additional context**
+<!-- Add any other context about the enhancement here. --> 

.github/ISSUE_TEMPLATE/minor_release.md

@@ -0,0 +1,99 @@
+---
+name: Minor Release
+about: Create a new minor release [for release managers only]
+title: 'Release MAJOR.MINOR+1.0'
+labels: 'release'
+assignees: ''
+
+---
+
+## Create a new minor release
+
+### Summary
+
+<--release summary to be used in announcements-->
+
+### Commit
+
+<--latest commit ID to include in this release-->
+
+### Changelog
+
+<--add notices from PRs merged since the prior release, see ["keep a changelog"]-->
+
+### Checklist
+
+Release numbering must follow [Semantic Versioning]. These steps assume the current `master`
+branch **development** version is *MAJOR.MINOR.0*.
+
+#### On the day of the feature freeze
+
+Change the `master` branch to the next MINOR+1 version:
+
+- [ ] Switch to the `master` branch.
+- [ ] Create a new PR branch called `bump_dev_MAJOR_MINOR+1`, eg. `bump_dev_0_22`.
+- [ ] Bump the `bump_dev_MAJOR_MINOR+1` branch to the next development MINOR+1 version.
+  - Change the `Cargo.toml` version value to `MAJOR.MINOR+1.0`.
+  - Update the `CHANGELOG.md` file.
+  - The commit message should be "Bump version to MAJOR.MINOR+1.0".
+- [ ] Create PR and merge the `bump_dev_MAJOR_MINOR+1` branch to `master`.
+  - Title PR "Bump version to MAJOR.MINOR+1.0".
+
+Create a new release branch and release candidate tag:
+
+- [ ] Double check that your local `master` is up-to-date with the upstream repo.
+- [ ] Create a new branch called `release/MAJOR.MINOR+1` from `master`.
+- [ ] Bump the `release/MAJOR.MINOR+1` branch to `MAJOR.MINOR+1.0-rc.1` version.
+  - Change the `Cargo.toml` version value to `MAJOR.MINOR+1.0-rc.1`.
+  - The commit message should be "Bump version to MAJOR.MINOR+1.0-rc.1".
+- [ ] Add a tag to the `HEAD` commit in the `release/MAJOR.MINOR+1` branch.
+  - The tag name should be `vMAJOR.MINOR+1.0-rc.1`
+  - Use message "Release MAJOR.MINOR+1.0 rc.1".
+  - Make sure the tag is signed, for extra safety use the explicit `--sign` flag.
+- [ ] Push the `release/MAJOR.MINOR` branch and new tag to the `bitcoindevkit/bdk` repo.
+  - Use `git push --tags` option to push the new `vMAJOR.MINOR+1.0-rc.1` tag.
+
+If any issues need to be fixed before the *MAJOR.MINOR+1.0* version is released:
+
+- [ ] Merge fix PRs to the `master` branch.
+- [ ] Git cherry-pick fix commits to the `release/MAJOR.MINOR+1` branch.
+- [ ] Verify fixes in `release/MAJOR.MINOR+1` branch.
+- [ ] Bump the `release/MAJOR.MINOR+1` branch to `MAJOR.MINOR+1.0-rc.x+1` version.
+  - Change the `Cargo.toml` version value to `MAJOR.MINOR+1.0-rc.x+1`.
+  - The commit message should be "Bump version to MAJOR.MINOR+1.0-rc.x+1".
+- [ ] Add a tag to the `HEAD` commit in the `release/MAJOR.MINOR+1` branch.
+  - The tag name should be `vMAJOR.MINOR+1.0-rc.x+1`, where x is the current release candidate number.
+  - Use tag message "Release MAJOR.MINOR+1.0 rc.x+1".
+  - Make sure the tag is signed, for extra safety use the explicit `--sign` flag.
+- [ ] Push the new tag to the `bitcoindevkit/bdk` repo.
+  - Use `git push --tags` option to push the new `vMAJOR.MINOR+1.0-rc.x+1` tag.
+
+#### On the day of the release
+
+Tag and publish new release:
+
+- [ ] Bump the `release/MAJOR.MINOR+1` branch to `MAJOR.MINOR+1.0` version.
+  - Change the `Cargo.toml` version value to `MAJOR.MINOR+1.0`.
+  - The commit message should be "Bump version to MAJOR.MINOR+1.0".
+- [ ] Add a tag to the `HEAD` commit in the `release/MAJOR.MINOR+1` branch.
+  - The tag name should be `vMAJOR.MINOR+1.0`
+  - The first line of the tag message should be "Release MAJOR.MINOR+1.0".
+  - In the body of the tag message put a copy of the **Summary** and **Changelog** for the release.
+  - Make sure the tag is signed, for extra safety use the explicit `--sign` flag.
+- [ ] Wait for the CI to finish one last time.
+- [ ] Push the new tag to the `bitcoindevkit/bdk` repo.
+- [ ] Publish **all** the updated crates to crates.io.
+- [ ] Create the release on GitHub.
+  - Go to "tags", click on the dots on the right and select "Create Release".
+  - Set the title to `Release MAJOR.MINOR+1.0`.
+  - In the release notes body put the **Summary** and **Changelog**.
+  - Use the "+ Auto-generate release notes" button to add details from included PRs.
+  - Until we reach a `1.0.0` release check the "Pre-release" box.
+- [ ] Make sure the new release shows up on [crates.io] and that the docs are built correctly on [docs.rs].
+- [ ] Announce the release, using the **Summary**, on Discord, Twitter and Mastodon.
+- [ ] Celebrate 🎉
+
+[Semantic Versioning]: https://semver.org/
+[crates.io]: https://crates.io/crates/bdk
+[docs.rs]: https://docs.rs/bdk/latest/bdk
+["keep a changelog"]: https://keepachangelog.com/en/1.0.0/

.github/ISSUE_TEMPLATE/patch_release.md

@@ -0,0 +1,71 @@
+---
+name: Patch Release
+about: Create a new patch release [for release managers only]
+title: 'Release MAJOR.MINOR.PATCH+1'
+labels: 'release'
+assignees: ''
+
+---
+
+## Create a new patch release
+
+### Summary
+
+<--release summary to be used in announcements-->
+
+### Commit
+
+<--latest commit ID to include in this release-->
+
+### Changelog
+
+<--add notices from PRs merged since the prior release, see ["keep a changelog"]-->
+
+### Checklist
+
+Release numbering must follow [Semantic Versioning]. These steps assume the current `master`
+branch **development** version is *MAJOR.MINOR.PATCH*.
+
+### On the day of the patch release
+
+Change the `master` branch to the new PATCH+1 version:
+
+- [ ] Switch to the `master` branch.
+- [ ] Create a new PR branch called `bump_dev_MAJOR_MINOR_PATCH+1`, eg. `bump_dev_0_22_1`.
+- [ ] Bump the `bump_dev_MAJOR_MINOR` branch to the next development PATCH+1 version.
+  - Change the `Cargo.toml` version value to `MAJOR.MINOR.PATCH+1`.
+  - Update the `CHANGELOG.md` file.
+  - The commit message should be "Bump version to MAJOR.MINOR.PATCH+1".
+- [ ] Create PR and merge the `bump_dev_MAJOR_MINOR_PATCH+1` branch to `master`.
+  - Title PR "Bump version to MAJOR.MINOR.PATCH+1".
+
+Cherry-pick, tag and publish new PATCH+1 release:
+
+- [ ] Merge fix PRs to the `master` branch.
+- [ ] Git cherry-pick fix commits to the `release/MAJOR.MINOR` branch to be patched.
+- [ ] Verify fixes in `release/MAJOR.MINOR` branch.
+- [ ] Bump the `release/MAJOR.MINOR.PATCH+1` branch to `MAJOR.MINOR.PATCH+1` version.
+  - Change the `Cargo.toml` version value to `MAJOR.MINOR.MINOR.PATCH+1`.
+  - The commit message should be "Bump version to MAJOR.MINOR.PATCH+1".
+- [ ] Add a tag to the `HEAD` commit in the `release/MAJOR.MINOR` branch.
+  - The tag name should be `vMAJOR.MINOR.PATCH+1`
+  - The first line of the tag message should be "Release MAJOR.MINOR.PATCH+1".
+  - In the body of the tag message put a copy of the **Summary** and **Changelog** for the release.
+  - Make sure the tag is signed, for extra safety use the explicit `--sign` flag.
+- [ ] Wait for the CI to finish one last time.
+- [ ] Push the new tag to the `bitcoindevkit/bdk` repo.
+- [ ] Publish **all** the updated crates to crates.io.
+- [ ] Create the release on GitHub.
+  - Go to "tags", click on the dots on the right and select "Create Release".
+  - Set the title to `Release MAJOR.MINOR.PATCH+1`.
+  - In the release notes body put the **Summary** and **Changelog**.
+  - Use the "+ Auto-generate release notes" button to add details from included PRs.
+  - Until we reach a `1.0.0` release check the "Pre-release" box.
+- [ ] Make sure the new release shows up on [crates.io] and that the docs are built correctly on [docs.rs].
+- [ ] Announce the release, using the **Summary**, on Discord, Twitter and Mastodon.
+- [ ] Celebrate 🎉
+
+[Semantic Versioning]: https://semver.org/
+[crates.io]: https://crates.io/crates/bdk
+[docs.rs]: https://docs.rs/bdk/latest/bdk
+["keep a changelog"]: https://keepachangelog.com/en/1.0.0/

.github/ISSUE_TEMPLATE/summer_project.md

@@ -0,0 +1,77 @@
+---
+name: Summer of Bitcoin Project
+about: Template to suggest a new https://www.summerofbitcoin.org/ project.
+title: ''
+labels: 'summer-of-bitcoin'
+assignees: ''
+
+---
+
+<!--
+## Overview  
+
+Project ideas are scoped for a university-level student with a basic background in CS and bitcoin 
+fundamentals - achievable over 12-weeks. Below are just a few types of ideas: 
+
+ - Low-hanging fruit: Relatively short projects with clear goals; requires basic technical knowledge 
+   and minimal familiarity with the codebase.
+ - Core development: These projects derive from the ongoing work from the core of your development 
+   team. The list of features and bugs is never-ending, and help is always welcome.
+ - Risky/Exploratory: These projects push the scope boundaries of your development effort. They 
+   might require expertise in an area not covered by your current development team. They might take 
+   advantage of a new technology. There is a reasonable chance that the project might be less 
+   successful, but the potential rewards make it worth the attempt.
+ - Infrastructure/Automation: These projects are the code that your organization uses to get its 
+   development work done; for example, projects that improve the automation of releases, regression 
+   tests and automated builds. This is a category where a Summer of Bitcoin student can be really 
+   helpful, doing work that the development team has been putting off while they focus on core 
+   development.
+ - Quality Assurance/Testing: Projects that work on and test your project's software development 
+   process. Additionally, projects that involve a thorough test and review of individual PRs.
+ - Fun/Peripheral: These projects might not be related to the current core development focus, but 
+   create new innovations and new perspectives for your project.
+-->
+
+**Description**
+<!-- Description: 3-7 sentences describing the project background and tasks to be done. -->  
+
+**Expected Outcomes**  
+<!-- Short bullet list describing what is to be accomplished -->   
+
+**Resources**  
+<!-- 2-3 reading materials for candidate to learn about the repo, project, scope etc -->  
+<!-- Recommended reading such as a developer/contributor guide -->  
+<!-- [Another example a paper citation](https://arxiv.org/pdf/1802.08091.pdf) -->  
+<!-- [Another example an existing issue](https://github.com/opencv/opencv/issues/11013) -->  
+<!-- [An existing related module](https://github.com/opencv/opencv_contrib/tree/master/modules/optflow) -->  
+
+**Skills Required**  
+<!-- 3-4 technical skills that the candidate should know -->  
+<!-- hands on experience with git -->  
+<!-- mastery plus experience coding in C++ -->  
+<!-- basic knowledge in matrix and tensor computations, college course work in cryptography -->  
+<!-- strong mathematical background -->
+<!-- Bonus - has experience with React Native. Best if you have also worked with OSSFuzz -->
+
+**Mentor(s)**  
+<!-- names of mentor(s) for this project go here -->
+
+**Difficulty**  
+<!-- Easy, Medium, Hard -->
+
+**Competency Test (optional)**  
+<!-- 2-3 technical tasks related to the project idea or repository you’d like a candidate to 
+    perform in order to demonstrate competency, good first bugs, warm-up exercises -->
+<!-- ex. Read the instructions here to get Bitcoin core running on your machine -->
+<!-- ex. pick an issue labeled as “newcomer” in the repository, and send a merge request to the 
+    repository. You can also suggest some other improvement that we did not think of yet, or 
+    something that you find interesting or useful -->
+<!-- ex. fixes for coding style are usually easy to do, and are good issues for first time 
+    contributions for those learning how to interact with the project. After you are done with the 
+    coding style issue, try making a different contribution. -->
+<!-- ex. setup a full Debian packaging development environment and learn the basics of Debian 
+    packaging. Then identify and package the missing dependencies to package Specter Desktop -->
+<!-- ex. write a pull parser for CSV files. You'll be judged by the decisions to store the parser 
+    state and how flexible it is to wrap this parser in other scenarios. -->
+<!-- ex. Stretch Goal: Implement some basic metaprogram/app to prove you're very familiar with BDK. 
+    Be prepared to make adjustments as we judge your solution. -->

.github/dependabot.yml

@@ -0,0 +1,8 @@
+# Set update schedule for GitHub Actions
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: "weekly"

.github/pull_request_template.md

@@ -0,0 +1,34 @@
+<!-- You can erase any parts of this template not applicable to your Pull Request. -->
+
+### Description
+
+<!-- Describe the purpose of this PR, what's being adding and/or fixed -->
+
+### Notes to the reviewers
+
+<!-- In this section you can include notes directed to the reviewers, like explaining why some parts
+of the PR were done in a specific way -->
+
+### Changelog notice
+
+<!-- Notice the release manager should include in the release tag message changelog -->
+<!-- See https://keepachangelog.com/en/1.0.0/ for examples -->
+
+### Checklists
+
+#### All Submissions:
+
+* [ ] I've signed all my commits
+* [ ] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
+* [ ] I ran `cargo fmt` and `cargo clippy` before committing
+
+#### New Features:
+
+* [ ] I've added tests for the new feature
+* [ ] I've added docs for the new feature
+
+#### Bugfixes:
+
+* [ ] This pull request breaks the existing API
+* [ ] I've added tests to reproduce the issue which are now passing
+* [ ] I'm linking the issue being fixed by this PR

.github/workflows/audit.yml

@@ -0,0 +1,19 @@
+name: Audit
+
+on:
+  push:
+    paths:
+      - '**/Cargo.toml'
+      - '**/Cargo.lock'
+  schedule:
+    - cron: '0 0 * * 0' # Once per week
+
+jobs:
+
+  security_audit:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/audit-check@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/code_coverage.yml

@@ -0,0 +1,57 @@
+on: [push, pull_request]
+
+name: Code Coverage
+
+jobs:
+  Codecov:
+    name: Code Coverage
+    runs-on: ubuntu-latest
+    env:
+      RUSTFLAGS: "-Cinstrument-coverage"
+      RUSTDOCFLAGS: "-Cinstrument-coverage"
+      LLVM_PROFILE_FILE: "./target/coverage/%p-%m.profraw"
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Install lcov tools
+        run: sudo apt-get install lcov -y
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+            profile: minimal
+            components: llvm-tools-preview
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@v2.2.1
+      - name: Install grcov
+        run: if [[ ! -e ~/.cargo/bin/grcov ]]; then cargo install grcov; fi
+        # TODO: re-enable the hwi tests
+      - name: Build simulator image
+        run: docker build -t hwi/ledger_emulator ./ci -f ci/Dockerfile.ledger
+      - name: Run simulator image
+        run: docker run --name simulator --network=host hwi/ledger_emulator &
+      - name: Install Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.9'
+      - name: Install python dependencies
+        run: pip install hwi==2.1.1 protobuf==3.20.1
+      - name: Test
+        run: cargo test --all-features
+      - name: Make coverage directory
+        run: mkdir coverage
+      - name: Run grcov
+        run: grcov . --binary-path ./target/debug/ -s . -t lcov --branch --ignore-not-existing --keep-only '**/crates/**' --ignore '**/tests/**' --ignore '**/examples/**' -o ./coverage/lcov.info
+      - name: Generate HTML coverage report
+        run: genhtml -o coverage-report.html --ignore-errors source ./coverage/lcov.info
+      - name: Coveralls upload
+        uses: coverallsapp/github-action@master
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+      - name: Upload artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: coverage-report
+          path: coverage-report.html

.github/workflows/cont_integration.yml

@@ -0,0 +1,132 @@
+on: [push, pull_request]
+
+name: CI
+
+jobs:
+
+  build-test:
+    name: Build and test
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust:
+          - version: stable
+            clippy: true
+          - version: 1.63.0 # MSRV
+        features:
+          - --no-default-features
+          - --all-features
+    steps:
+      - name: checkout
+        uses: actions/checkout@v2
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: ${{ matrix.rust.version }}
+            override: true
+            profile: minimal
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@v2.2.1
+      - name: Pin dependencies for MSRV
+        if: matrix.rust.version == '1.63.0'
+        run: |
+          cargo update -p zstd-sys --precise "2.0.8+zstd.1.5.5"
+          cargo update -p time --precise "0.3.20"
+          cargo update -p home --precise "0.5.5"
+          cargo update -p proptest --precise "1.2.0"
+          cargo update -p url --precise "2.5.0"
+          cargo update -p cc --precise "1.0.105"
+          cargo update -p tokio --precise "1.38.1"
+      - name: Build
+        run: cargo build ${{ matrix.features }}
+      - name: Test
+        run: cargo test ${{ matrix.features }}
+
+  check-no-std:
+    name: Check no_std
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          override: true
+          profile: minimal
+          # target: "thumbv6m-none-eabi"
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@v2.2.1
+      - name: Check bdk_chain
+        working-directory: ./crates/chain
+        # TODO "--target thumbv6m-none-eabi" should work but currently does not
+        run: cargo check --no-default-features --features miniscript/no-std,hashbrown
+      - name: Check bdk wallet
+        working-directory: ./crates/wallet
+        # TODO "--target thumbv6m-none-eabi" should work but currently does not
+        run: cargo check --no-default-features --features miniscript/no-std,bdk_chain/hashbrown
+      - name: Check esplora
+        working-directory: ./crates/esplora
+        # TODO "--target thumbv6m-none-eabi" should work but currently does not
+        run: cargo check --no-default-features --features miniscript/no-std,bdk_chain/hashbrown
+
+  check-wasm:
+    name: Check WASM
+    runs-on: ubuntu-20.04
+    env:
+      CC: clang-10
+      CFLAGS: -I/usr/include
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+        # Install a recent version of clang that supports wasm32
+      - run: wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add - || exit 1
+      - run: sudo apt-get update || exit 1
+      - run: sudo apt-get install -y libclang-common-10-dev clang-10 libc6-dev-i386 || exit 1
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+            profile: minimal
+            target: "wasm32-unknown-unknown"
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@v2.2.1
+      - name: Check bdk wallet
+        working-directory: ./crates/wallet
+        run: cargo check --target wasm32-unknown-unknown --no-default-features --features miniscript/no-std,bdk_chain/hashbrown
+      - name: Check esplora
+        working-directory: ./crates/esplora
+        run: cargo check --target wasm32-unknown-unknown --no-default-features --features miniscript/no-std,bdk_chain/hashbrown,async
+
+  fmt:
+    name: Rust fmt
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+            profile: minimal
+            components: rustfmt
+      - name: Check fmt
+        run: cargo fmt --all -- --config format_code_in_doc_comments=true --check
+
+  clippy_check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+            toolchain: 1.78.0
+            components: clippy
+            override: true
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@v2.2.1
+      - uses: actions-rs/clippy-check@v1
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          args: --all-features --all-targets -- -D warnings

.github/workflows/nightly_docs.yml

@@ -0,0 +1,57 @@
+name: Publish Nightly Docs
+
+on: [push, pull_request]
+
+jobs:
+  build_docs:
+    name: Build docs
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+      - name: Set default toolchain
+        run: rustup default nightly-2024-05-12
+      - name: Set profile
+        run: rustup set profile minimal
+      - name: Update toolchain
+        run: rustup update
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@v2.2.1
+      - name: Build docs
+        run: cargo doc --no-deps
+        env:
+          RUSTDOCFLAGS: '--cfg docsrs -Dwarnings'
+      - name: Upload artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: built-docs
+          path: ./target/doc/*
+
+  publish_docs:
+    name: 'Publish docs'
+    if: github.ref == 'refs/heads/master'
+    needs: [build_docs]
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout `bitcoindevkit.org`
+        uses: actions/checkout@v2
+        with:
+          ssh-key: ${{ secrets.DOCS_PUSH_SSH_KEY }}
+          repository: bitcoindevkit/bitcoindevkit.org
+          ref: master
+      - name: Create directories
+        run: mkdir -p ./docs/.vuepress/public/docs-rs/bdk/nightly
+      - name: Remove old latest
+        run: rm -rf ./docs/.vuepress/public/docs-rs/bdk/nightly/latest
+      - name: Download built docs
+        uses: actions/download-artifact@v1
+        with:
+          name: built-docs
+          path: ./docs/.vuepress/public/docs-rs/bdk/nightly/latest
+      - name: Configure git
+        run: git config user.email "github-actions@github.com" && git config user.name "github-actions"
+      - name: Commit
+        continue-on-error: true         # If there's nothing to commit this step fails, but it's fine
+        run: git add ./docs/.vuepress/public/docs-rs && git commit -m "Publish autogenerated nightly docs"
+      - name: Push
+        run: git push origin master

.gitignore

@@ -1,4 +1,10 @@
 /target
 Cargo.lock
+/.vscode
 
 *.swp
+.idea
+
+# Example persisted files.
+*.db
+*.sqlite*

.travis.yml

@@ -1,22 +0,0 @@
-language: rust
-rust:
-  - stable
-#  - 1.31.0
-#  - 1.22.0
-before_script:
-  - rustup component add rustfmt
-script:
-  - cargo fmt -- --check --verbose
-  - cargo test --verbose --all
-  - cargo build --verbose --all
-  - cargo build --verbose --no-default-features --features=minimal
-  - cargo build --verbose --no-default-features --features=minimal,esplora
-  - cargo build --verbose --no-default-features --features=key-value-db
-  - cargo build --verbose --no-default-features --features=electrum
-
-notifications:
-  email: false
-
-before_cache:
-  - rm -rf "$TRAVIS_HOME/.cargo/registry/src"
-cache: cargo

CHANGELOG.md

@@ -0,0 +1,645 @@
+# Changelog
+
+All notable changes to this project can be found here and in each release's git tag and can be viewed with `git tag -ln100 "v*"`. See also [DEVELOPMENT_CYCLE.md](DEVELOPMENT_CYCLE.md) for more details.
+
+Contributors do not need to change this file but do need to add changelog details in their PR descriptions. The person making the next release will collect changelog details from included PRs and edit this file prior to each release.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [v0.27.1]
+
+### Summary
+
+Fixes [RUSTSEC-2022-0090], this issue is only applicable if you are using the optional sqlite database feature.
+
+[RUSTSEC-2022-0090]: https://rustsec.org/advisories/RUSTSEC-2022-0090
+
+### Changed
+
+- Update optional sqlite dependency from 0.27.0 to 0.28.0. #867
+
+## [v0.27.0]
+
+### Summary
+
+A maintenance release with a bump in project MSRV to 1.57.0, updated dependence and a few developer oriented improvements. Improvements include  better error formatting, don't default to async/await for wasm32 and adding derived PartialEq and Eq on SyncTime.
+
+### Changed
+
+- Improve display error formatting #814
+- Don't default to use async/await on wasm32 #831
+- Project MSRV changed from 1.56.1 to 1.57.0 #842
+- Update rust-miniscript dependency to latest bug fix release 9.0 #844
+
+### Added
+
+- Derive PartialEq, Eq on SyncTime #837
+
+## [v0.26.0]
+
+### Summary
+
+This release improves Fulcrum electrum server compatibility and fixes public descriptor template key origin paths. We also snuck in small enhancements to configure the electrum client to validate the domain using SSL and sort TransactionDetails by block height and timestamp.
+  
+### Fixed
+  
+- Make electrum blockchain client `save_tx` function order independent to work with Fulcrum servers. #808
+- Fix wrong testnet key origin path in public descriptor templates. #818
+- Make README.md code examples compile without errors. #820
+
+### Changed
+
+- Bump `hwi` dependency to `0.4.0`. #825
+- Bump `esplora-client` dependency to `0.3` #830
+
+### Added
+  
+- For electrum blockchain client, allow user to configure whether to validate the domain using SSL. #805
+- Implement ordering for `TransactionDetails`. #812
+
+## [v0.25.0]
+
+### Summary
+
+This release fixes slow sync time and big script_pubkeys table with SQLite, the wallet rescan height for the FullyNodedExport and setting the network for keys in the KeyMap when using descriptor templates. Also added are new blockchain and mnemonic examples.
+  
+### Fixed
+  
+- Slow sync time and big script_pubkeys table with SQLite.
+- Wallet rescan height for the FullyNodedExport.
+- Setting the network for keys in the KeyMap when using descriptor templates.
+  
+### Added
+  
+- Examples for connecting to Esplora, Electrum Server, Neutrino and Bitcoin Core.
+- Example for using a mnemonic in a descriptors.
+
+## [v0.24.0]
+
+### Summary
+
+This release contains important dependency updates for `rust-bitcoin` to `0.29` and `rust-miniscript` to `8.0`, plus related crates that also depend on the latest version of `rust-bitcoin`. The release also includes a breaking change to the BDK signer which now produces low-R signatures by default, saving one byte. A bug was found in the `get_checksum` and `get_checksum_bytes` functions, which are now deprecated in favor of fixed versions called `calc_checksum` and `calc_checksum_bytes`. And finally a new `hardware-signer` features was added that re-exports the `hwi` crate, along with a new `hardware_signers.rs` example file.
+   
+### Changed
+
+- Updated dependency versions for `rust-bitcoin` to `0.29` and `rust-miniscript` to `8.0`, plus all related crates. @afilini #770
+- BDK Signer now produces low-R signatures by default, saving one byte. If you want to preserve the original behavior, set allow_grinding in the SignOptions to false. @vladimirfomene #779
+- Deprecated `get_checksum`and `get_checksum_bytes` due to bug where they calculates the checksum of a descriptor that already has a checksum.  Use `calc_checksum` and `calc_checksum_bytes` instead. @evanlinjin #765
+- Remove deprecated "address validators". @afilini #770
+  
+### Added
+
+- New `calc_checksum` and `calc_checksum_bytes`, replace deprecated `get_checksum` and `get_checksum_bytes`. @evanlinjin #765
+- Re-export the hwi crate when the feature hardware-signer is on.  @danielabrozzoni #758
+- New examples/hardware_signer.rs. @danielabrozzoni #758
+- Make psbt module public to expose PsbtUtils trait to downstream projects. @notmandatory #782
+
+## [v0.23.0]
+
+### Summary
+
+This release brings new utilities functions on PSBTs like `fee_amount()` and `fee_rate()` and migrates BDK to use our new external esplora client library.
+As always many bug fixes, docs and tests improvement are also included.
+
+### Changed
+
+- Update electrum-client to 0.11.0 by @afilini in https://github.com/bitcoindevkit/bdk/pull/737
+- Change configs for source-base code coverage by @wszdexdrf in https://github.com/bitcoindevkit/bdk/pull/708
+- Improve docs regarding PSBT finalization by @tnull in https://github.com/bitcoindevkit/bdk/pull/753
+- Update compiler example to a Policy example by @rajarshimaitra in https://github.com/bitcoindevkit/bdk/pull/730
+- Fix the release process by @afilini in https://github.com/bitcoindevkit/bdk/pull/754
+- Remove redundant duplicated keys check by @afilini in https://github.com/bitcoindevkit/bdk/pull/761
+- Remove genesis_block lazy initialization by @shobitb in https://github.com/bitcoindevkit/bdk/pull/756
+- Fix `Wallet::descriptor_checksum` to actually return the checksum by @evanlinjin in https://github.com/bitcoindevkit/bdk/pull/763
+- Use the esplora client crate by @afilini in https://github.com/bitcoindevkit/bdk/pull/764
+
+### Added
+
+- Run code coverage on every PR by @danielabrozzoni in https://github.com/bitcoindevkit/bdk/pull/747
+- Add psbt_signer.rs example by @notmandatory in https://github.com/bitcoindevkit/bdk/pull/744
+- Add fee_amount() and fee_rate() functions to PsbtUtils trait by @notmandatory in https://github.com/bitcoindevkit/bdk/pull/728
+- Add tests to improve coverage by @vladimirfomene in https://github.com/bitcoindevkit/bdk/pull/745
+- Enable signing taproot transactions with only `non_witness_utxos` by @afilini in https://github.com/bitcoindevkit/bdk/pull/757
+- Add datatype for is_spent sqlite column by @vladimirfomene in https://github.com/bitcoindevkit/bdk/pull/713
+- Add vscode filter to gitignore by @evanlinjin in https://github.com/bitcoindevkit/bdk/pull/762
+
+## [v0.22.0]
+
+### Summary
+
+This release brings support for hardware signers on desktop through the HWI library.
+It also includes fixes and improvements which are part of our ongoing effort of integrating
+BDK and LDK together.
+
+### Changed
+
+- FeeRate function name as_sat_vb to as_sat_per_vb. #678
+- Verify signatures after signing. #718
+- Dependency electrum-client to 0.11.0. #737
+
+### Added
+  
+- Functions to create FeeRate from sats/kvbytes and sats/kwu. #678
+- Custom hardware wallet signer HwiSigner in wallet::hardwaresigner module. #682
+- Function allow_dust on TxBuilder. #689
+- Implementation of Deref<Target=UrlClient> for EsploraBlockchain. #722
+- Implementation of Deref<Target=Client> for ElectrumBlockchain #705
+- Implementation of Deref<Target=Client> for RpcBlockchain. #731
+
+## [v0.21.0]
+
+- Add `descriptor::checksum::get_checksum_bytes` method.
+- Add `Excess` enum to handle remaining amount after coin selection.
+- Move change creation from `Wallet::create_tx` to `CoinSelectionAlgorithm::coin_select`.
+- Change the interface of `SqliteDatabase::new` to accept any type that implement AsRef<Path>
+- Add the ability to specify which leaves to sign in a taproot transaction through `TapLeavesOptions` in `SignOptions`
+- Add the ability to specify whether a taproot transaction should be signed using the internal key or not, using `sign_with_tap_internal_key` in `SignOptions`
+- Consolidate params `fee_amount` and `amount_needed` in `target_amount` in `CoinSelectionAlgorithm::coin_select` signature.
+- Change the meaning of the `fee_amount` field inside `CoinSelectionResult`: from now on the `fee_amount` will represent only the fees associated with the utxos in the `selected` field of `CoinSelectionResult`.
+- New `RpcBlockchain` implementation with various fixes.
+- Return balance in separate categories, namely `confirmed`, `trusted_pending`, `untrusted_pending` & `immature`.
+
+## [v0.20.0]
+
+- New MSRV set to `1.56.1`
+- Fee sniping discouraging through nLockTime - if the user specifies a `current_height`, we use that as a nlocktime, otherwise we use the last sync height (or 0 if we never synced)
+- Fix hang when `ElectrumBlockchainConfig::stop_gap` is zero.
+- Set coin type in BIP44, BIP49, and BIP84 templates
+- Get block hash given a block height - A `get_block_hash` method is now defined on the `GetBlockHash` trait and implemented on every blockchain backend. This method expects a block height and returns the corresponding block hash.
+- Add `remove_partial_sigs` and `try_finalize` to `SignOptions`
+- Deprecate `AddressValidator`
+- Fix Electrum wallet sync potentially causing address index decrement - compare proposed index and current index before applying batch operations during sync.
+
+## [v0.19.0]
+
+- added `OldestFirstCoinSelection` impl to `CoinSelectionAlgorithm`
+- New MSRV set to `1.56`
+- Unpinned tokio to `1`
+- Add traits to reuse `Blockchain`s across multiple wallets (`BlockchainFactory` and `StatelessBlockchain`).
+- Upgrade to rust-bitcoin `0.28`
+- If using the `sqlite-db` feature all cached wallet data is deleted due to a possible UTXO inconsistency, a wallet.sync will recreate it
+- Update `PkOrF` in the policy module to become an enum
+- Add experimental support for Taproot, including:
+  - Support for `tr()` descriptors with complex tapscript trees
+  - Creation of Taproot PSBTs (BIP-371)
+  - Signing Taproot PSBTs (key spend and script spend)
+  - Support for `tr()` descriptors in the `descriptor!()` macro
+- Add support for Bitcoin Core 23.0 when using the `rpc` blockchain
+
+## [v0.18.0]
+
+- Add `sqlite-bundled` feature for deployments that need a bundled version of sqlite, i.e. for mobile platforms.
+- Added `Wallet::get_signers()`, `Wallet::descriptor_checksum()` and `Wallet::get_address_validators()`, exposed the `AsDerived` trait.
+- Deprecate `database::Database::flush()`, the function is only needed for the sled database on mobile, instead for mobile use the sqlite database.
+- Add `keychain: KeychainKind` to `wallet::AddressInfo`.
+- Improve key generation traits
+- Rename `WalletExport` to `FullyNodedExport`, deprecate the former.
+- Bump `miniscript` dependency version to `^6.1`.
+
+## [v0.17.0]
+
+- Removed default verification from `wallet::sync`. sync-time verification is added in `script_sync` and is activated by `verify` feature flag.
+- `verify` flag removed from `TransactionDetails`.
+- Add `get_internal_address` to allow you to get internal addresses just as you get external addresses.
+- added `ensure_addresses_cached` to `Wallet` to let offline wallets load and cache addresses in their database
+- Add `is_spent` field to `LocalUtxo`; when we notice that a utxo has been spent we set `is_spent` field to true instead of deleting it from the db.
+
+### Sync API change
+
+To decouple the `Wallet` from the `Blockchain` we've made major changes:
+
+- Removed `Blockchain` from Wallet.
+- Removed `Wallet::broadcast` (just use `Blockchain::broadcast`)
+- Deprecated `Wallet::new_offline` (all wallets are offline now)
+- Changed `Wallet::sync` to take a `Blockchain`.
+- Stop making a request for the block height when calling `Wallet:new`.
+- Added `SyncOptions` to capture extra (future) arguments to `Wallet::sync`.
+- Removed `max_addresses` sync parameter which determined how many addresses to cache before syncing since this can just be done with `ensure_addresses_cached`.
+- remove `flush` method from the `Database` trait.
+
+## [v0.16.1]
+
+- Pin tokio dependency version to ~1.14 to prevent errors due to their new MSRV 1.49.0
+
+## [v0.16.0]
+
+- Disable `reqwest` default features.
+- Added `reqwest-default-tls` feature: Use this to restore the TLS defaults of reqwest if you don't want to add a dependency to it in your own manifest.
+- Use dust_value from rust-bitcoin
+- Fixed generating WIF in the correct network format.
+
+## [v0.15.0]
+
+- Overhauled sync logic for electrum and esplora.
+- Unify ureq and reqwest esplora backends to have the same configuration parameters. This means reqwest now has a timeout parameter and ureq has a concurrency parameter.
+- Fixed esplora fee estimation.
+
+## [v0.14.0]
+
+- BIP39 implementation dependency, in `keys::bip39` changed from tiny-bip39 to rust-bip39.
+- Add new method on the `TxBuilder` to embed data in the transaction via `OP_RETURN`. To allow that a fix to check the dust only on spendable output has been introduced.
+- Update the `Database` trait to store the last sync timestamp and block height
+- Rename `ConfirmationTime` to `BlockTime`
+
+## [v0.13.0]
+
+- Exposed `get_tx()` method from `Database` to `Wallet`.
+
+## [v0.12.0]
+
+- Activate `miniscript/use-serde` feature to allow consumers of the library to access it via the re-exported `miniscript` crate.
+- Add support for proxies in `EsploraBlockchain`
+- Added `SqliteDatabase` that implements `Database` backed by a sqlite database using `rusqlite` crate.
+
+## [v0.11.0]
+
+- Added `flush` method to the `Database` trait to explicitly flush to disk latest changes on the db.
+
+## [v0.10.0]
+
+- Added `RpcBlockchain` in the `AnyBlockchain` struct to allow using Rpc backend where `AnyBlockchain` is used (eg `bdk-cli`)
+- Removed hard dependency on `tokio`.
+
+### Wallet
+
+- Removed and replaced `set_single_recipient` with more general `drain_to` and replaced `maintain_single_recipient` with `allow_shrinking`.
+
+### Blockchain
+
+- Removed `stop_gap` from `Blockchain` trait and added it to only `ElectrumBlockchain` and `EsploraBlockchain` structs.
+- Added a `ureq` backend for use when not using feature `async-interface` or target WASM. `ureq` is a blocking HTTP client.
+
+## [v0.9.0]
+
+### Wallet
+
+- Added Bitcoin core RPC added as blockchain backend
+- Added a `verify` feature that can be enable to verify the unconfirmed txs we download against the consensus rules
+
+## [v0.8.0]
+
+### Wallet
+- Added an option that must be explicitly enabled to allow signing using non-`SIGHASH_ALL` sighashes (#350)
+#### Changed
+`get_address` now returns an `AddressInfo` struct that includes the index and derefs to `Address`.
+
+## [v0.7.0]
+
+### Policy
+#### Changed
+Removed `fill_satisfaction` method in favor of enum parameter in `extract_policy` method
+
+#### Added
+Timelocks are considered (optionally) in building the `satisfaction` field
+
+### Wallet
+
+- Changed `Wallet::{sign, finalize_psbt}` now take a `&mut psbt` rather than consuming it.
+- Require and validate `non_witness_utxo` for SegWit signatures by default, can be adjusted with `SignOptions`
+- Replace the opt-in builder option `force_non_witness_utxo` with the opposite `only_witness_utxo`. From now on we will provide the `non_witness_utxo`, unless explicitly asked not to.
+
+## [v0.6.0]
+
+### Misc
+#### Changed
+- New minimum supported rust version is 1.46.0
+- Changed `AnyBlockchainConfig` to use serde tagged representation.
+
+### Descriptor
+#### Added
+- Added ability to analyze a `PSBT` to check which and how many signatures are already available
+
+### Wallet
+#### Changed
+- `get_new_address()` refactored to `get_address(AddressIndex::New)` to support different `get_address()` index selection strategies
+
+#### Added
+- Added `get_address(AddressIndex::LastUnused)` which returns the last derived address if it has not been used or if used in a received transaction returns a new address
+- Added `get_address(AddressIndex::Peek(u32))` which returns a derived address for a specified descriptor index but does not change the current index
+- Added `get_address(AddressIndex::Reset(u32))` which returns a derived address for a specified descriptor index and resets current index to the given value
+- Added `get_psbt_input` to create the corresponding psbt input for a local utxo.
+
+#### Fixed
+- Fixed `coin_select` calculation for UTXOs where `value < fee` that caused over-/underflow errors.
+
+## [v0.5.1]
+
+### Misc
+#### Changed
+- Pin `hyper` to `=0.14.4` to make it compile on Rust 1.45
+
+## [v0.5.0]
+
+### Misc
+#### Changed
+- Updated `electrum-client` to version `0.7`
+
+### Wallet
+#### Changed
+- `FeeRate` constructors `from_sat_per_vb` and `default_min_relay_fee` are now `const` functions
+
+## [v0.4.0]
+
+### Keys
+#### Changed
+- Renamed `DerivableKey::add_metadata()` to `DerivableKey::into_descriptor_key()`
+- Renamed `ToDescriptorKey::to_descriptor_key()` to `IntoDescriptorKey::into_descriptor_key()`
+#### Added
+- Added an `ExtendedKey` type that is an enum of `bip32::ExtendedPubKey` and `bip32::ExtendedPrivKey`
+- Added `DerivableKey::into_extended_key()` as the only method that needs to be implemented
+
+### Misc
+#### Removed
+- Removed the `parse_descriptor` example, since it wasn't demonstrating any bdk-specific API anymore.
+#### Changed
+- Updated `bitcoin` to `0.26`, `miniscript` to `5.1` and `electrum-client` to `0.6`
+#### Added
+- Added support for the `signet` network (issue #62)
+- Added a function to get the version of BDK at runtime
+
+### Wallet
+#### Changed
+- Removed the explicit `id` argument from `Wallet::add_signer()` since that's now part of `Signer` itself
+- Renamed `ToWalletDescriptor::to_wallet_descriptor()` to `IntoWalletDescriptor::into_wallet_descriptor()`
+
+### Policy
+#### Changed
+- Removed unneeded `Result<(), PolicyError>` return type for `Satisfaction::finalize()`
+- Removed the `TooManyItemsSelected` policy error (see commit message for more details)
+
+## [v0.3.0]
+
+### Descriptor
+#### Changed
+- Added an alias `DescriptorError` for `descriptor::error::Error`
+- Changed the error returned by `descriptor!()` and `fragment!()` to `DescriptorError`
+- Changed the error type in `ToWalletDescriptor` to `DescriptorError`
+- Improved checks on descriptors built using the macros
+
+### Blockchain
+#### Changed
+- Remove `BlockchainMarker`, `OfflineClient` and `OfflineWallet` in favor of just using the unit
+  type to mark for a missing client.
+- Upgrade `tokio` to `1.0`.
+
+### Transaction Creation Overhaul
+
+The `TxBuilder` is now created from the `build_tx` or `build_fee_bump` functions on wallet and the
+final transaction is created by calling `finish` on the builder.
+
+- Removed `TxBuilder::utxos` in favor of `TxBuilder::add_utxos`
+- Added `Wallet::build_tx` to replace `Wallet::create_tx`
+- Added `Wallet::build_fee_bump` to replace `Wallet::bump_fee`
+- Added `Wallet::get_utxo`
+- Added `Wallet::get_descriptor_for_keychain`
+
+### `add_foreign_utxo`
+
+- Renamed `UTXO` to `LocalUtxo`
+- Added `WeightedUtxo` to replace floating `(UTXO, usize)`.
+- Added `Utxo` enum to incorporate both local utxos and foreign utxos
+- Added `TxBuilder::add_foreign_utxo` which allows adding a utxo external to the wallet.
+
+### CLI
+#### Changed
+- Remove `cli.rs` module, `cli-utils` feature and `repl.rs` example; moved to new [`bdk-cli`](https://github.com/bitcoindevkit/bdk-cli) repository
+
+## [v0.2.0]
+
+### Project
+#### Added
+- Add CONTRIBUTING.md
+- Add a Discord badge to the README
+- Add code coverage github actions workflow
+- Add scheduled audit check in CI
+- Add CHANGELOG.md
+
+#### Changed
+- Rename the library to `bdk`
+- Rename `ScriptType` to `KeychainKind`
+- Prettify README examples on github
+- Change CI to github actions
+- Bump rust-bitcoin to 0.25, fix Cargo dependencies
+- Enable clippy for stable and tests by default
+- Switch to "mainline" rust-miniscript
+- Generate a different cache key for every CI job
+- Fix to at least bitcoin ^0.25.2
+
+#### Fixed
+- Fix or ignore clippy warnings for all optional features except compact_filters
+- Pin cc version because last breaks rocksdb build
+
+### Blockchain
+#### Added
+- Add a trait to create `Blockchain`s from a configuration
+- Add an `AnyBlockchain` enum to allow switching at runtime
+- Document `AnyBlockchain` and `ConfigurableBlockchain`
+- Use our Instant struct to be compatible with wasm
+- Make esplora call in parallel
+- Allow to set concurrency in Esplora config and optionally pass it in repl
+
+#### Fixed
+- Fix receiving a coinbase using Electrum/Esplora
+- Use proper type for EsploraHeader, make conversion to BlockHeader infallible
+- Eagerly unwrap height option, save one collect
+
+#### Changed
+- Simplify the architecture of blockchain traits
+- Improve sync
+- Remove unused variant `HeaderParseFail`
+
+### CLI
+#### Added
+- Conditionally remove cli args according to enabled feature
+
+#### Changed
+- Add max_addresses param in sync
+- Split the internal and external policy paths
+
+### Database
+#### Added
+- Add `AnyDatabase` and `ConfigurableDatabase` traits
+
+### Descriptor
+#### Added
+- Add a macro to write descriptors from code
+- Add descriptor templates, add `DerivableKey`
+- Add ToWalletDescriptor trait tests
+- Add support for `sortedmulti` in `descriptor!`
+- Add ExtractPolicy trait tests
+- Add get_checksum tests, cleanup tests
+- Add descriptor macro tests
+
+#### Changes
+- Improve the descriptor macro, add traits for key and descriptor types
+
+#### Fixes
+- Fix the recovery of a descriptor given a PSBT
+
+### Keys
+#### Added
+- Add BIP39 support
+- Take `ScriptContext` into account when converting keys
+- Add a way to restrict the networks in which keys are valid
+- Add a trait for keys that can be generated
+- Fix entropy generation
+- Less convoluted entropy generation
+- Re-export tiny-bip39
+- Implement `GeneratableKey` trait for `bitcoin::PrivateKey`
+- Implement `ToDescriptorKey` trait for `GeneratedKey`
+- Add a shortcut to generate keys with the default options
+
+#### Fixed
+- Fix all-keys and cli-utils tests
+
+### Wallet
+#### Added
+- Allow to define static fees for transactions Fixes #137
+- Merging two match expressions for fee calculation
+- Incorporate RBF rules into utxo selection function
+- Add Branch and Bound coin selection
+- Add tests for BranchAndBoundCoinSelection::coin_select
+- Add tests for BranchAndBoundCoinSelection::bnb
+- Add tests for BranchAndBoundCoinSelection::single_random_draw
+- Add test that shwpkh populates witness_utxo
+- Add witness and redeem scripts to PSBT outputs
+- Add an option to include `PSBT_GLOBAL_XPUB`s in PSBTs
+- Eagerly finalize inputs
+
+#### Changed
+- Use collect to avoid iter unwrapping Options
+- Make coin_select take may/must use utxo lists
+- Improve `CoinSelectionAlgorithm`
+- Refactor `Wallet::bump_fee()`
+- Default to SIGHASH_ALL if not specified
+- Replace ChangeSpendPolicy::filter_utxos with a predicate
+- Make 'unspendable' into a HashSet
+- Stop implicitly enforcing manual selection by .add_utxo
+- Rename DumbCS to LargestFirstCoinSelection
+- Rename must_use_utxos to required_utxos
+- Rename may_use_utxos to optional_uxtos
+- Rename get_must_may_use_utxos to preselect_utxos
+- Remove redundant Box around address validators
+- Remove redundant Box around signers
+- Make Signer and AddressValidator Send and Sync
+- Split `send_all` into `set_single_recipient` and `drain_wallet`
+- Use TXIN_DEFAULT_WEIGHT constant in coin selection
+- Replace `must_use` with `required` in coin selection
+- Take both spending policies into account in create_tx
+- Check last derivation in cache to avoid recomputing
+- Use the branch-and-bound cs by default
+- Make coin_select return UTXOs instead of TxIns
+- Build output lookup inside complete transaction
+- Don't wrap SignersContainer arguments in Arc
+- More consistent references with 'signers' variables
+
+#### Fixed
+- Fix signing for `ShWpkh` inputs
+- Fix the recovery of a descriptor given a PSBT
+
+### Examples
+#### Added
+- Support esplora blockchain source in repl
+
+#### Changed
+- Revert back the REPL example to use Electrum
+- Remove the `magic` alias for `repl`
+- Require esplora feature for repl example
+
+#### Security
+- Use dirs-next instead of dirs since the latter is unmaintained
+
+## [0.1.0-beta.1] - 2020-09-08
+
+### Blockchain
+#### Added
+- Lightweight Electrum client with SSL/SOCKS5 support
+- Add a generalized "Blockchain" interface
+- Add Error::OfflineClient
+- Add the Esplora backend
+- Use async I/O in the various blockchain impls
+- Compact Filters blockchain implementation
+- Add support for Tor
+- Impl OnlineBlockchain for types wrapped in Arc
+
+### Database
+#### Added
+- Add a generalized database trait and a Sled-based implementation
+- Add an in-memory database
+
+### Descriptor
+#### Added
+- Wrap Miniscript descriptors to support xpubs
+- Policy and contribution
+- Transform a descriptor into its "public" version
+- Use `miniscript::DescriptorPublicKey`
+
+### Macros
+#### Added
+- Add a feature to enable the async interface on non-wasm32 platforms
+
+### Wallet
+#### Added
+- Wallet logic
+- Add `assume_height_reached` in PSBTSatisfier
+- Add an option to change the assumed current height
+- Specify the policy branch with a map
+- Add a few commands to handle psbts
+- Add hd_keypaths to outputs
+- Add a `TxBuilder` struct to simplify `create_tx()`'s interface
+- Abstract coin selection in a separate trait
+- Refill the address pool whenever necessary
+- Implement the wallet import/export format from FullyNoded
+- Add a type convert fee units, add `Wallet::estimate_fee()`
+- TxOrdering, shuffle/bip69 support
+- Add RBF and custom versions in TxBuilder
+- Allow limiting the use of internal utxos in TxBuilder
+- Add `force_non_witness_utxo()` to TxBuilder
+- RBF and add a few tests
+- Add AddressValidators
+- Add explicit ordering for the signers
+- Support signing the whole tx instead of individual inputs
+- Create a PSBT signer from an ExtendedDescriptor
+
+### Examples
+#### Added
+- Add REPL broadcast command
+- Add a miniscript compiler CLI
+- Expose list_transactions() in the REPL
+- Use `MemoryDatabase` in the compiler example
+- Make the REPL return JSON
+
+[0.1.0-beta.1]: https://github.com/bitcoindevkit/bdk/compare/96c87ea5...0.1.0-beta.1
+[v0.2.0]: https://github.com/bitcoindevkit/bdk/compare/0.1.0-beta.1...v0.2.0
+[v0.3.0]: https://github.com/bitcoindevkit/bdk/compare/v0.2.0...v0.3.0
+[v0.4.0]: https://github.com/bitcoindevkit/bdk/compare/v0.3.0...v0.4.0
+[v0.5.0]: https://github.com/bitcoindevkit/bdk/compare/v0.4.0...v0.5.0
+[v0.5.1]: https://github.com/bitcoindevkit/bdk/compare/v0.5.0...v0.5.1
+[v0.6.0]: https://github.com/bitcoindevkit/bdk/compare/v0.5.1...v0.6.0
+[v0.7.0]: https://github.com/bitcoindevkit/bdk/compare/v0.6.0...v0.7.0
+[v0.8.0]: https://github.com/bitcoindevkit/bdk/compare/v0.7.0...v0.8.0
+[v0.9.0]: https://github.com/bitcoindevkit/bdk/compare/v0.8.0...v0.9.0
+[v0.10.0]: https://github.com/bitcoindevkit/bdk/compare/v0.9.0...v0.10.0
+[v0.11.0]: https://github.com/bitcoindevkit/bdk/compare/v0.10.0...v0.11.0
+[v0.12.0]: https://github.com/bitcoindevkit/bdk/compare/v0.11.0...v0.12.0
+[v0.13.0]: https://github.com/bitcoindevkit/bdk/compare/v0.12.0...v0.13.0
+[v0.14.0]: https://github.com/bitcoindevkit/bdk/compare/v0.13.0...v0.14.0
+[v0.15.0]: https://github.com/bitcoindevkit/bdk/compare/v0.14.0...v0.15.0
+[v0.16.0]: https://github.com/bitcoindevkit/bdk/compare/v0.15.0...v0.16.0
+[v0.16.1]: https://github.com/bitcoindevkit/bdk/compare/v0.16.0...v0.16.1
+[v0.17.0]: https://github.com/bitcoindevkit/bdk/compare/v0.16.1...v0.17.0
+[v0.18.0]: https://github.com/bitcoindevkit/bdk/compare/v0.17.0...v0.18.0
+[v0.19.0]: https://github.com/bitcoindevkit/bdk/compare/v0.18.0...v0.19.0
+[v0.20.0]: https://github.com/bitcoindevkit/bdk/compare/v0.19.0...v0.20.0
+[v0.21.0]: https://github.com/bitcoindevkit/bdk/compare/v0.20.0...v0.21.0
+[v0.22.0]: https://github.com/bitcoindevkit/bdk/compare/v0.21.0...v0.22.0
+[v0.23.0]: https://github.com/bitcoindevkit/bdk/compare/v0.22.0...v0.23.0
+[v0.24.0]: https://github.com/bitcoindevkit/bdk/compare/v0.23.0...v0.24.0
+[v0.25.0]: https://github.com/bitcoindevkit/bdk/compare/v0.24.0...v0.25.0
+[v0.26.0]: https://github.com/bitcoindevkit/bdk/compare/v0.25.0...v0.26.0
+[v0.27.0]: https://github.com/bitcoindevkit/bdk/compare/v0.26.0...v0.27.0
+[v0.27.1]: https://github.com/bitcoindevkit/bdk/compare/v0.27.0...v0.27.1
+[Unreleased]: https://github.com/bitcoindevkit/bdk/compare/v0.27.1...HEAD

CONTRIBUTING.md

@@ -0,0 +1,118 @@
+Contributing to BDK
+==============================
+
+The BDK project operates an open contributor model where anyone is welcome to
+contribute towards development in the form of peer review, documentation,
+testing and patches.
+
+Anyone is invited to contribute without regard to technical experience,
+"expertise", OSS experience, age, or other concern. However, the development of
+cryptocurrencies demands a high-level of rigor, adversarial thinking, thorough
+testing and risk-minimization.
+Any bug may cost users real money. That being said, we deeply welcome people
+contributing for the first time to an open source project or picking up Rust while
+contributing. Don't be shy, you'll learn.
+
+Communications Channels
+-----------------------
+
+Communication about BDK happens primarily on the [BDK Discord](https://discord.gg/dstn4dQ).
+
+Discussion about code base improvements happens in GitHub [issues](https://github.com/bitcoindevkit/bdk/issues) and
+on [pull requests](https://github.com/bitcoindevkit/bdk/pulls).
+
+Contribution Workflow
+---------------------
+
+The codebase is maintained using the "contributor workflow" where everyone
+without exception contributes patch proposals using "pull requests". This
+facilitates social contribution, easy testing and peer review.
+
+To contribute a patch, the workflow is as follows:
+
+  1. Fork Repository
+  2. Create topic branch
+  3. Commit patches
+
+In general commits should be atomic and diffs should be easy to read.
+For this reason do not mix any formatting fixes or code moves with actual code
+changes. Further, each commit, individually, should compile and pass tests, in
+order to ensure git bisect and other automated tools function properly.
+
+When adding a new feature, thought must be given to the long term technical
+debt.
+Every new feature should be covered by functional tests where possible.
+
+When refactoring, structure your PR to make it easy to review and don't
+hesitate to split it into multiple small, focused PRs.
+
+The Minimal Supported Rust Version is **1.57.0** (enforced by our CI).
+
+Commits should cover both the issue fixed and the solution's rationale.
+These [guidelines](https://chris.beams.io/posts/git-commit/) should be kept in mind. Commit messages should follow the ["Conventional Commits 1.0.0"](https://www.conventionalcommits.org/en/v1.0.0/) to make commit histories easier to read by humans and automated tools. 
+
+To facilitate communication with other contributors, the project is making use
+of GitHub's "assignee" field. First check that no one is assigned and then
+comment suggesting that you're working on it. If someone is already assigned,
+don't hesitate to ask if the assigned party or previous commenter are still
+working on it if it has been awhile.
+
+Deprecation policy
+------------------
+
+Where possible, breaking existing APIs should be avoided. Instead, add new APIs and
+use [`#[deprecated]`](https://github.com/rust-lang/rfcs/blob/master/text/1270-deprecation.md)
+to discourage use of the old one.
+
+Deprecated APIs are typically maintained for one release cycle. In other words, an
+API that has been deprecated with the 0.10 release can be expected to be removed in the
+0.11 release. This allows for smoother upgrades without incurring too much technical
+debt inside this library.
+
+If you deprecated an API as part of a contribution, we encourage you to "own" that API
+and send a follow-up to remove it as part of the next release cycle.
+
+Peer review
+-----------
+
+Anyone may participate in peer review which is expressed by comments in the
+pull request. Typically reviewers will review the code for obvious errors, as
+well as test out the patch set and opine on the technical merits of the patch.
+PR should be reviewed first on the conceptual level before focusing on code
+style or grammar fixes.
+
+Coding Conventions
+------------------
+
+This codebase uses spaces, not tabs.
+Use `cargo fmt` with the default settings to format code before committing.
+This is also enforced by the CI.
+
+Security
+--------
+
+Security is a high priority of BDK; disclosure of security vulnerabilities helps
+prevent user loss of funds.
+
+Note that BDK is currently considered "pre-production" during this time, there
+is no special handling of security issues. Please simply open an issue on
+Github.
+
+Testing
+-------
+
+Related to the security aspect, BDK developers take testing very seriously.
+Due to the modular nature of the project, writing new functional tests is easy
+and good test coverage of the codebase is an important goal.
+Refactoring the project to enable fine-grained unit testing is also an ongoing
+effort.
+
+Going further
+-------------
+
+You may be interested by Jon Atacks guide on [How to review Bitcoin Core PRs](https://github.com/jonatack/bitcoin-development/blob/master/how-to-review-bitcoin-core-prs.md)
+and [How to make Bitcoin Core PRs](https://github.com/jonatack/bitcoin-development/blob/master/how-to-make-bitcoin-core-prs.md).
+While there are differences between the projects in terms of context and
+maturity, many of the suggestions offered apply to this project.
+
+Overall, have fun :)

Cargo.toml

@@ -1,58 +1,25 @@
-[package]
-name = "magical-bitcoin-wallet"
-version = "0.1.0"
-edition = "2018"
-authors = ["Riccardo Casatta <riccardo@casatta.it>", "Alekos Filini <alekos.filini@gmail.com>"]
-
-[dependencies]
-log = "^0.4"
-bitcoin = { version = "0.23", features = ["use-serde"] }
-miniscript = { version = "0.12" }
-serde = { version = "^1.0", features = ["derive"] }
-serde_json = { version = "^1.0" }
-base64 = "^0.11"
-async-trait = "0.1"
-
-# Optional dependencies
-sled = { version = "0.31.0", optional = true }
-electrum-client = { git = "https://github.com/MagicalBitcoin/rust-electrum-client.git", optional = true }
-reqwest = { version = "0.10", optional = true, features = ["json"] }
-futures = { version = "0.3", optional = true }
-clap = { version = "2.33", optional = true }
-
-[features]
-minimal = []
-compiler = ["miniscript/compiler"]
-default = ["key-value-db", "electrum"]
-electrum = ["electrum-client"]
-esplora = ["reqwest", "futures"]
-key-value-db = ["sled"]
-cli-utils = ["clap"]
-
-[dev-dependencies]
-tokio = { version = "0.2", features = ["macros"] }
-lazy_static = "1.4"
-rustyline = "6.0"
-dirs = "2.0"
-env_logger = "0.7"
-rand = "0.7"
-
-[[example]]
-name = "repl"
-required-features = ["cli-utils"]
-[[example]]
-name = "psbt"
-[[example]]
-name = "parse_descriptor"
-
-[[example]]
-name = "miniscriptc"
-path = "examples/compiler.rs"
-required-features = ["compiler"]
-
-# Provide a more user-friendly alias for the REPL
-[[example]]
-name = "magic"
-path = "examples/repl.rs"
-required-features = ["cli-utils"]
+[workspace]
+resolver = "2"
+members = [
+    "crates/wallet",
+    "crates/chain",
+    "crates/file_store",
+    "crates/electrum",
+    "crates/esplora",
+    "crates/bitcoind_rpc",
+    "crates/hwi",
+    "crates/testenv",
+    "example-crates/example_cli",
+    "example-crates/example_electrum",
+    "example-crates/example_esplora",
+    "example-crates/example_bitcoind_rpc_polling",
+    "example-crates/wallet_electrum",
+    "example-crates/wallet_esplora_blocking",
+    "example-crates/wallet_esplora_async",
+    "example-crates/wallet_rpc",
+    "nursery/tmp_plan",
+    "nursery/coin_select"
+]
 
+[workspace.package]
+authors = ["Bitcoin Dev Kit Developers"]

DEVELOPMENT_CYCLE.md

@@ -0,0 +1,16 @@
+# Development Cycle
+
+This project follows a regular releasing schedule similar to the one [used by the Rust language]. In short, this means that a new release is made at a regular cadence, with all the feature/bugfixes that made it to `master` in time. This ensures that we don't keep delaying releases waiting for "just one more little thing".
+
+This project uses [Semantic Versioning], but is currently at MAJOR version zero (0.y.z) meaning it is still in initial development. Anything MAY change at any time. The public API SHOULD NOT be considered stable. Until we reach version `1.0.0` we will do our best to document any breaking API changes in the changelog info attached to each release tag.
+
+We decided to maintain a faster release cycle while the library is still in "beta", i.e. before release `1.0.0`: since we are constantly adding new features and, even more importantly, fixing issues, we want developers to have access to those updates as fast as possible. For this reason we will make a release **every 4 weeks**.
+
+Once the project reaches a more mature state (>= `1.0.0`), we will very likely switch to longer release cycles of **6 weeks**.
+
+The "feature freeze" will happen **one week before the release date**. This means a new branch will be created originating from the `master` tip at that time, and in that branch we will stop adding new features and only focus on ensuring the ones we've added are working properly.
+
+To create a new release a release manager will create a new issue using the `Release` template and follow the template instructions.
+
+[used by the Rust language]: https://doc.rust-lang.org/book/appendix-07-nightly-rust.html
+[Semantic Versioning]: https://semver.org/

LICENSE

@@ -1,21 +1,14 @@
-MIT License
+This software is licensed under [Apache 2.0](LICENSE-APACHE) or
+[MIT](LICENSE-MIT), at your option.
 
-Copyright (c) 2020 Magical Bitcoin
+Some files retain their own copyright notice, however, for full authorship
+information, see version control history.
 
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
+Except as otherwise noted in individual files, all files in this repository are
+licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+http://www.apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
+http://opensource.org/licenses/MIT>, at your option.
 
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
+You may not use, copy, modify, merge, publish, distribute, sublicense, and/or
+sell copies of this software or any files in this repository except in
+accordance with one or both of these licenses.

LICENSE-APACHE

@@ -0,0 +1,201 @@
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright [yyyy] [name of copyright owner]
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

LICENSE-MIT

@@ -0,0 +1,16 @@
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -1,7 +1,94 @@
-# Magical Bitcoin Wallet
+# The Bitcoin Dev Kit
 
-A modern, lightweight, descriptor-based wallet written in Rust!
+<div align="center">
+  <h1>BDK</h1>
 
-## Getting Started
+  <img src="./static/bdk.png" width="220" />
 
-See the documentation at [magicalbitcoin.org](https://magicalbitcoin.org)
+  <p>
+    <strong>A modern, lightweight, descriptor-based wallet library written in Rust!</strong>
+  </p>
+
+  <p>
+    <a href="https://crates.io/crates/bdk_wallet"><img alt="Crate Info" src="https://img.shields.io/crates/v/bdk_wallet.svg"/></a>
+    <a href="https://github.com/bitcoindevkit/bdk/blob/master/LICENSE"><img alt="MIT or Apache-2.0 Licensed" src="https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg"/></a>
+    <a href="https://github.com/bitcoindevkit/bdk/actions?query=workflow%3ACI"><img alt="CI Status" src="https://github.com/bitcoindevkit/bdk/workflows/CI/badge.svg"></a>
+    <a href="https://coveralls.io/github/bitcoindevkit/bdk?branch=master"><img src="https://coveralls.io/repos/github/bitcoindevkit/bdk/badge.svg?branch=master"/></a>
+    <a href="https://docs.rs/bdk_wallet"><img alt="Wallet API Docs" src="https://img.shields.io/badge/docs.rs-bdk_wallet-green"/></a>
+    <a href="https://blog.rust-lang.org/2022/08/11/Rust-1.63.0.html"><img alt="Rustc Version 1.63.0+" src="https://img.shields.io/badge/rustc-1.63.0%2B-lightgrey.svg"/></a>
+    <a href="https://discord.gg/d7NkDKm"><img alt="Chat on Discord" src="https://img.shields.io/discord/753336465005608961?logo=discord"></a>
+  </p>
+
+  <h4>
+    <a href="https://bitcoindevkit.org">Project Homepage</a>
+    <span> | </span>
+    <a href="https://docs.rs/bdk_wallet">Documentation</a>
+  </h4>
+</div>
+
+## About
+
+The `bdk` libraries aims to provide well engineered and reviewed components for Bitcoin based applications.
+It is built upon the excellent [`rust-bitcoin`] and [`rust-miniscript`] crates.
+
+> ⚠ The Bitcoin Dev Kit developers are in the process of releasing a `v1.0` which is a fundamental re-write of how the library works.
+> See for some background on this project: https://bitcoindevkit.org/blog/road-to-bdk-1/ (ignore the timeline 😁)
+> For a release timeline see the [`BDK 1.0 project page`].
+
+## Architecture
+
+The project is split up into several crates in the `/crates` directory:
+
+- [`wallet`](./crates/wallet): Contains the central high level `Wallet` type that is built from the low-level mechanisms provided by the other components
+- [`chain`](./crates/chain): Tools for storing and indexing chain data
+- [`persist`](./crates/persist): Types that define data persistence of a BDK wallet
+- [`file_store`](./crates/file_store): A (experimental) persistence backend for storing chain data in a single file.
+- [`esplora`](./crates/esplora): Extends the [`esplora-client`] crate with methods to fetch chain data from an esplora HTTP server in the form that [`bdk_chain`] and `Wallet` can consume.
+- [`electrum`](./crates/electrum): Extends the [`electrum-client`] crate with methods to fetch chain data from an electrum server in the form that [`bdk_chain`] and `Wallet` can consume.
+
+Fully working examples of how to use these components are in `/example-crates`:
+- [`example_cli`](./example-crates/example_cli): Library used by the `example_*` crates. Provides utilities for syncing, showing the balance, generating addresses and creating transactions without using the bdk_wallet `Wallet`.
+- [`example_electrum`](./example-crates/example_electrum): A command line Bitcoin wallet application built on top of `example_cli` and the `electrum` crate. It shows the power of the bdk tools (`chain` + `file_store` + `electrum`), without depending on the main `bdk_wallet` library.
+- [`example_esplora`](./example-crates/example_esplora): A command line Bitcoin wallet application built on top of `example_cli` and the `esplora` crate. It shows the power of the bdk tools (`chain` + `file_store` + `esplora`), without depending on the main `bdk_wallet` library.
+- [`example_bitcoind_rpc_polling`](./example-crates/example_bitcoind_rpc_polling): A command line Bitcoin wallet application built on top of `example_cli` and the `bitcoind_rpc` crate. It shows the power of the bdk tools (`chain` + `file_store` + `bitcoind_rpc`), without depending on the main `bdk_wallet` library.
+- [`wallet_esplora_blocking`](./example-crates/wallet_esplora_blocking): Uses the `Wallet` to sync and spend using the Esplora blocking interface.
+- [`wallet_esplora_async`](./example-crates/wallet_esplora_async): Uses the `Wallet` to sync and spend using the Esplora asynchronous interface.
+- [`wallet_electrum`](./example-crates/wallet_electrum): Uses the `Wallet` to sync and spend using Electrum.
+
+[`BDK 1.0 project page`]: https://github.com/orgs/bitcoindevkit/projects/14
+[`rust-miniscript`]: https://github.com/rust-bitcoin/rust-miniscript
+[`rust-bitcoin`]: https://github.com/rust-bitcoin/rust-bitcoin
+[`esplora-client`]: https://docs.rs/esplora-client/
+[`electrum-client`]: https://docs.rs/electrum-client/
+[`bdk_chain`]: https://docs.rs/bdk-chain/
+
+## Minimum Supported Rust Version (MSRV)
+This library should compile with any combination of features with Rust 1.63.0.
+
+To build with the MSRV you will need to pin dependencies as follows:
+
+```shell
+cargo update -p zstd-sys --precise "2.0.8+zstd.1.5.5"
+cargo update -p time --precise "0.3.20"
+cargo update -p home --precise "0.5.5"
+cargo update -p proptest --precise "1.2.0"
+cargo update -p url --precise "2.5.0"
+cargo update -p cc --precise "1.0.105"
+cargo update -p tokio --precise "1.38.1"
+```
+
+## License
+
+Licensed under either of
+
+* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or <https://www.apache.org/licenses/LICENSE-2.0>)
+* MIT license ([LICENSE-MIT](LICENSE-MIT) or <https://opensource.org/licenses/MIT>)
+
+at your option.
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally
+submitted for inclusion in the work by you, as defined in the Apache-2.0
+license, shall be dual licensed as above, without any additional terms or
+conditions.

ci/Dockerfile.ledger

@@ -0,0 +1,9 @@
+# Taken from bitcoindevkit/rust-hwi
+FROM ghcr.io/ledgerhq/speculos
+
+RUN apt-get update
+RUN apt-get install wget -y
+RUN wget "https://github.com/LedgerHQ/speculos/blob/master/apps/nanos%23btc%232.1%231c8db8da.elf?raw=true" -O /speculos/btc.elf
+ADD automation.json /speculos/automation.json
+
+ENTRYPOINT ["python", "./speculos.py", "--automation", "file:automation.json", "--model", "nanos", "--display", "headless", "--vnc-port", "41000", "btc.elf"]

ci/automation.json

@@ -0,0 +1,30 @@
+{
+    "version": 1,
+    "rules": [
+        {
+            "regexp": "Address \\(\\d/\\d\\)|Message hash \\(\\d/\\d\\)|Confirm|Fees|Review|Amount",
+            "actions": [
+                [ "button", 2, true ],
+                [ "button", 2, false ]
+            ]
+        },
+        {
+            "text": "Sign",
+            "conditions": [
+                [ "seen", false ]
+            ],
+            "actions": [
+                [ "button", 2, true ],
+                [ "button", 2, false ],
+                [ "setbool", "seen", true ]
+            ]
+        },
+        {
+            "regexp": "Approve|Sign|Accept",
+            "actions": [
+                [ "button", 3, true ],
+                [ "button", 3, false ]
+            ]
+        }
+    ]
+}

ci/start-core.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env sh
+
+echo "Starting bitcoin node."
+mkdir $GITHUB_WORKSPACE/.bitcoin
+/root/bitcoind -regtest -server -daemon -datadir=$GITHUB_WORKSPACE/.bitcoin -fallbackfee=0.0002 -rpcallowip=0.0.0.0/0 -rpcbind=0.0.0.0 -blockfilterindex=1 -peerblockfilters=1
+
+echo "Waiting for bitcoin node."
+until /root/bitcoin-cli -regtest -datadir=$GITHUB_WORKSPACE/.bitcoin getblockchaininfo; do
+    sleep 1
+done
+/root/bitcoin-cli -regtest -datadir=$GITHUB_WORKSPACE/.bitcoin createwallet $BDK_RPC_WALLET
+echo "Generating 150 bitcoin blocks."
+ADDR=$(/root/bitcoin-cli -regtest -datadir=$GITHUB_WORKSPACE/.bitcoin -rpcwallet=$BDK_RPC_WALLET getnewaddress)
+/root/bitcoin-cli -regtest -datadir=$GITHUB_WORKSPACE/.bitcoin generatetoaddress 150 $ADDR

clippy.toml

@@ -0,0 +1 @@
+msrv="1.63.0"

crates/bitcoind_rpc/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "bdk_bitcoind_rpc"
+version = "0.13.0"
+edition = "2021"
+rust-version = "1.63"
+homepage = "https://bitcoindevkit.org"
+repository = "https://github.com/bitcoindevkit/bdk"
+documentation = "https://docs.rs/bdk_bitcoind_rpc"
+description = "This crate is used for emitting blockchain data from the `bitcoind` RPC interface."
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bitcoin = { version = "0.32.0", default-features = false }
+bitcoincore-rpc = { version = "0.19.0" }
+bdk_chain = { path = "../chain", version = "0.17", default-features = false }
+
+[dev-dependencies]
+bdk_testenv = { path = "../testenv", default-features = false }
+
+[features]
+default = ["std"]
+std = ["bitcoin/std", "bdk_chain/std"]
+serde = ["bitcoin/serde", "bdk_chain/serde"]

crates/bitcoind_rpc/README.md

@@ -0,0 +1,3 @@
+# BDK Bitcoind RPC
+
+This crate is used for emitting blockchain data from the `bitcoind` RPC interface.

crates/bitcoind_rpc/src/lib.rs

@@ -0,0 +1,328 @@
+//! This crate is used for emitting blockchain data from the `bitcoind` RPC interface. It does not
+//! use the wallet RPC API, so this crate can be used with wallet-disabled Bitcoin Core nodes.
+//!
+//! [`Emitter`] is the main structure which sources blockchain data from [`bitcoincore_rpc::Client`].
+//!
+//! To only get block updates (exclude mempool transactions), the caller can use
+//! [`Emitter::next_block`] or/and [`Emitter::next_header`] until it returns `Ok(None)` (which means
+//! the chain tip is reached). A separate method, [`Emitter::mempool`] can be used to emit the whole
+//! mempool.
+#![warn(missing_docs)]
+
+use bdk_chain::{local_chain::CheckPoint, BlockId};
+use bitcoin::{block::Header, Block, BlockHash, Transaction};
+pub use bitcoincore_rpc;
+use bitcoincore_rpc::bitcoincore_rpc_json;
+
+/// The [`Emitter`] is used to emit data sourced from [`bitcoincore_rpc::Client`].
+///
+/// Refer to [module-level documentation] for more.
+///
+/// [module-level documentation]: crate
+pub struct Emitter<'c, C> {
+    client: &'c C,
+    start_height: u32,
+
+    /// The checkpoint of the last-emitted block that is in the best chain. If it is later found
+    /// that the block is no longer in the best chain, it will be popped off from here.
+    last_cp: CheckPoint,
+
+    /// The block result returned from rpc of the last-emitted block. As this result contains the
+    /// next block's block hash (which we use to fetch the next block), we set this to `None`
+    /// whenever there are no more blocks, or the next block is no longer in the best chain. This
+    /// gives us an opportunity to re-fetch this result.
+    last_block: Option<bitcoincore_rpc_json::GetBlockResult>,
+
+    /// The latest first-seen epoch of emitted mempool transactions. This is used to determine
+    /// whether a mempool transaction is already emitted.
+    last_mempool_time: usize,
+
+    /// The last emitted block during our last mempool emission. This is used to determine whether
+    /// there has been a reorg since our last mempool emission.
+    last_mempool_tip: Option<u32>,
+}
+
+impl<'c, C: bitcoincore_rpc::RpcApi> Emitter<'c, C> {
+    /// Construct a new [`Emitter`].
+    ///
+    /// `last_cp` informs the emitter of the chain we are starting off with. This way, the emitter
+    /// can start emission from a block that connects to the original chain.
+    ///
+    /// `start_height` starts emission from a given height (if there are no conflicts with the
+    /// original chain).
+    pub fn new(client: &'c C, last_cp: CheckPoint, start_height: u32) -> Self {
+        Self {
+            client,
+            start_height,
+            last_cp,
+            last_block: None,
+            last_mempool_time: 0,
+            last_mempool_tip: None,
+        }
+    }
+
+    /// Emit mempool transactions, alongside their first-seen unix timestamps.
+    ///
+    /// This method emits each transaction only once, unless we cannot guarantee the transaction's
+    /// ancestors are already emitted.
+    ///
+    /// To understand why, consider a receiver which filters transactions based on whether it
+    /// alters the UTXO set of tracked script pubkeys. If an emitted mempool transaction spends a
+    /// tracked UTXO which is confirmed at height `h`, but the receiver has only seen up to block
+    /// of height `h-1`, we want to re-emit this transaction until the receiver has seen the block
+    /// at height `h`.
+    pub fn mempool(&mut self) -> Result<Vec<(Transaction, u64)>, bitcoincore_rpc::Error> {
+        let client = self.client;
+
+        // This is the emitted tip height during the last mempool emission.
+        let prev_mempool_tip = self
+            .last_mempool_tip
+            // We use `start_height - 1` as we cannot guarantee that the block at
+            // `start_height` has been emitted.
+            .unwrap_or(self.start_height.saturating_sub(1));
+
+        // Mempool txs come with a timestamp of when the tx is introduced to the mempool. We keep
+        // track of the latest mempool tx's timestamp to determine whether we have seen a tx
+        // before. `prev_mempool_time` is the previous timestamp and `last_time` records what will
+        // be the new latest timestamp.
+        let prev_mempool_time = self.last_mempool_time;
+        let mut latest_time = prev_mempool_time;
+
+        let txs_to_emit = client
+            .get_raw_mempool_verbose()?
+            .into_iter()
+            .filter_map({
+                let latest_time = &mut latest_time;
+                move |(txid, tx_entry)| -> Option<Result<_, bitcoincore_rpc::Error>> {
+                    let tx_time = tx_entry.time as usize;
+                    if tx_time > *latest_time {
+                        *latest_time = tx_time;
+                    }
+
+                    // Avoid emitting transactions that are already emitted if we can guarantee
+                    // blocks containing ancestors are already emitted. The bitcoind rpc interface
+                    // provides us with the block height that the tx is introduced to the mempool.
+                    // If we have already emitted the block of height, we can assume that all
+                    // ancestor txs have been processed by the receiver.
+                    let is_already_emitted = tx_time <= prev_mempool_time;
+                    let is_within_height = tx_entry.height <= prev_mempool_tip as _;
+                    if is_already_emitted && is_within_height {
+                        return None;
+                    }
+
+                    let tx = match client.get_raw_transaction(&txid, None) {
+                        Ok(tx) => tx,
+                        // the tx is confirmed or evicted since `get_raw_mempool_verbose`
+                        Err(err) if err.is_not_found_error() => return None,
+                        Err(err) => return Some(Err(err)),
+                    };
+
+                    Some(Ok((tx, tx_time as u64)))
+                }
+            })
+            .collect::<Result<Vec<_>, _>>()?;
+
+        self.last_mempool_time = latest_time;
+        self.last_mempool_tip = Some(self.last_cp.height());
+
+        Ok(txs_to_emit)
+    }
+
+    /// Emit the next block height and header (if any).
+    pub fn next_header(&mut self) -> Result<Option<BlockEvent<Header>>, bitcoincore_rpc::Error> {
+        Ok(poll(self, |hash| self.client.get_block_header(hash))?
+            .map(|(checkpoint, block)| BlockEvent { block, checkpoint }))
+    }
+
+    /// Emit the next block height and block (if any).
+    pub fn next_block(&mut self) -> Result<Option<BlockEvent<Block>>, bitcoincore_rpc::Error> {
+        Ok(poll(self, |hash| self.client.get_block(hash))?
+            .map(|(checkpoint, block)| BlockEvent { block, checkpoint }))
+    }
+}
+
+/// A newly emitted block from [`Emitter`].
+#[derive(Debug)]
+pub struct BlockEvent<B> {
+    /// Either a full [`Block`] or [`Header`] of the new block.
+    pub block: B,
+
+    /// The checkpoint of the new block.
+    ///
+    /// A [`CheckPoint`] is a node of a linked list of [`BlockId`]s. This checkpoint is linked to
+    /// all [`BlockId`]s originally passed in [`Emitter::new`] as well as emitted blocks since then.
+    /// These blocks are guaranteed to be of the same chain.
+    ///
+    /// This is important as BDK structures require block-to-apply to be connected with another
+    /// block in the original chain.
+    pub checkpoint: CheckPoint,
+}
+
+impl<B> BlockEvent<B> {
+    /// The block height of this new block.
+    pub fn block_height(&self) -> u32 {
+        self.checkpoint.height()
+    }
+
+    /// The block hash of this new block.
+    pub fn block_hash(&self) -> BlockHash {
+        self.checkpoint.hash()
+    }
+
+    /// The [`BlockId`] of a previous block that this block connects to.
+    ///
+    /// This either returns a [`BlockId`] of a previously emitted block or from the chain we started
+    /// with (passed in as `last_cp` in [`Emitter::new`]).
+    ///
+    /// This value is derived from [`BlockEvent::checkpoint`].
+    pub fn connected_to(&self) -> BlockId {
+        match self.checkpoint.prev() {
+            Some(prev_cp) => prev_cp.block_id(),
+            // there is no previous checkpoint, so just connect with itself
+            None => self.checkpoint.block_id(),
+        }
+    }
+}
+
+enum PollResponse {
+    Block(bitcoincore_rpc_json::GetBlockResult),
+    NoMoreBlocks,
+    /// Fetched block is not in the best chain.
+    BlockNotInBestChain,
+    AgreementFound(bitcoincore_rpc_json::GetBlockResult, CheckPoint),
+    /// Force the genesis checkpoint down the receiver's throat.
+    AgreementPointNotFound(BlockHash),
+}
+
+fn poll_once<C>(emitter: &Emitter<C>) -> Result<PollResponse, bitcoincore_rpc::Error>
+where
+    C: bitcoincore_rpc::RpcApi,
+{
+    let client = emitter.client;
+
+    if let Some(last_res) = &emitter.last_block {
+        let next_hash = if last_res.height < emitter.start_height as _ {
+            // enforce start height
+            let next_hash = client.get_block_hash(emitter.start_height as _)?;
+            // make sure last emission is still in best chain
+            if client.get_block_hash(last_res.height as _)? != last_res.hash {
+                return Ok(PollResponse::BlockNotInBestChain);
+            }
+            next_hash
+        } else {
+            match last_res.nextblockhash {
+                None => return Ok(PollResponse::NoMoreBlocks),
+                Some(next_hash) => next_hash,
+            }
+        };
+
+        let res = client.get_block_info(&next_hash)?;
+        if res.confirmations < 0 {
+            return Ok(PollResponse::BlockNotInBestChain);
+        }
+
+        return Ok(PollResponse::Block(res));
+    }
+
+    for cp in emitter.last_cp.iter() {
+        let res = match client.get_block_info(&cp.hash()) {
+            // block not in best chain
+            Ok(res) if res.confirmations < 0 => continue,
+            Ok(res) => res,
+            Err(e) if e.is_not_found_error() => {
+                if cp.height() > 0 {
+                    continue;
+                }
+                // if we can't find genesis block, we can't create an update that connects
+                break;
+            }
+            Err(e) => return Err(e),
+        };
+
+        // agreement point found
+        return Ok(PollResponse::AgreementFound(res, cp));
+    }
+
+    let genesis_hash = client.get_block_hash(0)?;
+    Ok(PollResponse::AgreementPointNotFound(genesis_hash))
+}
+
+fn poll<C, V, F>(
+    emitter: &mut Emitter<C>,
+    get_item: F,
+) -> Result<Option<(CheckPoint, V)>, bitcoincore_rpc::Error>
+where
+    C: bitcoincore_rpc::RpcApi,
+    F: Fn(&BlockHash) -> Result<V, bitcoincore_rpc::Error>,
+{
+    loop {
+        match poll_once(emitter)? {
+            PollResponse::Block(res) => {
+                let height = res.height as u32;
+                let hash = res.hash;
+                let item = get_item(&hash)?;
+
+                let new_cp = emitter
+                    .last_cp
+                    .clone()
+                    .push(BlockId { height, hash })
+                    .expect("must push");
+                emitter.last_cp = new_cp.clone();
+                emitter.last_block = Some(res);
+                return Ok(Some((new_cp, item)));
+            }
+            PollResponse::NoMoreBlocks => {
+                emitter.last_block = None;
+                return Ok(None);
+            }
+            PollResponse::BlockNotInBestChain => {
+                emitter.last_block = None;
+                continue;
+            }
+            PollResponse::AgreementFound(res, cp) => {
+                let agreement_h = res.height as u32;
+
+                // The tip during the last mempool emission needs to in the best chain, we reduce
+                // it if it is not.
+                if let Some(h) = emitter.last_mempool_tip.as_mut() {
+                    if *h > agreement_h {
+                        *h = agreement_h;
+                    }
+                }
+
+                // get rid of evicted blocks
+                emitter.last_cp = cp;
+                emitter.last_block = Some(res);
+                continue;
+            }
+            PollResponse::AgreementPointNotFound(genesis_hash) => {
+                emitter.last_cp = CheckPoint::new(BlockId {
+                    height: 0,
+                    hash: genesis_hash,
+                });
+                emitter.last_block = None;
+                continue;
+            }
+        }
+    }
+}
+
+/// Extends [`bitcoincore_rpc::Error`].
+pub trait BitcoindRpcErrorExt {
+    /// Returns whether the error is a "not found" error.
+    ///
+    /// This is useful since [`Emitter`] emits [`Result<_, bitcoincore_rpc::Error>`]s as
+    /// [`Iterator::Item`].
+    fn is_not_found_error(&self) -> bool;
+}
+
+impl BitcoindRpcErrorExt for bitcoincore_rpc::Error {
+    fn is_not_found_error(&self) -> bool {
+        if let bitcoincore_rpc::Error::JsonRpc(bitcoincore_rpc::jsonrpc::Error::Rpc(rpc_err)) = self
+        {
+            rpc_err.code == -5
+        } else {
+            false
+        }
+    }
+}

crates/bitcoind_rpc/tests/test_emitter.rs

@@ -0,0 +1,738 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+use bdk_bitcoind_rpc::Emitter;
+use bdk_chain::{
+    bitcoin::{Address, Amount, Txid},
+    local_chain::{CheckPoint, LocalChain},
+    spk_txout::SpkTxOutIndex,
+    Balance, BlockId, IndexedTxGraph, Merge,
+};
+use bdk_testenv::{anyhow, TestEnv};
+use bitcoin::{hashes::Hash, Block, OutPoint, ScriptBuf, WScriptHash};
+use bitcoincore_rpc::RpcApi;
+
+/// Ensure that blocks are emitted in order even after reorg.
+///
+/// 1. Mine 101 blocks.
+/// 2. Emit blocks from [`Emitter`] and update the [`LocalChain`].
+/// 3. Reorg highest 6 blocks.
+/// 4. Emit blocks from [`Emitter`] and re-update the [`LocalChain`].
+#[test]
+pub fn test_sync_local_chain() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+    let network_tip = env.rpc_client().get_block_count()?;
+    let (mut local_chain, _) = LocalChain::from_genesis_hash(env.rpc_client().get_block_hash(0)?);
+    let mut emitter = Emitter::new(env.rpc_client(), local_chain.tip(), 0);
+
+    // Mine some blocks and return the actual block hashes.
+    // Because initializing `ElectrsD` already mines some blocks, we must include those too when
+    // returning block hashes.
+    let exp_hashes = {
+        let mut hashes = (0..=network_tip)
+            .map(|height| env.rpc_client().get_block_hash(height))
+            .collect::<Result<Vec<_>, _>>()?;
+        hashes.extend(env.mine_blocks(101 - network_tip as usize, None)?);
+        hashes
+    };
+
+    // See if the emitter outputs the right blocks.
+    println!("first sync:");
+    while let Some(emission) = emitter.next_block()? {
+        let height = emission.block_height();
+        let hash = emission.block_hash();
+        assert_eq!(
+            emission.block_hash(),
+            exp_hashes[height as usize],
+            "emitted block hash is unexpected"
+        );
+
+        assert_eq!(
+            local_chain.apply_update(emission.checkpoint,)?,
+            [(height, Some(hash))].into(),
+            "chain update changeset is unexpected",
+        );
+    }
+
+    assert_eq!(
+        local_chain
+            .iter_checkpoints()
+            .map(|cp| (cp.height(), cp.hash()))
+            .collect::<BTreeSet<_>>(),
+        exp_hashes
+            .iter()
+            .enumerate()
+            .map(|(i, hash)| (i as u32, *hash))
+            .collect::<BTreeSet<_>>(),
+        "final local_chain state is unexpected",
+    );
+
+    // Perform reorg.
+    let reorged_blocks = env.reorg(6)?;
+    let exp_hashes = exp_hashes
+        .iter()
+        .take(exp_hashes.len() - reorged_blocks.len())
+        .chain(&reorged_blocks)
+        .cloned()
+        .collect::<Vec<_>>();
+
+    // See if the emitter outputs the right blocks.
+    println!("after reorg:");
+    let mut exp_height = exp_hashes.len() - reorged_blocks.len();
+    while let Some(emission) = emitter.next_block()? {
+        let height = emission.block_height();
+        let hash = emission.block_hash();
+        assert_eq!(
+            height, exp_height as u32,
+            "emitted block has unexpected height"
+        );
+
+        assert_eq!(
+            hash, exp_hashes[height as usize],
+            "emitted block is unexpected"
+        );
+
+        assert_eq!(
+            local_chain.apply_update(emission.checkpoint,)?,
+            if exp_height == exp_hashes.len() - reorged_blocks.len() {
+                bdk_chain::local_chain::ChangeSet {
+                    blocks: core::iter::once((height, Some(hash)))
+                        .chain((height + 1..exp_hashes.len() as u32).map(|h| (h, None)))
+                        .collect(),
+                }
+            } else {
+                [(height, Some(hash))].into()
+            },
+            "chain update changeset is unexpected",
+        );
+
+        exp_height += 1;
+    }
+
+    assert_eq!(
+        local_chain
+            .iter_checkpoints()
+            .map(|cp| (cp.height(), cp.hash()))
+            .collect::<BTreeSet<_>>(),
+        exp_hashes
+            .iter()
+            .enumerate()
+            .map(|(i, hash)| (i as u32, *hash))
+            .collect::<BTreeSet<_>>(),
+        "final local_chain state is unexpected after reorg",
+    );
+
+    Ok(())
+}
+
+/// Ensure that [`EmittedUpdate::into_tx_graph_update`] behaves appropriately for both mempool and
+/// block updates.
+///
+/// [`EmittedUpdate::into_tx_graph_update`]: bdk_bitcoind_rpc::EmittedUpdate::into_tx_graph_update
+#[test]
+fn test_into_tx_graph() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+
+    println!("getting new addresses!");
+    let addr_0 = env
+        .rpc_client()
+        .get_new_address(None, None)?
+        .assume_checked();
+    let addr_1 = env
+        .rpc_client()
+        .get_new_address(None, None)?
+        .assume_checked();
+    let addr_2 = env
+        .rpc_client()
+        .get_new_address(None, None)?
+        .assume_checked();
+    println!("got new addresses!");
+
+    println!("mining block!");
+    env.mine_blocks(101, None)?;
+    println!("mined blocks!");
+
+    let (mut chain, _) = LocalChain::from_genesis_hash(env.rpc_client().get_block_hash(0)?);
+    let mut indexed_tx_graph = IndexedTxGraph::<BlockId, _>::new({
+        let mut index = SpkTxOutIndex::<usize>::default();
+        index.insert_spk(0, addr_0.script_pubkey());
+        index.insert_spk(1, addr_1.script_pubkey());
+        index.insert_spk(2, addr_2.script_pubkey());
+        index
+    });
+
+    let emitter = &mut Emitter::new(env.rpc_client(), chain.tip(), 0);
+
+    while let Some(emission) = emitter.next_block()? {
+        let height = emission.block_height();
+        let _ = chain.apply_update(emission.checkpoint)?;
+        let indexed_additions = indexed_tx_graph.apply_block_relevant(&emission.block, height);
+        assert!(indexed_additions.is_empty());
+    }
+
+    // send 3 txs to a tracked address, these txs will be in the mempool
+    let exp_txids = {
+        let mut txids = BTreeSet::new();
+        for _ in 0..3 {
+            txids.insert(env.rpc_client().send_to_address(
+                &addr_0,
+                Amount::from_sat(10_000),
+                None,
+                None,
+                None,
+                None,
+                None,
+                None,
+            )?);
+        }
+        txids
+    };
+
+    // expect that the next block should be none and we should get 3 txs from mempool
+    {
+        // next block should be `None`
+        assert!(emitter.next_block()?.is_none());
+
+        let mempool_txs = emitter.mempool()?;
+        let indexed_additions = indexed_tx_graph.batch_insert_unconfirmed(mempool_txs);
+        assert_eq!(
+            indexed_additions
+                .tx_graph
+                .txs
+                .iter()
+                .map(|tx| tx.compute_txid())
+                .collect::<BTreeSet<Txid>>(),
+            exp_txids,
+            "changeset should have the 3 mempool transactions",
+        );
+        assert!(indexed_additions.tx_graph.anchors.is_empty());
+    }
+
+    // mine a block that confirms the 3 txs
+    let exp_block_hash = env.mine_blocks(1, None)?[0];
+    let exp_block_height = env.rpc_client().get_block_info(&exp_block_hash)?.height as u32;
+    let exp_anchors = exp_txids
+        .iter()
+        .map({
+            let anchor = BlockId {
+                height: exp_block_height,
+                hash: exp_block_hash,
+            };
+            move |&txid| (anchor, txid)
+        })
+        .collect::<BTreeSet<_>>();
+
+    // must receive mined block which will confirm the transactions.
+    {
+        let emission = emitter.next_block()?.expect("must get mined block");
+        let height = emission.block_height();
+        let _ = chain.apply_update(emission.checkpoint)?;
+        let indexed_additions = indexed_tx_graph.apply_block_relevant(&emission.block, height);
+        assert!(indexed_additions.tx_graph.txs.is_empty());
+        assert!(indexed_additions.tx_graph.txouts.is_empty());
+        assert_eq!(indexed_additions.tx_graph.anchors, exp_anchors);
+    }
+
+    Ok(())
+}
+
+/// Ensure next block emitted after reorg is at reorg height.
+///
+/// After a reorg, if the last-emitted block height is equal or greater than the reorg height, and
+/// the fallback height is equal to or lower than the reorg height, the next block/header emission
+/// should be at the reorg height.
+///
+/// TODO: If the reorg height is lower than the fallback height, how do we find a block height to
+/// emit that can connect with our receiver chain?
+#[test]
+fn ensure_block_emitted_after_reorg_is_at_reorg_height() -> anyhow::Result<()> {
+    const EMITTER_START_HEIGHT: usize = 100;
+    const CHAIN_TIP_HEIGHT: usize = 110;
+
+    let env = TestEnv::new()?;
+    let mut emitter = Emitter::new(
+        env.rpc_client(),
+        CheckPoint::new(BlockId {
+            height: 0,
+            hash: env.rpc_client().get_block_hash(0)?,
+        }),
+        EMITTER_START_HEIGHT as _,
+    );
+
+    env.mine_blocks(CHAIN_TIP_HEIGHT, None)?;
+    while emitter.next_header()?.is_some() {}
+
+    for reorg_count in 1..=10 {
+        let replaced_blocks = env.reorg_empty_blocks(reorg_count)?;
+        let next_emission = emitter.next_header()?.expect("must emit block after reorg");
+        assert_eq!(
+            (
+                next_emission.block_height() as usize,
+                next_emission.block_hash()
+            ),
+            replaced_blocks[0],
+            "block emitted after reorg should be at the reorg height"
+        );
+        while emitter.next_header()?.is_some() {}
+    }
+
+    Ok(())
+}
+
+fn process_block(
+    recv_chain: &mut LocalChain,
+    recv_graph: &mut IndexedTxGraph<BlockId, SpkTxOutIndex<()>>,
+    block: Block,
+    block_height: u32,
+) -> anyhow::Result<()> {
+    recv_chain.apply_update(CheckPoint::from_header(&block.header, block_height))?;
+    let _ = recv_graph.apply_block(block, block_height);
+    Ok(())
+}
+
+fn sync_from_emitter<C>(
+    recv_chain: &mut LocalChain,
+    recv_graph: &mut IndexedTxGraph<BlockId, SpkTxOutIndex<()>>,
+    emitter: &mut Emitter<C>,
+) -> anyhow::Result<()>
+where
+    C: bitcoincore_rpc::RpcApi,
+{
+    while let Some(emission) = emitter.next_block()? {
+        let height = emission.block_height();
+        process_block(recv_chain, recv_graph, emission.block, height)?;
+    }
+    Ok(())
+}
+
+fn get_balance(
+    recv_chain: &LocalChain,
+    recv_graph: &IndexedTxGraph<BlockId, SpkTxOutIndex<()>>,
+) -> anyhow::Result<Balance> {
+    let chain_tip = recv_chain.tip().block_id();
+    let outpoints = recv_graph.index.outpoints().clone();
+    let balance = recv_graph
+        .graph()
+        .balance(recv_chain, chain_tip, outpoints, |_, _| true);
+    Ok(balance)
+}
+
+/// If a block is reorged out, ensure that containing transactions that do not exist in the
+/// replacement block(s) become unconfirmed.
+#[test]
+fn tx_can_become_unconfirmed_after_reorg() -> anyhow::Result<()> {
+    const PREMINE_COUNT: usize = 101;
+    const ADDITIONAL_COUNT: usize = 11;
+    const SEND_AMOUNT: Amount = Amount::from_sat(10_000);
+
+    let env = TestEnv::new()?;
+    let mut emitter = Emitter::new(
+        env.rpc_client(),
+        CheckPoint::new(BlockId {
+            height: 0,
+            hash: env.rpc_client().get_block_hash(0)?,
+        }),
+        0,
+    );
+
+    // setup addresses
+    let addr_to_mine = env
+        .rpc_client()
+        .get_new_address(None, None)?
+        .assume_checked();
+    let spk_to_track = ScriptBuf::new_p2wsh(&WScriptHash::all_zeros());
+    let addr_to_track = Address::from_script(&spk_to_track, bitcoin::Network::Regtest)?;
+
+    // setup receiver
+    let (mut recv_chain, _) = LocalChain::from_genesis_hash(env.rpc_client().get_block_hash(0)?);
+    let mut recv_graph = IndexedTxGraph::<BlockId, _>::new({
+        let mut recv_index = SpkTxOutIndex::default();
+        recv_index.insert_spk((), spk_to_track.clone());
+        recv_index
+    });
+
+    // mine and sync receiver up to tip
+    env.mine_blocks(PREMINE_COUNT, Some(addr_to_mine))?;
+
+    // create transactions that are tracked by our receiver
+    for _ in 0..ADDITIONAL_COUNT {
+        let txid = env.send(&addr_to_track, SEND_AMOUNT)?;
+
+        // lock outputs that send to `addr_to_track`
+        let outpoints_to_lock = env
+            .rpc_client()
+            .get_transaction(&txid, None)?
+            .transaction()?
+            .output
+            .into_iter()
+            .enumerate()
+            .filter(|(_, txo)| txo.script_pubkey == spk_to_track)
+            .map(|(vout, _)| OutPoint::new(txid, vout as _))
+            .collect::<Vec<_>>();
+        env.rpc_client().lock_unspent(&outpoints_to_lock)?;
+
+        let _ = env.mine_blocks(1, None)?;
+    }
+
+    // get emitter up to tip
+    sync_from_emitter(&mut recv_chain, &mut recv_graph, &mut emitter)?;
+
+    assert_eq!(
+        get_balance(&recv_chain, &recv_graph)?,
+        Balance {
+            confirmed: SEND_AMOUNT * ADDITIONAL_COUNT as u64,
+            ..Balance::default()
+        },
+        "initial balance must be correct",
+    );
+
+    // perform reorgs with different depths
+    for reorg_count in 1..=ADDITIONAL_COUNT {
+        env.reorg_empty_blocks(reorg_count)?;
+        sync_from_emitter(&mut recv_chain, &mut recv_graph, &mut emitter)?;
+
+        assert_eq!(
+            get_balance(&recv_chain, &recv_graph)?,
+            Balance {
+                confirmed: SEND_AMOUNT * (ADDITIONAL_COUNT - reorg_count) as u64,
+                ..Balance::default()
+            },
+            "reorg_count: {}",
+            reorg_count,
+        );
+    }
+
+    Ok(())
+}
+
+/// Ensure avoid-re-emission-logic is sound when [`Emitter`] is synced to tip.
+///
+/// The receiver (bdk_chain structures) is synced to the chain tip, and there is txs in the mempool.
+/// When we call Emitter::mempool multiple times, mempool txs should not be re-emitted, even if the
+/// chain tip is extended.
+#[test]
+fn mempool_avoids_re_emission() -> anyhow::Result<()> {
+    const BLOCKS_TO_MINE: usize = 101;
+    const MEMPOOL_TX_COUNT: usize = 2;
+
+    let env = TestEnv::new()?;
+    let mut emitter = Emitter::new(
+        env.rpc_client(),
+        CheckPoint::new(BlockId {
+            height: 0,
+            hash: env.rpc_client().get_block_hash(0)?,
+        }),
+        0,
+    );
+
+    // mine blocks and sync up emitter
+    let addr = env
+        .rpc_client()
+        .get_new_address(None, None)?
+        .assume_checked();
+    env.mine_blocks(BLOCKS_TO_MINE, Some(addr.clone()))?;
+    while emitter.next_header()?.is_some() {}
+
+    // have some random txs in mempool
+    let exp_txids = (0..MEMPOOL_TX_COUNT)
+        .map(|_| env.send(&addr, Amount::from_sat(2100)))
+        .collect::<Result<BTreeSet<Txid>, _>>()?;
+
+    // the first emission should include all transactions
+    let emitted_txids = emitter
+        .mempool()?
+        .into_iter()
+        .map(|(tx, _)| tx.compute_txid())
+        .collect::<BTreeSet<Txid>>();
+    assert_eq!(
+        emitted_txids, exp_txids,
+        "all mempool txs should be emitted"
+    );
+
+    // second emission should be empty
+    assert!(
+        emitter.mempool()?.is_empty(),
+        "second emission should be empty"
+    );
+
+    // mine empty blocks + sync up our emitter -> we should still not re-emit
+    for _ in 0..BLOCKS_TO_MINE {
+        env.mine_empty_block()?;
+    }
+    while emitter.next_header()?.is_some() {}
+    assert!(
+        emitter.mempool()?.is_empty(),
+        "third emission, after chain tip is extended, should also be empty"
+    );
+
+    Ok(())
+}
+
+/// Ensure mempool tx is still re-emitted if [`Emitter`] has not reached the tx's introduction
+/// height.
+///
+/// We introduce a mempool tx after each block, where blocks are empty (does not confirm previous
+/// mempool txs). Then we emit blocks from [`Emitter`] (intertwining `mempool` calls). We check
+/// that `mempool` should always re-emit txs that have introduced at a height greater than the last
+/// emitted block height.
+#[test]
+fn mempool_re_emits_if_tx_introduction_height_not_reached() -> anyhow::Result<()> {
+    const PREMINE_COUNT: usize = 101;
+    const MEMPOOL_TX_COUNT: usize = 21;
+
+    let env = TestEnv::new()?;
+    let mut emitter = Emitter::new(
+        env.rpc_client(),
+        CheckPoint::new(BlockId {
+            height: 0,
+            hash: env.rpc_client().get_block_hash(0)?,
+        }),
+        0,
+    );
+
+    // mine blocks to get initial balance, sync emitter up to tip
+    let addr = env
+        .rpc_client()
+        .get_new_address(None, None)?
+        .assume_checked();
+    env.mine_blocks(PREMINE_COUNT, Some(addr.clone()))?;
+    while emitter.next_header()?.is_some() {}
+
+    // mine blocks to introduce txs to mempool at different heights
+    let tx_introductions = (0..MEMPOOL_TX_COUNT)
+        .map(|_| -> anyhow::Result<_> {
+            let (height, _) = env.mine_empty_block()?;
+            let txid = env.send(&addr, Amount::from_sat(2100))?;
+            Ok((height, txid))
+        })
+        .collect::<anyhow::Result<BTreeSet<_>>>()?;
+
+    assert_eq!(
+        emitter
+            .mempool()?
+            .into_iter()
+            .map(|(tx, _)| tx.compute_txid())
+            .collect::<BTreeSet<_>>(),
+        tx_introductions.iter().map(|&(_, txid)| txid).collect(),
+        "first mempool emission should include all txs",
+    );
+    assert_eq!(
+        emitter
+            .mempool()?
+            .into_iter()
+            .map(|(tx, _)| tx.compute_txid())
+            .collect::<BTreeSet<_>>(),
+        tx_introductions.iter().map(|&(_, txid)| txid).collect(),
+        "second mempool emission should still include all txs",
+    );
+
+    // At this point, the emitter has seen all mempool transactions. It should only re-emit those
+    // that have introduction heights less than the emitter's last-emitted block tip.
+    while let Some(emission) = emitter.next_header()? {
+        let height = emission.block_height();
+        // We call `mempool()` twice.
+        // The second call (at height `h`) should skip the tx introduced at height `h`.
+        for try_index in 0..2 {
+            let exp_txids = tx_introductions
+                .range((height as usize + try_index, Txid::all_zeros())..)
+                .map(|&(_, txid)| txid)
+                .collect::<BTreeSet<_>>();
+            let emitted_txids = emitter
+                .mempool()?
+                .into_iter()
+                .map(|(tx, _)| tx.compute_txid())
+                .collect::<BTreeSet<_>>();
+            assert_eq!(
+                emitted_txids, exp_txids,
+                "\n emission {} (try {}) must only contain txs introduced at that height or lower: \n\t missing: {:?} \n\t extra: {:?}",
+                height,
+                try_index,
+                exp_txids
+                    .difference(&emitted_txids)
+                    .map(|txid| (txid, tx_introductions.iter().find_map(|(h, id)| if id == txid { Some(h) } else { None }).unwrap()))
+                    .collect::<Vec<_>>(),
+                emitted_txids
+                    .difference(&exp_txids)
+                    .map(|txid| (txid, tx_introductions.iter().find_map(|(h, id)| if id == txid { Some(h) } else { None }).unwrap()))
+                    .collect::<Vec<_>>(),
+            );
+        }
+    }
+
+    Ok(())
+}
+
+/// Ensure we force re-emit all mempool txs after reorg.
+#[test]
+fn mempool_during_reorg() -> anyhow::Result<()> {
+    const TIP_DIFF: usize = 10;
+    const PREMINE_COUNT: usize = 101;
+
+    let env = TestEnv::new()?;
+    let mut emitter = Emitter::new(
+        env.rpc_client(),
+        CheckPoint::new(BlockId {
+            height: 0,
+            hash: env.rpc_client().get_block_hash(0)?,
+        }),
+        0,
+    );
+
+    // mine blocks to get initial balance
+    let addr = env
+        .rpc_client()
+        .get_new_address(None, None)?
+        .assume_checked();
+    env.mine_blocks(PREMINE_COUNT, Some(addr.clone()))?;
+
+    // introduce mempool tx at each block extension
+    for _ in 0..TIP_DIFF {
+        env.mine_empty_block()?;
+        env.send(&addr, Amount::from_sat(2100))?;
+    }
+
+    // sync emitter to tip, first mempool emission should include all txs (as we haven't emitted
+    // from the mempool yet)
+    while emitter.next_header()?.is_some() {}
+    assert_eq!(
+        emitter
+            .mempool()?
+            .into_iter()
+            .map(|(tx, _)| tx.compute_txid())
+            .collect::<BTreeSet<_>>(),
+        env.rpc_client()
+            .get_raw_mempool()?
+            .into_iter()
+            .collect::<BTreeSet<_>>(),
+        "first mempool emission should include all txs",
+    );
+
+    // perform reorgs at different heights, these reorgs will not confirm transactions in the
+    // mempool
+    for reorg_count in 1..TIP_DIFF {
+        println!("REORG COUNT: {}", reorg_count);
+        env.reorg_empty_blocks(reorg_count)?;
+
+        // This is a map of mempool txids to tip height where the tx was introduced to the mempool
+        // we recalculate this at every loop as reorgs may evict transactions from mempool. We use
+        // the introduction height to determine whether we expect a tx to appear in a mempool
+        // emission.
+        // TODO: How can have have reorg logic in `TestEnv` NOT blacklast old blocks first?
+        let tx_introductions = dbg!(env
+            .rpc_client()
+            .get_raw_mempool_verbose()?
+            .into_iter()
+            .map(|(txid, entry)| (txid, entry.height as usize))
+            .collect::<BTreeMap<_, _>>());
+
+        // `next_header` emits the replacement block of the reorg
+        if let Some(emission) = emitter.next_header()? {
+            let height = emission.block_height();
+            println!("\t- replacement height: {}", height);
+
+            // the mempool emission (that follows the first block emission after reorg) should only
+            // include mempool txs introduced at reorg height or greater
+            let mempool = emitter
+                .mempool()?
+                .into_iter()
+                .map(|(tx, _)| tx.compute_txid())
+                .collect::<BTreeSet<_>>();
+            let exp_mempool = tx_introductions
+                .iter()
+                .filter(|(_, &intro_h)| intro_h >= (height as usize))
+                .map(|(&txid, _)| txid)
+                .collect::<BTreeSet<_>>();
+            assert_eq!(
+                mempool, exp_mempool,
+                "the first mempool emission after reorg should only include mempool txs introduced at reorg height or greater"
+            );
+
+            let mempool = emitter
+                .mempool()?
+                .into_iter()
+                .map(|(tx, _)| tx.compute_txid())
+                .collect::<BTreeSet<_>>();
+            let exp_mempool = tx_introductions
+                .iter()
+                .filter(|&(_, &intro_height)| intro_height > (height as usize))
+                .map(|(&txid, _)| txid)
+                .collect::<BTreeSet<_>>();
+            assert_eq!(
+                mempool, exp_mempool,
+                "following mempool emissions after reorg should exclude mempool introduction heights <= last emitted block height: \n\t missing: {:?} \n\t extra: {:?}",
+                exp_mempool
+                    .difference(&mempool)
+                    .map(|txid| (txid, tx_introductions.get(txid).unwrap()))
+                    .collect::<Vec<_>>(),
+                mempool
+                    .difference(&exp_mempool)
+                    .map(|txid| (txid, tx_introductions.get(txid).unwrap()))
+                    .collect::<Vec<_>>(),
+            );
+        }
+
+        // sync emitter to tip
+        while emitter.next_header()?.is_some() {}
+    }
+
+    Ok(())
+}
+
+/// If blockchain re-org includes the start height, emit new start height block
+///
+/// 1. mine 101 blocks
+/// 2. emit blocks 99a, 100a
+/// 3. invalidate blocks 99a, 100a, 101a
+/// 4. mine new blocks 99b, 100b, 101b
+/// 5. emit block 99b
+///
+/// The block hash of 99b should be different than 99a, but their previous block hashes should
+/// be the same.
+#[test]
+fn no_agreement_point() -> anyhow::Result<()> {
+    const PREMINE_COUNT: usize = 101;
+
+    let env = TestEnv::new()?;
+
+    // start height is 99
+    let mut emitter = Emitter::new(
+        env.rpc_client(),
+        CheckPoint::new(BlockId {
+            height: 0,
+            hash: env.rpc_client().get_block_hash(0)?,
+        }),
+        (PREMINE_COUNT - 2) as u32,
+    );
+
+    // mine 101 blocks
+    env.mine_blocks(PREMINE_COUNT, None)?;
+
+    // emit block 99a
+    let block_header_99a = emitter.next_header()?.expect("block 99a header").block;
+    let block_hash_99a = block_header_99a.block_hash();
+    let block_hash_98a = block_header_99a.prev_blockhash;
+
+    // emit block 100a
+    let block_header_100a = emitter.next_header()?.expect("block 100a header").block;
+    let block_hash_100a = block_header_100a.block_hash();
+
+    // get hash for block 101a
+    let block_hash_101a = env.rpc_client().get_block_hash(101)?;
+
+    // invalidate blocks 99a, 100a, 101a
+    env.rpc_client().invalidate_block(&block_hash_99a)?;
+    env.rpc_client().invalidate_block(&block_hash_100a)?;
+    env.rpc_client().invalidate_block(&block_hash_101a)?;
+
+    // mine new blocks 99b, 100b, 101b
+    env.mine_blocks(3, None)?;
+
+    // emit block header 99b
+    let block_header_99b = emitter.next_header()?.expect("block 99b header").block;
+    let block_hash_99b = block_header_99b.block_hash();
+    let block_hash_98b = block_header_99b.prev_blockhash;
+
+    assert_ne!(block_hash_99a, block_hash_99b);
+    assert_eq!(block_hash_98a, block_hash_98b);
+
+    Ok(())
+}

crates/chain/Cargo.toml

@@ -0,0 +1,35 @@
+[package]
+name = "bdk_chain"
+version = "0.17.0"
+edition = "2021"
+rust-version = "1.63"
+homepage = "https://bitcoindevkit.org"
+repository = "https://github.com/bitcoindevkit/bdk"
+documentation = "https://docs.rs/bdk_chain"
+description = "Collection of core structures for Bitcoin Dev Kit."
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bitcoin = { version = "0.32.0", default-features = false }
+serde_crate = { package = "serde", version = "1", optional = true, features = ["derive", "rc"] }
+
+# Use hashbrown as a feature flag to have HashSet and HashMap from it.
+hashbrown = { version = "0.9.1", optional = true, features = ["serde"] }
+miniscript = { version = "12.0.0", optional = true, default-features = false }
+
+# Feature dependencies
+rusqlite_crate = { package = "rusqlite", version = "0.31.0", features = ["bundled"], optional = true }
+serde_json = {version = "1", optional = true }
+
+[dev-dependencies]
+rand = "0.8"
+proptest = "1.2.0"
+
+[features]
+default = ["std", "miniscript"]
+std = ["bitcoin/std", "miniscript?/std"]
+serde = ["serde_crate", "bitcoin/serde", "miniscript?/serde"]
+rusqlite = ["std", "rusqlite_crate", "serde", "serde_json"]

crates/chain/README.md

@@ -0,0 +1,3 @@
+# BDK Chain
+
+BDK keychain tracker, tools for storing and indexing chain data.

crates/chain/src/balance.rs

@@ -0,0 +1,57 @@
+use bitcoin::Amount;
+
+/// Balance, differentiated into various categories.
+#[derive(Debug, PartialEq, Eq, Clone, Default)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(crate = "serde_crate",)
+)]
+pub struct Balance {
+    /// All coinbase outputs not yet matured
+    pub immature: Amount,
+    /// Unconfirmed UTXOs generated by a wallet tx
+    pub trusted_pending: Amount,
+    /// Unconfirmed UTXOs received from an external wallet
+    pub untrusted_pending: Amount,
+    /// Confirmed and immediately spendable balance
+    pub confirmed: Amount,
+}
+
+impl Balance {
+    /// Get sum of trusted_pending and confirmed coins.
+    ///
+    /// This is the balance you can spend right now that shouldn't get cancelled via another party
+    /// double spending it.
+    pub fn trusted_spendable(&self) -> Amount {
+        self.confirmed + self.trusted_pending
+    }
+
+    /// Get the whole balance visible to the wallet.
+    pub fn total(&self) -> Amount {
+        self.confirmed + self.trusted_pending + self.untrusted_pending + self.immature
+    }
+}
+
+impl core::fmt::Display for Balance {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(
+            f,
+            "{{ immature: {}, trusted_pending: {}, untrusted_pending: {}, confirmed: {} }}",
+            self.immature, self.trusted_pending, self.untrusted_pending, self.confirmed
+        )
+    }
+}
+
+impl core::ops::Add for Balance {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        Self {
+            immature: self.immature + other.immature,
+            trusted_pending: self.trusted_pending + other.trusted_pending,
+            untrusted_pending: self.untrusted_pending + other.untrusted_pending,
+            confirmed: self.confirmed + other.confirmed,
+        }
+    }
+}

crates/chain/src/chain_data.rs

@@ -0,0 +1,287 @@
+use bitcoin::{hashes::Hash, BlockHash, OutPoint, TxOut, Txid};
+
+use crate::{Anchor, AnchorFromBlockPosition, COINBASE_MATURITY};
+
+/// Represents the observed position of some chain data.
+///
+/// The generic `A` should be a [`Anchor`] implementation.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, core::hash::Hash)]
+pub enum ChainPosition<A> {
+    /// The chain data is seen as confirmed, and in anchored by `A`.
+    Confirmed(A),
+    /// The chain data is not confirmed and last seen in the mempool at this timestamp.
+    Unconfirmed(u64),
+}
+
+impl<A> ChainPosition<A> {
+    /// Returns whether [`ChainPosition`] is confirmed or not.
+    pub fn is_confirmed(&self) -> bool {
+        matches!(self, Self::Confirmed(_))
+    }
+}
+
+impl<A: Clone> ChainPosition<&A> {
+    /// Maps a [`ChainPosition<&A>`] into a [`ChainPosition<A>`] by cloning the contents.
+    pub fn cloned(self) -> ChainPosition<A> {
+        match self {
+            ChainPosition::Confirmed(a) => ChainPosition::Confirmed(a.clone()),
+            ChainPosition::Unconfirmed(last_seen) => ChainPosition::Unconfirmed(last_seen),
+        }
+    }
+}
+
+impl<A: Anchor> ChainPosition<A> {
+    /// Determines the upper bound of the confirmation height.
+    pub fn confirmation_height_upper_bound(&self) -> Option<u32> {
+        match self {
+            ChainPosition::Confirmed(a) => Some(a.confirmation_height_upper_bound()),
+            ChainPosition::Unconfirmed(_) => None,
+        }
+    }
+}
+
+/// Block height and timestamp at which a transaction is confirmed.
+#[derive(Debug, Clone, PartialEq, Eq, Copy, PartialOrd, Ord, core::hash::Hash)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(crate = "serde_crate")
+)]
+pub enum ConfirmationTime {
+    /// The transaction is confirmed
+    Confirmed {
+        /// Confirmation height.
+        height: u32,
+        /// Confirmation time in unix seconds.
+        time: u64,
+    },
+    /// The transaction is unconfirmed
+    Unconfirmed {
+        /// The last-seen timestamp in unix seconds.
+        last_seen: u64,
+    },
+}
+
+impl ConfirmationTime {
+    /// Construct an unconfirmed variant using the given `last_seen` time in unix seconds.
+    pub fn unconfirmed(last_seen: u64) -> Self {
+        Self::Unconfirmed { last_seen }
+    }
+
+    /// Returns whether [`ConfirmationTime`] is the confirmed variant.
+    pub fn is_confirmed(&self) -> bool {
+        matches!(self, Self::Confirmed { .. })
+    }
+}
+
+impl From<ChainPosition<ConfirmationBlockTime>> for ConfirmationTime {
+    fn from(observed_as: ChainPosition<ConfirmationBlockTime>) -> Self {
+        match observed_as {
+            ChainPosition::Confirmed(a) => Self::Confirmed {
+                height: a.block_id.height,
+                time: a.confirmation_time,
+            },
+            ChainPosition::Unconfirmed(last_seen) => Self::Unconfirmed { last_seen },
+        }
+    }
+}
+
+/// A reference to a block in the canonical chain.
+///
+/// `BlockId` implements [`Anchor`]. When a transaction is anchored to `BlockId`, the confirmation
+/// block and anchor block are the same block.
+#[derive(Debug, Clone, PartialEq, Eq, Copy, PartialOrd, Ord, core::hash::Hash)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(crate = "serde_crate")
+)]
+pub struct BlockId {
+    /// The height of the block.
+    pub height: u32,
+    /// The hash of the block.
+    pub hash: BlockHash,
+}
+
+impl Anchor for BlockId {
+    fn anchor_block(&self) -> Self {
+        *self
+    }
+}
+
+impl AnchorFromBlockPosition for BlockId {
+    fn from_block_position(_block: &bitcoin::Block, block_id: BlockId, _tx_pos: usize) -> Self {
+        block_id
+    }
+}
+
+impl Default for BlockId {
+    fn default() -> Self {
+        Self {
+            height: Default::default(),
+            hash: BlockHash::all_zeros(),
+        }
+    }
+}
+
+impl From<(u32, BlockHash)> for BlockId {
+    fn from((height, hash): (u32, BlockHash)) -> Self {
+        Self { height, hash }
+    }
+}
+
+impl From<BlockId> for (u32, BlockHash) {
+    fn from(block_id: BlockId) -> Self {
+        (block_id.height, block_id.hash)
+    }
+}
+
+impl From<(&u32, &BlockHash)> for BlockId {
+    fn from((height, hash): (&u32, &BlockHash)) -> Self {
+        Self {
+            height: *height,
+            hash: *hash,
+        }
+    }
+}
+
+/// An [`Anchor`] implementation that also records the exact confirmation time of the transaction.
+///
+/// Refer to [`Anchor`] for more details.
+#[derive(Debug, Default, Clone, PartialEq, Eq, Copy, PartialOrd, Ord, core::hash::Hash)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(crate = "serde_crate")
+)]
+pub struct ConfirmationBlockTime {
+    /// The anchor block.
+    pub block_id: BlockId,
+    /// The confirmation time of the transaction being anchored.
+    pub confirmation_time: u64,
+}
+
+impl Anchor for ConfirmationBlockTime {
+    fn anchor_block(&self) -> BlockId {
+        self.block_id
+    }
+
+    fn confirmation_height_upper_bound(&self) -> u32 {
+        self.block_id.height
+    }
+}
+
+impl AnchorFromBlockPosition for ConfirmationBlockTime {
+    fn from_block_position(block: &bitcoin::Block, block_id: BlockId, _tx_pos: usize) -> Self {
+        Self {
+            block_id,
+            confirmation_time: block.header.time as _,
+        }
+    }
+}
+
+/// A `TxOut` with as much data as we can retrieve about it
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
+pub struct FullTxOut<A> {
+    /// The position of the transaction in `outpoint` in the overall chain.
+    pub chain_position: ChainPosition<A>,
+    /// The location of the `TxOut`.
+    pub outpoint: OutPoint,
+    /// The `TxOut`.
+    pub txout: TxOut,
+    /// The txid and chain position of the transaction (if any) that has spent this output.
+    pub spent_by: Option<(ChainPosition<A>, Txid)>,
+    /// Whether this output is on a coinbase transaction.
+    pub is_on_coinbase: bool,
+}
+
+impl<A: Anchor> FullTxOut<A> {
+    /// Whether the `txout` is considered mature.
+    ///
+    /// Depending on the implementation of [`confirmation_height_upper_bound`] in [`Anchor`], this
+    /// method may return false-negatives. In other words, interpreted confirmation count may be
+    /// less than the actual value.
+    ///
+    /// [`confirmation_height_upper_bound`]: Anchor::confirmation_height_upper_bound
+    pub fn is_mature(&self, tip: u32) -> bool {
+        if self.is_on_coinbase {
+            let tx_height = match &self.chain_position {
+                ChainPosition::Confirmed(anchor) => anchor.confirmation_height_upper_bound(),
+                ChainPosition::Unconfirmed(_) => {
+                    debug_assert!(false, "coinbase tx can never be unconfirmed");
+                    return false;
+                }
+            };
+            let age = tip.saturating_sub(tx_height);
+            if age + 1 < COINBASE_MATURITY {
+                return false;
+            }
+        }
+
+        true
+    }
+
+    /// Whether the utxo is/was/will be spendable with chain `tip`.
+    ///
+    /// This method does not take into account the lock time.
+    ///
+    /// Depending on the implementation of [`confirmation_height_upper_bound`] in [`Anchor`], this
+    /// method may return false-negatives. In other words, interpreted confirmation count may be
+    /// less than the actual value.
+    ///
+    /// [`confirmation_height_upper_bound`]: Anchor::confirmation_height_upper_bound
+    pub fn is_confirmed_and_spendable(&self, tip: u32) -> bool {
+        if !self.is_mature(tip) {
+            return false;
+        }
+
+        let confirmation_height = match &self.chain_position {
+            ChainPosition::Confirmed(anchor) => anchor.confirmation_height_upper_bound(),
+            ChainPosition::Unconfirmed(_) => return false,
+        };
+        if confirmation_height > tip {
+            return false;
+        }
+
+        // if the spending tx is confirmed within tip height, the txout is no longer spendable
+        if let Some((ChainPosition::Confirmed(spending_anchor), _)) = &self.spent_by {
+            if spending_anchor.anchor_block().height <= tip {
+                return false;
+            }
+        }
+
+        true
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn chain_position_ord() {
+        let unconf1 = ChainPosition::<ConfirmationBlockTime>::Unconfirmed(10);
+        let unconf2 = ChainPosition::<ConfirmationBlockTime>::Unconfirmed(20);
+        let conf1 = ChainPosition::Confirmed(ConfirmationBlockTime {
+            confirmation_time: 20,
+            block_id: BlockId {
+                height: 9,
+                ..Default::default()
+            },
+        });
+        let conf2 = ChainPosition::Confirmed(ConfirmationBlockTime {
+            confirmation_time: 15,
+            block_id: BlockId {
+                height: 12,
+                ..Default::default()
+            },
+        });
+
+        assert!(unconf2 > unconf1, "higher last_seen means higher ord");
+        assert!(unconf1 > conf1, "unconfirmed is higher ord than confirmed");
+        assert!(
+            conf2 > conf1,
+            "confirmation_height is higher then it should be higher ord"
+        );
+    }
+}

crates/chain/src/chain_oracle.rs

@@ -0,0 +1,25 @@
+use crate::BlockId;
+
+/// Represents a service that tracks the blockchain.
+///
+/// The main method is [`is_block_in_chain`] which determines whether a given block of [`BlockId`]
+/// is an ancestor of the `chain_tip`.
+///
+/// [`is_block_in_chain`]: Self::is_block_in_chain
+pub trait ChainOracle {
+    /// Error type.
+    type Error: core::fmt::Debug;
+
+    /// Determines whether `block` of [`BlockId`] exists as an ancestor of `chain_tip`.
+    ///
+    /// If `None` is returned, it means the implementation cannot determine whether `block` exists
+    /// under `chain_tip`.
+    fn is_block_in_chain(
+        &self,
+        block: BlockId,
+        chain_tip: BlockId,
+    ) -> Result<Option<bool>, Self::Error>;
+
+    /// Get the best chain's chain tip.
+    fn get_chain_tip(&self) -> Result<BlockId, Self::Error>;
+}

crates/chain/src/descriptor_ext.rs

@@ -0,0 +1,38 @@
+use crate::miniscript::{Descriptor, DescriptorPublicKey};
+use bitcoin::hashes::{hash_newtype, sha256, Hash};
+
+hash_newtype! {
+    /// Represents the unique ID of a descriptor.
+    ///
+    /// This is useful for having a fixed-length unique representation of a descriptor,
+    /// in particular, we use it to persist application state changes related to the
+    /// descriptor without having to re-write the whole descriptor each time.
+    ///
+    pub struct DescriptorId(pub sha256::Hash);
+}
+
+/// A trait to extend the functionality of a miniscript descriptor.
+pub trait DescriptorExt {
+    /// Returns the minimum value (in satoshis) at which an output is broadcastable.
+    /// Panics if the descriptor wildcard is hardened.
+    fn dust_value(&self) -> u64;
+
+    /// Returns the descriptor ID, calculated as the sha256 hash of the spk derived from the
+    /// descriptor at index 0.
+    fn descriptor_id(&self) -> DescriptorId;
+}
+
+impl DescriptorExt for Descriptor<DescriptorPublicKey> {
+    fn dust_value(&self) -> u64 {
+        self.at_derivation_index(0)
+            .expect("descriptor can't have hardened derivation")
+            .script_pubkey()
+            .minimal_non_dust()
+            .to_sat()
+    }
+
+    fn descriptor_id(&self) -> DescriptorId {
+        let spk = self.at_derivation_index(0).unwrap().script_pubkey();
+        DescriptorId(sha256::Hash::hash(spk.as_bytes()))
+    }
+}

crates/chain/src/example_utils.rs

@@ -0,0 +1,30 @@
+#![allow(unused)]
+use alloc::vec::Vec;
+use bitcoin::{
+    consensus,
+    hashes::{hex::FromHex, Hash},
+    Transaction,
+};
+
+use crate::BlockId;
+
+pub const RAW_TX_1: &str = "0200000000010116d6174da7183d70d0a7d4dc314d517a7d135db79ad63515028b293a76f4f9d10000000000feffffff023a21fc8350060000160014531c405e1881ef192294b8813631e258bf98ea7a1027000000000000225120a60869f0dbcf1dc659c9cecbaf8050135ea9e8cdc487053f1dc6880949dc684c024730440220591b1a172a122da49ba79a3e79f98aaa03fd7a372f9760da18890b6a327e6010022013e82319231da6c99abf8123d7c07e13cf9bd8d76e113e18dc452e5024db156d012102318a2d558b2936c52e320decd6d92a88d7f530be91b6fe0af5caf41661e77da3ef2e0100";
+pub const RAW_TX_2: &str = "02000000000101a688607020cfae91a61e7c516b5ef1264d5d77f17200c3866826c6c808ebf1620000000000feffffff021027000000000000225120a60869f0dbcf1dc659c9cecbaf8050135ea9e8cdc487053f1dc6880949dc684c20fd48ff530600001600146886c525e41d4522042bd0b159dfbade2504a6bb024730440220740ff7e665cd20565d4296b549df8d26b941be3f1e3af89a0b60e50c0dbeb69a02206213ab7030cf6edc6c90d4ccf33010644261e029950a688dc0b1a9ebe6ddcc5a012102f2ac6b396a97853cb6cd62242c8ae4842024742074475023532a51e9c53194253e760100";
+pub const RAW_TX_3: &str = "0200000000010135d67ee47b557e68b8c6223958f597381965ed719f1207ee2b9e20432a24a5dc0100000000feffffff021027000000000000225120a82f29944d65b86ae6b5e5cc75e294ead6c59391a1edc5e016e3498c67fc7bbb62215a5055060000160014070df7671dea67a50c4799a744b5c9be8f4bac690247304402207ebf8d29f71fd03e7e6977b3ea78ca5fcc5c49a42ae822348fc401862fdd766c02201d7e4ff0684ecb008b6142f36ead1b0b4d615524c4f58c261113d361f4427e25012103e6a75e2fab85e5ecad641afc4ffba7222f998649d9f18cac92f0fcc8618883b3ee760100";
+pub const RAW_TX_4: &str = "02000000000101d00e8f76ed313e19b339ee293c0f52b0325c95e24c8f3966fa353fb2bedbcf580100000000feffffff021027000000000000225120882d74e5d0572d5a816cef0041a96b6c1de832f6f9676d9605c44d5e9a97d3dc9cda55fe53060000160014852b5864b8edd42fab4060c87f818e50780865ff0247304402201dccbb9bed7fba924b6d249c5837cc9b37470c0e3d8fbea77cb59baba3efe6fa0220700cc170916913b9bfc2bc0fefb6af776e8b542c561702f136cddc1c7aa43141012103acec3fc79dbbca745815c2a807dc4e81010c80e308e84913f59cb42a275dad97f3760100";
+
+pub fn tx_from_hex(s: &str) -> Transaction {
+    let raw = Vec::from_hex(s).expect("data must be in hex");
+    consensus::deserialize(raw.as_slice()).expect("must deserialize")
+}
+
+pub fn new_hash<H: Hash>(s: &str) -> H {
+    <H as bitcoin::hashes::Hash>::hash(s.as_bytes())
+}
+
+pub fn new_block_id(height: u32, hash: &str) -> BlockId {
+    BlockId {
+        height,
+        hash: new_hash(hash),
+    }
+}

crates/chain/src/indexed_tx_graph.rs

@@ -0,0 +1,362 @@
+//! Contains the [`IndexedTxGraph`] and associated types. Refer to the
+//! [`IndexedTxGraph`] documentation for more.
+use core::fmt::Debug;
+
+use alloc::vec::Vec;
+use bitcoin::{Block, OutPoint, Transaction, TxOut, Txid};
+
+use crate::{
+    tx_graph::{self, TxGraph},
+    Anchor, AnchorFromBlockPosition, BlockId, Indexer, Merge,
+};
+
+/// The [`IndexedTxGraph`] combines a [`TxGraph`] and an [`Indexer`] implementation.
+///
+/// It ensures that [`TxGraph`] and [`Indexer`] are updated atomically.
+#[derive(Debug)]
+pub struct IndexedTxGraph<A, I> {
+    /// Transaction index.
+    pub index: I,
+    graph: TxGraph<A>,
+}
+
+impl<A, I: Default> Default for IndexedTxGraph<A, I> {
+    fn default() -> Self {
+        Self {
+            graph: Default::default(),
+            index: Default::default(),
+        }
+    }
+}
+
+impl<A, I> IndexedTxGraph<A, I> {
+    /// Construct a new [`IndexedTxGraph`] with a given `index`.
+    pub fn new(index: I) -> Self {
+        Self {
+            index,
+            graph: TxGraph::default(),
+        }
+    }
+
+    /// Get a reference of the internal transaction graph.
+    pub fn graph(&self) -> &TxGraph<A> {
+        &self.graph
+    }
+}
+
+impl<A: Anchor, I: Indexer> IndexedTxGraph<A, I> {
+    /// Applies the [`ChangeSet`] to the [`IndexedTxGraph`].
+    pub fn apply_changeset(&mut self, changeset: ChangeSet<A, I::ChangeSet>) {
+        self.index.apply_changeset(changeset.indexer);
+
+        for tx in &changeset.tx_graph.txs {
+            self.index.index_tx(tx);
+        }
+        for (&outpoint, txout) in &changeset.tx_graph.txouts {
+            self.index.index_txout(outpoint, txout);
+        }
+
+        self.graph.apply_changeset(changeset.tx_graph);
+    }
+
+    /// Determines the [`ChangeSet`] between `self` and an empty [`IndexedTxGraph`].
+    pub fn initial_changeset(&self) -> ChangeSet<A, I::ChangeSet> {
+        let graph = self.graph.initial_changeset();
+        let indexer = self.index.initial_changeset();
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+}
+
+impl<A: Anchor, I: Indexer> IndexedTxGraph<A, I>
+where
+    I::ChangeSet: Default + Merge,
+{
+    fn index_tx_graph_changeset(
+        &mut self,
+        tx_graph_changeset: &tx_graph::ChangeSet<A>,
+    ) -> I::ChangeSet {
+        let mut changeset = I::ChangeSet::default();
+        for added_tx in &tx_graph_changeset.txs {
+            changeset.merge(self.index.index_tx(added_tx));
+        }
+        for (&added_outpoint, added_txout) in &tx_graph_changeset.txouts {
+            changeset.merge(self.index.index_txout(added_outpoint, added_txout));
+        }
+        changeset
+    }
+
+    /// Apply an `update` directly.
+    ///
+    /// `update` is a [`TxGraph<A>`] and the resultant changes is returned as [`ChangeSet`].
+    pub fn apply_update(&mut self, update: TxGraph<A>) -> ChangeSet<A, I::ChangeSet> {
+        let graph = self.graph.apply_update(update);
+        let indexer = self.index_tx_graph_changeset(&graph);
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+
+    /// Insert a floating `txout` of given `outpoint`.
+    pub fn insert_txout(&mut self, outpoint: OutPoint, txout: TxOut) -> ChangeSet<A, I::ChangeSet> {
+        let graph = self.graph.insert_txout(outpoint, txout);
+        let indexer = self.index_tx_graph_changeset(&graph);
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+
+    /// Insert and index a transaction into the graph.
+    pub fn insert_tx(&mut self, tx: Transaction) -> ChangeSet<A, I::ChangeSet> {
+        let graph = self.graph.insert_tx(tx);
+        let indexer = self.index_tx_graph_changeset(&graph);
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+
+    /// Insert an `anchor` for a given transaction.
+    pub fn insert_anchor(&mut self, txid: Txid, anchor: A) -> ChangeSet<A, I::ChangeSet> {
+        self.graph.insert_anchor(txid, anchor).into()
+    }
+
+    /// Insert a unix timestamp of when a transaction is seen in the mempool.
+    ///
+    /// This is used for transaction conflict resolution in [`TxGraph`] where the transaction with
+    /// the later last-seen is prioritized.
+    pub fn insert_seen_at(&mut self, txid: Txid, seen_at: u64) -> ChangeSet<A, I::ChangeSet> {
+        self.graph.insert_seen_at(txid, seen_at).into()
+    }
+
+    /// Batch insert transactions, filtering out those that are irrelevant.
+    ///
+    /// Relevancy is determined by the [`Indexer::is_tx_relevant`] implementation of `I`. Irrelevant
+    /// transactions in `txs` will be ignored. `txs` do not need to be in topological order.
+    pub fn batch_insert_relevant<'t>(
+        &mut self,
+        txs: impl IntoIterator<Item = (&'t Transaction, impl IntoIterator<Item = A>)>,
+    ) -> ChangeSet<A, I::ChangeSet> {
+        // The algorithm below allows for non-topologically ordered transactions by using two loops.
+        // This is achieved by:
+        // 1. insert all txs into the index. If they are irrelevant then that's fine it will just
+        //    not store anything about them.
+        // 2. decide whether to insert them into the graph depending on whether `is_tx_relevant`
+        //    returns true or not. (in a second loop).
+        let txs = txs.into_iter().collect::<Vec<_>>();
+
+        let mut indexer = I::ChangeSet::default();
+        for (tx, _) in &txs {
+            indexer.merge(self.index.index_tx(tx));
+        }
+
+        let mut graph = tx_graph::ChangeSet::default();
+        for (tx, anchors) in txs {
+            if self.index.is_tx_relevant(tx) {
+                let txid = tx.compute_txid();
+                graph.merge(self.graph.insert_tx(tx.clone()));
+                for anchor in anchors {
+                    graph.merge(self.graph.insert_anchor(txid, anchor));
+                }
+            }
+        }
+
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+
+    /// Batch insert unconfirmed transactions, filtering out those that are irrelevant.
+    ///
+    /// Relevancy is determined by the internal [`Indexer::is_tx_relevant`] implementation of `I`.
+    /// Irrelevant transactions in `txs` will be ignored.
+    ///
+    /// Items of `txs` are tuples containing the transaction and a *last seen* timestamp. The
+    /// *last seen* communicates when the transaction is last seen in the mempool which is used for
+    /// conflict-resolution in [`TxGraph`] (refer to [`TxGraph::insert_seen_at`] for details).
+    pub fn batch_insert_relevant_unconfirmed<'t>(
+        &mut self,
+        unconfirmed_txs: impl IntoIterator<Item = (&'t Transaction, u64)>,
+    ) -> ChangeSet<A, I::ChangeSet> {
+        // The algorithm below allows for non-topologically ordered transactions by using two loops.
+        // This is achieved by:
+        // 1. insert all txs into the index. If they are irrelevant then that's fine it will just
+        //    not store anything about them.
+        // 2. decide whether to insert them into the graph depending on whether `is_tx_relevant`
+        //    returns true or not. (in a second loop).
+        let txs = unconfirmed_txs.into_iter().collect::<Vec<_>>();
+
+        let mut indexer = I::ChangeSet::default();
+        for (tx, _) in &txs {
+            indexer.merge(self.index.index_tx(tx));
+        }
+
+        let graph = self.graph.batch_insert_unconfirmed(
+            txs.into_iter()
+                .filter(|(tx, _)| self.index.is_tx_relevant(tx))
+                .map(|(tx, seen_at)| (tx.clone(), seen_at)),
+        );
+
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+
+    /// Batch insert unconfirmed transactions.
+    ///
+    /// Items of `txs` are tuples containing the transaction and a *last seen* timestamp. The
+    /// *last seen* communicates when the transaction is last seen in the mempool which is used for
+    /// conflict-resolution in [`TxGraph`] (refer to [`TxGraph::insert_seen_at`] for details).
+    ///
+    /// To filter out irrelevant transactions, use [`batch_insert_relevant_unconfirmed`] instead.
+    ///
+    /// [`batch_insert_relevant_unconfirmed`]: IndexedTxGraph::batch_insert_relevant_unconfirmed
+    pub fn batch_insert_unconfirmed(
+        &mut self,
+        txs: impl IntoIterator<Item = (Transaction, u64)>,
+    ) -> ChangeSet<A, I::ChangeSet> {
+        let graph = self.graph.batch_insert_unconfirmed(txs);
+        let indexer = self.index_tx_graph_changeset(&graph);
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+}
+
+/// Methods are available if the anchor (`A`) implements [`AnchorFromBlockPosition`].
+impl<A: Anchor, I: Indexer> IndexedTxGraph<A, I>
+where
+    I::ChangeSet: Default + Merge,
+    A: AnchorFromBlockPosition,
+{
+    /// Batch insert all transactions of the given `block` of `height`, filtering out those that are
+    /// irrelevant.
+    ///
+    /// Each inserted transaction's anchor will be constructed from
+    /// [`AnchorFromBlockPosition::from_block_position`].
+    ///
+    /// Relevancy is determined by the internal [`Indexer::is_tx_relevant`] implementation of `I`.
+    /// Irrelevant transactions in `txs` will be ignored.
+    pub fn apply_block_relevant(
+        &mut self,
+        block: &Block,
+        height: u32,
+    ) -> ChangeSet<A, I::ChangeSet> {
+        let block_id = BlockId {
+            hash: block.block_hash(),
+            height,
+        };
+        let mut changeset = ChangeSet::<A, I::ChangeSet>::default();
+        for (tx_pos, tx) in block.txdata.iter().enumerate() {
+            changeset.indexer.merge(self.index.index_tx(tx));
+            if self.index.is_tx_relevant(tx) {
+                let txid = tx.compute_txid();
+                let anchor = A::from_block_position(block, block_id, tx_pos);
+                changeset.tx_graph.merge(self.graph.insert_tx(tx.clone()));
+                changeset
+                    .tx_graph
+                    .merge(self.graph.insert_anchor(txid, anchor));
+            }
+        }
+        changeset
+    }
+
+    /// Batch insert all transactions of the given `block` of `height`.
+    ///
+    /// Each inserted transaction's anchor will be constructed from
+    /// [`AnchorFromBlockPosition::from_block_position`].
+    ///
+    /// To only insert relevant transactions, use [`apply_block_relevant`] instead.
+    ///
+    /// [`apply_block_relevant`]: IndexedTxGraph::apply_block_relevant
+    pub fn apply_block(&mut self, block: Block, height: u32) -> ChangeSet<A, I::ChangeSet> {
+        let block_id = BlockId {
+            hash: block.block_hash(),
+            height,
+        };
+        let mut graph = tx_graph::ChangeSet::default();
+        for (tx_pos, tx) in block.txdata.iter().enumerate() {
+            let anchor = A::from_block_position(&block, block_id, tx_pos);
+            graph.merge(self.graph.insert_anchor(tx.compute_txid(), anchor));
+            graph.merge(self.graph.insert_tx(tx.clone()));
+        }
+        let indexer = self.index_tx_graph_changeset(&graph);
+        ChangeSet {
+            tx_graph: graph,
+            indexer,
+        }
+    }
+}
+
+impl<A, I> AsRef<TxGraph<A>> for IndexedTxGraph<A, I> {
+    fn as_ref(&self) -> &TxGraph<A> {
+        &self.graph
+    }
+}
+
+/// Represents changes to an [`IndexedTxGraph`].
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(
+        crate = "serde_crate",
+        bound(
+            deserialize = "A: Ord + serde::Deserialize<'de>, IA: serde::Deserialize<'de>",
+            serialize = "A: Ord + serde::Serialize, IA: serde::Serialize"
+        )
+    )
+)]
+#[must_use]
+pub struct ChangeSet<A, IA> {
+    /// [`TxGraph`] changeset.
+    pub tx_graph: tx_graph::ChangeSet<A>,
+    /// [`Indexer`] changeset.
+    pub indexer: IA,
+}
+
+impl<A, IA: Default> Default for ChangeSet<A, IA> {
+    fn default() -> Self {
+        Self {
+            tx_graph: Default::default(),
+            indexer: Default::default(),
+        }
+    }
+}
+
+impl<A: Anchor, IA: Merge> Merge for ChangeSet<A, IA> {
+    fn merge(&mut self, other: Self) {
+        self.tx_graph.merge(other.tx_graph);
+        self.indexer.merge(other.indexer);
+    }
+
+    fn is_empty(&self) -> bool {
+        self.tx_graph.is_empty() && self.indexer.is_empty()
+    }
+}
+
+impl<A, IA: Default> From<tx_graph::ChangeSet<A>> for ChangeSet<A, IA> {
+    fn from(graph: tx_graph::ChangeSet<A>) -> Self {
+        Self {
+            tx_graph: graph,
+            ..Default::default()
+        }
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl<A> From<crate::keychain_txout::ChangeSet> for ChangeSet<A, crate::keychain_txout::ChangeSet> {
+    fn from(indexer: crate::keychain_txout::ChangeSet) -> Self {
+        Self {
+            tx_graph: Default::default(),
+            indexer,
+        }
+    }
+}

crates/chain/src/indexer.rs

@@ -0,0 +1,33 @@
+//! [`Indexer`] provides utilities for indexing transaction data.
+
+use bitcoin::{OutPoint, Transaction, TxOut};
+
+#[cfg(feature = "miniscript")]
+pub mod keychain_txout;
+pub mod spk_txout;
+
+/// Utilities for indexing transaction data.
+///
+/// Types which implement this trait can be used to construct an [`IndexedTxGraph`].
+/// This trait's methods should rarely be called directly.
+///
+/// [`IndexedTxGraph`]: crate::IndexedTxGraph
+pub trait Indexer {
+    /// The resultant "changeset" when new transaction data is indexed.
+    type ChangeSet;
+
+    /// Scan and index the given `outpoint` and `txout`.
+    fn index_txout(&mut self, outpoint: OutPoint, txout: &TxOut) -> Self::ChangeSet;
+
+    /// Scans a transaction for relevant outpoints, which are stored and indexed internally.
+    fn index_tx(&mut self, tx: &Transaction) -> Self::ChangeSet;
+
+    /// Apply changeset to itself.
+    fn apply_changeset(&mut self, changeset: Self::ChangeSet);
+
+    /// Determines the [`ChangeSet`](Indexer::ChangeSet) between `self` and an empty [`Indexer`].
+    fn initial_changeset(&self) -> Self::ChangeSet;
+
+    /// Determines whether the transaction should be included in the index.
+    fn is_tx_relevant(&self, tx: &Transaction) -> bool;
+}

crates/chain/src/indexer/keychain_txout.rs

@@ -0,0 +1,881 @@
+//! [`KeychainTxOutIndex`] controls how script pubkeys are revealed for multiple keychains and
+//! indexes [`TxOut`]s with them.
+
+use crate::{
+    collections::*,
+    miniscript::{Descriptor, DescriptorPublicKey},
+    spk_iter::BIP32_MAX_INDEX,
+    spk_txout::SpkTxOutIndex,
+    DescriptorExt, DescriptorId, Indexed, Indexer, KeychainIndexed, SpkIterator,
+};
+use alloc::{borrow::ToOwned, vec::Vec};
+use bitcoin::{Amount, OutPoint, ScriptBuf, SignedAmount, Transaction, TxOut, Txid};
+use core::{
+    fmt::Debug,
+    ops::{Bound, RangeBounds},
+};
+
+use crate::Merge;
+
+/// The default lookahead for a [`KeychainTxOutIndex`]
+pub const DEFAULT_LOOKAHEAD: u32 = 25;
+
+/// [`KeychainTxOutIndex`] controls how script pubkeys are revealed for multiple keychains, and
+/// indexes [`TxOut`]s with them.
+///
+/// A single keychain is a chain of script pubkeys derived from a single [`Descriptor`]. Keychains
+/// are identified using the `K` generic. Script pubkeys are identified by the keychain that they
+/// are derived from `K`, as well as the derivation index `u32`.
+///
+/// There is a strict 1-to-1 relationship between descriptors and keychains. Each keychain has one
+/// and only one descriptor and each descriptor has one and only one keychain. The
+/// [`insert_descriptor`] method will return an error if you try and violate this invariant. This
+/// rule is a proxy for a stronger rule: no two descriptors should produce the same script pubkey.
+/// Having two descriptors produce the same script pubkey should cause whichever keychain derives
+/// the script pubkey first to be the effective owner of it but you should not rely on this
+/// behaviour. ⚠ It is up you, the developer, not to violate this invariant.
+///
+/// # Revealed script pubkeys
+///
+/// Tracking how script pubkeys are revealed is useful for collecting chain data. For example, if
+/// the user has requested 5 script pubkeys (to receive money with), we only need to use those
+/// script pubkeys to scan for chain data.
+///
+/// Call [`reveal_to_target`] or [`reveal_next_spk`] to reveal more script pubkeys.
+/// Call [`revealed_keychain_spks`] or [`revealed_spks`] to iterate through revealed script pubkeys.
+///
+/// # Lookahead script pubkeys
+///
+/// When an user first recovers a wallet (i.e. from a recovery phrase and/or descriptor), we will
+/// NOT have knowledge of which script pubkeys are revealed. So when we index a transaction or
+/// txout (using [`index_tx`]/[`index_txout`]) we scan the txouts against script pubkeys derived
+/// above the last revealed index. These additionally-derived script pubkeys are called the
+/// lookahead.
+///
+/// The [`KeychainTxOutIndex`] is constructed with the `lookahead` and cannot be altered. See
+/// [`DEFAULT_LOOKAHEAD`] for the value used in the `Default` implementation. Use [`new`] to set a
+/// custom `lookahead`.
+///
+/// # Unbounded script pubkey iterator
+///
+/// For script-pubkey-based chain sources (such as Electrum/Esplora), an initial scan is best done
+/// by iterating though derived script pubkeys one by one and requesting transaction histories for
+/// each script pubkey. We will stop after x-number of script pubkeys have empty histories. An
+/// unbounded script pubkey iterator is useful to pass to such a chain source because it doesn't
+/// require holding a reference to the index.
+///
+/// Call [`unbounded_spk_iter`] to get an unbounded script pubkey iterator for a given keychain.
+/// Call [`all_unbounded_spk_iters`] to get unbounded script pubkey iterators for all keychains.
+///
+/// # Change sets
+///
+/// Methods that can update the last revealed index or add keychains will return [`ChangeSet`] to report
+/// these changes. This should be persisted for future recovery.
+///
+/// ## Synopsis
+///
+/// ```
+/// use bdk_chain::indexer::keychain_txout::KeychainTxOutIndex;
+/// # use bdk_chain::{ miniscript::{Descriptor, DescriptorPublicKey} };
+/// # use core::str::FromStr;
+///
+/// // imagine our service has internal and external addresses but also addresses for users
+/// #[derive(Clone, Debug, PartialEq, Eq, Ord, PartialOrd)]
+/// enum MyKeychain {
+///     External,
+///     Internal,
+///     MyAppUser {
+///         user_id: u32
+///     }
+/// }
+///
+/// let mut txout_index = KeychainTxOutIndex::<MyKeychain>::default();
+///
+/// # let secp = bdk_chain::bitcoin::secp256k1::Secp256k1::signing_only();
+/// # let (external_descriptor,_) = Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, "tr([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/0/*)").unwrap();
+/// # let (internal_descriptor,_) = Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, "tr([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/1/*)").unwrap();
+/// # let (descriptor_42, _) = Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, "tr([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/2/*)").unwrap();
+/// let _ = txout_index.insert_descriptor(MyKeychain::External, external_descriptor)?;
+/// let _ = txout_index.insert_descriptor(MyKeychain::Internal, internal_descriptor)?;
+/// let _ = txout_index.insert_descriptor(MyKeychain::MyAppUser { user_id: 42 }, descriptor_42)?;
+///
+/// let new_spk_for_user = txout_index.reveal_next_spk(MyKeychain::MyAppUser{ user_id: 42 });
+/// # Ok::<_, bdk_chain::indexer::keychain_txout::InsertDescriptorError<_>>(())
+/// ```
+///
+/// [`Ord`]: core::cmp::Ord
+/// [`SpkTxOutIndex`]: crate::spk_txout_index::SpkTxOutIndex
+/// [`Descriptor`]: crate::miniscript::Descriptor
+/// [`reveal_to_target`]: Self::reveal_to_target
+/// [`reveal_next_spk`]: Self::reveal_next_spk
+/// [`revealed_keychain_spks`]: Self::revealed_keychain_spks
+/// [`revealed_spks`]: Self::revealed_spks
+/// [`index_tx`]: Self::index_tx
+/// [`index_txout`]: Self::index_txout
+/// [`new`]: Self::new
+/// [`unbounded_spk_iter`]: Self::unbounded_spk_iter
+/// [`all_unbounded_spk_iters`]: Self::all_unbounded_spk_iters
+/// [`outpoints`]: Self::outpoints
+/// [`txouts`]: Self::txouts
+/// [`unused_spks`]: Self::unused_spks
+/// [`insert_descriptor`]: Self::insert_descriptor
+#[derive(Clone, Debug)]
+pub struct KeychainTxOutIndex<K> {
+    inner: SpkTxOutIndex<(K, u32)>,
+    keychain_to_descriptor_id: BTreeMap<K, DescriptorId>,
+    descriptor_id_to_keychain: HashMap<DescriptorId, K>,
+    descriptors: HashMap<DescriptorId, Descriptor<DescriptorPublicKey>>,
+    last_revealed: HashMap<DescriptorId, u32>,
+    lookahead: u32,
+}
+
+impl<K> Default for KeychainTxOutIndex<K> {
+    fn default() -> Self {
+        Self::new(DEFAULT_LOOKAHEAD)
+    }
+}
+
+impl<K: Clone + Ord + Debug> Indexer for KeychainTxOutIndex<K> {
+    type ChangeSet = ChangeSet;
+
+    fn index_txout(&mut self, outpoint: OutPoint, txout: &TxOut) -> Self::ChangeSet {
+        let mut changeset = ChangeSet::default();
+        if let Some((keychain, index)) = self.inner.scan_txout(outpoint, txout).cloned() {
+            let did = self
+                .keychain_to_descriptor_id
+                .get(&keychain)
+                .expect("invariant");
+            if self.last_revealed.get(did) < Some(&index) {
+                self.last_revealed.insert(*did, index);
+                changeset.last_revealed.insert(*did, index);
+                self.replenish_inner_index(*did, &keychain, self.lookahead);
+            }
+        }
+        changeset
+    }
+
+    fn index_tx(&mut self, tx: &bitcoin::Transaction) -> Self::ChangeSet {
+        let mut changeset = ChangeSet::default();
+        let txid = tx.compute_txid();
+        for (op, txout) in tx.output.iter().enumerate() {
+            changeset.merge(self.index_txout(OutPoint::new(txid, op as u32), txout));
+        }
+        changeset
+    }
+
+    fn initial_changeset(&self) -> Self::ChangeSet {
+        ChangeSet {
+            last_revealed: self.last_revealed.clone().into_iter().collect(),
+        }
+    }
+
+    fn apply_changeset(&mut self, changeset: Self::ChangeSet) {
+        self.apply_changeset(changeset)
+    }
+
+    fn is_tx_relevant(&self, tx: &bitcoin::Transaction) -> bool {
+        self.inner.is_relevant(tx)
+    }
+}
+
+impl<K> KeychainTxOutIndex<K> {
+    /// Construct a [`KeychainTxOutIndex`] with the given `lookahead`.
+    ///
+    /// The `lookahead` is the number of script pubkeys to derive and cache from the internal
+    /// descriptors over and above the last revealed script index. Without a lookahead the index
+    /// will miss outputs you own when processing transactions whose output script pubkeys lie
+    /// beyond the last revealed index. In certain situations, such as when performing an initial
+    /// scan of the blockchain during wallet import, it may be uncertain or unknown what the index
+    /// of the last revealed script pubkey actually is.
+    ///
+    /// Refer to [struct-level docs](KeychainTxOutIndex) for more about `lookahead`.
+    pub fn new(lookahead: u32) -> Self {
+        Self {
+            inner: SpkTxOutIndex::default(),
+            keychain_to_descriptor_id: Default::default(),
+            descriptors: Default::default(),
+            descriptor_id_to_keychain: Default::default(),
+            last_revealed: Default::default(),
+            lookahead,
+        }
+    }
+}
+
+/// Methods that are *re-exposed* from the internal [`SpkTxOutIndex`].
+impl<K: Clone + Ord + Debug> KeychainTxOutIndex<K> {
+    /// Return a reference to the internal [`SpkTxOutIndex`].
+    ///
+    /// **WARNING**: The internal index will contain lookahead spks. Refer to
+    /// [struct-level docs](KeychainTxOutIndex) for more about `lookahead`.
+    pub fn inner(&self) -> &SpkTxOutIndex<(K, u32)> {
+        &self.inner
+    }
+
+    /// Get the set of indexed outpoints, corresponding to tracked keychains.
+    pub fn outpoints(&self) -> &BTreeSet<KeychainIndexed<K, OutPoint>> {
+        self.inner.outpoints()
+    }
+
+    /// Iterate over known txouts that spend to tracked script pubkeys.
+    pub fn txouts(
+        &self,
+    ) -> impl DoubleEndedIterator<Item = KeychainIndexed<K, (OutPoint, &TxOut)>> + ExactSizeIterator
+    {
+        self.inner
+            .txouts()
+            .map(|(index, op, txout)| (index.clone(), (op, txout)))
+    }
+
+    /// Finds all txouts on a transaction that has previously been scanned and indexed.
+    pub fn txouts_in_tx(
+        &self,
+        txid: Txid,
+    ) -> impl DoubleEndedIterator<Item = KeychainIndexed<K, (OutPoint, &TxOut)>> {
+        self.inner
+            .txouts_in_tx(txid)
+            .map(|(index, op, txout)| (index.clone(), (op, txout)))
+    }
+
+    /// Return the [`TxOut`] of `outpoint` if it has been indexed, and if it corresponds to a
+    /// tracked keychain.
+    ///
+    /// The associated keychain and keychain index of the txout's spk is also returned.
+    ///
+    /// This calls [`SpkTxOutIndex::txout`] internally.
+    pub fn txout(&self, outpoint: OutPoint) -> Option<KeychainIndexed<K, &TxOut>> {
+        self.inner
+            .txout(outpoint)
+            .map(|(index, txout)| (index.clone(), txout))
+    }
+
+    /// Return the script that exists under the given `keychain`'s `index`.
+    ///
+    /// This calls [`SpkTxOutIndex::spk_at_index`] internally.
+    pub fn spk_at_index(&self, keychain: K, index: u32) -> Option<ScriptBuf> {
+        self.inner.spk_at_index(&(keychain.clone(), index))
+    }
+
+    /// Returns the keychain and keychain index associated with the spk.
+    ///
+    /// This calls [`SpkTxOutIndex::index_of_spk`] internally.
+    pub fn index_of_spk(&self, script: ScriptBuf) -> Option<&(K, u32)> {
+        self.inner.index_of_spk(script)
+    }
+
+    /// Returns whether the spk under the `keychain`'s `index` has been used.
+    ///
+    /// Here, "unused" means that after the script pubkey was stored in the index, the index has
+    /// never scanned a transaction output with it.
+    ///
+    /// This calls [`SpkTxOutIndex::is_used`] internally.
+    pub fn is_used(&self, keychain: K, index: u32) -> bool {
+        self.inner.is_used(&(keychain, index))
+    }
+
+    /// Marks the script pubkey at `index` as used even though the tracker hasn't seen an output
+    /// with it.
+    ///
+    /// This only has an effect when the `index` had been added to `self` already and was unused.
+    ///
+    /// Returns whether the spk under the given `keychain` and `index` is successfully
+    /// marked as used. Returns false either when there is no descriptor under the given
+    /// keychain, or when the spk is already marked as used.
+    ///
+    /// This is useful when you want to reserve a script pubkey for something but don't want to add
+    /// the transaction output using it to the index yet. Other callers will consider `index` on
+    /// `keychain` used until you call [`unmark_used`].
+    ///
+    /// This calls [`SpkTxOutIndex::mark_used`] internally.
+    ///
+    /// [`unmark_used`]: Self::unmark_used
+    pub fn mark_used(&mut self, keychain: K, index: u32) -> bool {
+        self.inner.mark_used(&(keychain, index))
+    }
+
+    /// Undoes the effect of [`mark_used`]. Returns whether the `index` is inserted back into
+    /// `unused`.
+    ///
+    /// Note that if `self` has scanned an output with this script pubkey, then this will have no
+    /// effect.
+    ///
+    /// This calls [`SpkTxOutIndex::unmark_used`] internally.
+    ///
+    /// [`mark_used`]: Self::mark_used
+    pub fn unmark_used(&mut self, keychain: K, index: u32) -> bool {
+        self.inner.unmark_used(&(keychain, index))
+    }
+
+    /// Computes the total value transfer effect `tx` has on the script pubkeys belonging to the
+    /// keychains in `range`. Value is *sent* when a script pubkey in the `range` is on an input and
+    /// *received* when it is on an output. For `sent` to be computed correctly, the output being
+    /// spent must have already been scanned by the index. Calculating received just uses the
+    /// [`Transaction`] outputs directly, so it will be correct even if it has not been scanned.
+    pub fn sent_and_received(
+        &self,
+        tx: &Transaction,
+        range: impl RangeBounds<K>,
+    ) -> (Amount, Amount) {
+        self.inner
+            .sent_and_received(tx, self.map_to_inner_bounds(range))
+    }
+
+    /// Computes the net value that this transaction gives to the script pubkeys in the index and
+    /// *takes* from the transaction outputs in the index. Shorthand for calling
+    /// [`sent_and_received`] and subtracting sent from received.
+    ///
+    /// This calls [`SpkTxOutIndex::net_value`] internally.
+    ///
+    /// [`sent_and_received`]: Self::sent_and_received
+    pub fn net_value(&self, tx: &Transaction, range: impl RangeBounds<K>) -> SignedAmount {
+        self.inner.net_value(tx, self.map_to_inner_bounds(range))
+    }
+}
+
+impl<K: Clone + Ord + Debug> KeychainTxOutIndex<K> {
+    /// Return all keychains and their corresponding descriptors.
+    pub fn keychains(
+        &self,
+    ) -> impl DoubleEndedIterator<Item = (K, &Descriptor<DescriptorPublicKey>)> + ExactSizeIterator + '_
+    {
+        self.keychain_to_descriptor_id
+            .iter()
+            .map(|(k, did)| (k.clone(), self.descriptors.get(did).expect("invariant")))
+    }
+
+    /// Insert a descriptor with a keychain associated to it.
+    ///
+    /// Adding a descriptor means you will be able to derive new script pubkeys under it and the
+    /// txout index will discover transaction outputs with those script pubkeys (once they've been
+    /// derived and added to the index).
+    ///
+    /// keychain <-> descriptor is a one-to-one mapping that cannot be changed. Attempting to do so
+    /// will return a [`InsertDescriptorError<K>`].
+    ///
+    /// [`KeychainTxOutIndex`] will prevent you from inserting two descriptors which derive the same
+    /// script pubkey at index 0, but it's up to you to ensure that descriptors don't collide at
+    /// other indices. If they do nothing catastrophic happens at the `KeychainTxOutIndex` level
+    /// (one keychain just becomes the defacto owner of that spk arbitrarily) but this may have
+    /// subtle implications up the application stack like one UTXO being missing from one keychain
+    /// because it has been assigned to another which produces the same script pubkey.
+    pub fn insert_descriptor(
+        &mut self,
+        keychain: K,
+        descriptor: Descriptor<DescriptorPublicKey>,
+    ) -> Result<bool, InsertDescriptorError<K>> {
+        let did = descriptor.descriptor_id();
+        if !self.keychain_to_descriptor_id.contains_key(&keychain)
+            && !self.descriptor_id_to_keychain.contains_key(&did)
+        {
+            self.descriptors.insert(did, descriptor.clone());
+            self.keychain_to_descriptor_id.insert(keychain.clone(), did);
+            self.descriptor_id_to_keychain.insert(did, keychain.clone());
+            self.replenish_inner_index(did, &keychain, self.lookahead);
+            return Ok(true);
+        }
+
+        if let Some(existing_desc_id) = self.keychain_to_descriptor_id.get(&keychain) {
+            let descriptor = self.descriptors.get(existing_desc_id).expect("invariant");
+            if *existing_desc_id != did {
+                return Err(InsertDescriptorError::KeychainAlreadyAssigned {
+                    existing_assignment: descriptor.clone(),
+                    keychain,
+                });
+            }
+        }
+
+        if let Some(existing_keychain) = self.descriptor_id_to_keychain.get(&did) {
+            let descriptor = self.descriptors.get(&did).expect("invariant").clone();
+
+            if *existing_keychain != keychain {
+                return Err(InsertDescriptorError::DescriptorAlreadyAssigned {
+                    existing_assignment: existing_keychain.clone(),
+                    descriptor,
+                });
+            }
+        }
+
+        Ok(false)
+    }
+
+    /// Gets the descriptor associated with the keychain. Returns `None` if the keychain doesn't
+    /// have a descriptor associated with it.
+    pub fn get_descriptor(&self, keychain: K) -> Option<&Descriptor<DescriptorPublicKey>> {
+        let did = self.keychain_to_descriptor_id.get(&keychain)?;
+        self.descriptors.get(did)
+    }
+
+    /// Get the lookahead setting.
+    ///
+    /// Refer to [`new`] for more information on the `lookahead`.
+    ///
+    /// [`new`]: Self::new
+    pub fn lookahead(&self) -> u32 {
+        self.lookahead
+    }
+
+    /// Store lookahead scripts until `target_index` (inclusive).
+    ///
+    /// This does not change the global `lookahead` setting.
+    pub fn lookahead_to_target(&mut self, keychain: K, target_index: u32) {
+        if let Some((next_index, _)) = self.next_index(keychain.clone()) {
+            let temp_lookahead = (target_index + 1)
+                .checked_sub(next_index)
+                .filter(|&index| index > 0);
+
+            if let Some(temp_lookahead) = temp_lookahead {
+                self.replenish_inner_index_keychain(keychain, temp_lookahead);
+            }
+        }
+    }
+
+    fn replenish_inner_index_did(&mut self, did: DescriptorId, lookahead: u32) {
+        if let Some(keychain) = self.descriptor_id_to_keychain.get(&did).cloned() {
+            self.replenish_inner_index(did, &keychain, lookahead);
+        }
+    }
+
+    fn replenish_inner_index_keychain(&mut self, keychain: K, lookahead: u32) {
+        if let Some(did) = self.keychain_to_descriptor_id.get(&keychain) {
+            self.replenish_inner_index(*did, &keychain, lookahead);
+        }
+    }
+
+    /// Syncs the state of the inner spk index after changes to a keychain
+    fn replenish_inner_index(&mut self, did: DescriptorId, keychain: &K, lookahead: u32) {
+        let descriptor = self.descriptors.get(&did).expect("invariant");
+        let next_store_index = self
+            .inner
+            .all_spks()
+            .range(&(keychain.clone(), u32::MIN)..=&(keychain.clone(), u32::MAX))
+            .last()
+            .map_or(0, |((_, index), _)| *index + 1);
+        let next_reveal_index = self.last_revealed.get(&did).map_or(0, |v| *v + 1);
+        for (new_index, new_spk) in
+            SpkIterator::new_with_range(descriptor, next_store_index..next_reveal_index + lookahead)
+        {
+            let _inserted = self
+                .inner
+                .insert_spk((keychain.clone(), new_index), new_spk);
+            debug_assert!(_inserted, "replenish lookahead: must not have existing spk: keychain={:?}, lookahead={}, next_store_index={}, next_reveal_index={}", keychain, lookahead, next_store_index, next_reveal_index);
+        }
+    }
+
+    /// Get an unbounded spk iterator over a given `keychain`. Returns `None` if the provided
+    /// keychain doesn't exist
+    pub fn unbounded_spk_iter(
+        &self,
+        keychain: K,
+    ) -> Option<SpkIterator<Descriptor<DescriptorPublicKey>>> {
+        let descriptor = self.get_descriptor(keychain)?.clone();
+        Some(SpkIterator::new(descriptor))
+    }
+
+    /// Get unbounded spk iterators for all keychains.
+    pub fn all_unbounded_spk_iters(
+        &self,
+    ) -> BTreeMap<K, SpkIterator<Descriptor<DescriptorPublicKey>>> {
+        self.keychain_to_descriptor_id
+            .iter()
+            .map(|(k, did)| {
+                (
+                    k.clone(),
+                    SpkIterator::new(self.descriptors.get(did).expect("invariant").clone()),
+                )
+            })
+            .collect()
+    }
+
+    /// Iterate over revealed spks of keychains in `range`
+    pub fn revealed_spks(
+        &self,
+        range: impl RangeBounds<K>,
+    ) -> impl Iterator<Item = KeychainIndexed<K, ScriptBuf>> + '_ {
+        let start = range.start_bound();
+        let end = range.end_bound();
+        let mut iter_last_revealed = self
+            .keychain_to_descriptor_id
+            .range((start, end))
+            .map(|(k, did)| (k, self.last_revealed.get(did).cloned()));
+        let mut iter_spks = self
+            .inner
+            .all_spks()
+            .range(self.map_to_inner_bounds((start, end)));
+        let mut current_keychain = iter_last_revealed.next();
+        // The reason we need a tricky algorithm is because of the "lookahead" feature which means
+        // that some of the spks in the SpkTxoutIndex will not have been revealed yet. So we need to
+        // filter out those spks that are above the last_revealed for that keychain. To do this we
+        // iterate through the last_revealed for each keychain and the spks for each keychain in
+        // tandem. This minimizes BTreeMap queries.
+        core::iter::from_fn(move || loop {
+            let ((keychain, index), spk) = iter_spks.next()?;
+            // We need to find the last revealed that matches the current spk we are considering so
+            // we skip ahead.
+            while current_keychain?.0 < keychain {
+                current_keychain = iter_last_revealed.next();
+            }
+            let (current_keychain, last_revealed) = current_keychain?;
+
+            if current_keychain == keychain && Some(*index) <= last_revealed {
+                break Some(((keychain.clone(), *index), spk.clone()));
+            }
+        })
+    }
+
+    /// Iterate over revealed spks of the given `keychain` with ascending indices.
+    ///
+    /// This is a double ended iterator so you can easily reverse it to get an iterator where
+    /// the script pubkeys that were most recently revealed are first.
+    pub fn revealed_keychain_spks(
+        &self,
+        keychain: K,
+    ) -> impl DoubleEndedIterator<Item = Indexed<ScriptBuf>> + '_ {
+        let end = self
+            .last_revealed_index(keychain.clone())
+            .map(|v| v + 1)
+            .unwrap_or(0);
+        self.inner
+            .all_spks()
+            .range((keychain.clone(), 0)..(keychain.clone(), end))
+            .map(|((_, index), spk)| (*index, spk.clone()))
+    }
+
+    /// Iterate over revealed, but unused, spks of all keychains.
+    pub fn unused_spks(
+        &self,
+    ) -> impl DoubleEndedIterator<Item = KeychainIndexed<K, ScriptBuf>> + Clone + '_ {
+        self.keychain_to_descriptor_id.keys().flat_map(|keychain| {
+            self.unused_keychain_spks(keychain.clone())
+                .map(|(i, spk)| ((keychain.clone(), i), spk.clone()))
+        })
+    }
+
+    /// Iterate over revealed, but unused, spks of the given `keychain`.
+    /// Returns an empty iterator if the provided keychain doesn't exist.
+    pub fn unused_keychain_spks(
+        &self,
+        keychain: K,
+    ) -> impl DoubleEndedIterator<Item = Indexed<ScriptBuf>> + Clone + '_ {
+        let end = match self.keychain_to_descriptor_id.get(&keychain) {
+            Some(did) => self.last_revealed.get(did).map(|v| *v + 1).unwrap_or(0),
+            None => 0,
+        };
+
+        self.inner
+            .unused_spks((keychain.clone(), 0)..(keychain.clone(), end))
+            .map(|((_, i), spk)| (*i, spk))
+    }
+
+    /// Get the next derivation index for `keychain`. The next index is the index after the last revealed
+    /// derivation index.
+    ///
+    /// The second field in the returned tuple represents whether the next derivation index is new.
+    /// There are two scenarios where the next derivation index is reused (not new):
+    ///
+    /// 1. The keychain's descriptor has no wildcard, and a script has already been revealed.
+    /// 2. The number of revealed scripts has already reached 2^31 (refer to BIP-32).
+    ///
+    /// Not checking the second field of the tuple may result in address reuse.
+    ///
+    /// Returns None if the provided `keychain` doesn't exist.
+    pub fn next_index(&self, keychain: K) -> Option<(u32, bool)> {
+        let did = self.keychain_to_descriptor_id.get(&keychain)?;
+        let last_index = self.last_revealed.get(did).cloned();
+        let descriptor = self.descriptors.get(did).expect("invariant");
+
+        // we can only get the next index if the wildcard exists.
+        let has_wildcard = descriptor.has_wildcard();
+
+        Some(match last_index {
+            // if there is no index, next_index is always 0.
+            None => (0, true),
+            // descriptors without wildcards can only have one index.
+            Some(_) if !has_wildcard => (0, false),
+            // derivation index must be < 2^31 (BIP-32).
+            Some(index) if index > BIP32_MAX_INDEX => {
+                unreachable!("index is out of bounds")
+            }
+            Some(index) if index == BIP32_MAX_INDEX => (index, false),
+            // get the next derivation index.
+            Some(index) => (index + 1, true),
+        })
+    }
+
+    /// Get the last derivation index that is revealed for each keychain.
+    ///
+    /// Keychains with no revealed indices will not be included in the returned [`BTreeMap`].
+    pub fn last_revealed_indices(&self) -> BTreeMap<K, u32> {
+        self.last_revealed
+            .iter()
+            .filter_map(|(desc_id, index)| {
+                let keychain = self.descriptor_id_to_keychain.get(desc_id)?;
+                Some((keychain.clone(), *index))
+            })
+            .collect()
+    }
+
+    /// Get the last derivation index revealed for `keychain`. Returns None if the keychain doesn't
+    /// exist, or if the keychain doesn't have any revealed scripts.
+    pub fn last_revealed_index(&self, keychain: K) -> Option<u32> {
+        let descriptor_id = self.keychain_to_descriptor_id.get(&keychain)?;
+        self.last_revealed.get(descriptor_id).cloned()
+    }
+
+    /// Convenience method to call [`Self::reveal_to_target`] on multiple keychains.
+    pub fn reveal_to_target_multi(&mut self, keychains: &BTreeMap<K, u32>) -> ChangeSet {
+        let mut changeset = ChangeSet::default();
+
+        for (keychain, &index) in keychains {
+            if let Some((_, new_changeset)) = self.reveal_to_target(keychain.clone(), index) {
+                changeset.merge(new_changeset);
+            }
+        }
+
+        changeset
+    }
+
+    /// Reveals script pubkeys of the `keychain`'s descriptor **up to and including** the
+    /// `target_index`.
+    ///
+    /// If the `target_index` cannot be reached (due to the descriptor having no wildcard and/or
+    /// the `target_index` is in the hardened index range), this method will make a best-effort and
+    /// reveal up to the last possible index.
+    ///
+    /// This returns list of newly revealed indices (alongside their scripts) and a
+    /// [`ChangeSet`], which reports updates to the latest revealed index. If no new script
+    /// pubkeys are revealed, then both of these will be empty.
+    ///
+    /// Returns None if the provided `keychain` doesn't exist.
+    #[must_use]
+    pub fn reveal_to_target(
+        &mut self,
+        keychain: K,
+        target_index: u32,
+    ) -> Option<(Vec<Indexed<ScriptBuf>>, ChangeSet)> {
+        let mut changeset = ChangeSet::default();
+        let mut spks: Vec<Indexed<ScriptBuf>> = vec![];
+        while let Some((i, new)) = self.next_index(keychain.clone()) {
+            if !new || i > target_index {
+                break;
+            }
+            match self.reveal_next_spk(keychain.clone()) {
+                Some(((i, spk), change)) => {
+                    spks.push((i, spk));
+                    changeset.merge(change);
+                }
+                None => break,
+            }
+        }
+
+        Some((spks, changeset))
+    }
+
+    /// Attempts to reveal the next script pubkey for `keychain`.
+    ///
+    /// Returns the derivation index of the revealed script pubkey, the revealed script pubkey and a
+    /// [`ChangeSet`] which represents changes in the last revealed index (if any).
+    /// Returns None if the provided keychain doesn't exist.
+    ///
+    /// When a new script cannot be revealed, we return the last revealed script and an empty
+    /// [`ChangeSet`]. There are two scenarios when a new script pubkey cannot be derived:
+    ///
+    ///  1. The descriptor has no wildcard and already has one script revealed.
+    ///  2. The descriptor has already revealed scripts up to the numeric bound.
+    ///  3. There is no descriptor associated with the given keychain.
+    pub fn reveal_next_spk(&mut self, keychain: K) -> Option<(Indexed<ScriptBuf>, ChangeSet)> {
+        let (next_index, new) = self.next_index(keychain.clone())?;
+        let mut changeset = ChangeSet::default();
+
+        if new {
+            let did = self.keychain_to_descriptor_id.get(&keychain)?;
+            self.last_revealed.insert(*did, next_index);
+            changeset.last_revealed.insert(*did, next_index);
+            self.replenish_inner_index(*did, &keychain, self.lookahead);
+        }
+        let script = self
+            .inner
+            .spk_at_index(&(keychain.clone(), next_index))
+            .expect("we just inserted it");
+        Some(((next_index, script), changeset))
+    }
+
+    /// Gets the next unused script pubkey in the keychain. I.e., the script pubkey with the lowest
+    /// index that has not been used yet.
+    ///
+    /// This will derive and reveal a new script pubkey if no more unused script pubkeys exist.
+    ///
+    /// If the descriptor has no wildcard and already has a used script pubkey or if a descriptor
+    /// has used all scripts up to the derivation bounds, then the last derived script pubkey will be
+    /// returned.
+    ///
+    /// Returns `None` if there are no script pubkeys that have been used and no new script pubkey
+    /// could be revealed (see [`reveal_next_spk`] for when this happens).
+    ///
+    /// [`reveal_next_spk`]: Self::reveal_next_spk
+    pub fn next_unused_spk(&mut self, keychain: K) -> Option<(Indexed<ScriptBuf>, ChangeSet)> {
+        let next_unused = self
+            .unused_keychain_spks(keychain.clone())
+            .next()
+            .map(|(i, spk)| ((i, spk.to_owned()), ChangeSet::default()));
+
+        next_unused.or_else(|| self.reveal_next_spk(keychain))
+    }
+
+    /// Iterate over all [`OutPoint`]s that have `TxOut`s with script pubkeys derived from
+    /// `keychain`.
+    pub fn keychain_outpoints(
+        &self,
+        keychain: K,
+    ) -> impl DoubleEndedIterator<Item = Indexed<OutPoint>> + '_ {
+        self.keychain_outpoints_in_range(keychain.clone()..=keychain)
+            .map(|((_, i), op)| (i, op))
+    }
+
+    /// Iterate over [`OutPoint`]s that have script pubkeys derived from keychains in `range`.
+    pub fn keychain_outpoints_in_range<'a>(
+        &'a self,
+        range: impl RangeBounds<K> + 'a,
+    ) -> impl DoubleEndedIterator<Item = KeychainIndexed<K, OutPoint>> + 'a {
+        self.inner
+            .outputs_in_range(self.map_to_inner_bounds(range))
+            .map(|((k, i), op)| ((k.clone(), *i), op))
+    }
+
+    fn map_to_inner_bounds(&self, bound: impl RangeBounds<K>) -> impl RangeBounds<(K, u32)> {
+        let start = match bound.start_bound() {
+            Bound::Included(keychain) => Bound::Included((keychain.clone(), u32::MIN)),
+            Bound::Excluded(keychain) => Bound::Excluded((keychain.clone(), u32::MAX)),
+            Bound::Unbounded => Bound::Unbounded,
+        };
+        let end = match bound.end_bound() {
+            Bound::Included(keychain) => Bound::Included((keychain.clone(), u32::MAX)),
+            Bound::Excluded(keychain) => Bound::Excluded((keychain.clone(), u32::MIN)),
+            Bound::Unbounded => Bound::Unbounded,
+        };
+
+        (start, end)
+    }
+
+    /// Returns the highest derivation index of the `keychain` where [`KeychainTxOutIndex`] has
+    /// found a [`TxOut`] with it's script pubkey.
+    pub fn last_used_index(&self, keychain: K) -> Option<u32> {
+        self.keychain_outpoints(keychain).last().map(|(i, _)| i)
+    }
+
+    /// Returns the highest derivation index of each keychain that [`KeychainTxOutIndex`] has found
+    /// a [`TxOut`] with it's script pubkey.
+    pub fn last_used_indices(&self) -> BTreeMap<K, u32> {
+        self.keychain_to_descriptor_id
+            .iter()
+            .filter_map(|(keychain, _)| {
+                self.last_used_index(keychain.clone())
+                    .map(|index| (keychain.clone(), index))
+            })
+            .collect()
+    }
+
+    /// Applies the `ChangeSet<K>` to the [`KeychainTxOutIndex<K>`]
+    pub fn apply_changeset(&mut self, changeset: ChangeSet) {
+        for (&desc_id, &index) in &changeset.last_revealed {
+            let v = self.last_revealed.entry(desc_id).or_default();
+            *v = index.max(*v);
+            self.replenish_inner_index_did(desc_id, self.lookahead);
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+/// Error returned from [`KeychainTxOutIndex::insert_descriptor`]
+pub enum InsertDescriptorError<K> {
+    /// The descriptor has already been assigned to a keychain so you can't assign it to another
+    DescriptorAlreadyAssigned {
+        /// The descriptor you have attempted to reassign
+        descriptor: Descriptor<DescriptorPublicKey>,
+        /// The keychain that the descriptor is already assigned to
+        existing_assignment: K,
+    },
+    /// The keychain is already assigned to a descriptor so you can't reassign it
+    KeychainAlreadyAssigned {
+        /// The keychain that you have attempted to reassign
+        keychain: K,
+        /// The descriptor that the keychain is already assigned to
+        existing_assignment: Descriptor<DescriptorPublicKey>,
+    },
+}
+
+impl<K: core::fmt::Debug> core::fmt::Display for InsertDescriptorError<K> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            InsertDescriptorError::DescriptorAlreadyAssigned {
+                existing_assignment: existing,
+                descriptor,
+            } => {
+                write!(
+                    f,
+                    "attempt to re-assign descriptor {descriptor:?} already assigned to {existing:?}"
+                )
+            }
+            InsertDescriptorError::KeychainAlreadyAssigned {
+                existing_assignment: existing,
+                keychain,
+            } => {
+                write!(
+                    f,
+                    "attempt to re-assign keychain {keychain:?} already assigned to {existing:?}"
+                )
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<K: core::fmt::Debug> std::error::Error for InsertDescriptorError<K> {}
+
+/// Represents updates to the derivation index of a [`KeychainTxOutIndex`].
+/// It maps each keychain `K` to a descriptor and its last revealed index.
+///
+/// It can be applied to [`KeychainTxOutIndex`] with [`apply_changeset`].
+///
+/// The `last_revealed` field is monotone in that [`merge`] will never decrease it.
+/// `keychains_added` is *not* monotone, once it is set any attempt to change it is subject to the
+/// same *one-to-one* keychain <-> descriptor mapping invariant as [`KeychainTxOutIndex`] itself.
+///
+/// [`KeychainTxOutIndex`]: crate::keychain_txout::KeychainTxOutIndex
+/// [`apply_changeset`]: crate::keychain_txout::KeychainTxOutIndex::apply_changeset
+/// [`merge`]: Self::merge
+#[derive(Clone, Debug, Default, PartialEq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(crate = "serde_crate")
+)]
+#[must_use]
+pub struct ChangeSet {
+    /// Contains for each descriptor_id the last revealed index of derivation
+    pub last_revealed: BTreeMap<DescriptorId, u32>,
+}
+
+impl Merge for ChangeSet {
+    /// Merge another [`ChangeSet`] into self.
+    fn merge(&mut self, other: Self) {
+        // for `last_revealed`, entries of `other` will take precedence ONLY if it is greater than
+        // what was originally in `self`.
+        for (desc_id, index) in other.last_revealed {
+            use crate::collections::btree_map::Entry;
+            match self.last_revealed.entry(desc_id) {
+                Entry::Vacant(entry) => {
+                    entry.insert(index);
+                }
+                Entry::Occupied(mut entry) => {
+                    if *entry.get() < index {
+                        entry.insert(index);
+                    }
+                }
+            }
+        }
+    }
+
+    /// Returns whether the changeset are empty.
+    fn is_empty(&self) -> bool {
+        self.last_revealed.is_empty()
+    }
+}

crates/chain/src/indexer/spk_txout.rs

@@ -0,0 +1,337 @@
+//! [`SpkTxOutIndex`] is an index storing [`TxOut`]s that have a script pubkey that matches those in a list.
+
+use core::ops::RangeBounds;
+
+use crate::{
+    collections::{hash_map::Entry, BTreeMap, BTreeSet, HashMap},
+    Indexer,
+};
+use bitcoin::{Amount, OutPoint, ScriptBuf, SignedAmount, Transaction, TxOut, Txid};
+
+/// An index storing [`TxOut`]s that have a script pubkey that matches those in a list.
+///
+/// The basic idea is that you insert script pubkeys you care about into the index with
+/// [`insert_spk`] and then when you call [`Indexer::index_tx`] or [`Indexer::index_txout`], the
+/// index will look at any txouts you pass in and store and index any txouts matching one of its
+/// script pubkeys.
+///
+/// Each script pubkey is associated with an application-defined index script index `I`, which must be
+/// [`Ord`]. Usually, this is used to associate the derivation index of the script pubkey or even a
+/// combination of `(keychain, derivation_index)`.
+///
+/// Note there is no harm in scanning transactions that disappear from the blockchain or were never
+/// in there in the first place. `SpkTxOutIndex` is intentionally *monotone* -- you cannot delete or
+/// modify txouts that have been indexed. To find out which txouts from the index are actually in the
+/// chain or unspent, you must use other sources of information like a [`TxGraph`].
+///
+/// [`TxOut`]: bitcoin::TxOut
+/// [`insert_spk`]: Self::insert_spk
+/// [`Ord`]: core::cmp::Ord
+/// [`TxGraph`]: crate::tx_graph::TxGraph
+#[derive(Clone, Debug)]
+pub struct SpkTxOutIndex<I> {
+    /// script pubkeys ordered by index
+    spks: BTreeMap<I, ScriptBuf>,
+    /// A reverse lookup from spk to spk index
+    spk_indices: HashMap<ScriptBuf, I>,
+    /// The set of unused indexes.
+    unused: BTreeSet<I>,
+    /// Lookup index and txout by outpoint.
+    txouts: BTreeMap<OutPoint, (I, TxOut)>,
+    /// Lookup from spk index to outpoints that had that spk
+    spk_txouts: BTreeSet<(I, OutPoint)>,
+}
+
+impl<I> Default for SpkTxOutIndex<I> {
+    fn default() -> Self {
+        Self {
+            txouts: Default::default(),
+            spks: Default::default(),
+            spk_indices: Default::default(),
+            spk_txouts: Default::default(),
+            unused: Default::default(),
+        }
+    }
+}
+
+impl<I: Clone + Ord + core::fmt::Debug> Indexer for SpkTxOutIndex<I> {
+    type ChangeSet = ();
+
+    fn index_txout(&mut self, outpoint: OutPoint, txout: &TxOut) -> Self::ChangeSet {
+        self.scan_txout(outpoint, txout);
+        Default::default()
+    }
+
+    fn index_tx(&mut self, tx: &Transaction) -> Self::ChangeSet {
+        self.scan(tx);
+        Default::default()
+    }
+
+    fn initial_changeset(&self) -> Self::ChangeSet {}
+
+    fn apply_changeset(&mut self, _changeset: Self::ChangeSet) {
+        // This applies nothing.
+    }
+
+    fn is_tx_relevant(&self, tx: &Transaction) -> bool {
+        self.is_relevant(tx)
+    }
+}
+
+impl<I: Clone + Ord + core::fmt::Debug> SpkTxOutIndex<I> {
+    /// Scans a transaction's outputs for matching script pubkeys.
+    ///
+    /// Typically, this is used in two situations:
+    ///
+    /// 1. After loading transaction data from the disk, you may scan over all the txouts to restore all
+    ///    your txouts.
+    /// 2. When getting new data from the chain, you usually scan it before incorporating it into your chain state.
+    pub fn scan(&mut self, tx: &Transaction) -> BTreeSet<I> {
+        let mut scanned_indices = BTreeSet::new();
+        let txid = tx.compute_txid();
+        for (i, txout) in tx.output.iter().enumerate() {
+            let op = OutPoint::new(txid, i as u32);
+            if let Some(spk_i) = self.scan_txout(op, txout) {
+                scanned_indices.insert(spk_i.clone());
+            }
+        }
+
+        scanned_indices
+    }
+
+    /// Scan a single `TxOut` for a matching script pubkey and returns the index that matches the
+    /// script pubkey (if any).
+    pub fn scan_txout(&mut self, op: OutPoint, txout: &TxOut) -> Option<&I> {
+        let spk_i = self.spk_indices.get(&txout.script_pubkey);
+        if let Some(spk_i) = spk_i {
+            self.txouts.insert(op, (spk_i.clone(), txout.clone()));
+            self.spk_txouts.insert((spk_i.clone(), op));
+            self.unused.remove(spk_i);
+        }
+        spk_i
+    }
+
+    /// Get a reference to the set of indexed outpoints.
+    pub fn outpoints(&self) -> &BTreeSet<(I, OutPoint)> {
+        &self.spk_txouts
+    }
+
+    /// Iterate over all known txouts that spend to tracked script pubkeys.
+    pub fn txouts(
+        &self,
+    ) -> impl DoubleEndedIterator<Item = (&I, OutPoint, &TxOut)> + ExactSizeIterator {
+        self.txouts
+            .iter()
+            .map(|(op, (index, txout))| (index, *op, txout))
+    }
+
+    /// Finds all txouts on a transaction that has previously been scanned and indexed.
+    pub fn txouts_in_tx(
+        &self,
+        txid: Txid,
+    ) -> impl DoubleEndedIterator<Item = (&I, OutPoint, &TxOut)> {
+        self.txouts
+            .range(OutPoint::new(txid, u32::MIN)..=OutPoint::new(txid, u32::MAX))
+            .map(|(op, (index, txout))| (index, *op, txout))
+    }
+
+    /// Iterates over all the outputs with script pubkeys in an index range.
+    pub fn outputs_in_range(
+        &self,
+        range: impl RangeBounds<I>,
+    ) -> impl DoubleEndedIterator<Item = (&I, OutPoint)> {
+        use bitcoin::hashes::Hash;
+        use core::ops::Bound::*;
+        let min_op = OutPoint {
+            txid: Txid::all_zeros(),
+            vout: u32::MIN,
+        };
+        let max_op = OutPoint {
+            txid: Txid::from_byte_array([0xff; Txid::LEN]),
+            vout: u32::MAX,
+        };
+
+        let start = match range.start_bound() {
+            Included(index) => Included((index.clone(), min_op)),
+            Excluded(index) => Excluded((index.clone(), max_op)),
+            Unbounded => Unbounded,
+        };
+
+        let end = match range.end_bound() {
+            Included(index) => Included((index.clone(), max_op)),
+            Excluded(index) => Excluded((index.clone(), min_op)),
+            Unbounded => Unbounded,
+        };
+
+        self.spk_txouts.range((start, end)).map(|(i, op)| (i, *op))
+    }
+
+    /// Returns the txout and script pubkey index of the `TxOut` at `OutPoint`.
+    ///
+    /// Returns `None` if the `TxOut` hasn't been scanned or if nothing matching was found there.
+    pub fn txout(&self, outpoint: OutPoint) -> Option<(&I, &TxOut)> {
+        self.txouts.get(&outpoint).map(|v| (&v.0, &v.1))
+    }
+
+    /// Returns the script that has been inserted at the `index`.
+    ///
+    /// If that index hasn't been inserted yet, it will return `None`.
+    pub fn spk_at_index(&self, index: &I) -> Option<ScriptBuf> {
+        self.spks.get(index).cloned()
+    }
+
+    /// The script pubkeys that are being tracked by the index.
+    pub fn all_spks(&self) -> &BTreeMap<I, ScriptBuf> {
+        &self.spks
+    }
+
+    /// Adds a script pubkey to scan for. Returns `false` and does nothing if spk already exists in the map
+    ///
+    /// the index will look for outputs spending to this spk whenever it scans new data.
+    pub fn insert_spk(&mut self, index: I, spk: ScriptBuf) -> bool {
+        match self.spk_indices.entry(spk.clone()) {
+            Entry::Vacant(value) => {
+                value.insert(index.clone());
+                self.spks.insert(index.clone(), spk);
+                self.unused.insert(index);
+                true
+            }
+            Entry::Occupied(_) => false,
+        }
+    }
+
+    /// Iterates over all unused script pubkeys in an index range.
+    ///
+    /// Here, "unused" means that after the script pubkey was stored in the index, the index has
+    /// never scanned a transaction output with it.
+    ///
+    /// # Example
+    ///
+    /// ```rust
+    /// # use bdk_chain::spk_txout::SpkTxOutIndex;
+    ///
+    /// // imagine our spks are indexed like (keychain, derivation_index).
+    /// let txout_index = SpkTxOutIndex::<(u32, u32)>::default();
+    /// let all_unused_spks = txout_index.unused_spks(..);
+    /// let change_index = 1;
+    /// let unused_change_spks =
+    ///     txout_index.unused_spks((change_index, u32::MIN)..(change_index, u32::MAX));
+    /// ```
+    pub fn unused_spks<R>(
+        &self,
+        range: R,
+    ) -> impl DoubleEndedIterator<Item = (&I, ScriptBuf)> + Clone + '_
+    where
+        R: RangeBounds<I>,
+    {
+        self.unused
+            .range(range)
+            .map(move |index| (index, self.spk_at_index(index).expect("must exist")))
+    }
+
+    /// Returns whether the script pubkey at `index` has been used or not.
+    ///
+    /// Here, "unused" means that after the script pubkey was stored in the index, the index has
+    /// never scanned a transaction output with it.
+    pub fn is_used(&self, index: &I) -> bool {
+        !self.unused.contains(index)
+    }
+
+    /// Marks the script pubkey at `index` as used even though it hasn't seen an output spending to it.
+    /// This only affects when the `index` had already been added to `self` and was unused.
+    ///
+    /// Returns whether the `index` was initially present as `unused`.
+    ///
+    /// This is useful when you want to reserve a script pubkey for something but don't want to add
+    /// the transaction output using it to the index yet. Other callers will consider the `index` used
+    /// until you call [`unmark_used`].
+    ///
+    /// [`unmark_used`]: Self::unmark_used
+    pub fn mark_used(&mut self, index: &I) -> bool {
+        self.unused.remove(index)
+    }
+
+    /// Undoes the effect of [`mark_used`]. Returns whether the `index` is inserted back into
+    /// `unused`.
+    ///
+    /// Note that if `self` has scanned an output with this script pubkey then this will have no
+    /// effect.
+    ///
+    /// [`mark_used`]: Self::mark_used
+    pub fn unmark_used(&mut self, index: &I) -> bool {
+        // we cannot set the index as unused when it does not exist
+        if !self.spks.contains_key(index) {
+            return false;
+        }
+        // we cannot set the index as unused when txouts are indexed under it
+        if self.outputs_in_range(index..=index).next().is_some() {
+            return false;
+        }
+        self.unused.insert(index.clone())
+    }
+
+    /// Returns the index associated with the script pubkey.
+    pub fn index_of_spk(&self, script: ScriptBuf) -> Option<&I> {
+        self.spk_indices.get(script.as_script())
+    }
+
+    /// Computes the total value transfer effect `tx` has on the script pubkeys in `range`. Value is
+    /// *sent* when a script pubkey in the `range` is on an input and *received* when it is on an
+    /// output. For `sent` to be computed correctly, the output being spent must have already been
+    /// scanned by the index. Calculating received just uses the [`Transaction`] outputs directly,
+    /// so it will be correct even if it has not been scanned.
+    pub fn sent_and_received(
+        &self,
+        tx: &Transaction,
+        range: impl RangeBounds<I>,
+    ) -> (Amount, Amount) {
+        let mut sent = Amount::ZERO;
+        let mut received = Amount::ZERO;
+
+        for txin in &tx.input {
+            if let Some((index, txout)) = self.txout(txin.previous_output) {
+                if range.contains(index) {
+                    sent += txout.value;
+                }
+            }
+        }
+        for txout in &tx.output {
+            if let Some(index) = self.index_of_spk(txout.script_pubkey.clone()) {
+                if range.contains(index) {
+                    received += txout.value;
+                }
+            }
+        }
+
+        (sent, received)
+    }
+
+    /// Computes the net value transfer effect of `tx` on the script pubkeys in `range`. Shorthand
+    /// for calling [`sent_and_received`] and subtracting sent from received.
+    ///
+    /// [`sent_and_received`]: Self::sent_and_received
+    pub fn net_value(&self, tx: &Transaction, range: impl RangeBounds<I>) -> SignedAmount {
+        let (sent, received) = self.sent_and_received(tx, range);
+        received.to_signed().expect("valid `SignedAmount`")
+            - sent.to_signed().expect("valid `SignedAmount`")
+    }
+
+    /// Whether any of the inputs of this transaction spend a txout tracked or whether any output
+    /// matches one of our script pubkeys.
+    ///
+    /// It is easily possible to misuse this method and get false negatives by calling it before you
+    /// have scanned the `TxOut`s the transaction is spending. For example, if you want to filter out
+    /// all the transactions in a block that are irrelevant, you **must first scan all the
+    /// transactions in the block** and only then use this method.
+    pub fn is_relevant(&self, tx: &Transaction) -> bool {
+        let input_matches = tx
+            .input
+            .iter()
+            .any(|input| self.txouts.contains_key(&input.previous_output));
+        let output_matches = tx
+            .output
+            .iter()
+            .any(|output| self.spk_indices.contains_key(&output.script_pubkey));
+        input_matches || output_matches
+    }
+}

crates/chain/src/lib.rs

@@ -0,0 +1,128 @@
+//! This crate is a collection of core structures for [Bitcoin Dev Kit].
+//!
+//! The goal of this crate is to give wallets the mechanisms needed to:
+//!
+//! 1. Figure out what data they need to fetch.
+//! 2. Process the data in a way that never leads to inconsistent states.
+//! 3. Fully index that data and expose it to be consumed without friction.
+//!
+//! Our design goals for these mechanisms are:
+//!
+//! 1. Data source agnostic -- nothing in `bdk_chain` cares about where you get data from or whether
+//!    you do it synchronously or asynchronously. If you know a fact about the blockchain, you can just
+//!    tell `bdk_chain`'s APIs about it, and that information will be integrated, if it can be done
+//!    consistently.
+//! 2. Data persistence agnostic -- `bdk_chain` does not care where you cache on-chain data, what you
+//!    cache or how you retrieve it from persistent storage.
+//!
+//! [Bitcoin Dev Kit]: https://bitcoindevkit.org/
+
+#![no_std]
+#![warn(missing_docs)]
+
+pub use bitcoin;
+mod balance;
+pub use balance::*;
+mod chain_data;
+pub use chain_data::*;
+pub mod indexed_tx_graph;
+pub use indexed_tx_graph::IndexedTxGraph;
+pub mod indexer;
+pub use indexer::spk_txout;
+pub use indexer::Indexer;
+pub mod local_chain;
+mod tx_data_traits;
+pub mod tx_graph;
+pub use tx_data_traits::*;
+pub use tx_graph::TxGraph;
+mod chain_oracle;
+pub use chain_oracle::*;
+mod persist;
+pub use persist::*;
+
+#[doc(hidden)]
+pub mod example_utils;
+
+#[cfg(feature = "miniscript")]
+pub use miniscript;
+#[cfg(feature = "miniscript")]
+mod descriptor_ext;
+#[cfg(feature = "miniscript")]
+pub use descriptor_ext::{DescriptorExt, DescriptorId};
+#[cfg(feature = "miniscript")]
+mod spk_iter;
+#[cfg(feature = "miniscript")]
+pub use indexer::keychain_txout;
+#[cfg(feature = "miniscript")]
+pub use spk_iter::*;
+#[cfg(feature = "rusqlite")]
+pub mod rusqlite_impl;
+pub mod spk_client;
+
+#[allow(unused_imports)]
+#[macro_use]
+extern crate alloc;
+#[cfg(feature = "rusqlite")]
+pub extern crate rusqlite_crate as rusqlite;
+#[cfg(feature = "serde")]
+pub extern crate serde_crate as serde;
+
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+#[cfg(all(not(feature = "std"), feature = "hashbrown"))]
+extern crate hashbrown;
+
+// When no-std use `alloc`'s Hash collections. This is activated by default
+#[cfg(all(not(feature = "std"), not(feature = "hashbrown")))]
+#[doc(hidden)]
+pub mod collections {
+    #![allow(dead_code)]
+    pub type HashSet<K> = alloc::collections::BTreeSet<K>;
+    pub type HashMap<K, V> = alloc::collections::BTreeMap<K, V>;
+    pub use alloc::collections::{btree_map as hash_map, *};
+}
+
+// When we have std, use `std`'s all collections
+#[cfg(all(feature = "std", not(feature = "hashbrown")))]
+#[doc(hidden)]
+pub mod collections {
+    pub use std::collections::{hash_map, *};
+}
+
+// With this special feature `hashbrown`, use `hashbrown`'s hash collections, and else from `alloc`.
+#[cfg(feature = "hashbrown")]
+#[doc(hidden)]
+pub mod collections {
+    #![allow(dead_code)]
+    pub type HashSet<K> = hashbrown::HashSet<K>;
+    pub type HashMap<K, V> = hashbrown::HashMap<K, V>;
+    pub use alloc::collections::*;
+    pub use hashbrown::hash_map;
+}
+
+/// How many confirmations are needed f or a coinbase output to be spent.
+pub const COINBASE_MATURITY: u32 = 100;
+
+/// A tuple of keychain index and `T` representing the indexed value.
+pub type Indexed<T> = (u32, T);
+/// A tuple of keychain `K`, derivation index (`u32`) and a `T` associated with them.
+pub type KeychainIndexed<K, T> = ((K, u32), T);
+
+/// A wrapper that we use to impl remote traits for types in our crate or dependency crates.
+pub struct Impl<T>(pub T);
+
+impl<T> From<T> for Impl<T> {
+    fn from(value: T) -> Self {
+        Self(value)
+    }
+}
+
+impl<T> core::ops::Deref for Impl<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}

crates/chain/src/local_chain.rs

@@ -0,0 +1,902 @@
+//! The [`LocalChain`] is a local implementation of [`ChainOracle`].
+
+use core::convert::Infallible;
+use core::ops::RangeBounds;
+
+use crate::collections::BTreeMap;
+use crate::{BlockId, ChainOracle, Merge};
+use alloc::sync::Arc;
+use bitcoin::block::Header;
+use bitcoin::BlockHash;
+
+/// A [`LocalChain`] checkpoint is used to find the agreement point between two chains and as a
+/// transaction anchor.
+///
+/// Each checkpoint contains the height and hash of a block ([`BlockId`]).
+///
+/// Internally, checkpoints are nodes of a reference-counted linked-list. This allows the caller to
+/// cheaply clone a [`CheckPoint`] without copying the whole list and to view the entire chain
+/// without holding a lock on [`LocalChain`].
+#[derive(Debug, Clone)]
+pub struct CheckPoint(Arc<CPInner>);
+
+/// The internal contents of [`CheckPoint`].
+#[derive(Debug, Clone)]
+struct CPInner {
+    /// Block id (hash and height).
+    block: BlockId,
+    /// Previous checkpoint (if any).
+    prev: Option<Arc<CPInner>>,
+}
+
+impl PartialEq for CheckPoint {
+    fn eq(&self, other: &Self) -> bool {
+        let self_cps = self.iter().map(|cp| cp.block_id());
+        let other_cps = other.iter().map(|cp| cp.block_id());
+        self_cps.eq(other_cps)
+    }
+}
+
+impl CheckPoint {
+    /// Construct a new base block at the front of a linked list.
+    pub fn new(block: BlockId) -> Self {
+        Self(Arc::new(CPInner { block, prev: None }))
+    }
+
+    /// Construct a checkpoint from a list of [`BlockId`]s in ascending height order.
+    ///
+    /// # Errors
+    ///
+    /// This method will error if any of the follow occurs:
+    ///
+    /// - The `blocks` iterator is empty, in which case, the error will be `None`.
+    /// - The `blocks` iterator is not in ascending height order.
+    /// - The `blocks` iterator contains multiple [`BlockId`]s of the same height.
+    ///
+    /// The error type is the last successful checkpoint constructed (if any).
+    pub fn from_block_ids(
+        block_ids: impl IntoIterator<Item = BlockId>,
+    ) -> Result<Self, Option<Self>> {
+        let mut blocks = block_ids.into_iter();
+        let mut acc = CheckPoint::new(blocks.next().ok_or(None)?);
+        for id in blocks {
+            acc = acc.push(id).map_err(Some)?;
+        }
+        Ok(acc)
+    }
+
+    /// Construct a checkpoint from the given `header` and block `height`.
+    ///
+    /// If `header` is of the genesis block, the checkpoint won't have a [`prev`] node. Otherwise,
+    /// we return a checkpoint linked with the previous block.
+    ///
+    /// [`prev`]: CheckPoint::prev
+    pub fn from_header(header: &bitcoin::block::Header, height: u32) -> Self {
+        let hash = header.block_hash();
+        let this_block_id = BlockId { height, hash };
+
+        let prev_height = match height.checked_sub(1) {
+            Some(h) => h,
+            None => return Self::new(this_block_id),
+        };
+
+        let prev_block_id = BlockId {
+            height: prev_height,
+            hash: header.prev_blockhash,
+        };
+
+        CheckPoint::new(prev_block_id)
+            .push(this_block_id)
+            .expect("must construct checkpoint")
+    }
+
+    /// Puts another checkpoint onto the linked list representing the blockchain.
+    ///
+    /// Returns an `Err(self)` if the block you are pushing on is not at a greater height that the one you
+    /// are pushing on to.
+    pub fn push(self, block: BlockId) -> Result<Self, Self> {
+        if self.height() < block.height {
+            Ok(Self(Arc::new(CPInner {
+                block,
+                prev: Some(self.0),
+            })))
+        } else {
+            Err(self)
+        }
+    }
+
+    /// Extends the checkpoint linked list by a iterator of block ids.
+    ///
+    /// Returns an `Err(self)` if there is block which does not have a greater height than the
+    /// previous one.
+    pub fn extend(self, blocks: impl IntoIterator<Item = BlockId>) -> Result<Self, Self> {
+        let mut curr = self.clone();
+        for block in blocks {
+            curr = curr.push(block).map_err(|_| self.clone())?;
+        }
+        Ok(curr)
+    }
+
+    /// Get the [`BlockId`] of the checkpoint.
+    pub fn block_id(&self) -> BlockId {
+        self.0.block
+    }
+
+    /// Get the height of the checkpoint.
+    pub fn height(&self) -> u32 {
+        self.0.block.height
+    }
+
+    /// Get the block hash of the checkpoint.
+    pub fn hash(&self) -> BlockHash {
+        self.0.block.hash
+    }
+
+    /// Get the previous checkpoint in the chain
+    pub fn prev(&self) -> Option<CheckPoint> {
+        self.0.prev.clone().map(CheckPoint)
+    }
+
+    /// Iterate from this checkpoint in descending height.
+    pub fn iter(&self) -> CheckPointIter {
+        self.clone().into_iter()
+    }
+
+    /// Get checkpoint at `height`.
+    ///
+    /// Returns `None` if checkpoint at `height` does not exist`.
+    pub fn get(&self, height: u32) -> Option<Self> {
+        self.range(height..=height).next()
+    }
+
+    /// Iterate checkpoints over a height range.
+    ///
+    /// Note that we always iterate checkpoints in reverse height order (iteration starts at tip
+    /// height).
+    pub fn range<R>(&self, range: R) -> impl Iterator<Item = CheckPoint>
+    where
+        R: RangeBounds<u32>,
+    {
+        let start_bound = range.start_bound().cloned();
+        let end_bound = range.end_bound().cloned();
+        self.iter()
+            .skip_while(move |cp| match end_bound {
+                core::ops::Bound::Included(inc_bound) => cp.height() > inc_bound,
+                core::ops::Bound::Excluded(exc_bound) => cp.height() >= exc_bound,
+                core::ops::Bound::Unbounded => false,
+            })
+            .take_while(move |cp| match start_bound {
+                core::ops::Bound::Included(inc_bound) => cp.height() >= inc_bound,
+                core::ops::Bound::Excluded(exc_bound) => cp.height() > exc_bound,
+                core::ops::Bound::Unbounded => true,
+            })
+    }
+
+    /// Inserts `block_id` at its height within the chain.
+    ///
+    /// The effect of `insert` depends on whether a height already exists. If it doesn't the
+    /// `block_id` we inserted and all pre-existing blocks higher than it will be re-inserted after
+    /// it. If the height already existed and has a conflicting block hash then it will be purged
+    /// along with all block followin it. The returned chain will have a tip of the `block_id`
+    /// passed in. Of course, if the `block_id` was already present then this just returns `self`.
+    #[must_use]
+    pub fn insert(self, block_id: BlockId) -> Self {
+        assert_ne!(block_id.height, 0, "cannot insert the genesis block");
+
+        let mut cp = self.clone();
+        let mut tail = vec![];
+        let base = loop {
+            if cp.height() == block_id.height {
+                if cp.hash() == block_id.hash {
+                    return self;
+                }
+                // if we have a conflict we just return the inserted block because the tail is by
+                // implication invalid.
+                tail = vec![];
+                break cp.prev().expect("can't be called on genesis block");
+            }
+
+            if cp.height() < block_id.height {
+                break cp;
+            }
+
+            tail.push(cp.block_id());
+            cp = cp.prev().expect("will break before genesis block");
+        };
+
+        base.extend(core::iter::once(block_id).chain(tail.into_iter().rev()))
+            .expect("tail is in order")
+    }
+
+    /// Apply `changeset` to the checkpoint.
+    fn apply_changeset(mut self, changeset: &ChangeSet) -> Result<CheckPoint, MissingGenesisError> {
+        if let Some(start_height) = changeset.blocks.keys().next().cloned() {
+            // changes after point of agreement
+            let mut extension = BTreeMap::default();
+            // point of agreement
+            let mut base: Option<CheckPoint> = None;
+
+            for cp in self.iter() {
+                if cp.height() >= start_height {
+                    extension.insert(cp.height(), cp.hash());
+                } else {
+                    base = Some(cp);
+                    break;
+                }
+            }
+
+            for (&height, &hash) in &changeset.blocks {
+                match hash {
+                    Some(hash) => {
+                        extension.insert(height, hash);
+                    }
+                    None => {
+                        extension.remove(&height);
+                    }
+                };
+            }
+
+            let new_tip = match base {
+                Some(base) => base
+                    .extend(extension.into_iter().map(BlockId::from))
+                    .expect("extension is strictly greater than base"),
+                None => LocalChain::from_blocks(extension)?.tip(),
+            };
+            self = new_tip;
+        }
+
+        Ok(self)
+    }
+}
+
+/// Iterates over checkpoints backwards.
+pub struct CheckPointIter {
+    current: Option<Arc<CPInner>>,
+}
+
+impl Iterator for CheckPointIter {
+    type Item = CheckPoint;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let current = self.current.clone()?;
+        self.current.clone_from(&current.prev);
+        Some(CheckPoint(current))
+    }
+}
+
+impl IntoIterator for CheckPoint {
+    type Item = CheckPoint;
+    type IntoIter = CheckPointIter;
+
+    fn into_iter(self) -> Self::IntoIter {
+        CheckPointIter {
+            current: Some(self.0),
+        }
+    }
+}
+
+/// This is a local implementation of [`ChainOracle`].
+#[derive(Debug, Clone, PartialEq)]
+pub struct LocalChain {
+    tip: CheckPoint,
+}
+
+impl ChainOracle for LocalChain {
+    type Error = Infallible;
+
+    fn is_block_in_chain(
+        &self,
+        block: BlockId,
+        chain_tip: BlockId,
+    ) -> Result<Option<bool>, Self::Error> {
+        let chain_tip_cp = match self.tip.get(chain_tip.height) {
+            // we can only determine whether `block` is in chain of `chain_tip` if `chain_tip` can
+            // be identified in chain
+            Some(cp) if cp.hash() == chain_tip.hash => cp,
+            _ => return Ok(None),
+        };
+        match chain_tip_cp.get(block.height) {
+            Some(cp) => Ok(Some(cp.hash() == block.hash)),
+            None => Ok(None),
+        }
+    }
+
+    fn get_chain_tip(&self) -> Result<BlockId, Self::Error> {
+        Ok(self.tip.block_id())
+    }
+}
+
+impl LocalChain {
+    /// Get the genesis hash.
+    pub fn genesis_hash(&self) -> BlockHash {
+        self.tip.get(0).expect("genesis must exist").hash()
+    }
+
+    /// Construct [`LocalChain`] from genesis `hash`.
+    #[must_use]
+    pub fn from_genesis_hash(hash: BlockHash) -> (Self, ChangeSet) {
+        let height = 0;
+        let chain = Self {
+            tip: CheckPoint::new(BlockId { height, hash }),
+        };
+        let changeset = chain.initial_changeset();
+        (chain, changeset)
+    }
+
+    /// Construct a [`LocalChain`] from an initial `changeset`.
+    pub fn from_changeset(changeset: ChangeSet) -> Result<Self, MissingGenesisError> {
+        let genesis_entry = changeset.blocks.get(&0).copied().flatten();
+        let genesis_hash = match genesis_entry {
+            Some(hash) => hash,
+            None => return Err(MissingGenesisError),
+        };
+
+        let (mut chain, _) = Self::from_genesis_hash(genesis_hash);
+        chain.apply_changeset(&changeset)?;
+
+        debug_assert!(chain._check_changeset_is_applied(&changeset));
+
+        Ok(chain)
+    }
+
+    /// Construct a [`LocalChain`] from a given `checkpoint` tip.
+    pub fn from_tip(tip: CheckPoint) -> Result<Self, MissingGenesisError> {
+        let genesis_cp = tip.iter().last().expect("must have at least one element");
+        if genesis_cp.height() != 0 {
+            return Err(MissingGenesisError);
+        }
+        Ok(Self { tip })
+    }
+
+    /// Constructs a [`LocalChain`] from a [`BTreeMap`] of height to [`BlockHash`].
+    ///
+    /// The [`BTreeMap`] enforces the height order. However, the caller must ensure the blocks are
+    /// all of the same chain.
+    pub fn from_blocks(blocks: BTreeMap<u32, BlockHash>) -> Result<Self, MissingGenesisError> {
+        if !blocks.contains_key(&0) {
+            return Err(MissingGenesisError);
+        }
+
+        let mut tip: Option<CheckPoint> = None;
+        for block in &blocks {
+            match tip {
+                Some(curr) => {
+                    tip = Some(
+                        curr.push(BlockId::from(block))
+                            .expect("BTreeMap is ordered"),
+                    )
+                }
+                None => tip = Some(CheckPoint::new(BlockId::from(block))),
+            }
+        }
+
+        Ok(Self {
+            tip: tip.expect("already checked to have genesis"),
+        })
+    }
+
+    /// Get the highest checkpoint.
+    pub fn tip(&self) -> CheckPoint {
+        self.tip.clone()
+    }
+
+    /// Applies the given `update` to the chain.
+    ///
+    /// The method returns [`ChangeSet`] on success. This represents the changes applied to `self`.
+    ///
+    /// There must be no ambiguity about which of the existing chain's blocks are still valid and
+    /// which are now invalid. That is, the new chain must implicitly connect to a definite block in
+    /// the existing chain and invalidate the block after it (if it exists) by including a block at
+    /// the same height but with a different hash to explicitly exclude it as a connection point.
+    ///
+    /// # Errors
+    ///
+    /// An error will occur if the update does not correctly connect with `self`.
+    ///
+    /// [module-level documentation]: crate::local_chain
+    pub fn apply_update(&mut self, update: CheckPoint) -> Result<ChangeSet, CannotConnectError> {
+        let (new_tip, changeset) = merge_chains(self.tip.clone(), update)?;
+        self.tip = new_tip;
+        self._check_changeset_is_applied(&changeset);
+        Ok(changeset)
+    }
+
+    /// Update the chain with a given [`Header`] at `height` which you claim is connected to a existing block in the chain.
+    ///
+    /// This is useful when you have a block header that you want to record as part of the chain but
+    /// don't necessarily know that the `prev_blockhash` is in the chain.
+    ///
+    /// This will usually insert two new [`BlockId`]s into the chain: the header's block and the
+    /// header's `prev_blockhash` block. `connected_to` must already be in the chain but is allowed
+    /// to be `prev_blockhash` (in which case only one new block id will be inserted).
+    /// To be successful, `connected_to` must be chosen carefully so that `LocalChain`'s [update
+    /// rules][`apply_update`] are satisfied.
+    ///
+    /// # Errors
+    ///
+    /// [`ApplyHeaderError::InconsistentBlocks`] occurs if the `connected_to` block and the
+    /// [`Header`] is inconsistent. For example, if the `connected_to` block is the same height as
+    /// `header` or `prev_blockhash`, but has a different block hash. Or if the `connected_to`
+    /// height is greater than the header's `height`.
+    ///
+    /// [`ApplyHeaderError::CannotConnect`] occurs if the internal call to [`apply_update`] fails.
+    ///
+    /// [`apply_update`]: Self::apply_update
+    pub fn apply_header_connected_to(
+        &mut self,
+        header: &Header,
+        height: u32,
+        connected_to: BlockId,
+    ) -> Result<ChangeSet, ApplyHeaderError> {
+        let this = BlockId {
+            height,
+            hash: header.block_hash(),
+        };
+        let prev = height.checked_sub(1).map(|prev_height| BlockId {
+            height: prev_height,
+            hash: header.prev_blockhash,
+        });
+        let conn = match connected_to {
+            // `connected_to` can be ignored if same as `this` or `prev` (duplicate)
+            conn if conn == this || Some(conn) == prev => None,
+            // this occurs if:
+            // - `connected_to` height is the same as `prev`, but different hash
+            // - `connected_to` height is the same as `this`, but different hash
+            // - `connected_to` height is greater than `this` (this is not allowed)
+            conn if conn.height >= height.saturating_sub(1) => {
+                return Err(ApplyHeaderError::InconsistentBlocks)
+            }
+            conn => Some(conn),
+        };
+
+        let update = CheckPoint::from_block_ids([conn, prev, Some(this)].into_iter().flatten())
+            .expect("block ids must be in order");
+
+        self.apply_update(update)
+            .map_err(ApplyHeaderError::CannotConnect)
+    }
+
+    /// Update the chain with a given [`Header`] connecting it with the previous block.
+    ///
+    /// This is a convenience method to call [`apply_header_connected_to`] with the `connected_to`
+    /// parameter being `height-1:prev_blockhash`. If there is no previous block (i.e. genesis), we
+    /// use the current block as `connected_to`.
+    ///
+    /// [`apply_header_connected_to`]: LocalChain::apply_header_connected_to
+    pub fn apply_header(
+        &mut self,
+        header: &Header,
+        height: u32,
+    ) -> Result<ChangeSet, CannotConnectError> {
+        let connected_to = match height.checked_sub(1) {
+            Some(prev_height) => BlockId {
+                height: prev_height,
+                hash: header.prev_blockhash,
+            },
+            None => BlockId {
+                height,
+                hash: header.block_hash(),
+            },
+        };
+        self.apply_header_connected_to(header, height, connected_to)
+            .map_err(|err| match err {
+                ApplyHeaderError::InconsistentBlocks => {
+                    unreachable!("connected_to is derived from the block so is always consistent")
+                }
+                ApplyHeaderError::CannotConnect(err) => err,
+            })
+    }
+
+    /// Apply the given `changeset`.
+    pub fn apply_changeset(&mut self, changeset: &ChangeSet) -> Result<(), MissingGenesisError> {
+        let old_tip = self.tip.clone();
+        let new_tip = old_tip.apply_changeset(changeset)?;
+        self.tip = new_tip;
+        debug_assert!(self._check_changeset_is_applied(changeset));
+        Ok(())
+    }
+
+    /// Insert a [`BlockId`].
+    ///
+    /// # Errors
+    ///
+    /// Replacing the block hash of an existing checkpoint will result in an error.
+    pub fn insert_block(&mut self, block_id: BlockId) -> Result<ChangeSet, AlterCheckPointError> {
+        if let Some(original_cp) = self.tip.get(block_id.height) {
+            let original_hash = original_cp.hash();
+            if original_hash != block_id.hash {
+                return Err(AlterCheckPointError {
+                    height: block_id.height,
+                    original_hash,
+                    update_hash: Some(block_id.hash),
+                });
+            }
+            return Ok(ChangeSet::default());
+        }
+
+        let mut changeset = ChangeSet::default();
+        changeset
+            .blocks
+            .insert(block_id.height, Some(block_id.hash));
+        self.apply_changeset(&changeset)
+            .map_err(|_| AlterCheckPointError {
+                height: 0,
+                original_hash: self.genesis_hash(),
+                update_hash: changeset.blocks.get(&0).cloned().flatten(),
+            })?;
+        Ok(changeset)
+    }
+
+    /// Removes blocks from (and inclusive of) the given `block_id`.
+    ///
+    /// This will remove blocks with a height equal or greater than `block_id`, but only if
+    /// `block_id` exists in the chain.
+    ///
+    /// # Errors
+    ///
+    /// This will fail with [`MissingGenesisError`] if the caller attempts to disconnect from the
+    /// genesis block.
+    pub fn disconnect_from(&mut self, block_id: BlockId) -> Result<ChangeSet, MissingGenesisError> {
+        let mut remove_from = Option::<CheckPoint>::None;
+        let mut changeset = ChangeSet::default();
+        for cp in self.tip().iter() {
+            let cp_id = cp.block_id();
+            if cp_id.height < block_id.height {
+                break;
+            }
+            changeset.blocks.insert(cp_id.height, None);
+            if cp_id == block_id {
+                remove_from = Some(cp);
+            }
+        }
+        self.tip = match remove_from.map(|cp| cp.prev()) {
+            // The checkpoint below the earliest checkpoint to remove will be the new tip.
+            Some(Some(new_tip)) => new_tip,
+            // If there is no checkpoint below the earliest checkpoint to remove, it means the
+            // "earliest checkpoint to remove" is the genesis block. We disallow removing the
+            // genesis block.
+            Some(None) => return Err(MissingGenesisError),
+            // If there is nothing to remove, we return an empty changeset.
+            None => return Ok(ChangeSet::default()),
+        };
+        Ok(changeset)
+    }
+
+    /// Derives an initial [`ChangeSet`], meaning that it can be applied to an empty chain to
+    /// recover the current chain.
+    pub fn initial_changeset(&self) -> ChangeSet {
+        ChangeSet {
+            blocks: self
+                .tip
+                .iter()
+                .map(|cp| {
+                    let block_id = cp.block_id();
+                    (block_id.height, Some(block_id.hash))
+                })
+                .collect(),
+        }
+    }
+
+    /// Iterate over checkpoints in descending height order.
+    pub fn iter_checkpoints(&self) -> CheckPointIter {
+        CheckPointIter {
+            current: Some(self.tip.0.clone()),
+        }
+    }
+
+    fn _check_changeset_is_applied(&self, changeset: &ChangeSet) -> bool {
+        let mut curr_cp = self.tip.clone();
+        for (height, exp_hash) in changeset.blocks.iter().rev() {
+            match curr_cp.get(*height) {
+                Some(query_cp) => {
+                    if query_cp.height() != *height || Some(query_cp.hash()) != *exp_hash {
+                        return false;
+                    }
+                    curr_cp = query_cp;
+                }
+                None => {
+                    if exp_hash.is_some() {
+                        return false;
+                    }
+                }
+            }
+        }
+        true
+    }
+
+    /// Get checkpoint at given `height` (if it exists).
+    ///
+    /// This is a shorthand for calling [`CheckPoint::get`] on the [`tip`].
+    ///
+    /// [`tip`]: LocalChain::tip
+    pub fn get(&self, height: u32) -> Option<CheckPoint> {
+        self.tip.get(height)
+    }
+
+    /// Iterate checkpoints over a height range.
+    ///
+    /// Note that we always iterate checkpoints in reverse height order (iteration starts at tip
+    /// height).
+    ///
+    /// This is a shorthand for calling [`CheckPoint::range`] on the [`tip`].
+    ///
+    /// [`tip`]: LocalChain::tip
+    pub fn range<R>(&self, range: R) -> impl Iterator<Item = CheckPoint>
+    where
+        R: RangeBounds<u32>,
+    {
+        self.tip.range(range)
+    }
+}
+
+/// The [`ChangeSet`] represents changes to [`LocalChain`].
+#[derive(Debug, Default, Clone, PartialEq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Deserialize, serde::Serialize),
+    serde(crate = "serde_crate")
+)]
+pub struct ChangeSet {
+    /// Changes to the [`LocalChain`] blocks.
+    ///
+    /// The key represents the block height, and the value either represents added a new [`CheckPoint`]
+    /// (if [`Some`]), or removing a [`CheckPoint`] (if [`None`]).
+    pub blocks: BTreeMap<u32, Option<BlockHash>>,
+}
+
+impl Merge for ChangeSet {
+    fn merge(&mut self, other: Self) {
+        Merge::merge(&mut self.blocks, other.blocks)
+    }
+
+    fn is_empty(&self) -> bool {
+        self.blocks.is_empty()
+    }
+}
+
+impl<B: IntoIterator<Item = (u32, Option<BlockHash>)>> From<B> for ChangeSet {
+    fn from(blocks: B) -> Self {
+        Self {
+            blocks: blocks.into_iter().collect(),
+        }
+    }
+}
+
+impl FromIterator<(u32, Option<BlockHash>)> for ChangeSet {
+    fn from_iter<T: IntoIterator<Item = (u32, Option<BlockHash>)>>(iter: T) -> Self {
+        Self {
+            blocks: iter.into_iter().collect(),
+        }
+    }
+}
+
+impl FromIterator<(u32, BlockHash)> for ChangeSet {
+    fn from_iter<T: IntoIterator<Item = (u32, BlockHash)>>(iter: T) -> Self {
+        Self {
+            blocks: iter
+                .into_iter()
+                .map(|(height, hash)| (height, Some(hash)))
+                .collect(),
+        }
+    }
+}
+
+/// An error which occurs when a [`LocalChain`] is constructed without a genesis checkpoint.
+#[derive(Clone, Debug, PartialEq)]
+pub struct MissingGenesisError;
+
+impl core::fmt::Display for MissingGenesisError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(
+            f,
+            "cannot construct `LocalChain` without a genesis checkpoint"
+        )
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for MissingGenesisError {}
+
+/// Represents a failure when trying to insert/remove a checkpoint to/from [`LocalChain`].
+#[derive(Clone, Debug, PartialEq)]
+pub struct AlterCheckPointError {
+    /// The checkpoint's height.
+    pub height: u32,
+    /// The original checkpoint's block hash which cannot be replaced/removed.
+    pub original_hash: BlockHash,
+    /// The attempted update to the `original_block` hash.
+    pub update_hash: Option<BlockHash>,
+}
+
+impl core::fmt::Display for AlterCheckPointError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self.update_hash {
+            Some(update_hash) => write!(
+                f,
+                "failed to insert block at height {}: original={} update={}",
+                self.height, self.original_hash, update_hash
+            ),
+            None => write!(
+                f,
+                "failed to remove block at height {}: original={}",
+                self.height, self.original_hash
+            ),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for AlterCheckPointError {}
+
+/// Occurs when an update does not have a common checkpoint with the original chain.
+#[derive(Clone, Debug, PartialEq)]
+pub struct CannotConnectError {
+    /// The suggested checkpoint to include to connect the two chains.
+    pub try_include_height: u32,
+}
+
+impl core::fmt::Display for CannotConnectError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(
+            f,
+            "introduced chain cannot connect with the original chain, try include height {}",
+            self.try_include_height,
+        )
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for CannotConnectError {}
+
+/// The error type for [`LocalChain::apply_header_connected_to`].
+#[derive(Debug, Clone, PartialEq)]
+pub enum ApplyHeaderError {
+    /// Occurs when `connected_to` block conflicts with either the current block or previous block.
+    InconsistentBlocks,
+    /// Occurs when the update cannot connect with the original chain.
+    CannotConnect(CannotConnectError),
+}
+
+impl core::fmt::Display for ApplyHeaderError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            ApplyHeaderError::InconsistentBlocks => write!(
+                f,
+                "the `connected_to` block conflicts with either the current or previous block"
+            ),
+            ApplyHeaderError::CannotConnect(err) => core::fmt::Display::fmt(err, f),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for ApplyHeaderError {}
+
+/// Applies `update_tip` onto `original_tip`.
+///
+/// On success, a tuple is returned `(changeset, can_replace)`. If `can_replace` is true, then the
+/// `update_tip` can replace the `original_tip`.
+fn merge_chains(
+    original_tip: CheckPoint,
+    update_tip: CheckPoint,
+) -> Result<(CheckPoint, ChangeSet), CannotConnectError> {
+    let mut changeset = ChangeSet::default();
+    let mut orig = original_tip.iter();
+    let mut update = update_tip.iter();
+    let mut curr_orig = None;
+    let mut curr_update = None;
+    let mut prev_orig: Option<CheckPoint> = None;
+    let mut prev_update: Option<CheckPoint> = None;
+    let mut point_of_agreement_found = false;
+    let mut prev_orig_was_invalidated = false;
+    let mut potentially_invalidated_heights = vec![];
+
+    // If we can, we want to return the update tip as the new tip because this allows checkpoints
+    // in multiple locations to keep the same `Arc` pointers when they are being updated from each
+    // other using this function. We can do this as long as long as the update contains every
+    // block's height of the original chain.
+    let mut is_update_height_superset_of_original = true;
+
+    // To find the difference between the new chain and the original we iterate over both of them
+    // from the tip backwards in tandem. We always dealing with the highest one from either chain
+    // first and move to the next highest. The crucial logic is applied when they have blocks at the
+    // same height.
+    loop {
+        if curr_orig.is_none() {
+            curr_orig = orig.next();
+        }
+        if curr_update.is_none() {
+            curr_update = update.next();
+        }
+
+        match (curr_orig.as_ref(), curr_update.as_ref()) {
+            // Update block that doesn't exist in the original chain
+            (o, Some(u)) if Some(u.height()) > o.map(|o| o.height()) => {
+                changeset.blocks.insert(u.height(), Some(u.hash()));
+                prev_update = curr_update.take();
+            }
+            // Original block that isn't in the update
+            (Some(o), u) if Some(o.height()) > u.map(|u| u.height()) => {
+                // this block might be gone if an earlier block gets invalidated
+                potentially_invalidated_heights.push(o.height());
+                prev_orig_was_invalidated = false;
+                prev_orig = curr_orig.take();
+
+                is_update_height_superset_of_original = false;
+
+                // OPTIMIZATION: we have run out of update blocks so we don't need to continue
+                // iterating because there's no possibility of adding anything to changeset.
+                if u.is_none() {
+                    break;
+                }
+            }
+            (Some(o), Some(u)) => {
+                if o.hash() == u.hash() {
+                    // We have found our point of agreement 🎉 -- we require that the previous (i.e.
+                    // higher because we are iterating backwards) block in the original chain was
+                    // invalidated (if it exists). This ensures that there is an unambiguous point of
+                    // connection to the original chain from the update chain (i.e. we know the
+                    // precisely which original blocks are invalid).
+                    if !prev_orig_was_invalidated && !point_of_agreement_found {
+                        if let (Some(prev_orig), Some(_prev_update)) = (&prev_orig, &prev_update) {
+                            return Err(CannotConnectError {
+                                try_include_height: prev_orig.height(),
+                            });
+                        }
+                    }
+                    point_of_agreement_found = true;
+                    prev_orig_was_invalidated = false;
+                    // OPTIMIZATION 2 -- if we have the same underlying pointer at this point, we
+                    // can guarantee that no older blocks are introduced.
+                    if Arc::as_ptr(&o.0) == Arc::as_ptr(&u.0) {
+                        if is_update_height_superset_of_original {
+                            return Ok((update_tip, changeset));
+                        } else {
+                            let new_tip =
+                                original_tip.apply_changeset(&changeset).map_err(|_| {
+                                    CannotConnectError {
+                                        try_include_height: 0,
+                                    }
+                                })?;
+                            return Ok((new_tip, changeset));
+                        }
+                    }
+                } else {
+                    // We have an invalidation height so we set the height to the updated hash and
+                    // also purge all the original chain block hashes above this block.
+                    changeset.blocks.insert(u.height(), Some(u.hash()));
+                    for invalidated_height in potentially_invalidated_heights.drain(..) {
+                        changeset.blocks.insert(invalidated_height, None);
+                    }
+                    prev_orig_was_invalidated = true;
+                }
+                prev_update = curr_update.take();
+                prev_orig = curr_orig.take();
+            }
+            (None, None) => {
+                break;
+            }
+            _ => {
+                unreachable!("compiler cannot tell that everything has been covered")
+            }
+        }
+    }
+
+    // When we don't have a point of agreement you can imagine it is implicitly the
+    // genesis block so we need to do the final connectivity check which in this case
+    // just means making sure the entire original chain was invalidated.
+    if !prev_orig_was_invalidated && !point_of_agreement_found {
+        if let Some(prev_orig) = prev_orig {
+            return Err(CannotConnectError {
+                try_include_height: prev_orig.height(),
+            });
+        }
+    }
+
+    let new_tip = original_tip
+        .apply_changeset(&changeset)
+        .map_err(|_| CannotConnectError {
+            try_include_height: 0,
+        })?;
+    Ok((new_tip, changeset))
+}

crates/chain/src/persist.rs

@@ -0,0 +1,169 @@
+use core::{
+    future::Future,
+    ops::{Deref, DerefMut},
+    pin::Pin,
+};
+
+use alloc::boxed::Box;
+
+use crate::Merge;
+
+/// Represents a type that contains staged changes.
+pub trait Staged {
+    /// Type for staged changes.
+    type ChangeSet: Merge;
+
+    /// Get mutable reference of staged changes.
+    fn staged(&mut self) -> &mut Self::ChangeSet;
+}
+
+/// Trait that persists the type with `Db`.
+///
+/// Methods of this trait should not be called directly.
+pub trait PersistWith<Db>: Staged + Sized {
+    /// Parameters for [`PersistWith::create`].
+    type CreateParams;
+    /// Parameters for [`PersistWith::load`].
+    type LoadParams;
+    /// Error type of [`PersistWith::create`].
+    type CreateError;
+    /// Error type of [`PersistWith::load`].
+    type LoadError;
+    /// Error type of [`PersistWith::persist`].
+    type PersistError;
+
+    /// Initialize the `Db` and create `Self`.
+    fn create(db: &mut Db, params: Self::CreateParams) -> Result<Self, Self::CreateError>;
+
+    /// Initialize the `Db` and load a previously-persisted `Self`.
+    fn load(db: &mut Db, params: Self::LoadParams) -> Result<Option<Self>, Self::LoadError>;
+
+    /// Persist changes to the `Db`.
+    fn persist(
+        db: &mut Db,
+        changeset: &<Self as Staged>::ChangeSet,
+    ) -> Result<(), Self::PersistError>;
+}
+
+type FutureResult<'a, T, E> = Pin<Box<dyn Future<Output = Result<T, E>> + Send + 'a>>;
+
+/// Trait that persists the type with an async `Db`.
+pub trait PersistAsyncWith<Db>: Staged + Sized {
+    /// Parameters for [`PersistAsyncWith::create`].
+    type CreateParams;
+    /// Parameters for [`PersistAsyncWith::load`].
+    type LoadParams;
+    /// Error type of [`PersistAsyncWith::create`].
+    type CreateError;
+    /// Error type of [`PersistAsyncWith::load`].
+    type LoadError;
+    /// Error type of [`PersistAsyncWith::persist`].
+    type PersistError;
+
+    /// Initialize the `Db` and create `Self`.
+    fn create(db: &mut Db, params: Self::CreateParams) -> FutureResult<Self, Self::CreateError>;
+
+    /// Initialize the `Db` and load a previously-persisted `Self`.
+    fn load(db: &mut Db, params: Self::LoadParams) -> FutureResult<Option<Self>, Self::LoadError>;
+
+    /// Persist changes to the `Db`.
+    fn persist<'a>(
+        db: &'a mut Db,
+        changeset: &'a <Self as Staged>::ChangeSet,
+    ) -> FutureResult<'a, (), Self::PersistError>;
+}
+
+/// Represents a persisted `T`.
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Persisted<T> {
+    inner: T,
+}
+
+impl<T> Persisted<T> {
+    /// Create a new persisted `T`.
+    pub fn create<Db>(db: &mut Db, params: T::CreateParams) -> Result<Self, T::CreateError>
+    where
+        T: PersistWith<Db>,
+    {
+        T::create(db, params).map(|inner| Self { inner })
+    }
+
+    /// Create a new persisted `T` with async `Db`.
+    pub async fn create_async<Db>(
+        db: &mut Db,
+        params: T::CreateParams,
+    ) -> Result<Self, T::CreateError>
+    where
+        T: PersistAsyncWith<Db>,
+    {
+        T::create(db, params).await.map(|inner| Self { inner })
+    }
+
+    /// Construct a persisted `T` from `Db`.
+    pub fn load<Db>(db: &mut Db, params: T::LoadParams) -> Result<Option<Self>, T::LoadError>
+    where
+        T: PersistWith<Db>,
+    {
+        Ok(T::load(db, params)?.map(|inner| Self { inner }))
+    }
+
+    /// Construct a persisted `T` from an async `Db`.
+    pub async fn load_async<Db>(
+        db: &mut Db,
+        params: T::LoadParams,
+    ) -> Result<Option<Self>, T::LoadError>
+    where
+        T: PersistAsyncWith<Db>,
+    {
+        Ok(T::load(db, params).await?.map(|inner| Self { inner }))
+    }
+
+    /// Persist staged changes of `T` into `Db`.
+    ///
+    /// If the database errors, the staged changes will not be cleared.
+    pub fn persist<Db>(&mut self, db: &mut Db) -> Result<bool, T::PersistError>
+    where
+        T: PersistWith<Db>,
+    {
+        let stage = T::staged(&mut self.inner);
+        if stage.is_empty() {
+            return Ok(false);
+        }
+        T::persist(db, &*stage)?;
+        stage.take();
+        Ok(true)
+    }
+
+    /// Persist staged changes of `T` into an async `Db`.
+    ///
+    /// If the database errors, the staged changes will not be cleared.
+    pub async fn persist_async<'a, Db>(
+        &'a mut self,
+        db: &'a mut Db,
+    ) -> Result<bool, T::PersistError>
+    where
+        T: PersistAsyncWith<Db>,
+    {
+        let stage = T::staged(&mut self.inner);
+        if stage.is_empty() {
+            return Ok(false);
+        }
+        T::persist(db, &*stage).await?;
+        stage.take();
+        Ok(true)
+    }
+}
+
+impl<T> Deref for Persisted<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T> DerefMut for Persisted<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.inner
+    }
+}

crates/chain/src/rusqlite_impl.rs

@@ -0,0 +1,530 @@
+//! Module for stuff
+
+use crate::*;
+use core::str::FromStr;
+
+use alloc::{borrow::ToOwned, boxed::Box, string::ToString, sync::Arc, vec::Vec};
+use bitcoin::consensus::{Decodable, Encodable};
+use rusqlite;
+use rusqlite::named_params;
+use rusqlite::types::{FromSql, FromSqlError, FromSqlResult, ToSql, ToSqlOutput, ValueRef};
+use rusqlite::OptionalExtension;
+use rusqlite::Transaction;
+
+/// Table name for schemas.
+pub const SCHEMAS_TABLE_NAME: &str = "bdk_schemas";
+
+/// Initialize the schema table.
+fn init_schemas_table(db_tx: &Transaction) -> rusqlite::Result<()> {
+    let sql = format!("CREATE TABLE IF NOT EXISTS {}( name TEXT PRIMARY KEY NOT NULL, version INTEGER NOT NULL ) STRICT", SCHEMAS_TABLE_NAME);
+    db_tx.execute(&sql, ())?;
+    Ok(())
+}
+
+/// Get schema version of `schema_name`.
+fn schema_version(db_tx: &Transaction, schema_name: &str) -> rusqlite::Result<Option<u32>> {
+    let sql = format!(
+        "SELECT version FROM {} WHERE name=:name",
+        SCHEMAS_TABLE_NAME
+    );
+    db_tx
+        .query_row(&sql, named_params! { ":name": schema_name }, |row| {
+            row.get::<_, u32>("version")
+        })
+        .optional()
+}
+
+/// Set the `schema_version` of `schema_name`.
+fn set_schema_version(
+    db_tx: &Transaction,
+    schema_name: &str,
+    schema_version: u32,
+) -> rusqlite::Result<()> {
+    let sql = format!(
+        "REPLACE INTO {}(name, version) VALUES(:name, :version)",
+        SCHEMAS_TABLE_NAME,
+    );
+    db_tx.execute(
+        &sql,
+        named_params! { ":name": schema_name, ":version": schema_version },
+    )?;
+    Ok(())
+}
+
+/// Runs logic that initializes/migrates the table schemas.
+pub fn migrate_schema(
+    db_tx: &Transaction,
+    schema_name: &str,
+    versioned_scripts: &[&[&str]],
+) -> rusqlite::Result<()> {
+    init_schemas_table(db_tx)?;
+    let current_version = schema_version(db_tx, schema_name)?;
+    let exec_from = current_version.map_or(0_usize, |v| v as usize + 1);
+    let scripts_to_exec = versioned_scripts.iter().enumerate().skip(exec_from);
+    for (version, &script) in scripts_to_exec {
+        set_schema_version(db_tx, schema_name, version as u32)?;
+        for statement in script {
+            db_tx.execute(statement, ())?;
+        }
+    }
+    Ok(())
+}
+
+impl FromSql for Impl<bitcoin::Txid> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        bitcoin::Txid::from_str(value.as_str()?)
+            .map(Self)
+            .map_err(from_sql_error)
+    }
+}
+
+impl ToSql for Impl<bitcoin::Txid> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        Ok(self.to_string().into())
+    }
+}
+
+impl FromSql for Impl<bitcoin::BlockHash> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        bitcoin::BlockHash::from_str(value.as_str()?)
+            .map(Self)
+            .map_err(from_sql_error)
+    }
+}
+
+impl ToSql for Impl<bitcoin::BlockHash> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        Ok(self.to_string().into())
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl FromSql for Impl<DescriptorId> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        DescriptorId::from_str(value.as_str()?)
+            .map(Self)
+            .map_err(from_sql_error)
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl ToSql for Impl<DescriptorId> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        Ok(self.to_string().into())
+    }
+}
+
+impl FromSql for Impl<bitcoin::Transaction> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        bitcoin::Transaction::consensus_decode_from_finite_reader(&mut value.as_bytes()?)
+            .map(Self)
+            .map_err(from_sql_error)
+    }
+}
+
+impl ToSql for Impl<bitcoin::Transaction> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        let mut bytes = Vec::<u8>::new();
+        self.consensus_encode(&mut bytes).map_err(to_sql_error)?;
+        Ok(bytes.into())
+    }
+}
+
+impl FromSql for Impl<bitcoin::ScriptBuf> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        Ok(bitcoin::Script::from_bytes(value.as_bytes()?)
+            .to_owned()
+            .into())
+    }
+}
+
+impl ToSql for Impl<bitcoin::ScriptBuf> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        Ok(self.as_bytes().into())
+    }
+}
+
+impl FromSql for Impl<bitcoin::Amount> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        Ok(bitcoin::Amount::from_sat(value.as_i64()?.try_into().map_err(from_sql_error)?).into())
+    }
+}
+
+impl ToSql for Impl<bitcoin::Amount> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        let amount: i64 = self.to_sat().try_into().map_err(to_sql_error)?;
+        Ok(amount.into())
+    }
+}
+
+impl<A: Anchor + serde_crate::de::DeserializeOwned> FromSql for Impl<A> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        serde_json::from_str(value.as_str()?)
+            .map(Impl)
+            .map_err(from_sql_error)
+    }
+}
+
+impl<A: Anchor + serde_crate::Serialize> ToSql for Impl<A> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        serde_json::to_string(&self.0)
+            .map(Into::into)
+            .map_err(to_sql_error)
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl FromSql for Impl<miniscript::Descriptor<miniscript::DescriptorPublicKey>> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        miniscript::Descriptor::from_str(value.as_str()?)
+            .map(Self)
+            .map_err(from_sql_error)
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl ToSql for Impl<miniscript::Descriptor<miniscript::DescriptorPublicKey>> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        Ok(self.to_string().into())
+    }
+}
+
+impl FromSql for Impl<bitcoin::Network> {
+    fn column_result(value: ValueRef<'_>) -> FromSqlResult<Self> {
+        bitcoin::Network::from_str(value.as_str()?)
+            .map(Self)
+            .map_err(from_sql_error)
+    }
+}
+
+impl ToSql for Impl<bitcoin::Network> {
+    fn to_sql(&self) -> rusqlite::Result<ToSqlOutput<'_>> {
+        Ok(self.to_string().into())
+    }
+}
+
+fn from_sql_error<E: std::error::Error + Send + Sync + 'static>(err: E) -> FromSqlError {
+    FromSqlError::Other(Box::new(err))
+}
+
+fn to_sql_error<E: std::error::Error + Send + Sync + 'static>(err: E) -> rusqlite::Error {
+    rusqlite::Error::ToSqlConversionFailure(Box::new(err))
+}
+
+impl<A> tx_graph::ChangeSet<A>
+where
+    A: Anchor + Clone + Ord + serde::Serialize + serde::de::DeserializeOwned,
+{
+    /// Schema name for [`tx_graph::ChangeSet`].
+    pub const SCHEMA_NAME: &'static str = "bdk_txgraph";
+    /// Name of table that stores full transactions and `last_seen` timestamps.
+    pub const TXS_TABLE_NAME: &'static str = "bdk_txs";
+    /// Name of table that stores floating txouts.
+    pub const TXOUTS_TABLE_NAME: &'static str = "bdk_txouts";
+    /// Name of table that stores [`Anchor`]s.
+    pub const ANCHORS_TABLE_NAME: &'static str = "bdk_anchors";
+
+    /// Initialize sqlite tables.
+    fn init_sqlite_tables(db_tx: &rusqlite::Transaction) -> rusqlite::Result<()> {
+        let schema_v0: &[&str] = &[
+            // full transactions
+            &format!(
+                "CREATE TABLE {} ( \
+                txid TEXT PRIMARY KEY NOT NULL, \
+                raw_tx BLOB, \
+                last_seen INTEGER \
+                ) STRICT",
+                Self::TXS_TABLE_NAME,
+            ),
+            // floating txouts
+            &format!(
+                "CREATE TABLE {} ( \
+                txid TEXT NOT NULL, \
+                vout INTEGER NOT NULL, \
+                value INTEGER NOT NULL, \
+                script BLOB NOT NULL, \
+                PRIMARY KEY (txid, vout) \
+                ) STRICT",
+                Self::TXOUTS_TABLE_NAME,
+            ),
+            // anchors
+            &format!(
+                "CREATE TABLE {} ( \
+                txid TEXT NOT NULL REFERENCES {} (txid), \
+                block_height INTEGER NOT NULL, \
+                block_hash TEXT NOT NULL, \
+                anchor BLOB NOT NULL, \
+                PRIMARY KEY (txid, block_height, block_hash) \
+                ) STRICT",
+                Self::ANCHORS_TABLE_NAME,
+                Self::TXS_TABLE_NAME,
+            ),
+        ];
+        migrate_schema(db_tx, Self::SCHEMA_NAME, &[schema_v0])
+    }
+
+    /// Construct a [`TxGraph`] from an sqlite database.
+    pub fn from_sqlite(db_tx: &rusqlite::Transaction) -> rusqlite::Result<Self> {
+        Self::init_sqlite_tables(db_tx)?;
+
+        let mut changeset = Self::default();
+
+        let mut statement = db_tx.prepare(&format!(
+            "SELECT txid, raw_tx, last_seen FROM {}",
+            Self::TXS_TABLE_NAME,
+        ))?;
+        let row_iter = statement.query_map([], |row| {
+            Ok((
+                row.get::<_, Impl<bitcoin::Txid>>("txid")?,
+                row.get::<_, Option<Impl<bitcoin::Transaction>>>("raw_tx")?,
+                row.get::<_, Option<u64>>("last_seen")?,
+            ))
+        })?;
+        for row in row_iter {
+            let (Impl(txid), tx, last_seen) = row?;
+            if let Some(Impl(tx)) = tx {
+                changeset.txs.insert(Arc::new(tx));
+            }
+            if let Some(last_seen) = last_seen {
+                changeset.last_seen.insert(txid, last_seen);
+            }
+        }
+
+        let mut statement = db_tx.prepare(&format!(
+            "SELECT txid, vout, value, script FROM {}",
+            Self::TXOUTS_TABLE_NAME,
+        ))?;
+        let row_iter = statement.query_map([], |row| {
+            Ok((
+                row.get::<_, Impl<bitcoin::Txid>>("txid")?,
+                row.get::<_, u32>("vout")?,
+                row.get::<_, Impl<bitcoin::Amount>>("value")?,
+                row.get::<_, Impl<bitcoin::ScriptBuf>>("script")?,
+            ))
+        })?;
+        for row in row_iter {
+            let (Impl(txid), vout, Impl(value), Impl(script_pubkey)) = row?;
+            changeset.txouts.insert(
+                bitcoin::OutPoint { txid, vout },
+                bitcoin::TxOut {
+                    value,
+                    script_pubkey,
+                },
+            );
+        }
+
+        let mut statement = db_tx.prepare(&format!(
+            "SELECT json(anchor), txid FROM {}",
+            Self::ANCHORS_TABLE_NAME,
+        ))?;
+        let row_iter = statement.query_map([], |row| {
+            Ok((
+                row.get::<_, Impl<A>>("json(anchor)")?,
+                row.get::<_, Impl<bitcoin::Txid>>("txid")?,
+            ))
+        })?;
+        for row in row_iter {
+            let (Impl(anchor), Impl(txid)) = row?;
+            changeset.anchors.insert((anchor, txid));
+        }
+
+        Ok(changeset)
+    }
+
+    /// Persist `changeset` to the sqlite database.
+    pub fn persist_to_sqlite(&self, db_tx: &rusqlite::Transaction) -> rusqlite::Result<()> {
+        Self::init_sqlite_tables(db_tx)?;
+
+        let mut statement = db_tx.prepare_cached(&format!(
+            "INSERT INTO {}(txid, raw_tx) VALUES(:txid, :raw_tx) ON CONFLICT(txid) DO UPDATE SET raw_tx=:raw_tx",
+            Self::TXS_TABLE_NAME,
+        ))?;
+        for tx in &self.txs {
+            statement.execute(named_params! {
+                ":txid": Impl(tx.compute_txid()),
+                ":raw_tx": Impl(tx.as_ref().clone()),
+            })?;
+        }
+
+        let mut statement = db_tx
+            .prepare_cached(&format!(
+                "INSERT INTO {}(txid, last_seen) VALUES(:txid, :last_seen) ON CONFLICT(txid) DO UPDATE SET last_seen=:last_seen",
+                Self::TXS_TABLE_NAME,
+            ))?;
+        for (&txid, &last_seen) in &self.last_seen {
+            statement.execute(named_params! {
+                ":txid": Impl(txid),
+                ":last_seen": Some(last_seen),
+            })?;
+        }
+
+        let mut statement = db_tx.prepare_cached(&format!(
+            "REPLACE INTO {}(txid, vout, value, script) VALUES(:txid, :vout, :value, :script)",
+            Self::TXOUTS_TABLE_NAME,
+        ))?;
+        for (op, txo) in &self.txouts {
+            statement.execute(named_params! {
+                ":txid": Impl(op.txid),
+                ":vout": op.vout,
+                ":value": Impl(txo.value),
+                ":script": Impl(txo.script_pubkey.clone()),
+            })?;
+        }
+
+        let mut statement = db_tx.prepare_cached(&format!(
+            "REPLACE INTO {}(txid, block_height, block_hash, anchor) VALUES(:txid, :block_height, :block_hash, jsonb(:anchor))",
+            Self::ANCHORS_TABLE_NAME,
+        ))?;
+        for (anchor, txid) in &self.anchors {
+            let anchor_block = anchor.anchor_block();
+            statement.execute(named_params! {
+                ":txid": Impl(*txid),
+                ":block_height": anchor_block.height,
+                ":block_hash": Impl(anchor_block.hash),
+                ":anchor": Impl(anchor.clone()),
+            })?;
+        }
+
+        Ok(())
+    }
+}
+
+impl local_chain::ChangeSet {
+    /// Schema name for the changeset.
+    pub const SCHEMA_NAME: &'static str = "bdk_localchain";
+    /// Name of sqlite table that stores blocks of [`LocalChain`](local_chain::LocalChain).
+    pub const BLOCKS_TABLE_NAME: &'static str = "bdk_blocks";
+
+    /// Initialize sqlite tables for persisting [`local_chain::LocalChain`].
+    fn init_sqlite_tables(db_tx: &rusqlite::Transaction) -> rusqlite::Result<()> {
+        let schema_v0: &[&str] = &[
+            // blocks
+            &format!(
+                "CREATE TABLE {} ( \
+                block_height INTEGER PRIMARY KEY NOT NULL, \
+                block_hash TEXT NOT NULL \
+                ) STRICT",
+                Self::BLOCKS_TABLE_NAME,
+            ),
+        ];
+        migrate_schema(db_tx, Self::SCHEMA_NAME, &[schema_v0])
+    }
+
+    /// Construct a [`LocalChain`](local_chain::LocalChain) from sqlite database.
+    pub fn from_sqlite(db_tx: &rusqlite::Transaction) -> rusqlite::Result<Self> {
+        Self::init_sqlite_tables(db_tx)?;
+
+        let mut changeset = Self::default();
+
+        let mut statement = db_tx.prepare(&format!(
+            "SELECT block_height, block_hash FROM {}",
+            Self::BLOCKS_TABLE_NAME,
+        ))?;
+        let row_iter = statement.query_map([], |row| {
+            Ok((
+                row.get::<_, u32>("block_height")?,
+                row.get::<_, Impl<bitcoin::BlockHash>>("block_hash")?,
+            ))
+        })?;
+        for row in row_iter {
+            let (height, Impl(hash)) = row?;
+            changeset.blocks.insert(height, Some(hash));
+        }
+
+        Ok(changeset)
+    }
+
+    /// Persist `changeset` to the sqlite database.
+    pub fn persist_to_sqlite(&self, db_tx: &rusqlite::Transaction) -> rusqlite::Result<()> {
+        Self::init_sqlite_tables(db_tx)?;
+
+        let mut replace_statement = db_tx.prepare_cached(&format!(
+            "REPLACE INTO {}(block_height, block_hash) VALUES(:block_height, :block_hash)",
+            Self::BLOCKS_TABLE_NAME,
+        ))?;
+        let mut delete_statement = db_tx.prepare_cached(&format!(
+            "DELETE FROM {} WHERE block_height=:block_height",
+            Self::BLOCKS_TABLE_NAME,
+        ))?;
+        for (&height, &hash) in &self.blocks {
+            match hash {
+                Some(hash) => replace_statement.execute(named_params! {
+                    ":block_height": height,
+                    ":block_hash": Impl(hash),
+                })?,
+                None => delete_statement.execute(named_params! {
+                    ":block_height": height,
+                })?,
+            };
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(feature = "miniscript")]
+impl keychain_txout::ChangeSet {
+    /// Schema name for the changeset.
+    pub const SCHEMA_NAME: &'static str = "bdk_keychaintxout";
+    /// Name for table that stores last revealed indices per descriptor id.
+    pub const LAST_REVEALED_TABLE_NAME: &'static str = "bdk_descriptor_last_revealed";
+
+    /// Initialize sqlite tables for persisting
+    /// [`KeychainTxOutIndex`](keychain_txout::KeychainTxOutIndex).
+    fn init_sqlite_tables(db_tx: &rusqlite::Transaction) -> rusqlite::Result<()> {
+        let schema_v0: &[&str] = &[
+            // last revealed
+            &format!(
+                "CREATE TABLE {} ( \
+                descriptor_id TEXT PRIMARY KEY NOT NULL, \
+                last_revealed INTEGER NOT NULL \
+                ) STRICT",
+                Self::LAST_REVEALED_TABLE_NAME,
+            ),
+        ];
+        migrate_schema(db_tx, Self::SCHEMA_NAME, &[schema_v0])
+    }
+
+    /// Construct [`KeychainTxOutIndex`](keychain_txout::KeychainTxOutIndex) from sqlite database
+    /// and given parameters.
+    pub fn from_sqlite(db_tx: &rusqlite::Transaction) -> rusqlite::Result<Self> {
+        Self::init_sqlite_tables(db_tx)?;
+
+        let mut changeset = Self::default();
+
+        let mut statement = db_tx.prepare(&format!(
+            "SELECT descriptor_id, last_revealed FROM {}",
+            Self::LAST_REVEALED_TABLE_NAME,
+        ))?;
+        let row_iter = statement.query_map([], |row| {
+            Ok((
+                row.get::<_, Impl<DescriptorId>>("descriptor_id")?,
+                row.get::<_, u32>("last_revealed")?,
+            ))
+        })?;
+        for row in row_iter {
+            let (Impl(descriptor_id), last_revealed) = row?;
+            changeset.last_revealed.insert(descriptor_id, last_revealed);
+        }
+
+        Ok(changeset)
+    }
+
+    /// Persist `changeset` to the sqlite database.
+    pub fn persist_to_sqlite(&self, db_tx: &rusqlite::Transaction) -> rusqlite::Result<()> {
+        Self::init_sqlite_tables(db_tx)?;
+
+        let mut statement = db_tx.prepare_cached(&format!(
+            "REPLACE INTO {}(descriptor_id, last_revealed) VALUES(:descriptor_id, :last_revealed)",
+            Self::LAST_REVEALED_TABLE_NAME,
+        ))?;
+        for (&descriptor_id, &last_revealed) in &self.last_revealed {
+            statement.execute(named_params! {
+                ":descriptor_id": Impl(descriptor_id),
+                ":last_revealed": last_revealed,
+            })?;
+        }
+
+        Ok(())
+    }
+}

crates/chain/src/spk_client.rs

@@ -0,0 +1,388 @@
+//! Helper types for spk-based blockchain clients.
+
+use crate::{
+    collections::BTreeMap, local_chain::CheckPoint, ConfirmationBlockTime, Indexed, TxGraph,
+};
+use alloc::boxed::Box;
+use bitcoin::{OutPoint, Script, ScriptBuf, Txid};
+use core::marker::PhantomData;
+
+/// Data required to perform a spk-based blockchain client sync.
+///
+/// A client sync fetches relevant chain data for a known list of scripts, transaction ids and
+/// outpoints. The sync process also updates the chain from the given [`CheckPoint`].
+pub struct SyncRequest {
+    /// A checkpoint for the current chain [`LocalChain::tip`].
+    /// The sync process will return a new chain update that extends this tip.
+    ///
+    /// [`LocalChain::tip`]: crate::local_chain::LocalChain::tip
+    pub chain_tip: CheckPoint,
+    /// Transactions that spend from or to these indexed script pubkeys.
+    pub spks: Box<dyn ExactSizeIterator<Item = ScriptBuf> + Send>,
+    /// Transactions with these txids.
+    pub txids: Box<dyn ExactSizeIterator<Item = Txid> + Send>,
+    /// Transactions with these outpoints or spent from these outpoints.
+    pub outpoints: Box<dyn ExactSizeIterator<Item = OutPoint> + Send>,
+}
+
+impl SyncRequest {
+    /// Construct a new [`SyncRequest`] from a given `cp` tip.
+    pub fn from_chain_tip(cp: CheckPoint) -> Self {
+        Self {
+            chain_tip: cp,
+            spks: Box::new(core::iter::empty()),
+            txids: Box::new(core::iter::empty()),
+            outpoints: Box::new(core::iter::empty()),
+        }
+    }
+
+    /// Set the [`Script`]s that will be synced against.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn set_spks(
+        mut self,
+        spks: impl IntoIterator<IntoIter = impl ExactSizeIterator<Item = ScriptBuf> + Send + 'static>,
+    ) -> Self {
+        self.spks = Box::new(spks.into_iter());
+        self
+    }
+
+    /// Set the [`Txid`]s that will be synced against.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn set_txids(
+        mut self,
+        txids: impl IntoIterator<IntoIter = impl ExactSizeIterator<Item = Txid> + Send + 'static>,
+    ) -> Self {
+        self.txids = Box::new(txids.into_iter());
+        self
+    }
+
+    /// Set the [`OutPoint`]s that will be synced against.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn set_outpoints(
+        mut self,
+        outpoints: impl IntoIterator<
+            IntoIter = impl ExactSizeIterator<Item = OutPoint> + Send + 'static,
+        >,
+    ) -> Self {
+        self.outpoints = Box::new(outpoints.into_iter());
+        self
+    }
+
+    /// Chain on additional [`Script`]s that will be synced against.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn chain_spks(
+        mut self,
+        spks: impl IntoIterator<
+            IntoIter = impl ExactSizeIterator<Item = ScriptBuf> + Send + 'static,
+            Item = ScriptBuf,
+        >,
+    ) -> Self {
+        self.spks = Box::new(ExactSizeChain::new(self.spks, spks.into_iter()));
+        self
+    }
+
+    /// Chain on additional [`Txid`]s that will be synced against.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn chain_txids(
+        mut self,
+        txids: impl IntoIterator<
+            IntoIter = impl ExactSizeIterator<Item = Txid> + Send + 'static,
+            Item = Txid,
+        >,
+    ) -> Self {
+        self.txids = Box::new(ExactSizeChain::new(self.txids, txids.into_iter()));
+        self
+    }
+
+    /// Chain on additional [`OutPoint`]s that will be synced against.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn chain_outpoints(
+        mut self,
+        outpoints: impl IntoIterator<
+            IntoIter = impl ExactSizeIterator<Item = OutPoint> + Send + 'static,
+            Item = OutPoint,
+        >,
+    ) -> Self {
+        self.outpoints = Box::new(ExactSizeChain::new(self.outpoints, outpoints.into_iter()));
+        self
+    }
+
+    /// Add a closure that will be called for [`Script`]s previously added to this request.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn inspect_spks(
+        mut self,
+        mut inspect: impl FnMut(&Script) + Send + Sync + 'static,
+    ) -> Self {
+        self.spks = Box::new(self.spks.inspect(move |spk| inspect(spk)));
+        self
+    }
+
+    /// Add a closure that will be called for [`Txid`]s previously added to this request.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn inspect_txids(mut self, mut inspect: impl FnMut(&Txid) + Send + Sync + 'static) -> Self {
+        self.txids = Box::new(self.txids.inspect(move |txid| inspect(txid)));
+        self
+    }
+
+    /// Add a closure that will be called for [`OutPoint`]s previously added to this request.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn inspect_outpoints(
+        mut self,
+        mut inspect: impl FnMut(&OutPoint) + Send + Sync + 'static,
+    ) -> Self {
+        self.outpoints = Box::new(self.outpoints.inspect(move |op| inspect(op)));
+        self
+    }
+
+    /// Populate the request with revealed script pubkeys from `index` with the given `spk_range`.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[cfg(feature = "miniscript")]
+    #[must_use]
+    pub fn populate_with_revealed_spks<K: Clone + Ord + core::fmt::Debug + Send + Sync>(
+        self,
+        index: &crate::indexer::keychain_txout::KeychainTxOutIndex<K>,
+        spk_range: impl core::ops::RangeBounds<K>,
+    ) -> Self {
+        use alloc::borrow::ToOwned;
+        use alloc::vec::Vec;
+        self.chain_spks(
+            index
+                .revealed_spks(spk_range)
+                .map(|(_, spk)| spk.to_owned())
+                .collect::<Vec<_>>(),
+        )
+    }
+}
+
+/// Data returned from a spk-based blockchain client sync.
+///
+/// See also [`SyncRequest`].
+pub struct SyncResult<A = ConfirmationBlockTime> {
+    /// The update to apply to the receiving [`TxGraph`].
+    pub graph_update: TxGraph<A>,
+    /// The update to apply to the receiving [`LocalChain`](crate::local_chain::LocalChain).
+    pub chain_update: CheckPoint,
+}
+
+/// Data required to perform a spk-based blockchain client full scan.
+///
+/// A client full scan iterates through all the scripts for the given keychains, fetching relevant
+/// data until some stop gap number of scripts is found that have no data. This operation is
+/// generally only used when importing or restoring previously used keychains in which the list of
+/// used scripts is not known. The full scan process also updates the chain from the given [`CheckPoint`].
+pub struct FullScanRequest<K> {
+    /// A checkpoint for the current [`LocalChain::tip`].
+    /// The full scan process will return a new chain update that extends this tip.
+    ///
+    /// [`LocalChain::tip`]: crate::local_chain::LocalChain::tip
+    pub chain_tip: CheckPoint,
+    /// Iterators of script pubkeys indexed by the keychain index.
+    pub spks_by_keychain: BTreeMap<K, Box<dyn Iterator<Item = Indexed<ScriptBuf>> + Send>>,
+}
+
+impl<K: Ord + Clone> FullScanRequest<K> {
+    /// Construct a new [`FullScanRequest`] from a given `chain_tip`.
+    #[must_use]
+    pub fn from_chain_tip(chain_tip: CheckPoint) -> Self {
+        Self {
+            chain_tip,
+            spks_by_keychain: BTreeMap::new(),
+        }
+    }
+
+    /// Construct a new [`FullScanRequest`] from a given `chain_tip` and `index`.
+    ///
+    /// Unbounded script pubkey iterators for each keychain (`K`) are extracted using
+    /// [`KeychainTxOutIndex::all_unbounded_spk_iters`] and is used to populate the
+    /// [`FullScanRequest`].
+    ///
+    /// [`KeychainTxOutIndex::all_unbounded_spk_iters`]: crate::indexer::keychain_txout::KeychainTxOutIndex::all_unbounded_spk_iters
+    #[cfg(feature = "miniscript")]
+    #[must_use]
+    pub fn from_keychain_txout_index(
+        chain_tip: CheckPoint,
+        index: &crate::indexer::keychain_txout::KeychainTxOutIndex<K>,
+    ) -> Self
+    where
+        K: core::fmt::Debug,
+    {
+        let mut req = Self::from_chain_tip(chain_tip);
+        for (keychain, spks) in index.all_unbounded_spk_iters() {
+            req = req.set_spks_for_keychain(keychain, spks);
+        }
+        req
+    }
+
+    /// Set the [`Script`]s for a given `keychain`.
+    ///
+    /// This consumes the [`FullScanRequest`] and returns the updated one.
+    #[must_use]
+    pub fn set_spks_for_keychain(
+        mut self,
+        keychain: K,
+        spks: impl IntoIterator<IntoIter = impl Iterator<Item = Indexed<ScriptBuf>> + Send + 'static>,
+    ) -> Self {
+        self.spks_by_keychain
+            .insert(keychain, Box::new(spks.into_iter()));
+        self
+    }
+
+    /// Chain on additional [`Script`]s that will be synced against.
+    ///
+    /// This consumes the [`FullScanRequest`] and returns the updated one.
+    #[must_use]
+    pub fn chain_spks_for_keychain(
+        mut self,
+        keychain: K,
+        spks: impl IntoIterator<IntoIter = impl Iterator<Item = Indexed<ScriptBuf>> + Send + 'static>,
+    ) -> Self {
+        match self.spks_by_keychain.remove(&keychain) {
+            // clippy here suggests to remove `into_iter` from `spks.into_iter()`, but doing so
+            // results in a compilation error
+            #[allow(clippy::useless_conversion)]
+            Some(keychain_spks) => self
+                .spks_by_keychain
+                .insert(keychain, Box::new(keychain_spks.chain(spks.into_iter()))),
+            None => self
+                .spks_by_keychain
+                .insert(keychain, Box::new(spks.into_iter())),
+        };
+        self
+    }
+
+    /// Add a closure that will be called for every [`Script`] previously added to any keychain in
+    /// this request.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn inspect_spks_for_all_keychains(
+        mut self,
+        inspect: impl FnMut(K, u32, &Script) + Send + Sync + Clone + 'static,
+    ) -> Self
+    where
+        K: Send + 'static,
+    {
+        for (keychain, spks) in core::mem::take(&mut self.spks_by_keychain) {
+            let mut inspect = inspect.clone();
+            self.spks_by_keychain.insert(
+                keychain.clone(),
+                Box::new(spks.inspect(move |(i, spk)| inspect(keychain.clone(), *i, spk))),
+            );
+        }
+        self
+    }
+
+    /// Add a closure that will be called for every [`Script`] previously added to a given
+    /// `keychain` in this request.
+    ///
+    /// This consumes the [`SyncRequest`] and returns the updated one.
+    #[must_use]
+    pub fn inspect_spks_for_keychain(
+        mut self,
+        keychain: K,
+        mut inspect: impl FnMut(u32, &Script) + Send + Sync + 'static,
+    ) -> Self
+    where
+        K: Send + 'static,
+    {
+        if let Some(spks) = self.spks_by_keychain.remove(&keychain) {
+            self.spks_by_keychain.insert(
+                keychain,
+                Box::new(spks.inspect(move |(i, spk)| inspect(*i, spk))),
+            );
+        }
+        self
+    }
+}
+
+/// Data returned from a spk-based blockchain client full scan.
+///
+/// See also [`FullScanRequest`].
+pub struct FullScanResult<K, A = ConfirmationBlockTime> {
+    /// The update to apply to the receiving [`LocalChain`](crate::local_chain::LocalChain).
+    pub graph_update: TxGraph<A>,
+    /// The update to apply to the receiving [`TxGraph`].
+    pub chain_update: CheckPoint,
+    /// Last active indices for the corresponding keychains (`K`).
+    pub last_active_indices: BTreeMap<K, u32>,
+}
+
+/// A version of [`core::iter::Chain`] which can combine two [`ExactSizeIterator`]s to form a new
+/// [`ExactSizeIterator`].
+///
+/// The danger of this is explained in [the `ExactSizeIterator` docs]
+/// (https://doc.rust-lang.org/core/iter/trait.ExactSizeIterator.html#when-shouldnt-an-adapter-be-exactsizeiterator).
+/// This does not apply here since it would be impossible to scan an item count that overflows
+/// `usize` anyway.
+struct ExactSizeChain<A, B, I> {
+    a: Option<A>,
+    b: Option<B>,
+    i: PhantomData<I>,
+}
+
+impl<A, B, I> ExactSizeChain<A, B, I> {
+    fn new(a: A, b: B) -> Self {
+        ExactSizeChain {
+            a: Some(a),
+            b: Some(b),
+            i: PhantomData,
+        }
+    }
+}
+
+impl<A, B, I> Iterator for ExactSizeChain<A, B, I>
+where
+    A: Iterator<Item = I>,
+    B: Iterator<Item = I>,
+{
+    type Item = I;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(a) = &mut self.a {
+            let item = a.next();
+            if item.is_some() {
+                return item;
+            }
+            self.a = None;
+        }
+        if let Some(b) = &mut self.b {
+            let item = b.next();
+            if item.is_some() {
+                return item;
+            }
+            self.b = None;
+        }
+        None
+    }
+}
+
+impl<A, B, I> ExactSizeIterator for ExactSizeChain<A, B, I>
+where
+    A: ExactSizeIterator<Item = I>,
+    B: ExactSizeIterator<Item = I>,
+{
+    fn len(&self) -> usize {
+        let a_len = self.a.as_ref().map(|a| a.len()).unwrap_or(0);
+        let b_len = self.b.as_ref().map(|a| a.len()).unwrap_or(0);
+        a_len + b_len
+    }
+}

crates/chain/src/spk_iter.rs

@@ -0,0 +1,272 @@
+use crate::{
+    bitcoin::{secp256k1::Secp256k1, ScriptBuf},
+    miniscript::{Descriptor, DescriptorPublicKey},
+    Indexed,
+};
+use core::{borrow::Borrow, ops::Bound, ops::RangeBounds};
+
+/// Maximum [BIP32](https://bips.xyz/32) derivation index.
+pub const BIP32_MAX_INDEX: u32 = (1 << 31) - 1;
+
+/// An iterator for derived script pubkeys.
+///
+/// [`SpkIterator`] is an implementation of the [`Iterator`] trait which possesses its own `next()`
+/// and `nth()` functions, both of which circumvent the unnecessary intermediate derivations required
+/// when using their default implementations.
+///
+/// ## Examples
+///
+/// ```
+/// use bdk_chain::SpkIterator;
+/// # use miniscript::{Descriptor, DescriptorPublicKey};
+/// # use bitcoin::{secp256k1::Secp256k1};
+/// # use std::str::FromStr;
+/// # let secp = bitcoin::secp256k1::Secp256k1::signing_only();
+/// # let (descriptor, _) = Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, "wpkh([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/1/0)").unwrap();
+/// # let external_spk_0 = descriptor.at_derivation_index(0).unwrap().script_pubkey();
+/// # let external_spk_3 = descriptor.at_derivation_index(3).unwrap().script_pubkey();
+/// # let external_spk_4 = descriptor.at_derivation_index(4).unwrap().script_pubkey();
+///
+/// // Creates a new script pubkey iterator starting at 0 from a descriptor.
+/// let mut spk_iter = SpkIterator::new(&descriptor);
+/// assert_eq!(spk_iter.next(), Some((0, external_spk_0)));
+/// assert_eq!(spk_iter.next(), None);
+/// ```
+#[derive(Clone)]
+pub struct SpkIterator<D> {
+    next_index: u32,
+    end: u32,
+    descriptor: D,
+    secp: Secp256k1<bitcoin::secp256k1::VerifyOnly>,
+}
+
+impl<D> SpkIterator<D>
+where
+    D: Borrow<Descriptor<DescriptorPublicKey>>,
+{
+    /// Create a new script pubkey iterator from `descriptor`.
+    ///
+    /// This iterates from derivation index 0 and stops at index 0x7FFFFFFF (as specified in
+    /// BIP-32). Non-wildcard descriptors will only return one script pubkey at derivation index 0.
+    ///
+    /// Use [`new_with_range`](SpkIterator::new_with_range) to create an iterator with a specified
+    /// derivation index range.
+    pub fn new(descriptor: D) -> Self {
+        SpkIterator::new_with_range(descriptor, 0..=BIP32_MAX_INDEX)
+    }
+
+    /// Create a new script pubkey iterator from `descriptor` and a given `range`.
+    ///
+    /// Non-wildcard descriptors will only emit a single script pubkey (at derivation index 0).
+    /// Wildcard descriptors have an end-bound of 0x7FFFFFFF (inclusive).
+    ///
+    /// Refer to [`new`](SpkIterator::new) for more.
+    pub fn new_with_range<R>(descriptor: D, range: R) -> Self
+    where
+        R: RangeBounds<u32>,
+    {
+        let start = match range.start_bound() {
+            Bound::Included(start) => *start,
+            Bound::Excluded(start) => *start + 1,
+            Bound::Unbounded => u32::MIN,
+        };
+
+        let mut end = match range.end_bound() {
+            Bound::Included(end) => *end + 1,
+            Bound::Excluded(end) => *end,
+            Bound::Unbounded => u32::MAX,
+        };
+
+        // Because `end` is exclusive, we want the maximum value to be BIP32_MAX_INDEX + 1.
+        end = end.min(BIP32_MAX_INDEX + 1);
+
+        Self {
+            next_index: start,
+            end,
+            descriptor,
+            secp: Secp256k1::verification_only(),
+        }
+    }
+
+    /// Get a reference to the internal descriptor.
+    pub fn descriptor(&self) -> &D {
+        &self.descriptor
+    }
+}
+
+impl<D> Iterator for SpkIterator<D>
+where
+    D: Borrow<Descriptor<DescriptorPublicKey>>,
+{
+    type Item = Indexed<ScriptBuf>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        // For non-wildcard descriptors, we expect the first element to be Some((0, spk)), then None after.
+        // For wildcard descriptors, we expect it to keep iterating until exhausted.
+        if self.next_index >= self.end {
+            return None;
+        }
+
+        // If the descriptor is non-wildcard, only index 0 will return an spk.
+        if !self.descriptor.borrow().has_wildcard() && self.next_index != 0 {
+            return None;
+        }
+
+        let script = self
+            .descriptor
+            .borrow()
+            .derived_descriptor(&self.secp, self.next_index)
+            .expect("the descriptor cannot need hardened derivation")
+            .script_pubkey();
+        let output = (self.next_index, script);
+
+        self.next_index += 1;
+
+        Some(output)
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        self.next_index = self
+            .next_index
+            .saturating_add(u32::try_from(n).unwrap_or(u32::MAX));
+        self.next()
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::{
+        bitcoin::secp256k1::Secp256k1,
+        indexer::keychain_txout::KeychainTxOutIndex,
+        miniscript::{Descriptor, DescriptorPublicKey},
+        spk_iter::{SpkIterator, BIP32_MAX_INDEX},
+    };
+
+    #[derive(Clone, Debug, PartialEq, Eq, Ord, PartialOrd)]
+    enum TestKeychain {
+        External,
+        Internal,
+    }
+
+    fn init_txout_index() -> (
+        KeychainTxOutIndex<TestKeychain>,
+        Descriptor<DescriptorPublicKey>,
+        Descriptor<DescriptorPublicKey>,
+    ) {
+        let mut txout_index = KeychainTxOutIndex::<TestKeychain>::new(0);
+
+        let secp = Secp256k1::signing_only();
+        let (external_descriptor,_) = Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, "tr([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/0/*)").unwrap();
+        let (internal_descriptor,_) = Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, "tr([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/1/*)").unwrap();
+
+        let _ = txout_index
+            .insert_descriptor(TestKeychain::External, external_descriptor.clone())
+            .unwrap();
+        let _ = txout_index
+            .insert_descriptor(TestKeychain::Internal, internal_descriptor.clone())
+            .unwrap();
+
+        (txout_index, external_descriptor, internal_descriptor)
+    }
+
+    #[test]
+    #[allow(clippy::iter_nth_zero)]
+    #[rustfmt::skip]
+    fn test_spkiterator_wildcard() {
+        let (_, external_desc, _) = init_txout_index();
+        let external_spk_0 = external_desc.at_derivation_index(0).unwrap().script_pubkey();
+        let external_spk_16 = external_desc.at_derivation_index(16).unwrap().script_pubkey();
+        let external_spk_20 = external_desc.at_derivation_index(20).unwrap().script_pubkey();
+        let external_spk_21 = external_desc.at_derivation_index(21).unwrap().script_pubkey();
+        let external_spk_max = external_desc.at_derivation_index(BIP32_MAX_INDEX).unwrap().script_pubkey();
+
+        let mut external_spk = SpkIterator::new(&external_desc);
+        let max_index = BIP32_MAX_INDEX - 22;
+
+        assert_eq!(external_spk.next(), Some((0, external_spk_0)));
+        assert_eq!(external_spk.nth(15), Some((16, external_spk_16)));
+        assert_eq!(external_spk.nth(3), Some((20, external_spk_20.clone())));
+        assert_eq!(external_spk.next(), Some((21, external_spk_21)));
+        assert_eq!(
+            external_spk.nth(max_index as usize),
+            Some((BIP32_MAX_INDEX, external_spk_max))
+        );
+        assert_eq!(external_spk.nth(0), None);
+
+        let mut external_spk = SpkIterator::new_with_range(&external_desc, 0..21);
+        assert_eq!(external_spk.nth(20), Some((20, external_spk_20)));
+        assert_eq!(external_spk.next(), None);
+
+        let mut external_spk = SpkIterator::new_with_range(&external_desc, 0..21);
+        assert_eq!(external_spk.nth(21), None);
+    }
+
+    #[test]
+    #[allow(clippy::iter_nth_zero)]
+    fn test_spkiterator_non_wildcard() {
+        let secp = bitcoin::secp256k1::Secp256k1::signing_only();
+        let (no_wildcard_descriptor, _) = Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, "wpkh([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/1/0)").unwrap();
+        let external_spk_0 = no_wildcard_descriptor
+            .at_derivation_index(0)
+            .unwrap()
+            .script_pubkey();
+
+        let mut external_spk = SpkIterator::new(&no_wildcard_descriptor);
+
+        assert_eq!(external_spk.next(), Some((0, external_spk_0.clone())));
+        assert_eq!(external_spk.next(), None);
+
+        let mut external_spk = SpkIterator::new(&no_wildcard_descriptor);
+
+        assert_eq!(external_spk.nth(0), Some((0, external_spk_0.clone())));
+        assert_eq!(external_spk.nth(0), None);
+
+        let mut external_spk = SpkIterator::new_with_range(&no_wildcard_descriptor, 0..0);
+
+        assert_eq!(external_spk.next(), None);
+
+        let mut external_spk = SpkIterator::new_with_range(&no_wildcard_descriptor, 0..1);
+
+        assert_eq!(external_spk.nth(0), Some((0, external_spk_0.clone())));
+        assert_eq!(external_spk.next(), None);
+
+        // We test that using new_with_range with range_len > 1 gives back an iterator with
+        // range_len = 1
+        let mut external_spk = SpkIterator::new_with_range(&no_wildcard_descriptor, 0..10);
+
+        assert_eq!(external_spk.nth(0), Some((0, external_spk_0)));
+        assert_eq!(external_spk.nth(0), None);
+
+        // non index-0 should NOT return an spk
+        assert_eq!(
+            SpkIterator::new_with_range(&no_wildcard_descriptor, 1..1).next(),
+            None
+        );
+        assert_eq!(
+            SpkIterator::new_with_range(&no_wildcard_descriptor, 1..=1).next(),
+            None
+        );
+        assert_eq!(
+            SpkIterator::new_with_range(&no_wildcard_descriptor, 1..2).next(),
+            None
+        );
+        assert_eq!(
+            SpkIterator::new_with_range(&no_wildcard_descriptor, 1..=2).next(),
+            None
+        );
+        assert_eq!(
+            SpkIterator::new_with_range(&no_wildcard_descriptor, 10..11).next(),
+            None
+        );
+        assert_eq!(
+            SpkIterator::new_with_range(&no_wildcard_descriptor, 10..=10).next(),
+            None
+        );
+    }
+}
+
+#[test]
+fn spk_iterator_is_send_and_static() {
+    fn is_send_and_static<A: Send + 'static>() {}
+    is_send_and_static::<SpkIterator<Descriptor<DescriptorPublicKey>>>()
+}

crates/chain/src/tx_data_traits.rs

@@ -0,0 +1,173 @@
+use crate::collections::BTreeMap;
+use crate::collections::BTreeSet;
+use crate::BlockId;
+use alloc::vec::Vec;
+
+/// Trait that "anchors" blockchain data to a specific block of height and hash.
+///
+/// If transaction A is anchored in block B, and block B is in the best chain, we can
+/// assume that transaction A is also confirmed in the best chain. This does not necessarily mean
+/// that transaction A is confirmed in block B. It could also mean transaction A is confirmed in a
+/// parent block of B.
+///
+/// Every [`Anchor`] implementation must contain a [`BlockId`] parameter, and must implement
+/// [`Ord`]. When implementing [`Ord`], the anchors' [`BlockId`]s should take precedence
+/// over other elements inside the [`Anchor`]s for comparison purposes, i.e., you should first
+/// compare the anchors' [`BlockId`]s and then care about the rest.
+///
+/// The example shows different types of anchors:
+/// ```
+/// # use bdk_chain::local_chain::LocalChain;
+/// # use bdk_chain::tx_graph::TxGraph;
+/// # use bdk_chain::BlockId;
+/// # use bdk_chain::ConfirmationBlockTime;
+/// # use bdk_chain::example_utils::*;
+/// # use bitcoin::hashes::Hash;
+/// // Initialize the local chain with two blocks.
+/// let chain = LocalChain::from_blocks(
+///     [
+///         (1, Hash::hash("first".as_bytes())),
+///         (2, Hash::hash("second".as_bytes())),
+///     ]
+///     .into_iter()
+///     .collect(),
+/// );
+///
+/// // Transaction to be inserted into `TxGraph`s with different anchor types.
+/// let tx = tx_from_hex(RAW_TX_1);
+///
+/// // Insert `tx` into a `TxGraph` that uses `BlockId` as the anchor type.
+/// // When a transaction is anchored with `BlockId`, the anchor block and the confirmation block of
+/// // the transaction is the same block.
+/// let mut graph_a = TxGraph::<BlockId>::default();
+/// let _ = graph_a.insert_tx(tx.clone());
+/// graph_a.insert_anchor(
+///     tx.compute_txid(),
+///     BlockId {
+///         height: 1,
+///         hash: Hash::hash("first".as_bytes()),
+///     },
+/// );
+///
+/// // Insert `tx` into a `TxGraph` that uses `ConfirmationBlockTime` as the anchor type.
+/// // This anchor records the anchor block and the confirmation time of the transaction. When a
+/// // transaction is anchored with `ConfirmationBlockTime`, the anchor block and confirmation block
+/// // of the transaction is the same block.
+/// let mut graph_c = TxGraph::<ConfirmationBlockTime>::default();
+/// let _ = graph_c.insert_tx(tx.clone());
+/// graph_c.insert_anchor(
+///     tx.compute_txid(),
+///     ConfirmationBlockTime {
+///         block_id: BlockId {
+///             height: 2,
+///             hash: Hash::hash("third".as_bytes()),
+///         },
+///         confirmation_time: 123,
+///     },
+/// );
+/// ```
+pub trait Anchor: core::fmt::Debug + Clone + Eq + PartialOrd + Ord + core::hash::Hash {
+    /// Returns the [`BlockId`] that the associated blockchain data is "anchored" in.
+    fn anchor_block(&self) -> BlockId;
+
+    /// Get the upper bound of the chain data's confirmation height.
+    ///
+    /// The default definition gives a pessimistic answer. This can be overridden by the `Anchor`
+    /// implementation for a more accurate value.
+    fn confirmation_height_upper_bound(&self) -> u32 {
+        self.anchor_block().height
+    }
+}
+
+impl<'a, A: Anchor> Anchor for &'a A {
+    fn anchor_block(&self) -> BlockId {
+        <A as Anchor>::anchor_block(self)
+    }
+}
+
+/// An [`Anchor`] that can be constructed from a given block, block height and transaction position
+/// within the block.
+pub trait AnchorFromBlockPosition: Anchor {
+    /// Construct the anchor from a given `block`, block height and `tx_pos` within the block.
+    fn from_block_position(block: &bitcoin::Block, block_id: BlockId, tx_pos: usize) -> Self;
+}
+
+/// Trait that makes an object mergeable.
+pub trait Merge: Default {
+    /// Merge another object of the same type onto `self`.
+    fn merge(&mut self, other: Self);
+
+    /// Returns whether the structure is considered empty.
+    fn is_empty(&self) -> bool;
+
+    /// Take the value, replacing it with the default value.
+    fn take(&mut self) -> Option<Self> {
+        if self.is_empty() {
+            None
+        } else {
+            Some(core::mem::take(self))
+        }
+    }
+}
+
+impl<K: Ord, V> Merge for BTreeMap<K, V> {
+    fn merge(&mut self, other: Self) {
+        // We use `extend` instead of `BTreeMap::append` due to performance issues with `append`.
+        // Refer to https://github.com/rust-lang/rust/issues/34666#issuecomment-675658420
+        BTreeMap::extend(self, other)
+    }
+
+    fn is_empty(&self) -> bool {
+        BTreeMap::is_empty(self)
+    }
+}
+
+impl<T: Ord> Merge for BTreeSet<T> {
+    fn merge(&mut self, other: Self) {
+        // We use `extend` instead of `BTreeMap::append` due to performance issues with `append`.
+        // Refer to https://github.com/rust-lang/rust/issues/34666#issuecomment-675658420
+        BTreeSet::extend(self, other)
+    }
+
+    fn is_empty(&self) -> bool {
+        BTreeSet::is_empty(self)
+    }
+}
+
+impl<T> Merge for Vec<T> {
+    fn merge(&mut self, mut other: Self) {
+        Vec::append(self, &mut other)
+    }
+
+    fn is_empty(&self) -> bool {
+        Vec::is_empty(self)
+    }
+}
+
+macro_rules! impl_merge_for_tuple {
+    ($($a:ident $b:tt)*) => {
+        impl<$($a),*> Merge for ($($a,)*) where $($a: Merge),* {
+
+            fn merge(&mut self, _other: Self) {
+                $(Merge::merge(&mut self.$b, _other.$b) );*
+            }
+
+            fn is_empty(&self) -> bool {
+                $(Merge::is_empty(&self.$b) && )* true
+            }
+        }
+    }
+}
+
+impl_merge_for_tuple!();
+impl_merge_for_tuple!(T0 0);
+impl_merge_for_tuple!(T0 0 T1 1);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3 T4 4);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3 T4 4 T5 5);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3 T4 4 T5 5 T6 6);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3 T4 4 T5 5 T6 6 T7 7);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3 T4 4 T5 5 T6 6 T7 7 T8 8);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3 T4 4 T5 5 T6 6 T7 7 T8 8 T9 9);
+impl_merge_for_tuple!(T0 0 T1 1 T2 2 T3 3 T4 4 T5 5 T6 6 T7 7 T8 8 T9 9 T10 10);

crates/chain/tests/common/mod.rs

@@ -0,0 +1,89 @@
+#![cfg(feature = "miniscript")]
+
+mod tx_template;
+#[allow(unused_imports)]
+pub use tx_template::*;
+
+#[allow(unused_macros)]
+macro_rules! block_id {
+    ($height:expr, $hash:literal) => {{
+        bdk_chain::BlockId {
+            height: $height,
+            hash: bitcoin::hashes::Hash::hash($hash.as_bytes()),
+        }
+    }};
+}
+
+#[allow(unused_macros)]
+macro_rules! h {
+    ($index:literal) => {{
+        bitcoin::hashes::Hash::hash($index.as_bytes())
+    }};
+}
+
+#[allow(unused_macros)]
+macro_rules! local_chain {
+    [ $(($height:expr, $block_hash:expr)), * ] => {{
+        #[allow(unused_mut)]
+        bdk_chain::local_chain::LocalChain::from_blocks([$(($height, $block_hash).into()),*].into_iter().collect())
+            .expect("chain must have genesis block")
+    }};
+}
+
+#[allow(unused_macros)]
+macro_rules! chain_update {
+    [ $(($height:expr, $hash:expr)), * ] => {{
+        #[allow(unused_mut)]
+        bdk_chain::local_chain::LocalChain::from_blocks([$(($height, $hash).into()),*].into_iter().collect())
+            .expect("chain must have genesis block")
+            .tip()
+    }};
+}
+
+#[allow(unused_macros)]
+macro_rules! changeset {
+    (checkpoints: $($tail:tt)*) => { changeset!(index: TxHeight, checkpoints: $($tail)*) };
+    (
+        index: $ind:ty,
+        checkpoints: [ $(( $height:expr, $cp_to:expr )),* ]
+        $(,txids: [ $(( $txid:expr, $tx_to:expr )),* ])?
+    ) => {{
+        use bdk_chain::collections::BTreeMap;
+
+        #[allow(unused_mut)]
+        bdk_chain::sparse_chain::ChangeSet::<$ind> {
+            checkpoints: {
+                let mut changes = BTreeMap::default();
+                $(changes.insert($height, $cp_to);)*
+                changes
+            },
+            txids: {
+                let mut changes = BTreeMap::default();
+                $($(changes.insert($txid, $tx_to.map(|h: TxHeight| h.into()));)*)?
+                changes
+            }
+        }
+    }};
+}
+
+#[allow(unused)]
+pub fn new_tx(lt: u32) -> bitcoin::Transaction {
+    bitcoin::Transaction {
+        version: bitcoin::transaction::Version::non_standard(0x00),
+        lock_time: bitcoin::absolute::LockTime::from_consensus(lt),
+        input: vec![],
+        output: vec![],
+    }
+}
+
+#[allow(unused)]
+pub const DESCRIPTORS: [&str; 7] = [
+    "tr([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/0/*)",
+    "tr([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/1/*)",
+    "wpkh([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/1/0/*)",
+    "tr(tprv8ZgxMBicQKsPd3krDUsBAmtnRsK3rb8u5yi1zhQgMhF1tR8MW7xfE4rnrbbsrbPR52e7rKapu6ztw1jXveJSCGHEriUGZV7mCe88duLp5pj/86'/1'/0'/0/*)",
+    "tr(tprv8ZgxMBicQKsPd3krDUsBAmtnRsK3rb8u5yi1zhQgMhF1tR8MW7xfE4rnrbbsrbPR52e7rKapu6ztw1jXveJSCGHEriUGZV7mCe88duLp5pj/86'/1'/0'/1/*)",
+    "wpkh(xprv9s21ZrQH143K4EXURwMHuLS469fFzZyXk7UUpdKfQwhoHcAiYTakpe8pMU2RiEdvrU9McyuE7YDoKcXkoAwEGoK53WBDnKKv2zZbb9BzttX/1/0/*)",
+    // non-wildcard
+    "wpkh([73c5da0a/86'/0'/0']xprv9xgqHN7yz9MwCkxsBPN5qetuNdQSUttZNKw1dcYTV4mkaAFiBVGQziHs3NRSWMkCzvgjEe3n9xV8oYywvM8at9yRqyaZVz6TYYhX98VjsUk/1/0)",
+];

crates/chain/tests/common/tx_template.rs

@@ -0,0 +1,137 @@
+#![cfg(feature = "miniscript")]
+
+use rand::distributions::{Alphanumeric, DistString};
+use std::collections::HashMap;
+
+use bdk_chain::{spk_txout::SpkTxOutIndex, tx_graph::TxGraph, Anchor};
+use bitcoin::{
+    locktime::absolute::LockTime, secp256k1::Secp256k1, transaction, Amount, OutPoint, ScriptBuf,
+    Sequence, Transaction, TxIn, TxOut, Txid, Witness,
+};
+use miniscript::Descriptor;
+
+/// Template for creating a transaction in `TxGraph`.
+///
+/// The incentive for transaction templates is to create a transaction history in a simple manner to
+/// avoid having to explicitly hash previous transactions to form previous outpoints of later
+/// transactions.
+#[derive(Clone, Copy, Default)]
+pub struct TxTemplate<'a, A> {
+    /// Uniquely identifies the transaction, before it can have a txid.
+    pub tx_name: &'a str,
+    pub inputs: &'a [TxInTemplate<'a>],
+    pub outputs: &'a [TxOutTemplate],
+    pub anchors: &'a [A],
+    pub last_seen: Option<u64>,
+}
+
+#[allow(dead_code)]
+pub enum TxInTemplate<'a> {
+    /// This will give a random txid and vout.
+    Bogus,
+
+    /// This is used for coinbase transactions because they do not have previous outputs.
+    Coinbase,
+
+    /// Contains the `tx_name` and `vout` that we are spending. The rule is that we must only spend
+    /// from tx of a previous `TxTemplate`.
+    PrevTx(&'a str, usize),
+}
+
+pub struct TxOutTemplate {
+    pub value: u64,
+    pub spk_index: Option<u32>, // some = get spk from SpkTxOutIndex, none = random spk
+}
+
+#[allow(unused)]
+impl TxOutTemplate {
+    pub fn new(value: u64, spk_index: Option<u32>) -> Self {
+        TxOutTemplate { value, spk_index }
+    }
+}
+
+#[allow(dead_code)]
+pub fn init_graph<'a, A: Anchor + Clone + 'a>(
+    tx_templates: impl IntoIterator<Item = &'a TxTemplate<'a, A>>,
+) -> (TxGraph<A>, SpkTxOutIndex<u32>, HashMap<&'a str, Txid>) {
+    let (descriptor, _) =
+        Descriptor::parse_descriptor(&Secp256k1::signing_only(), super::DESCRIPTORS[2]).unwrap();
+    let mut graph = TxGraph::<A>::default();
+    let mut spk_index = SpkTxOutIndex::default();
+    (0..10).for_each(|index| {
+        spk_index.insert_spk(
+            index,
+            descriptor
+                .at_derivation_index(index)
+                .unwrap()
+                .script_pubkey(),
+        );
+    });
+    let mut tx_ids = HashMap::<&'a str, Txid>::new();
+
+    for (bogus_txin_vout, tx_tmp) in tx_templates.into_iter().enumerate() {
+        let tx = Transaction {
+            version: transaction::Version::non_standard(0),
+            lock_time: LockTime::ZERO,
+            input: tx_tmp
+                .inputs
+                .iter()
+                .map(|input| match input {
+                    TxInTemplate::Bogus => TxIn {
+                        previous_output: OutPoint::new(
+                            bitcoin::hashes::Hash::hash(
+                                Alphanumeric
+                                    .sample_string(&mut rand::thread_rng(), 20)
+                                    .as_bytes(),
+                            ),
+                            bogus_txin_vout as u32,
+                        ),
+                        script_sig: ScriptBuf::new(),
+                        sequence: Sequence::default(),
+                        witness: Witness::new(),
+                    },
+                    TxInTemplate::Coinbase => TxIn {
+                        previous_output: OutPoint::null(),
+                        script_sig: ScriptBuf::new(),
+                        sequence: Sequence::MAX,
+                        witness: Witness::new(),
+                    },
+                    TxInTemplate::PrevTx(prev_name, prev_vout) => {
+                        let prev_txid = tx_ids.get(prev_name).expect(
+                            "txin template must spend from tx of template that comes before",
+                        );
+                        TxIn {
+                            previous_output: OutPoint::new(*prev_txid, *prev_vout as _),
+                            script_sig: ScriptBuf::new(),
+                            sequence: Sequence::default(),
+                            witness: Witness::new(),
+                        }
+                    }
+                })
+                .collect(),
+            output: tx_tmp
+                .outputs
+                .iter()
+                .map(|output| match &output.spk_index {
+                    None => TxOut {
+                        value: Amount::from_sat(output.value),
+                        script_pubkey: ScriptBuf::new(),
+                    },
+                    Some(index) => TxOut {
+                        value: Amount::from_sat(output.value),
+                        script_pubkey: spk_index.spk_at_index(index).unwrap(),
+                    },
+                })
+                .collect(),
+        };
+
+        tx_ids.insert(tx_tmp.tx_name, tx.compute_txid());
+        spk_index.scan(&tx);
+        let _ = graph.insert_tx(tx.clone());
+        for anchor in tx_tmp.anchors.iter() {
+            let _ = graph.insert_anchor(tx.compute_txid(), anchor.clone());
+        }
+        let _ = graph.insert_seen_at(tx.compute_txid(), tx_tmp.last_seen.unwrap_or(0));
+    }
+    (graph, spk_index, tx_ids)
+}

crates/chain/tests/test_indexed_tx_graph.rs

@@ -0,0 +1,660 @@
+#![cfg(feature = "miniscript")]
+
+#[macro_use]
+mod common;
+
+use std::{collections::BTreeSet, sync::Arc};
+
+use crate::common::DESCRIPTORS;
+use bdk_chain::{
+    indexed_tx_graph::{self, IndexedTxGraph},
+    indexer::keychain_txout::KeychainTxOutIndex,
+    local_chain::LocalChain,
+    tx_graph, Balance, ChainPosition, ConfirmationBlockTime, DescriptorExt,
+};
+use bitcoin::{secp256k1::Secp256k1, Amount, OutPoint, ScriptBuf, Transaction, TxIn, TxOut};
+use miniscript::Descriptor;
+
+/// Ensure [`IndexedTxGraph::insert_relevant_txs`] can successfully index transactions NOT presented
+/// in topological order.
+///
+/// Given 3 transactions (A, B, C), where A has 2 owned outputs. B and C spends an output each of A.
+/// Typically, we would only know whether B and C are relevant if we have indexed A (A's outpoints
+/// are associated with owned spks in the index). Ensure insertion and indexing is topological-
+/// agnostic.
+#[test]
+fn insert_relevant_txs() {
+    use bdk_chain::indexer::keychain_txout;
+    let (descriptor, _) = Descriptor::parse_descriptor(&Secp256k1::signing_only(), DESCRIPTORS[0])
+        .expect("must be valid");
+    let spk_0 = descriptor.at_derivation_index(0).unwrap().script_pubkey();
+    let spk_1 = descriptor.at_derivation_index(9).unwrap().script_pubkey();
+
+    let mut graph = IndexedTxGraph::<ConfirmationBlockTime, KeychainTxOutIndex<()>>::new(
+        KeychainTxOutIndex::new(10),
+    );
+    let _ = graph
+        .index
+        .insert_descriptor((), descriptor.clone())
+        .unwrap();
+
+    let tx_a = Transaction {
+        output: vec![
+            TxOut {
+                value: Amount::from_sat(10_000),
+                script_pubkey: spk_0,
+            },
+            TxOut {
+                value: Amount::from_sat(20_000),
+                script_pubkey: spk_1,
+            },
+        ],
+        ..common::new_tx(0)
+    };
+
+    let tx_b = Transaction {
+        input: vec![TxIn {
+            previous_output: OutPoint::new(tx_a.compute_txid(), 0),
+            ..Default::default()
+        }],
+        ..common::new_tx(1)
+    };
+
+    let tx_c = Transaction {
+        input: vec![TxIn {
+            previous_output: OutPoint::new(tx_a.compute_txid(), 1),
+            ..Default::default()
+        }],
+        ..common::new_tx(2)
+    };
+
+    let txs = [tx_c, tx_b, tx_a];
+
+    let changeset = indexed_tx_graph::ChangeSet {
+        tx_graph: tx_graph::ChangeSet {
+            txs: txs.iter().cloned().map(Arc::new).collect(),
+            ..Default::default()
+        },
+        indexer: keychain_txout::ChangeSet {
+            last_revealed: [(descriptor.descriptor_id(), 9_u32)].into(),
+        },
+    };
+
+    assert_eq!(
+        graph.batch_insert_relevant(txs.iter().map(|tx| (tx, None))),
+        changeset,
+    );
+
+    // The initial changeset will also contain info about the keychain we added
+    let initial_changeset = indexed_tx_graph::ChangeSet {
+        tx_graph: changeset.tx_graph,
+        indexer: keychain_txout::ChangeSet {
+            last_revealed: changeset.indexer.last_revealed,
+        },
+    };
+
+    assert_eq!(graph.initial_changeset(), initial_changeset);
+}
+
+/// Ensure consistency IndexedTxGraph list_* and balance methods. These methods lists
+/// relevant txouts and utxos from the information fetched from a ChainOracle (here a LocalChain).
+///
+/// Test Setup:
+///
+/// Local Chain =>  <0> ----- <1> ----- <2> ----- <3> ---- ... ---- <150>
+///
+/// Keychains:
+///
+/// keychain_1: Trusted
+/// keychain_2: Untrusted
+///
+/// Transactions:
+///
+/// tx1: A Coinbase, sending 70000 sats to "trusted" address. [Block 0]
+/// tx2: A external Receive, sending 30000 sats to "untrusted" address. [Block 1]
+/// tx3: Internal Spend. Spends tx2 and returns change of 10000 to "trusted" address. [Block 2]
+/// tx4: Mempool tx, sending 20000 sats to "untrusted" address.
+/// tx5: Mempool tx, sending 15000 sats to "trusted" address.
+/// tx6: Complete unrelated tx. [Block 3]
+///
+/// Different transactions are added via `insert_relevant_txs`.
+/// `list_owned_txout`, `list_owned_utxos` and `balance` method is asserted
+/// with expected values at Block height 0, 1, and 2.
+///
+/// Finally Add more blocks to local chain until tx1 coinbase maturity hits.
+/// Assert maturity at coinbase maturity inflection height. Block height 98 and 99.
+#[test]
+fn test_list_owned_txouts() {
+    // Create Local chains
+    let local_chain = LocalChain::from_blocks((0..150).map(|i| (i as u32, h!("random"))).collect())
+        .expect("must have genesis hash");
+
+    // Initiate IndexedTxGraph
+
+    let (desc_1, _) =
+        Descriptor::parse_descriptor(&Secp256k1::signing_only(), common::DESCRIPTORS[2]).unwrap();
+    let (desc_2, _) =
+        Descriptor::parse_descriptor(&Secp256k1::signing_only(), common::DESCRIPTORS[3]).unwrap();
+
+    let mut graph = IndexedTxGraph::<ConfirmationBlockTime, KeychainTxOutIndex<String>>::new(
+        KeychainTxOutIndex::new(10),
+    );
+
+    assert!(graph
+        .index
+        .insert_descriptor("keychain_1".into(), desc_1)
+        .unwrap());
+    assert!(graph
+        .index
+        .insert_descriptor("keychain_2".into(), desc_2)
+        .unwrap());
+
+    // Get trusted and untrusted addresses
+
+    let mut trusted_spks: Vec<ScriptBuf> = Vec::new();
+    let mut untrusted_spks: Vec<ScriptBuf> = Vec::new();
+
+    {
+        // we need to scope here to take immutable reference of the graph
+        for _ in 0..10 {
+            let ((_, script), _) = graph
+                .index
+                .reveal_next_spk("keychain_1".to_string())
+                .unwrap();
+            // TODO Assert indexes
+            trusted_spks.push(script.to_owned());
+        }
+    }
+    {
+        for _ in 0..10 {
+            let ((_, script), _) = graph
+                .index
+                .reveal_next_spk("keychain_2".to_string())
+                .unwrap();
+            untrusted_spks.push(script.to_owned());
+        }
+    }
+
+    // Create test transactions
+
+    // tx1 is the genesis coinbase
+    let tx1 = Transaction {
+        input: vec![TxIn {
+            previous_output: OutPoint::null(),
+            ..Default::default()
+        }],
+        output: vec![TxOut {
+            value: Amount::from_sat(70000),
+            script_pubkey: trusted_spks[0].to_owned(),
+        }],
+        ..common::new_tx(0)
+    };
+
+    // tx2 is an incoming transaction received at untrusted keychain at block 1.
+    let tx2 = Transaction {
+        output: vec![TxOut {
+            value: Amount::from_sat(30000),
+            script_pubkey: untrusted_spks[0].to_owned(),
+        }],
+        ..common::new_tx(0)
+    };
+
+    // tx3 spends tx2 and gives a change back in trusted keychain. Confirmed at Block 2.
+    let tx3 = Transaction {
+        input: vec![TxIn {
+            previous_output: OutPoint::new(tx2.compute_txid(), 0),
+            ..Default::default()
+        }],
+        output: vec![TxOut {
+            value: Amount::from_sat(10000),
+            script_pubkey: trusted_spks[1].to_owned(),
+        }],
+        ..common::new_tx(0)
+    };
+
+    // tx4 is an external transaction receiving at untrusted keychain, unconfirmed.
+    let tx4 = Transaction {
+        output: vec![TxOut {
+            value: Amount::from_sat(20000),
+            script_pubkey: untrusted_spks[1].to_owned(),
+        }],
+        ..common::new_tx(0)
+    };
+
+    // tx5 is an external transaction receiving at trusted keychain, unconfirmed.
+    let tx5 = Transaction {
+        output: vec![TxOut {
+            value: Amount::from_sat(15000),
+            script_pubkey: trusted_spks[2].to_owned(),
+        }],
+        ..common::new_tx(0)
+    };
+
+    // tx6 is an unrelated transaction confirmed at 3.
+    let tx6 = common::new_tx(0);
+
+    // Insert transactions into graph with respective anchors
+    // Insert unconfirmed txs with a last_seen timestamp
+
+    let _ =
+        graph.batch_insert_relevant([&tx1, &tx2, &tx3, &tx6].iter().enumerate().map(|(i, tx)| {
+            let height = i as u32;
+            (
+                *tx,
+                local_chain
+                    .get(height)
+                    .map(|cp| cp.block_id())
+                    .map(|block_id| ConfirmationBlockTime {
+                        block_id,
+                        confirmation_time: 100,
+                    }),
+            )
+        }));
+
+    let _ = graph.batch_insert_relevant_unconfirmed([&tx4, &tx5].iter().map(|tx| (*tx, 100)));
+
+    // A helper lambda to extract and filter data from the graph.
+    let fetch =
+        |height: u32, graph: &IndexedTxGraph<ConfirmationBlockTime, KeychainTxOutIndex<String>>| {
+            let chain_tip = local_chain
+                .get(height)
+                .map(|cp| cp.block_id())
+                .unwrap_or_else(|| panic!("block must exist at {}", height));
+            let txouts = graph
+                .graph()
+                .filter_chain_txouts(
+                    &local_chain,
+                    chain_tip,
+                    graph.index.outpoints().iter().cloned(),
+                )
+                .collect::<Vec<_>>();
+
+            let utxos = graph
+                .graph()
+                .filter_chain_unspents(
+                    &local_chain,
+                    chain_tip,
+                    graph.index.outpoints().iter().cloned(),
+                )
+                .collect::<Vec<_>>();
+
+            let balance = graph.graph().balance(
+                &local_chain,
+                chain_tip,
+                graph.index.outpoints().iter().cloned(),
+                |_, spk: ScriptBuf| trusted_spks.contains(&spk),
+            );
+
+            let confirmed_txouts_txid = txouts
+                .iter()
+                .filter_map(|(_, full_txout)| {
+                    if matches!(full_txout.chain_position, ChainPosition::Confirmed(_)) {
+                        Some(full_txout.outpoint.txid)
+                    } else {
+                        None
+                    }
+                })
+                .collect::<BTreeSet<_>>();
+
+            let unconfirmed_txouts_txid = txouts
+                .iter()
+                .filter_map(|(_, full_txout)| {
+                    if matches!(full_txout.chain_position, ChainPosition::Unconfirmed(_)) {
+                        Some(full_txout.outpoint.txid)
+                    } else {
+                        None
+                    }
+                })
+                .collect::<BTreeSet<_>>();
+
+            let confirmed_utxos_txid = utxos
+                .iter()
+                .filter_map(|(_, full_txout)| {
+                    if matches!(full_txout.chain_position, ChainPosition::Confirmed(_)) {
+                        Some(full_txout.outpoint.txid)
+                    } else {
+                        None
+                    }
+                })
+                .collect::<BTreeSet<_>>();
+
+            let unconfirmed_utxos_txid = utxos
+                .iter()
+                .filter_map(|(_, full_txout)| {
+                    if matches!(full_txout.chain_position, ChainPosition::Unconfirmed(_)) {
+                        Some(full_txout.outpoint.txid)
+                    } else {
+                        None
+                    }
+                })
+                .collect::<BTreeSet<_>>();
+
+            (
+                confirmed_txouts_txid,
+                unconfirmed_txouts_txid,
+                confirmed_utxos_txid,
+                unconfirmed_utxos_txid,
+                balance,
+            )
+        };
+
+    // ----- TEST BLOCK -----
+
+    // AT Block 0
+    {
+        let (
+            confirmed_txouts_txid,
+            unconfirmed_txouts_txid,
+            confirmed_utxos_txid,
+            unconfirmed_utxos_txid,
+            balance,
+        ) = fetch(0, &graph);
+
+        // tx1 is a confirmed txout and is unspent
+        // tx4, tx5 are unconfirmed
+        assert_eq!(confirmed_txouts_txid, [tx1.compute_txid()].into());
+        assert_eq!(
+            unconfirmed_txouts_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        assert_eq!(confirmed_utxos_txid, [tx1.compute_txid()].into());
+        assert_eq!(
+            unconfirmed_utxos_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        assert_eq!(
+            balance,
+            Balance {
+                immature: Amount::from_sat(70000),          // immature coinbase
+                trusted_pending: Amount::from_sat(15000),   // tx5
+                untrusted_pending: Amount::from_sat(20000), // tx4
+                confirmed: Amount::ZERO                     // Nothing is confirmed yet
+            }
+        );
+    }
+
+    // AT Block 1
+    {
+        let (
+            confirmed_txouts_txid,
+            unconfirmed_txouts_txid,
+            confirmed_utxos_txid,
+            unconfirmed_utxos_txid,
+            balance,
+        ) = fetch(1, &graph);
+
+        // tx2 gets into confirmed txout set
+        assert_eq!(
+            confirmed_txouts_txid,
+            [tx1.compute_txid(), tx2.compute_txid()].into()
+        );
+        assert_eq!(
+            unconfirmed_txouts_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        // tx2 gets into confirmed utxos set
+        assert_eq!(
+            confirmed_utxos_txid,
+            [tx1.compute_txid(), tx2.compute_txid()].into()
+        );
+        assert_eq!(
+            unconfirmed_utxos_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        assert_eq!(
+            balance,
+            Balance {
+                immature: Amount::from_sat(70000),          // immature coinbase
+                trusted_pending: Amount::from_sat(15000),   // tx5
+                untrusted_pending: Amount::from_sat(20000), // tx4
+                confirmed: Amount::from_sat(30_000)         // tx2 got confirmed
+            }
+        );
+    }
+
+    // AT Block 2
+    {
+        let (
+            confirmed_txouts_txid,
+            unconfirmed_txouts_txid,
+            confirmed_utxos_txid,
+            unconfirmed_utxos_txid,
+            balance,
+        ) = fetch(2, &graph);
+
+        // tx3 now gets into the confirmed txout set
+        assert_eq!(
+            confirmed_txouts_txid,
+            [tx1.compute_txid(), tx2.compute_txid(), tx3.compute_txid()].into()
+        );
+        assert_eq!(
+            unconfirmed_txouts_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        // tx3 also gets into confirmed utxo set
+        assert_eq!(
+            confirmed_utxos_txid,
+            [tx1.compute_txid(), tx3.compute_txid()].into()
+        );
+        assert_eq!(
+            unconfirmed_utxos_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        assert_eq!(
+            balance,
+            Balance {
+                immature: Amount::from_sat(70000),          // immature coinbase
+                trusted_pending: Amount::from_sat(15000),   // tx5
+                untrusted_pending: Amount::from_sat(20000), // tx4
+                confirmed: Amount::from_sat(10000)          // tx3 got confirmed
+            }
+        );
+    }
+
+    // AT Block 98
+    {
+        let (
+            confirmed_txouts_txid,
+            unconfirmed_txouts_txid,
+            confirmed_utxos_txid,
+            unconfirmed_utxos_txid,
+            balance,
+        ) = fetch(98, &graph);
+
+        // no change compared to block 2
+        assert_eq!(
+            confirmed_txouts_txid,
+            [tx1.compute_txid(), tx2.compute_txid(), tx3.compute_txid()].into()
+        );
+        assert_eq!(
+            unconfirmed_txouts_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        assert_eq!(
+            confirmed_utxos_txid,
+            [tx1.compute_txid(), tx3.compute_txid()].into()
+        );
+        assert_eq!(
+            unconfirmed_utxos_txid,
+            [tx4.compute_txid(), tx5.compute_txid()].into()
+        );
+
+        // Coinbase is still immature
+        assert_eq!(
+            balance,
+            Balance {
+                immature: Amount::from_sat(70000),          // immature coinbase
+                trusted_pending: Amount::from_sat(15000),   // tx5
+                untrusted_pending: Amount::from_sat(20000), // tx4
+                confirmed: Amount::from_sat(10000)          // tx3 is confirmed
+            }
+        );
+    }
+
+    // AT Block 99
+    {
+        let (_, _, _, _, balance) = fetch(99, &graph);
+
+        // Coinbase maturity hits
+        assert_eq!(
+            balance,
+            Balance {
+                immature: Amount::ZERO,                     // coinbase matured
+                trusted_pending: Amount::from_sat(15000),   // tx5
+                untrusted_pending: Amount::from_sat(20000), // tx4
+                confirmed: Amount::from_sat(80000)          // tx1 + tx3
+            }
+        );
+    }
+}
+
+/// Given a `LocalChain`, `IndexedTxGraph`, and a `Transaction`, when we insert some anchor
+/// (possibly non-canonical) and/or a last-seen timestamp into the graph, we expect the
+/// result of `get_chain_position` in these cases:
+///
+/// - tx with no anchors or last_seen has no `ChainPosition`
+/// - tx with any last_seen will be `Unconfirmed`
+/// - tx with an anchor in best chain will be `Confirmed`
+/// - tx with an anchor not in best chain (no last_seen) has no `ChainPosition`
+#[test]
+fn test_get_chain_position() {
+    use bdk_chain::local_chain::CheckPoint;
+    use bdk_chain::spk_txout::SpkTxOutIndex;
+    use bdk_chain::BlockId;
+
+    struct TestCase<A> {
+        name: &'static str,
+        tx: Transaction,
+        anchor: Option<A>,
+        last_seen: Option<u64>,
+        exp_pos: Option<ChainPosition<A>>,
+    }
+
+    // addr: bcrt1qc6fweuf4xjvz4x3gx3t9e0fh4hvqyu2qw4wvxm
+    let spk = ScriptBuf::from_hex("0014c692ecf13534982a9a2834565cbd37add8027140").unwrap();
+    let mut graph = IndexedTxGraph::new({
+        let mut index = SpkTxOutIndex::default();
+        let _ = index.insert_spk(0u32, spk.clone());
+        index
+    });
+
+    // Anchors to test
+    let blocks = vec![block_id!(0, "g"), block_id!(1, "A"), block_id!(2, "B")];
+
+    let cp = CheckPoint::from_block_ids(blocks.clone()).unwrap();
+    let chain = LocalChain::from_tip(cp).unwrap();
+
+    // The test will insert a transaction into the indexed tx graph
+    // along with any anchors and timestamps, then check the value
+    // returned by `get_chain_position`.
+    fn run(
+        chain: &LocalChain,
+        graph: &mut IndexedTxGraph<BlockId, SpkTxOutIndex<u32>>,
+        test: TestCase<BlockId>,
+    ) {
+        let TestCase {
+            name,
+            tx,
+            anchor,
+            last_seen,
+            exp_pos,
+        } = test;
+
+        // add data to graph
+        let txid = tx.compute_txid();
+        let _ = graph.insert_tx(tx);
+        if let Some(anchor) = anchor {
+            let _ = graph.insert_anchor(txid, anchor);
+        }
+        if let Some(seen_at) = last_seen {
+            let _ = graph.insert_seen_at(txid, seen_at);
+        }
+
+        // check chain position
+        let res = graph
+            .graph()
+            .get_chain_position(chain, chain.tip().block_id(), txid);
+        assert_eq!(
+            res.map(ChainPosition::cloned),
+            exp_pos,
+            "failed test case: {name}"
+        );
+    }
+
+    [
+        TestCase {
+            name: "tx no anchors or last_seen - no chain pos",
+            tx: Transaction {
+                output: vec![TxOut {
+                    value: Amount::ONE_BTC,
+                    script_pubkey: spk.clone(),
+                }],
+                ..common::new_tx(0)
+            },
+            anchor: None,
+            last_seen: None,
+            exp_pos: None,
+        },
+        TestCase {
+            name: "tx last_seen - unconfirmed",
+            tx: Transaction {
+                output: vec![TxOut {
+                    value: Amount::ONE_BTC,
+                    script_pubkey: spk.clone(),
+                }],
+                ..common::new_tx(1)
+            },
+            anchor: None,
+            last_seen: Some(2),
+            exp_pos: Some(ChainPosition::Unconfirmed(2)),
+        },
+        TestCase {
+            name: "tx anchor in best chain - confirmed",
+            tx: Transaction {
+                output: vec![TxOut {
+                    value: Amount::ONE_BTC,
+                    script_pubkey: spk.clone(),
+                }],
+                ..common::new_tx(2)
+            },
+            anchor: Some(blocks[1]),
+            last_seen: None,
+            exp_pos: Some(ChainPosition::Confirmed(blocks[1])),
+        },
+        TestCase {
+            name: "tx unknown anchor with last_seen - unconfirmed",
+            tx: Transaction {
+                output: vec![TxOut {
+                    value: Amount::ONE_BTC,
+                    script_pubkey: spk.clone(),
+                }],
+                ..common::new_tx(3)
+            },
+            anchor: Some(block_id!(2, "B'")),
+            last_seen: Some(2),
+            exp_pos: Some(ChainPosition::Unconfirmed(2)),
+        },
+        TestCase {
+            name: "tx unknown anchor - no chain pos",
+            tx: Transaction {
+                output: vec![TxOut {
+                    value: Amount::ONE_BTC,
+                    script_pubkey: spk.clone(),
+                }],
+                ..common::new_tx(4)
+            },
+            anchor: Some(block_id!(2, "B'")),
+            last_seen: None,
+            exp_pos: None,
+        },
+    ]
+    .into_iter()
+    .for_each(|t| run(&chain, &mut graph, t));
+}

crates/chain/tests/test_keychain_txout_index.rs

@@ -0,0 +1,689 @@
+#![cfg(feature = "miniscript")]
+
+#[macro_use]
+mod common;
+use bdk_chain::{
+    collections::BTreeMap,
+    indexer::keychain_txout::{ChangeSet, KeychainTxOutIndex},
+    DescriptorExt, DescriptorId, Indexer, Merge,
+};
+
+use bitcoin::{secp256k1::Secp256k1, Amount, OutPoint, ScriptBuf, Transaction, TxOut};
+use miniscript::{Descriptor, DescriptorPublicKey};
+
+use crate::common::DESCRIPTORS;
+
+#[derive(Clone, Debug, PartialEq, Eq, Ord, PartialOrd)]
+enum TestKeychain {
+    External,
+    Internal,
+}
+
+fn parse_descriptor(descriptor: &str) -> Descriptor<DescriptorPublicKey> {
+    let secp = bdk_chain::bitcoin::secp256k1::Secp256k1::signing_only();
+    Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, descriptor)
+        .unwrap()
+        .0
+}
+
+fn init_txout_index(
+    external_descriptor: Descriptor<DescriptorPublicKey>,
+    internal_descriptor: Descriptor<DescriptorPublicKey>,
+    lookahead: u32,
+) -> KeychainTxOutIndex<TestKeychain> {
+    let mut txout_index = KeychainTxOutIndex::<TestKeychain>::new(lookahead);
+
+    let _ = txout_index
+        .insert_descriptor(TestKeychain::External, external_descriptor)
+        .unwrap();
+    let _ = txout_index
+        .insert_descriptor(TestKeychain::Internal, internal_descriptor)
+        .unwrap();
+
+    txout_index
+}
+
+fn spk_at_index(descriptor: &Descriptor<DescriptorPublicKey>, index: u32) -> ScriptBuf {
+    descriptor
+        .derived_descriptor(&Secp256k1::verification_only(), index)
+        .expect("must derive")
+        .script_pubkey()
+}
+
+// We create two empty changesets lhs and rhs, we then insert various descriptors with various
+// last_revealed, merge rhs to lhs, and check that the result is consistent with these rules:
+// - Existing index doesn't update if the new index in `other` is lower than `self`.
+// - Existing index updates if the new index in `other` is higher than `self`.
+// - Existing index is unchanged if keychain doesn't exist in `other`.
+// - New keychain gets added if the keychain is in `other` but not in `self`.
+#[test]
+fn merge_changesets_check_last_revealed() {
+    let secp = bitcoin::secp256k1::Secp256k1::signing_only();
+    let descriptor_ids: Vec<_> = DESCRIPTORS
+        .iter()
+        .take(4)
+        .map(|d| {
+            Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, d)
+                .unwrap()
+                .0
+                .descriptor_id()
+        })
+        .collect();
+
+    let mut lhs_di = BTreeMap::<DescriptorId, u32>::default();
+    let mut rhs_di = BTreeMap::<DescriptorId, u32>::default();
+    lhs_di.insert(descriptor_ids[0], 7);
+    lhs_di.insert(descriptor_ids[1], 0);
+    lhs_di.insert(descriptor_ids[2], 3);
+
+    rhs_di.insert(descriptor_ids[0], 3); // value less than lhs desc 0
+    rhs_di.insert(descriptor_ids[1], 5); // value more than lhs desc 1
+    lhs_di.insert(descriptor_ids[3], 4); // key doesn't exist in lhs
+
+    let mut lhs = ChangeSet {
+        last_revealed: lhs_di,
+    };
+    let rhs = ChangeSet {
+        last_revealed: rhs_di,
+    };
+    lhs.merge(rhs);
+
+    // Existing index doesn't update if the new index in `other` is lower than `self`.
+    assert_eq!(lhs.last_revealed.get(&descriptor_ids[0]), Some(&7));
+    // Existing index updates if the new index in `other` is higher than `self`.
+    assert_eq!(lhs.last_revealed.get(&descriptor_ids[1]), Some(&5));
+    // Existing index is unchanged if keychain doesn't exist in `other`.
+    assert_eq!(lhs.last_revealed.get(&descriptor_ids[2]), Some(&3));
+    // New keychain gets added if the keychain is in `other` but not in `self`.
+    assert_eq!(lhs.last_revealed.get(&descriptor_ids[3]), Some(&4));
+}
+
+#[test]
+fn test_set_all_derivation_indices() {
+    let external_descriptor = parse_descriptor(DESCRIPTORS[0]);
+    let internal_descriptor = parse_descriptor(DESCRIPTORS[1]);
+    let mut txout_index =
+        init_txout_index(external_descriptor.clone(), internal_descriptor.clone(), 0);
+    let derive_to: BTreeMap<_, _> =
+        [(TestKeychain::External, 12), (TestKeychain::Internal, 24)].into();
+    let last_revealed: BTreeMap<_, _> = [
+        (external_descriptor.descriptor_id(), 12),
+        (internal_descriptor.descriptor_id(), 24),
+    ]
+    .into();
+    assert_eq!(
+        txout_index.reveal_to_target_multi(&derive_to),
+        ChangeSet {
+            last_revealed: last_revealed.clone()
+        }
+    );
+    assert_eq!(txout_index.last_revealed_indices(), derive_to);
+    assert_eq!(
+        txout_index.reveal_to_target_multi(&derive_to),
+        ChangeSet::default(),
+        "no changes if we set to the same thing"
+    );
+    assert_eq!(txout_index.initial_changeset().last_revealed, last_revealed);
+}
+
+#[test]
+fn test_lookahead() {
+    let external_descriptor = parse_descriptor(DESCRIPTORS[0]);
+    let internal_descriptor = parse_descriptor(DESCRIPTORS[1]);
+    let mut txout_index =
+        init_txout_index(external_descriptor.clone(), internal_descriptor.clone(), 10);
+
+    // given:
+    // - external lookahead set to 10
+    // when:
+    // - set external derivation index to value higher than last, but within the lookahead value
+    // expect:
+    // - scripts cached in spk_txout_index should increase correctly
+    // - stored scripts of external keychain should be of expected counts
+    for index in (0..20).skip_while(|i| i % 2 == 1) {
+        let (revealed_spks, revealed_changeset) = txout_index
+            .reveal_to_target(TestKeychain::External, index)
+            .unwrap();
+        assert_eq!(
+            revealed_spks,
+            vec![(index, spk_at_index(&external_descriptor, index))],
+        );
+        assert_eq!(
+            &revealed_changeset.last_revealed,
+            &[(external_descriptor.descriptor_id(), index)].into()
+        );
+
+        assert_eq!(
+            txout_index.inner().all_spks().len(),
+            10 /* external lookahead */ +
+            10 /* internal lookahead */ +
+            index as usize + 1 /* `derived` count */
+        );
+        assert_eq!(
+            txout_index
+                .revealed_keychain_spks(TestKeychain::External)
+                .count(),
+            index as usize + 1,
+        );
+        assert_eq!(
+            txout_index
+                .revealed_keychain_spks(TestKeychain::Internal)
+                .count(),
+            0,
+        );
+        assert_eq!(
+            txout_index
+                .unused_keychain_spks(TestKeychain::External)
+                .count(),
+            index as usize + 1,
+        );
+        assert_eq!(
+            txout_index
+                .unused_keychain_spks(TestKeychain::Internal)
+                .count(),
+            0,
+        );
+    }
+
+    // given:
+    // - internal lookahead is 10
+    // - internal derivation index is `None`
+    // when:
+    // - derivation index is set ahead of current derivation index + lookahead
+    // expect:
+    // - scripts cached in spk_txout_index should increase correctly, a.k.a. no scripts are skipped
+    let (revealed_spks, revealed_changeset) = txout_index
+        .reveal_to_target(TestKeychain::Internal, 24)
+        .unwrap();
+    assert_eq!(
+        revealed_spks,
+        (0..=24)
+            .map(|index| (index, spk_at_index(&internal_descriptor, index)))
+            .collect::<Vec<_>>(),
+    );
+    assert_eq!(
+        &revealed_changeset.last_revealed,
+        &[(internal_descriptor.descriptor_id(), 24)].into()
+    );
+    assert_eq!(
+        txout_index.inner().all_spks().len(),
+        10 /* external lookahead */ +
+        10 /* internal lookahead */ +
+        20 /* external stored index count */ +
+        25 /* internal stored index count */
+    );
+    assert_eq!(
+        txout_index
+            .revealed_keychain_spks(TestKeychain::Internal)
+            .count(),
+        25,
+    );
+
+    // ensure derivation indices are expected for each keychain
+    let last_external_index = txout_index
+        .last_revealed_index(TestKeychain::External)
+        .expect("already derived");
+    let last_internal_index = txout_index
+        .last_revealed_index(TestKeychain::Internal)
+        .expect("already derived");
+    assert_eq!(last_external_index, 19);
+    assert_eq!(last_internal_index, 24);
+
+    // when:
+    // - scanning txouts with spks within stored indexes
+    // expect:
+    // - no changes to stored index counts
+    let external_iter = 0..=last_external_index;
+    let internal_iter = last_internal_index - last_external_index..=last_internal_index;
+    for (external_index, internal_index) in external_iter.zip(internal_iter) {
+        let tx = Transaction {
+            output: vec![
+                TxOut {
+                    script_pubkey: external_descriptor
+                        .at_derivation_index(external_index)
+                        .unwrap()
+                        .script_pubkey(),
+                    value: Amount::from_sat(10_000),
+                },
+                TxOut {
+                    script_pubkey: internal_descriptor
+                        .at_derivation_index(internal_index)
+                        .unwrap()
+                        .script_pubkey(),
+                    value: Amount::from_sat(10_000),
+                },
+            ],
+            ..common::new_tx(external_index)
+        };
+        assert_eq!(txout_index.index_tx(&tx), ChangeSet::default());
+        assert_eq!(
+            txout_index.last_revealed_index(TestKeychain::External),
+            Some(last_external_index)
+        );
+        assert_eq!(
+            txout_index.last_revealed_index(TestKeychain::Internal),
+            Some(last_internal_index)
+        );
+        assert_eq!(
+            txout_index
+                .revealed_keychain_spks(TestKeychain::External)
+                .count(),
+            last_external_index as usize + 1,
+        );
+        assert_eq!(
+            txout_index
+                .revealed_keychain_spks(TestKeychain::Internal)
+                .count(),
+            last_internal_index as usize + 1,
+        );
+    }
+}
+
+// when:
+// - scanning txouts with spks above last stored index
+// expect:
+// - last revealed index should increase as expected
+// - last used index should change as expected
+#[test]
+fn test_scan_with_lookahead() {
+    let external_descriptor = parse_descriptor(DESCRIPTORS[0]);
+    let internal_descriptor = parse_descriptor(DESCRIPTORS[1]);
+    let mut txout_index =
+        init_txout_index(external_descriptor.clone(), internal_descriptor.clone(), 10);
+
+    let spks: BTreeMap<u32, ScriptBuf> = [0, 10, 20, 30]
+        .into_iter()
+        .map(|i| {
+            (
+                i,
+                external_descriptor
+                    .at_derivation_index(i)
+                    .unwrap()
+                    .script_pubkey(),
+            )
+        })
+        .collect();
+
+    for (&spk_i, spk) in &spks {
+        let op = OutPoint::new(h!("fake tx"), spk_i);
+        let txout = TxOut {
+            script_pubkey: spk.clone(),
+            value: Amount::ZERO,
+        };
+
+        let changeset = txout_index.index_txout(op, &txout);
+        assert_eq!(
+            &changeset.last_revealed,
+            &[(external_descriptor.descriptor_id(), spk_i)].into()
+        );
+        assert_eq!(
+            txout_index.last_revealed_index(TestKeychain::External),
+            Some(spk_i)
+        );
+        assert_eq!(
+            txout_index.last_used_index(TestKeychain::External),
+            Some(spk_i)
+        );
+    }
+
+    // now try with index 41 (lookahead surpassed), we expect that the txout to not be indexed
+    let spk_41 = external_descriptor
+        .at_derivation_index(41)
+        .unwrap()
+        .script_pubkey();
+    let op = OutPoint::new(h!("fake tx"), 41);
+    let txout = TxOut {
+        script_pubkey: spk_41,
+        value: Amount::ZERO,
+    };
+    let changeset = txout_index.index_txout(op, &txout);
+    assert!(changeset.is_empty());
+}
+
+#[test]
+#[rustfmt::skip]
+fn test_wildcard_derivations() {
+    let external_descriptor = parse_descriptor(DESCRIPTORS[0]);
+    let internal_descriptor = parse_descriptor(DESCRIPTORS[1]);
+    let mut txout_index = init_txout_index(external_descriptor.clone(), internal_descriptor.clone(), 0);
+    let external_spk_0 = external_descriptor.at_derivation_index(0).unwrap().script_pubkey();
+    let external_spk_16 = external_descriptor.at_derivation_index(16).unwrap().script_pubkey();
+    let external_spk_26 = external_descriptor.at_derivation_index(26).unwrap().script_pubkey();
+    let external_spk_27 = external_descriptor.at_derivation_index(27).unwrap().script_pubkey();
+
+    // - nothing is derived
+    // - unused list is also empty
+    //
+    // - next_derivation_index() == (0, true)
+    // - derive_new() == ((0, <spk>), keychain::ChangeSet)
+    // - next_unused() == ((0, <spk>), keychain::ChangeSet:is_empty())
+    assert_eq!(txout_index.next_index(TestKeychain::External).unwrap(), (0, true));
+    let (spk, changeset) = txout_index.reveal_next_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (0_u32, external_spk_0.clone()));
+    assert_eq!(&changeset.last_revealed, &[(external_descriptor.descriptor_id(), 0)].into());
+    let (spk, changeset) = txout_index.next_unused_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (0_u32, external_spk_0.clone()));
+    assert_eq!(&changeset.last_revealed, &[].into());
+
+    // - derived till 25
+    // - used all spks till 15.
+    // - used list : [0..=15, 17, 20, 23]
+    // - unused list: [16, 18, 19, 21, 22, 24, 25]
+
+    // - next_derivation_index() = (26, true)
+    // - derive_new() = ((26, <spk>), keychain::ChangeSet)
+    // - next_unused() == ((16, <spk>), keychain::ChangeSet::is_empty())
+    let _ = txout_index.reveal_to_target(TestKeychain::External, 25);
+
+    (0..=15)
+        .chain([17, 20, 23])
+        .for_each(|index| assert!(txout_index.mark_used(TestKeychain::External, index)));
+
+    assert_eq!(txout_index.next_index(TestKeychain::External).unwrap(), (26, true));
+
+    let (spk, changeset) = txout_index.reveal_next_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (26, external_spk_26));
+
+    assert_eq!(&changeset.last_revealed, &[(external_descriptor.descriptor_id(), 26)].into());
+
+    let (spk, changeset) = txout_index.next_unused_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (16, external_spk_16));
+    assert_eq!(&changeset.last_revealed, &[].into());
+
+    // - Use all the derived till 26.
+    // - next_unused() = ((27, <spk>), keychain::ChangeSet)
+    (0..=26).for_each(|index| {
+        txout_index.mark_used(TestKeychain::External, index);
+    });
+
+    let (spk, changeset) = txout_index.next_unused_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (27, external_spk_27));
+    assert_eq!(&changeset.last_revealed, &[(external_descriptor.descriptor_id(), 27)].into());
+}
+
+#[test]
+fn test_non_wildcard_derivations() {
+    let mut txout_index = KeychainTxOutIndex::<TestKeychain>::new(0);
+
+    let secp = bitcoin::secp256k1::Secp256k1::signing_only();
+    let (no_wildcard_descriptor, _) =
+        Descriptor::<DescriptorPublicKey>::parse_descriptor(&secp, DESCRIPTORS[6]).unwrap();
+    let external_spk = no_wildcard_descriptor
+        .at_derivation_index(0)
+        .unwrap()
+        .script_pubkey();
+
+    let _ = txout_index
+        .insert_descriptor(TestKeychain::External, no_wildcard_descriptor.clone())
+        .unwrap();
+
+    // given:
+    // - `txout_index` with no stored scripts
+    // expect:
+    // - next derivation index should be new
+    // - when we derive a new script, script @ index 0
+    // - when we get the next unused script, script @ index 0
+    assert_eq!(
+        txout_index.next_index(TestKeychain::External).unwrap(),
+        (0, true)
+    );
+    let (spk, changeset) = txout_index.reveal_next_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (0, external_spk.clone()));
+    assert_eq!(
+        &changeset.last_revealed,
+        &[(no_wildcard_descriptor.descriptor_id(), 0)].into()
+    );
+
+    let (spk, changeset) = txout_index.next_unused_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (0, external_spk.clone()));
+    assert_eq!(&changeset.last_revealed, &[].into());
+
+    // given:
+    // - the non-wildcard descriptor already has a stored and used script
+    // expect:
+    // - next derivation index should not be new
+    // - derive new and next unused should return the old script
+    // - store_up_to should not panic and return empty changeset
+    assert_eq!(
+        txout_index.next_index(TestKeychain::External).unwrap(),
+        (0, false)
+    );
+    txout_index.mark_used(TestKeychain::External, 0);
+
+    let (spk, changeset) = txout_index.reveal_next_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (0, external_spk.clone()));
+    assert_eq!(&changeset.last_revealed, &[].into());
+
+    let (spk, changeset) = txout_index.next_unused_spk(TestKeychain::External).unwrap();
+    assert_eq!(spk, (0, external_spk.clone()));
+    assert_eq!(&changeset.last_revealed, &[].into());
+    let (revealed_spks, revealed_changeset) = txout_index
+        .reveal_to_target(TestKeychain::External, 200)
+        .unwrap();
+    assert_eq!(revealed_spks.len(), 0);
+    assert!(revealed_changeset.is_empty());
+
+    // we check that spks_of_keychain returns a SpkIterator with just one element
+    assert_eq!(
+        txout_index
+            .revealed_keychain_spks(TestKeychain::External)
+            .count(),
+        1,
+    );
+}
+
+/// Check that calling `lookahead_to_target` stores the expected spks.
+#[test]
+fn lookahead_to_target() {
+    #[derive(Default)]
+    struct TestCase {
+        /// Global lookahead value.
+        lookahead: u32,
+        /// Last revealed index for external keychain.
+        external_last_revealed: Option<u32>,
+        /// Last revealed index for internal keychain.
+        internal_last_revealed: Option<u32>,
+        /// Call `lookahead_to_target(External, u32)`.
+        external_target: Option<u32>,
+        /// Call `lookahead_to_target(Internal, u32)`.
+        internal_target: Option<u32>,
+    }
+
+    let test_cases = &[
+        TestCase {
+            lookahead: 0,
+            external_target: Some(100),
+            ..Default::default()
+        },
+        TestCase {
+            lookahead: 10,
+            internal_target: Some(99),
+            ..Default::default()
+        },
+        TestCase {
+            lookahead: 100,
+            internal_target: Some(9),
+            external_target: Some(10),
+            ..Default::default()
+        },
+        TestCase {
+            lookahead: 12,
+            external_last_revealed: Some(2),
+            internal_last_revealed: Some(2),
+            internal_target: Some(15),
+            external_target: Some(13),
+        },
+        TestCase {
+            lookahead: 13,
+            external_last_revealed: Some(100),
+            internal_last_revealed: Some(21),
+            internal_target: Some(120),
+            external_target: Some(130),
+        },
+    ];
+
+    for t in test_cases {
+        let external_descriptor = parse_descriptor(DESCRIPTORS[0]);
+        let internal_descriptor = parse_descriptor(DESCRIPTORS[1]);
+        let mut index = init_txout_index(
+            external_descriptor.clone(),
+            internal_descriptor.clone(),
+            t.lookahead,
+        );
+
+        if let Some(last_revealed) = t.external_last_revealed {
+            let _ = index.reveal_to_target(TestKeychain::External, last_revealed);
+        }
+        if let Some(last_revealed) = t.internal_last_revealed {
+            let _ = index.reveal_to_target(TestKeychain::Internal, last_revealed);
+        }
+
+        let keychain_test_cases = [
+            (
+                TestKeychain::External,
+                t.external_last_revealed,
+                t.external_target,
+            ),
+            (
+                TestKeychain::Internal,
+                t.internal_last_revealed,
+                t.internal_target,
+            ),
+        ];
+        for (keychain, last_revealed, target) in keychain_test_cases {
+            if let Some(target) = target {
+                let original_last_stored_index = match last_revealed {
+                    Some(last_revealed) => Some(last_revealed + t.lookahead),
+                    None => t.lookahead.checked_sub(1),
+                };
+                let exp_last_stored_index = match original_last_stored_index {
+                    Some(original_last_stored_index) => {
+                        Ord::max(target, original_last_stored_index)
+                    }
+                    None => target,
+                };
+                index.lookahead_to_target(keychain.clone(), target);
+                let keys = index
+                    .inner()
+                    .all_spks()
+                    .range((keychain.clone(), 0)..=(keychain.clone(), u32::MAX))
+                    .map(|(k, _)| k.clone())
+                    .collect::<Vec<_>>();
+                let exp_keys = core::iter::repeat(keychain)
+                    .zip(0_u32..=exp_last_stored_index)
+                    .collect::<Vec<_>>();
+                assert_eq!(keys, exp_keys);
+            }
+        }
+    }
+}
+
+#[test]
+fn applying_changesets_one_by_one_vs_aggregate_must_have_same_result() {
+    let desc = parse_descriptor(DESCRIPTORS[0]);
+    let changesets: &[ChangeSet] = &[
+        ChangeSet {
+            last_revealed: [(desc.descriptor_id(), 10)].into(),
+        },
+        ChangeSet {
+            last_revealed: [(desc.descriptor_id(), 12)].into(),
+        },
+    ];
+
+    let mut indexer_a = KeychainTxOutIndex::<TestKeychain>::new(0);
+    indexer_a
+        .insert_descriptor(TestKeychain::External, desc.clone())
+        .expect("must insert keychain");
+    for changeset in changesets {
+        indexer_a.apply_changeset(changeset.clone());
+    }
+
+    let mut indexer_b = KeychainTxOutIndex::<TestKeychain>::new(0);
+    indexer_b
+        .insert_descriptor(TestKeychain::External, desc.clone())
+        .expect("must insert keychain");
+    let aggregate_changesets = changesets
+        .iter()
+        .cloned()
+        .reduce(|mut agg, cs| {
+            agg.merge(cs);
+            agg
+        })
+        .expect("must aggregate changesets");
+    indexer_b.apply_changeset(aggregate_changesets);
+
+    assert_eq!(
+        indexer_a.keychains().collect::<Vec<_>>(),
+        indexer_b.keychains().collect::<Vec<_>>()
+    );
+    assert_eq!(
+        indexer_a.spk_at_index(TestKeychain::External, 0),
+        indexer_b.spk_at_index(TestKeychain::External, 0)
+    );
+    assert_eq!(
+        indexer_a.spk_at_index(TestKeychain::Internal, 0),
+        indexer_b.spk_at_index(TestKeychain::Internal, 0)
+    );
+    assert_eq!(
+        indexer_a.last_revealed_indices(),
+        indexer_b.last_revealed_indices()
+    );
+}
+
+#[test]
+fn assigning_same_descriptor_to_multiple_keychains_should_error() {
+    let desc = parse_descriptor(DESCRIPTORS[0]);
+    let mut indexer = KeychainTxOutIndex::<TestKeychain>::new(0);
+    let _ = indexer
+        .insert_descriptor(TestKeychain::Internal, desc.clone())
+        .unwrap();
+    assert!(indexer
+        .insert_descriptor(TestKeychain::External, desc)
+        .is_err())
+}
+
+#[test]
+fn reassigning_keychain_to_a_new_descriptor_should_error() {
+    let desc1 = parse_descriptor(DESCRIPTORS[0]);
+    let desc2 = parse_descriptor(DESCRIPTORS[1]);
+    let mut indexer = KeychainTxOutIndex::<TestKeychain>::new(0);
+    let _ = indexer.insert_descriptor(TestKeychain::Internal, desc1);
+    assert!(indexer
+        .insert_descriptor(TestKeychain::Internal, desc2)
+        .is_err());
+}
+
+#[test]
+fn when_querying_over_a_range_of_keychains_the_utxos_should_show_up() {
+    let mut indexer = KeychainTxOutIndex::<usize>::new(0);
+    let mut tx = common::new_tx(0);
+
+    for (i, descriptor) in DESCRIPTORS.iter().enumerate() {
+        let descriptor = parse_descriptor(descriptor);
+        let _ = indexer.insert_descriptor(i, descriptor.clone()).unwrap();
+        if i != 4 {
+            // skip one in the middle to see if uncovers any bugs
+            indexer.reveal_next_spk(i);
+        }
+        tx.output.push(TxOut {
+            script_pubkey: descriptor.at_derivation_index(0).unwrap().script_pubkey(),
+            value: Amount::from_sat(10_000),
+        });
+    }
+
+    let n_spks = DESCRIPTORS.len() - /*we skipped one*/ 1;
+
+    let _ = indexer.index_tx(&tx);
+    assert_eq!(indexer.outpoints().len(), n_spks);
+
+    assert_eq!(indexer.revealed_spks(0..DESCRIPTORS.len()).count(), n_spks);
+    assert_eq!(indexer.revealed_spks(1..4).count(), 4 - 1);
+    assert_eq!(
+        indexer.net_value(&tx, 0..DESCRIPTORS.len()).to_sat(),
+        (10_000 * n_spks) as i64
+    );
+    assert_eq!(
+        indexer.net_value(&tx, 3..6).to_sat(),
+        (10_000 * (6 - 3 - /*the skipped one*/ 1)) as i64
+    );
+}

crates/chain/tests/test_local_chain.rs

@@ -0,0 +1,848 @@
+#![cfg(feature = "miniscript")]
+
+use std::ops::{Bound, RangeBounds};
+
+use bdk_chain::{
+    local_chain::{
+        AlterCheckPointError, ApplyHeaderError, CannotConnectError, ChangeSet, CheckPoint,
+        LocalChain, MissingGenesisError,
+    },
+    BlockId,
+};
+use bitcoin::{block::Header, hashes::Hash, BlockHash};
+use proptest::prelude::*;
+
+#[macro_use]
+mod common;
+
+#[derive(Debug)]
+struct TestLocalChain<'a> {
+    name: &'static str,
+    chain: LocalChain,
+    update: CheckPoint,
+    exp: ExpectedResult<'a>,
+}
+
+#[derive(Debug, PartialEq)]
+enum ExpectedResult<'a> {
+    Ok {
+        changeset: &'a [(u32, Option<BlockHash>)],
+        init_changeset: &'a [(u32, Option<BlockHash>)],
+    },
+    Err(CannotConnectError),
+}
+
+impl<'a> TestLocalChain<'a> {
+    fn run(mut self) {
+        println!("[TestLocalChain] test: {}", self.name);
+        let got_changeset = match self.chain.apply_update(self.update) {
+            Ok(changeset) => changeset,
+            Err(got_err) => {
+                assert_eq!(
+                    ExpectedResult::Err(got_err),
+                    self.exp,
+                    "{}: unexpected error",
+                    self.name
+                );
+                return;
+            }
+        };
+
+        match self.exp {
+            ExpectedResult::Ok {
+                changeset,
+                init_changeset,
+            } => {
+                assert_eq!(
+                    got_changeset,
+                    changeset.iter().cloned().collect(),
+                    "{}: unexpected changeset",
+                    self.name
+                );
+                assert_eq!(
+                    self.chain.initial_changeset(),
+                    init_changeset.iter().cloned().collect(),
+                    "{}: unexpected initial changeset",
+                    self.name
+                );
+            }
+            ExpectedResult::Err(err) => panic!(
+                "{}: expected error ({}), got non-error result: {:?}",
+                self.name, err, got_changeset
+            ),
+        }
+    }
+}
+
+#[test]
+fn update_local_chain() {
+    [
+        TestLocalChain {
+            name: "add first tip",
+            chain: local_chain![(0, h!("A"))],
+            update: chain_update![(0, h!("A"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[],
+                init_changeset: &[(0, Some(h!("A")))],
+            },
+        },
+        TestLocalChain {
+            name: "add second tip",
+            chain: local_chain![(0, h!("A"))],
+            update: chain_update![(0, h!("A")), (1, h!("B"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[(1, Some(h!("B")))],
+                init_changeset: &[(0, Some(h!("A"))), (1, Some(h!("B")))],
+            },
+        },
+        TestLocalChain {
+            name: "two disjoint chains cannot merge",
+            chain: local_chain![(0, h!("_")), (1, h!("A"))],
+            update: chain_update![(0, h!("_")), (2, h!("B"))],
+            exp: ExpectedResult::Err(CannotConnectError {
+                try_include_height: 1,
+            }),
+        },
+        TestLocalChain {
+            name: "two disjoint chains cannot merge (existing chain longer)",
+            chain: local_chain![(0, h!("_")), (2, h!("A"))],
+            update: chain_update![(0, h!("_")), (1, h!("B"))],
+            exp: ExpectedResult::Err(CannotConnectError {
+                try_include_height: 2,
+            }),
+        },
+        TestLocalChain {
+            name: "duplicate chains should merge",
+            chain: local_chain![(0, h!("A"))],
+            update: chain_update![(0, h!("A"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[],
+                init_changeset: &[(0, Some(h!("A")))],
+            },
+        },
+        // Introduce an older checkpoint (B)
+        //        | 0 | 1 | 2 | 3
+        // chain  | _       C   D
+        // update | _   B   C
+        TestLocalChain {
+            name: "can introduce older checkpoint",
+            chain: local_chain![(0, h!("_")), (2, h!("C")), (3, h!("D"))],
+            update: chain_update![(0, h!("_")), (1, h!("B")), (2, h!("C"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[(1, Some(h!("B")))],
+                init_changeset: &[(0, Some(h!("_"))), (1, Some(h!("B"))), (2, Some(h!("C"))), (3, Some(h!("D")))],
+            },
+        },
+        // Introduce an older checkpoint (A) that is not directly behind PoA
+        //        | 0 | 2 | 3 | 4
+        // chain  | _       B   C
+        // update | _   A       C
+        TestLocalChain {
+            name: "can introduce older checkpoint 2",
+            chain: local_chain![(0, h!("_")), (3, h!("B")), (4, h!("C"))],
+            update: chain_update![(0, h!("_")), (2, h!("A")), (4, h!("C"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[(2, Some(h!("A")))],
+                init_changeset: &[(0, Some(h!("_"))), (2, Some(h!("A"))), (3, Some(h!("B"))), (4, Some(h!("C")))],
+            }
+        },
+        // Introduce an older checkpoint (B) that is not the oldest checkpoint
+        //        | 0 | 1 | 2 | 3
+        // chain  | _   A       C
+        // update | _       B   C
+        TestLocalChain {
+            name: "can introduce older checkpoint 3",
+            chain: local_chain![(0, h!("_")), (1, h!("A")), (3, h!("C"))],
+            update: chain_update![(0, h!("_")), (2, h!("B")), (3, h!("C"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[(2, Some(h!("B")))],
+                init_changeset: &[(0, Some(h!("_"))), (1, Some(h!("A"))), (2, Some(h!("B"))), (3, Some(h!("C")))],
+            }
+        },
+        // Introduce two older checkpoints below the PoA
+        //        | 0 | 1 | 2 | 3
+        // chain  | _           C
+        // update | _   A   B   C
+        TestLocalChain {
+            name: "introduce two older checkpoints below PoA",
+            chain: local_chain![(0, h!("_")), (3, h!("C"))],
+            update: chain_update![(0, h!("_")), (1, h!("A")), (2, h!("B")), (3, h!("C"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[(1, Some(h!("A"))), (2, Some(h!("B")))],
+                init_changeset: &[(0, Some(h!("_"))), (1, Some(h!("A"))), (2, Some(h!("B"))), (3, Some(h!("C")))],
+            },
+        },
+        TestLocalChain {
+            name: "fix blockhash before agreement point",
+            chain: local_chain![(0, h!("im-wrong")), (1, h!("we-agree"))],
+            update: chain_update![(0, h!("fix")), (1, h!("we-agree"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[(0, Some(h!("fix")))],
+                init_changeset: &[(0, Some(h!("fix"))), (1, Some(h!("we-agree")))],
+            },
+        },
+        // B and C are in both chain and update
+        //        | 0 | 1 | 2 | 3 | 4
+        // chain  | _       B   C
+        // update | _   A   B   C   D
+        // This should succeed with the point of agreement being C and A should be added in addition.
+        TestLocalChain {
+            name: "two points of agreement",
+            chain: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C"))],
+            update: chain_update![(0, h!("_")), (1, h!("A")), (2, h!("B")), (3, h!("C")), (4, h!("D"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[(1, Some(h!("A"))), (4, Some(h!("D")))],
+                init_changeset: &[
+                    (0, Some(h!("_"))),
+                    (1, Some(h!("A"))),
+                    (2, Some(h!("B"))),
+                    (3, Some(h!("C"))),
+                    (4, Some(h!("D"))),
+                ],
+            },
+        },
+        // Update and chain does not connect:
+        //        | 0 | 1 | 2 | 3 | 4
+        // chain  | _       B   C
+        // update | _   A   B       D
+        // This should fail as we cannot figure out whether C & D are on the same chain
+        TestLocalChain {
+            name: "update and chain does not connect",
+            chain: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C"))],
+            update: chain_update![(0, h!("_")), (1, h!("A")), (2, h!("B")), (4, h!("D"))],
+            exp: ExpectedResult::Err(CannotConnectError {
+                try_include_height: 3,
+            }),
+        },
+        // Transient invalidation:
+        //        | 0 | 1 | 2 | 3 | 4 | 5
+        // chain  | _       B   C       E
+        // update | _       B'  C'  D
+        // This should succeed and invalidate B,C and E with point of agreement being A.
+        TestLocalChain {
+            name: "transitive invalidation applies to checkpoints higher than invalidation",
+            chain: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C")), (5, h!("E"))],
+            update: chain_update![(0, h!("_")), (2, h!("B'")), (3, h!("C'")), (4, h!("D"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[
+                    (2, Some(h!("B'"))),
+                    (3, Some(h!("C'"))),
+                    (4, Some(h!("D"))),
+                    (5, None),
+                ],
+                init_changeset: &[
+                    (0, Some(h!("_"))),
+                    (2, Some(h!("B'"))),
+                    (3, Some(h!("C'"))),
+                    (4, Some(h!("D"))),
+                ],
+            },
+        },
+        // Transient invalidation:
+        //        | 0 | 1 | 2 | 3 | 4
+        // chain  | _   B   C       E
+        // update | _   B'  C'  D
+        // This should succeed and invalidate B, C and E with no point of agreement
+        TestLocalChain {
+            name: "transitive invalidation applies to checkpoints higher than invalidation no point of agreement",
+            chain: local_chain![(0, h!("_")), (1, h!("B")), (2, h!("C")), (4, h!("E"))],
+            update: chain_update![(0, h!("_")), (1, h!("B'")), (2, h!("C'")), (3, h!("D"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[
+                    (1, Some(h!("B'"))),
+                    (2, Some(h!("C'"))),
+                    (3, Some(h!("D"))),
+                    (4, None)
+                ],
+                init_changeset: &[
+                    (0, Some(h!("_"))), 
+                    (1, Some(h!("B'"))),
+                    (2, Some(h!("C'"))),
+                    (3, Some(h!("D"))),
+                ],
+            },
+        },
+        // Transient invalidation:
+        //        | 0 | 1 | 2 | 3 | 4 | 5
+        // chain  | _   A   B   C       E
+        // update | _       B'  C'  D
+        // This should fail since although it tells us that B and C are invalid it doesn't tell us whether
+        // A was invalid.
+        TestLocalChain {
+            name: "invalidation but no connection",
+            chain: local_chain![(0, h!("_")), (1, h!("A")), (2, h!("B")), (3, h!("C")), (5, h!("E"))],
+            update: chain_update![(0, h!("_")), (2, h!("B'")), (3, h!("C'")), (4, h!("D"))],
+            exp: ExpectedResult::Err(CannotConnectError { try_include_height: 1 }),
+        },
+        // Introduce blocks between two points of agreement
+        //        | 0 | 1 | 2 | 3 | 4 | 5
+        // chain  | A   B       D   E
+        // update | A       C       E   F
+        TestLocalChain {
+            name: "introduce blocks between two points of agreement",
+            chain: local_chain![(0, h!("A")), (1, h!("B")), (3, h!("D")), (4, h!("E"))],
+            update: chain_update![(0, h!("A")), (2, h!("C")), (4, h!("E")), (5, h!("F"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[
+                    (2, Some(h!("C"))),
+                    (5, Some(h!("F"))),
+                ],
+                init_changeset: &[
+                    (0, Some(h!("A"))),
+                    (1, Some(h!("B"))),
+                    (2, Some(h!("C"))),
+                    (3, Some(h!("D"))),
+                    (4, Some(h!("E"))),
+                    (5, Some(h!("F"))),
+                ],
+            },
+        },
+        // Allow update that is shorter than original chain
+        //        | 0 | 1 | 2 | 3 | 4 | 5
+        // chain  | A       C   D   E   F
+        // update | A       C   D'
+        TestLocalChain {
+            name: "allow update that is shorter than original chain",
+            chain: local_chain![(0, h!("_")), (2, h!("C")), (3, h!("D")), (4, h!("E")), (5, h!("F"))],
+            update: chain_update![(0, h!("_")), (2, h!("C")), (3, h!("D'"))],
+            exp: ExpectedResult::Ok {
+                changeset: &[
+                    (3, Some(h!("D'"))),
+                    (4, None),
+                    (5, None),
+                ],
+                init_changeset: &[
+                    (0, Some(h!("_"))),
+                    (2, Some(h!("C"))),
+                    (3, Some(h!("D'"))),
+                ],
+            },
+        },
+    ]
+    .into_iter()
+    .for_each(TestLocalChain::run);
+}
+
+#[test]
+fn local_chain_insert_block() {
+    struct TestCase {
+        original: LocalChain,
+        insert: (u32, BlockHash),
+        expected_result: Result<ChangeSet, AlterCheckPointError>,
+        expected_final: LocalChain,
+    }
+
+    let test_cases = [
+        TestCase {
+            original: local_chain![(0, h!("_"))],
+            insert: (5, h!("block5")),
+            expected_result: Ok([(5, Some(h!("block5")))].into()),
+            expected_final: local_chain![(0, h!("_")), (5, h!("block5"))],
+        },
+        TestCase {
+            original: local_chain![(0, h!("_")), (3, h!("A"))],
+            insert: (4, h!("B")),
+            expected_result: Ok([(4, Some(h!("B")))].into()),
+            expected_final: local_chain![(0, h!("_")), (3, h!("A")), (4, h!("B"))],
+        },
+        TestCase {
+            original: local_chain![(0, h!("_")), (4, h!("B"))],
+            insert: (3, h!("A")),
+            expected_result: Ok([(3, Some(h!("A")))].into()),
+            expected_final: local_chain![(0, h!("_")), (3, h!("A")), (4, h!("B"))],
+        },
+        TestCase {
+            original: local_chain![(0, h!("_")), (2, h!("K"))],
+            insert: (2, h!("K")),
+            expected_result: Ok([].into()),
+            expected_final: local_chain![(0, h!("_")), (2, h!("K"))],
+        },
+        TestCase {
+            original: local_chain![(0, h!("_")), (2, h!("K"))],
+            insert: (2, h!("J")),
+            expected_result: Err(AlterCheckPointError {
+                height: 2,
+                original_hash: h!("K"),
+                update_hash: Some(h!("J")),
+            }),
+            expected_final: local_chain![(0, h!("_")), (2, h!("K"))],
+        },
+    ];
+
+    for (i, t) in test_cases.into_iter().enumerate() {
+        let mut chain = t.original;
+        assert_eq!(
+            chain.insert_block(t.insert.into()),
+            t.expected_result,
+            "[{}] unexpected result when inserting block",
+            i,
+        );
+        assert_eq!(chain, t.expected_final, "[{}] unexpected final chain", i,);
+    }
+}
+
+#[test]
+fn local_chain_disconnect_from() {
+    struct TestCase {
+        name: &'static str,
+        original: LocalChain,
+        disconnect_from: (u32, BlockHash),
+        exp_result: Result<ChangeSet, MissingGenesisError>,
+        exp_final: LocalChain,
+    }
+
+    let test_cases = [
+        TestCase {
+            name: "try_replace_genesis_should_fail",
+            original: local_chain![(0, h!("_"))],
+            disconnect_from: (0, h!("_")),
+            exp_result: Err(MissingGenesisError),
+            exp_final: local_chain![(0, h!("_"))],
+        },
+        TestCase {
+            name: "try_replace_genesis_should_fail_2",
+            original: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C"))],
+            disconnect_from: (0, h!("_")),
+            exp_result: Err(MissingGenesisError),
+            exp_final: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C"))],
+        },
+        TestCase {
+            name: "from_does_not_exist",
+            original: local_chain![(0, h!("_")), (3, h!("C"))],
+            disconnect_from: (2, h!("B")),
+            exp_result: Ok(ChangeSet::default()),
+            exp_final: local_chain![(0, h!("_")), (3, h!("C"))],
+        },
+        TestCase {
+            name: "from_has_different_blockhash",
+            original: local_chain![(0, h!("_")), (2, h!("B"))],
+            disconnect_from: (2, h!("not_B")),
+            exp_result: Ok(ChangeSet::default()),
+            exp_final: local_chain![(0, h!("_")), (2, h!("B"))],
+        },
+        TestCase {
+            name: "disconnect_one",
+            original: local_chain![(0, h!("_")), (2, h!("B"))],
+            disconnect_from: (2, h!("B")),
+            exp_result: Ok(ChangeSet::from_iter([(2, None)])),
+            exp_final: local_chain![(0, h!("_"))],
+        },
+        TestCase {
+            name: "disconnect_three",
+            original: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C")), (4, h!("D"))],
+            disconnect_from: (2, h!("B")),
+            exp_result: Ok(ChangeSet::from_iter([(2, None), (3, None), (4, None)])),
+            exp_final: local_chain![(0, h!("_"))],
+        },
+    ];
+
+    for (i, t) in test_cases.into_iter().enumerate() {
+        println!("Case {}: {}", i, t.name);
+
+        let mut chain = t.original;
+        let result = chain.disconnect_from(t.disconnect_from.into());
+        assert_eq!(
+            result, t.exp_result,
+            "[{}:{}] unexpected changeset result",
+            i, t.name
+        );
+        assert_eq!(
+            chain, t.exp_final,
+            "[{}:{}] unexpected final chain",
+            i, t.name
+        );
+    }
+}
+
+#[test]
+fn checkpoint_from_block_ids() {
+    struct TestCase<'a> {
+        name: &'a str,
+        blocks: &'a [(u32, BlockHash)],
+        exp_result: Result<(), Option<(u32, BlockHash)>>,
+    }
+
+    let test_cases = [
+        TestCase {
+            name: "in_order",
+            blocks: &[(0, h!("A")), (1, h!("B")), (3, h!("D"))],
+            exp_result: Ok(()),
+        },
+        TestCase {
+            name: "with_duplicates",
+            blocks: &[(1, h!("B")), (2, h!("C")), (2, h!("C'"))],
+            exp_result: Err(Some((2, h!("C")))),
+        },
+        TestCase {
+            name: "not_in_order",
+            blocks: &[(1, h!("B")), (3, h!("D")), (2, h!("C"))],
+            exp_result: Err(Some((3, h!("D")))),
+        },
+        TestCase {
+            name: "empty",
+            blocks: &[],
+            exp_result: Err(None),
+        },
+        TestCase {
+            name: "single",
+            blocks: &[(21, h!("million"))],
+            exp_result: Ok(()),
+        },
+    ];
+
+    for (i, t) in test_cases.into_iter().enumerate() {
+        println!("running test case {}: '{}'", i, t.name);
+        let result = CheckPoint::from_block_ids(
+            t.blocks
+                .iter()
+                .map(|&(height, hash)| BlockId { height, hash }),
+        );
+        match t.exp_result {
+            Ok(_) => {
+                assert!(result.is_ok(), "[{}:{}] should be Ok", i, t.name);
+                let result_vec = {
+                    let mut v = result
+                        .unwrap()
+                        .into_iter()
+                        .map(|cp| (cp.height(), cp.hash()))
+                        .collect::<Vec<_>>();
+                    v.reverse();
+                    v
+                };
+                assert_eq!(
+                    &result_vec, t.blocks,
+                    "[{}:{}] not equal to original block ids",
+                    i, t.name
+                );
+            }
+            Err(exp_last) => {
+                assert!(result.is_err(), "[{}:{}] should be Err", i, t.name);
+                let err = result.unwrap_err();
+                assert_eq!(
+                    err.as_ref()
+                        .map(|last_cp| (last_cp.height(), last_cp.hash())),
+                    exp_last,
+                    "[{}:{}] error's last cp height should be {:?}, got {:?}",
+                    i,
+                    t.name,
+                    exp_last,
+                    err
+                );
+            }
+        }
+    }
+}
+
+#[test]
+fn checkpoint_query() {
+    struct TestCase {
+        chain: LocalChain,
+        /// The heights we want to call [`CheckPoint::query`] with, represented as an inclusive
+        /// range.
+        ///
+        /// If a [`CheckPoint`] exists at that height, we expect [`CheckPoint::query`] to return
+        /// it. If not, [`CheckPoint::query`] should return `None`.
+        query_range: (u32, u32),
+    }
+
+    let test_cases = [
+        TestCase {
+            chain: local_chain![(0, h!("_")), (1, h!("A"))],
+            query_range: (0, 2),
+        },
+        TestCase {
+            chain: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C"))],
+            query_range: (0, 3),
+        },
+    ];
+
+    for t in test_cases.into_iter() {
+        let tip = t.chain.tip();
+        for h in t.query_range.0..=t.query_range.1 {
+            let query_result = tip.get(h);
+
+            // perform an exhausitive search for the checkpoint at height `h`
+            let exp_hash = t
+                .chain
+                .iter_checkpoints()
+                .find(|cp| cp.height() == h)
+                .map(|cp| cp.hash());
+
+            match query_result {
+                Some(cp) => {
+                    assert_eq!(Some(cp.hash()), exp_hash);
+                    assert_eq!(cp.height(), h);
+                }
+                None => assert!(exp_hash.is_none()),
+            }
+        }
+    }
+}
+
+#[test]
+fn checkpoint_insert() {
+    struct TestCase<'a> {
+        /// The name of the test.
+        name: &'a str,
+        /// The original checkpoint chain to call [`CheckPoint::insert`] on.
+        chain: &'a [(u32, BlockHash)],
+        /// The `block_id` to insert.
+        to_insert: (u32, BlockHash),
+        /// The expected final checkpoint chain after calling [`CheckPoint::insert`].
+        exp_final_chain: &'a [(u32, BlockHash)],
+    }
+
+    let test_cases = [
+        TestCase {
+            name: "insert_above_tip",
+            chain: &[(1, h!("a")), (2, h!("b"))],
+            to_insert: (4, h!("d")),
+            exp_final_chain: &[(1, h!("a")), (2, h!("b")), (4, h!("d"))],
+        },
+        TestCase {
+            name: "insert_already_exists_expect_no_change",
+            chain: &[(1, h!("a")), (2, h!("b")), (3, h!("c"))],
+            to_insert: (2, h!("b")),
+            exp_final_chain: &[(1, h!("a")), (2, h!("b")), (3, h!("c"))],
+        },
+        TestCase {
+            name: "insert_in_middle",
+            chain: &[(2, h!("b")), (4, h!("d")), (5, h!("e"))],
+            to_insert: (3, h!("c")),
+            exp_final_chain: &[(2, h!("b")), (3, h!("c")), (4, h!("d")), (5, h!("e"))],
+        },
+        TestCase {
+            name: "replace_one",
+            chain: &[(3, h!("c")), (4, h!("d")), (5, h!("e"))],
+            to_insert: (5, h!("E")),
+            exp_final_chain: &[(3, h!("c")), (4, h!("d")), (5, h!("E"))],
+        },
+        TestCase {
+            name: "insert_conflict_should_evict",
+            chain: &[(3, h!("c")), (4, h!("d")), (5, h!("e")), (6, h!("f"))],
+            to_insert: (4, h!("D")),
+            exp_final_chain: &[(3, h!("c")), (4, h!("D"))],
+        },
+    ];
+
+    fn genesis_block() -> impl Iterator<Item = BlockId> {
+        core::iter::once((0, h!("_"))).map(BlockId::from)
+    }
+
+    for (i, t) in test_cases.into_iter().enumerate() {
+        println!("Running [{}] '{}'", i, t.name);
+
+        let chain = CheckPoint::from_block_ids(
+            genesis_block().chain(t.chain.iter().copied().map(BlockId::from)),
+        )
+        .expect("test formed incorrectly, must construct checkpoint chain");
+
+        let exp_final_chain = CheckPoint::from_block_ids(
+            genesis_block().chain(t.exp_final_chain.iter().copied().map(BlockId::from)),
+        )
+        .expect("test formed incorrectly, must construct checkpoint chain");
+
+        assert_eq!(
+            chain.insert(t.to_insert.into()),
+            exp_final_chain,
+            "unexpected final chain"
+        );
+    }
+}
+
+#[test]
+fn local_chain_apply_header_connected_to() {
+    fn header_from_prev_blockhash(prev_blockhash: BlockHash) -> Header {
+        Header {
+            version: bitcoin::block::Version::default(),
+            prev_blockhash,
+            merkle_root: bitcoin::hash_types::TxMerkleNode::all_zeros(),
+            time: 0,
+            bits: bitcoin::CompactTarget::default(),
+            nonce: 0,
+        }
+    }
+
+    struct TestCase {
+        name: &'static str,
+        chain: LocalChain,
+        header: Header,
+        height: u32,
+        connected_to: BlockId,
+        exp_result: Result<Vec<(u32, Option<BlockHash>)>, ApplyHeaderError>,
+    }
+
+    let test_cases = [
+        {
+            let header = header_from_prev_blockhash(h!("_"));
+            let hash = header.block_hash();
+            let height = 1;
+            let connected_to = BlockId { height, hash };
+            TestCase {
+                name: "connected_to_self_header_applied_to_self",
+                chain: local_chain![(0, h!("_")), (height, hash)],
+                header,
+                height,
+                connected_to,
+                exp_result: Ok(vec![]),
+            }
+        },
+        {
+            let prev_hash = h!("A");
+            let prev_height = 1;
+            let header = header_from_prev_blockhash(prev_hash);
+            let hash = header.block_hash();
+            let height = prev_height + 1;
+            let connected_to = BlockId {
+                height: prev_height,
+                hash: prev_hash,
+            };
+            TestCase {
+                name: "connected_to_prev_header_applied_to_self",
+                chain: local_chain![(0, h!("_")), (prev_height, prev_hash)],
+                header,
+                height,
+                connected_to,
+                exp_result: Ok(vec![(height, Some(hash))]),
+            }
+        },
+        {
+            let header = header_from_prev_blockhash(BlockHash::all_zeros());
+            let hash = header.block_hash();
+            let height = 0;
+            let connected_to = BlockId { height, hash };
+            TestCase {
+                name: "genesis_applied_to_self",
+                chain: local_chain![(0, hash)],
+                header,
+                height,
+                connected_to,
+                exp_result: Ok(vec![]),
+            }
+        },
+        {
+            let header = header_from_prev_blockhash(h!("Z"));
+            let height = 10;
+            let hash = header.block_hash();
+            let prev_height = height - 1;
+            let prev_hash = header.prev_blockhash;
+            TestCase {
+                name: "connect_at_connected_to",
+                chain: local_chain![(0, h!("_")), (2, h!("B")), (3, h!("C"))],
+                header,
+                height: 10,
+                connected_to: BlockId {
+                    height: 3,
+                    hash: h!("C"),
+                },
+                exp_result: Ok(vec![(prev_height, Some(prev_hash)), (height, Some(hash))]),
+            }
+        },
+        {
+            let prev_hash = h!("A");
+            let prev_height = 1;
+            let header = header_from_prev_blockhash(prev_hash);
+            let connected_to = BlockId {
+                height: prev_height,
+                hash: h!("not_prev_hash"),
+            };
+            TestCase {
+                name: "inconsistent_prev_hash",
+                chain: local_chain![(0, h!("_")), (prev_height, h!("not_prev_hash"))],
+                header,
+                height: prev_height + 1,
+                connected_to,
+                exp_result: Err(ApplyHeaderError::InconsistentBlocks),
+            }
+        },
+        {
+            let prev_hash = h!("A");
+            let prev_height = 1;
+            let header = header_from_prev_blockhash(prev_hash);
+            let height = prev_height + 1;
+            let connected_to = BlockId {
+                height,
+                hash: h!("not_current_hash"),
+            };
+            TestCase {
+                name: "inconsistent_current_block",
+                chain: local_chain![(0, h!("_")), (height, h!("not_current_hash"))],
+                header,
+                height,
+                connected_to,
+                exp_result: Err(ApplyHeaderError::InconsistentBlocks),
+            }
+        },
+        {
+            let header = header_from_prev_blockhash(h!("B"));
+            let height = 3;
+            let connected_to = BlockId {
+                height: 4,
+                hash: h!("D"),
+            };
+            TestCase {
+                name: "connected_to_is_greater",
+                chain: local_chain![(0, h!("_")), (2, h!("B"))],
+                header,
+                height,
+                connected_to,
+                exp_result: Err(ApplyHeaderError::InconsistentBlocks),
+            }
+        },
+    ];
+
+    for (i, t) in test_cases.into_iter().enumerate() {
+        println!("running test case {}: '{}'", i, t.name);
+        let mut chain = t.chain;
+        let result = chain.apply_header_connected_to(&t.header, t.height, t.connected_to);
+        let exp_result = t
+            .exp_result
+            .map(|cs| cs.iter().cloned().collect::<ChangeSet>());
+        assert_eq!(result, exp_result, "[{}:{}] unexpected result", i, t.name);
+    }
+}
+
+fn generate_height_range_bounds(
+    height_upper_bound: u32,
+) -> impl Strategy<Value = (Bound<u32>, Bound<u32>)> {
+    fn generate_height_bound(height_upper_bound: u32) -> impl Strategy<Value = Bound<u32>> {
+        prop_oneof![
+            (0..height_upper_bound).prop_map(Bound::Included),
+            (0..height_upper_bound).prop_map(Bound::Excluded),
+            Just(Bound::Unbounded),
+        ]
+    }
+    (
+        generate_height_bound(height_upper_bound),
+        generate_height_bound(height_upper_bound),
+    )
+}
+
+fn generate_checkpoints(max_height: u32, max_count: usize) -> impl Strategy<Value = CheckPoint> {
+    proptest::collection::btree_set(1..max_height, 0..max_count).prop_map(|mut heights| {
+        heights.insert(0); // must have genesis
+        CheckPoint::from_block_ids(heights.into_iter().map(|height| {
+            let hash = bitcoin::hashes::Hash::hash(height.to_le_bytes().as_slice());
+            BlockId { height, hash }
+        }))
+        .expect("blocks must be in order as it comes from btreeset")
+    })
+}
+
+proptest! {
+    #![proptest_config(ProptestConfig {
+        ..Default::default()
+    })]
+
+    /// Ensure that [`CheckPoint::range`] returns the expected checkpoint heights by comparing it
+    /// against a more primitive approach.
+    #[test]
+    fn checkpoint_range(
+        range in generate_height_range_bounds(21_000),
+        cp in generate_checkpoints(21_000, 2100)
+    ) {
+        let exp_heights = cp.iter().map(|cp| cp.height()).filter(|h| range.contains(h)).collect::<Vec<u32>>();
+        let heights = cp.range(range).map(|cp| cp.height()).collect::<Vec<u32>>();
+        prop_assert_eq!(heights, exp_heights);
+    }
+}

crates/chain/tests/test_spk_txout_index.rs

@@ -0,0 +1,124 @@
+use bdk_chain::{spk_txout::SpkTxOutIndex, Indexer};
+use bitcoin::{
+    absolute, transaction, Amount, OutPoint, ScriptBuf, SignedAmount, Transaction, TxIn, TxOut,
+};
+
+#[test]
+fn spk_txout_sent_and_received() {
+    let spk1 = ScriptBuf::from_hex("001404f1e52ce2bab3423c6a8c63b7cd730d8f12542c").unwrap();
+    let spk2 = ScriptBuf::from_hex("00142b57404ae14f08c3a0c903feb2af7830605eb00f").unwrap();
+
+    let mut index = SpkTxOutIndex::default();
+    index.insert_spk(0, spk1.clone());
+    index.insert_spk(1, spk2.clone());
+
+    let tx1 = Transaction {
+        version: transaction::Version::TWO,
+        lock_time: absolute::LockTime::ZERO,
+        input: vec![],
+        output: vec![TxOut {
+            value: Amount::from_sat(42_000),
+            script_pubkey: spk1.clone(),
+        }],
+    };
+
+    assert_eq!(
+        index.sent_and_received(&tx1, ..),
+        (Amount::from_sat(0), Amount::from_sat(42_000))
+    );
+    assert_eq!(
+        index.sent_and_received(&tx1, ..1),
+        (Amount::from_sat(0), Amount::from_sat(42_000))
+    );
+    assert_eq!(
+        index.sent_and_received(&tx1, 1..),
+        (Amount::from_sat(0), Amount::from_sat(0))
+    );
+    assert_eq!(index.net_value(&tx1, ..), SignedAmount::from_sat(42_000));
+    index.index_tx(&tx1);
+    assert_eq!(
+        index.sent_and_received(&tx1, ..),
+        (Amount::from_sat(0), Amount::from_sat(42_000)),
+        "shouldn't change after scanning"
+    );
+
+    let tx2 = Transaction {
+        version: transaction::Version::ONE,
+        lock_time: absolute::LockTime::ZERO,
+        input: vec![TxIn {
+            previous_output: OutPoint {
+                txid: tx1.compute_txid(),
+                vout: 0,
+            },
+            ..Default::default()
+        }],
+        output: vec![
+            TxOut {
+                value: Amount::from_sat(20_000),
+                script_pubkey: spk2,
+            },
+            TxOut {
+                script_pubkey: spk1,
+                value: Amount::from_sat(30_000),
+            },
+        ],
+    };
+
+    assert_eq!(
+        index.sent_and_received(&tx2, ..),
+        (Amount::from_sat(42_000), Amount::from_sat(50_000))
+    );
+    assert_eq!(
+        index.sent_and_received(&tx2, ..1),
+        (Amount::from_sat(42_000), Amount::from_sat(30_000))
+    );
+    assert_eq!(
+        index.sent_and_received(&tx2, 1..),
+        (Amount::from_sat(0), Amount::from_sat(20_000))
+    );
+    assert_eq!(index.net_value(&tx2, ..), SignedAmount::from_sat(8_000));
+}
+
+#[test]
+fn mark_used() {
+    let spk1 = ScriptBuf::from_hex("001404f1e52ce2bab3423c6a8c63b7cd730d8f12542c").unwrap();
+    let spk2 = ScriptBuf::from_hex("00142b57404ae14f08c3a0c903feb2af7830605eb00f").unwrap();
+
+    let mut spk_index = SpkTxOutIndex::default();
+    spk_index.insert_spk(1, spk1.clone());
+    spk_index.insert_spk(2, spk2);
+
+    assert!(!spk_index.is_used(&1));
+    spk_index.mark_used(&1);
+    assert!(spk_index.is_used(&1));
+    spk_index.unmark_used(&1);
+    assert!(!spk_index.is_used(&1));
+    spk_index.mark_used(&1);
+    assert!(spk_index.is_used(&1));
+
+    let tx1 = Transaction {
+        version: transaction::Version::TWO,
+        lock_time: absolute::LockTime::ZERO,
+        input: vec![],
+        output: vec![TxOut {
+            value: Amount::from_sat(42_000),
+            script_pubkey: spk1,
+        }],
+    };
+
+    spk_index.index_tx(&tx1);
+    spk_index.unmark_used(&1);
+    assert!(
+        spk_index.is_used(&1),
+        "even though we unmark_used it doesn't matter because there was a tx scanned that used it"
+    );
+}
+
+#[test]
+fn unmark_used_does_not_result_in_invalid_representation() {
+    let mut spk_index = SpkTxOutIndex::default();
+    assert!(!spk_index.unmark_used(&0));
+    assert!(!spk_index.unmark_used(&1));
+    assert!(!spk_index.unmark_used(&2));
+    assert!(spk_index.unused_spks(..).collect::<Vec<_>>().is_empty());
+}

crates/chain/tests/test_tx_graph_conflicts.rs

@@ -0,0 +1,670 @@
+#![cfg(feature = "miniscript")]
+
+#[macro_use]
+mod common;
+
+use std::collections::{BTreeSet, HashSet};
+
+use bdk_chain::{Balance, BlockId};
+use bitcoin::{Amount, OutPoint, ScriptBuf};
+use common::*;
+
+#[allow(dead_code)]
+struct Scenario<'a> {
+    /// Name of the test scenario
+    name: &'a str,
+    /// Transaction templates
+    tx_templates: &'a [TxTemplate<'a, BlockId>],
+    /// Names of txs that must exist in the output of `list_canonical_txs`
+    exp_chain_txs: HashSet<&'a str>,
+    /// Outpoints that must exist in the output of `filter_chain_txouts`
+    exp_chain_txouts: HashSet<(&'a str, u32)>,
+    /// Outpoints of UTXOs that must exist in the output of `filter_chain_unspents`
+    exp_unspents: HashSet<(&'a str, u32)>,
+    /// Expected balances
+    exp_balance: Balance,
+}
+
+/// This test ensures that [`TxGraph`] will reliably filter out irrelevant transactions when
+/// presented with multiple conflicting transaction scenarios using the [`TxTemplate`] structure.
+/// This test also checks that [`TxGraph::list_canonical_txs`], [`TxGraph::filter_chain_txouts`],
+/// [`TxGraph::filter_chain_unspents`], and [`TxGraph::balance`] return correct data.
+#[test]
+fn test_tx_conflict_handling() {
+    // Create Local chains
+    let local_chain = local_chain!(
+        (0, h!("A")),
+        (1, h!("B")),
+        (2, h!("C")),
+        (3, h!("D")),
+        (4, h!("E")),
+        (5, h!("F")),
+        (6, h!("G"))
+    );
+    let chain_tip = local_chain.tip().block_id();
+
+    let scenarios = [
+        Scenario {
+            name: "coinbase tx cannot be in mempool and be unconfirmed",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "unconfirmed_coinbase",
+                    inputs: &[TxInTemplate::Coinbase],
+                    outputs: &[TxOutTemplate::new(5000, Some(0))],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "confirmed_genesis",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(1))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "unconfirmed_conflict",
+                    inputs: &[
+                        TxInTemplate::PrevTx("confirmed_genesis", 0), 
+                        TxInTemplate::PrevTx("unconfirmed_coinbase", 0)
+                    ],
+                    outputs: &[TxOutTemplate::new(20000, Some(2))],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "confirmed_conflict",
+                    inputs: &[TxInTemplate::PrevTx("confirmed_genesis", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(3))],
+                    anchors: &[block_id!(4, "E")],
+                    ..Default::default()
+                },
+            ],
+            exp_chain_txs: HashSet::from(["confirmed_genesis", "confirmed_conflict"]),
+            exp_chain_txouts: HashSet::from([("confirmed_genesis", 0), ("confirmed_conflict", 0)]),
+            exp_unspents: HashSet::from([("confirmed_conflict", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::ZERO,
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::from_sat(20000),
+            },
+        },
+        Scenario {
+            name: "2 unconfirmed txs with same last_seens conflict",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "tx1",
+                    outputs: &[TxOutTemplate::new(40000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_1",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(2))],
+                    last_seen: Some(300),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_2",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(3))],
+                    last_seen: Some(300),
+                    ..Default::default()
+                },
+            ],
+            // the txgraph is going to pick tx_conflict_2 because of higher lexicographical txid
+            exp_chain_txs: HashSet::from(["tx1", "tx_conflict_2"]),
+            exp_chain_txouts: HashSet::from([("tx1", 0), ("tx_conflict_2", 0)]),
+            exp_unspents: HashSet::from([("tx_conflict_2", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(30000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "2 unconfirmed txs with different last_seens conflict",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "tx1",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0)), TxOutTemplate::new(10000, Some(1))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_1",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(2))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_2",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0),  TxInTemplate::PrevTx("tx1", 1)],
+                    outputs: &[TxOutTemplate::new(30000, Some(3))],
+                    last_seen: Some(300),
+                    ..Default::default()
+                },
+            ],
+            exp_chain_txs: HashSet::from(["tx1", "tx_conflict_2"]),
+            exp_chain_txouts: HashSet::from([("tx1", 0), ("tx1", 1), ("tx_conflict_2", 0)]),
+            exp_unspents: HashSet::from([("tx_conflict_2", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(30000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "3 unconfirmed txs with different last_seens conflict",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "tx1",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_1",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_2",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(2))],
+                    last_seen: Some(300),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_3",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(40000, Some(3))],
+                    last_seen: Some(400),
+                    ..Default::default()
+                },
+            ],
+            exp_chain_txs: HashSet::from(["tx1", "tx_conflict_3"]),
+            exp_chain_txouts: HashSet::from([("tx1", 0), ("tx_conflict_3", 0)]),
+            exp_unspents: HashSet::from([("tx_conflict_3", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(40000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "unconfirmed tx conflicts with tx in orphaned block, orphaned higher last_seen",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "tx1",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_1",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_orphaned_conflict",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(2))],
+                    anchors: &[block_id!(4, "Orphaned Block")],
+                    last_seen: Some(300),
+                },
+            ],
+            exp_chain_txs: HashSet::from(["tx1", "tx_orphaned_conflict"]),
+            exp_chain_txouts: HashSet::from([("tx1", 0), ("tx_orphaned_conflict", 0)]),
+            exp_unspents: HashSet::from([("tx_orphaned_conflict", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(30000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "unconfirmed tx conflicts with tx in orphaned block, orphaned lower last_seen",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "tx1",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_1",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_orphaned_conflict",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(2))],
+                    anchors: &[block_id!(4, "Orphaned Block")],
+                    last_seen: Some(100),
+                },
+            ],
+            exp_chain_txs: HashSet::from(["tx1", "tx_conflict_1"]),
+            exp_chain_txouts: HashSet::from([("tx1", 0), ("tx_conflict_1", 0)]),
+            exp_unspents: HashSet::from([("tx_conflict_1", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(20000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "multiple unconfirmed txs conflict with a confirmed tx",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "tx1",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_1",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_2",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(2))],
+                    last_seen: Some(300),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_conflict_3",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(40000, Some(3))],
+                    last_seen: Some(400),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "tx_confirmed_conflict",
+                    inputs: &[TxInTemplate::PrevTx("tx1", 0)],
+                    outputs: &[TxOutTemplate::new(50000, Some(4))],
+                    anchors: &[block_id!(1, "B")],
+                    ..Default::default()
+                },
+            ],
+            exp_chain_txs: HashSet::from(["tx1", "tx_confirmed_conflict"]),
+            exp_chain_txouts: HashSet::from([("tx1", 0), ("tx_confirmed_conflict", 0)]),
+            exp_unspents: HashSet::from([("tx_confirmed_conflict", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::ZERO,
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::from_sat(50000),
+            },
+        },
+        Scenario {
+            name: "B and B' spend A and conflict, C spends B, all the transactions are unconfirmed, B' has higher last_seen than B",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "A",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    last_seen: Some(22),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "B",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(23),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "B'",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(2))],
+                    last_seen: Some(24),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "C",
+                    inputs: &[TxInTemplate::PrevTx("B", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(3))],
+                    last_seen: Some(25),
+                    ..Default::default()
+                },
+            ],
+            // A, B, C will appear in the list methods
+            // This is because B' has a higher last seen than B, but C has a higher
+            // last seen than B', so B and C are considered canonical
+            exp_chain_txs: HashSet::from(["A", "B", "C"]),
+            exp_chain_txouts: HashSet::from([("A", 0), ("B", 0), ("C", 0)]),
+            exp_unspents: HashSet::from([("C", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(30000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "B and B' spend A and conflict, C spends B, A and B' are in best chain",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "A",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "B",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "B'",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(2))],
+                    anchors: &[block_id!(4, "E")],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "C",
+                    inputs: &[TxInTemplate::PrevTx("B", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(3))],
+                    ..Default::default()
+                },
+            ],
+            // B and C should not appear in the list methods
+            exp_chain_txs: HashSet::from(["A", "B'"]),
+            exp_chain_txouts: HashSet::from([("A", 0), ("B'", 0)]),
+            exp_unspents: HashSet::from([("B'", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::ZERO,
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::from_sat(20000),
+            },
+        },
+        Scenario {
+            name: "B and B' spend A and conflict, C spends B', A and B' are in best chain",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "A",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "B",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "B'",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(2))],
+                    anchors: &[block_id!(4, "E")],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "C",
+                    inputs: &[TxInTemplate::PrevTx("B'", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(3))],
+                    ..Default::default()
+                },
+            ],
+            // B should not appear in the list methods
+            exp_chain_txs: HashSet::from(["A", "B'", "C"]),
+            exp_chain_txouts: HashSet::from([
+                ("A", 0),
+                ("B'", 0),
+                ("C", 0),
+            ]),
+            exp_unspents: HashSet::from([("C", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(30000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "B and B' spend A and conflict, C spends both B and B', A is in best chain",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "A",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "B",
+                    inputs: &[TxInTemplate::PrevTx("A", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "B'",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(30000, Some(2))],
+                    last_seen: Some(300),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "C",
+                    inputs: &[
+                        TxInTemplate::PrevTx("B", 0),
+                        TxInTemplate::PrevTx("B'", 0),
+                    ],
+                    outputs: &[TxOutTemplate::new(20000, Some(3))],
+                    ..Default::default()
+                },
+            ],
+            // C should not appear in the list methods
+            exp_chain_txs: HashSet::from(["A", "B'"]),
+            exp_chain_txouts: HashSet::from([("A", 0), ("B'", 0)]),
+            exp_unspents: HashSet::from([("B'", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::from_sat(30000),
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::ZERO,
+            },
+        },
+        Scenario {
+            name: "B and B' spend A and conflict, B' is confirmed, C spends both B and B', A is in best chain",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "A",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "B",
+                    inputs: &[TxInTemplate::PrevTx("A", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "B'",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(50000, Some(4))],
+                    anchors: &[block_id!(1, "B")],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "C",
+                    inputs: &[
+                        TxInTemplate::PrevTx("B", 0),
+                        TxInTemplate::PrevTx("B'", 0),
+                    ],
+                    outputs: &[TxOutTemplate::new(20000, Some(5))],
+                    ..Default::default()
+                },
+            ],
+            // C should not appear in the list methods
+            exp_chain_txs: HashSet::from(["A", "B'"]),
+            exp_chain_txouts: HashSet::from([("A", 0), ("B'", 0)]),
+            exp_unspents: HashSet::from([("B'", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::ZERO,
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::from_sat(50000),
+            },
+        },
+        Scenario {
+            name: "B and B' spend A and conflict, B' is confirmed, C spends both B and B', D spends C, A is in best chain",
+            tx_templates: &[
+                TxTemplate {
+                    tx_name: "A",
+                    inputs: &[TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(10000, Some(0))],
+                    anchors: &[block_id!(1, "B")],
+                    last_seen: None,
+                },
+                TxTemplate {
+                    tx_name: "B",
+                    inputs: &[TxInTemplate::PrevTx("A", 0), TxInTemplate::Bogus],
+                    outputs: &[TxOutTemplate::new(20000, Some(1))],
+                    last_seen: Some(200),
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "B'",
+                    inputs: &[TxInTemplate::PrevTx("A", 0)],
+                    outputs: &[TxOutTemplate::new(50000, Some(4))],
+                    anchors: &[block_id!(1, "B")],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "C",
+                    inputs: &[
+                        TxInTemplate::PrevTx("B", 0),
+                        TxInTemplate::PrevTx("B'", 0),
+                    ],
+                    outputs: &[TxOutTemplate::new(20000, Some(5))],
+                    ..Default::default()
+                },
+                TxTemplate {
+                    tx_name: "D",
+                    inputs: &[TxInTemplate::PrevTx("C", 0)],
+                    outputs: &[TxOutTemplate::new(20000, Some(6))],
+                    ..Default::default()
+                },
+            ],
+            // D should not appear in the list methods
+            exp_chain_txs: HashSet::from(["A", "B'"]),
+            exp_chain_txouts: HashSet::from([("A", 0), ("B'", 0)]),
+            exp_unspents: HashSet::from([("B'", 0)]),
+            exp_balance: Balance {
+                immature: Amount::ZERO,
+                trusted_pending: Amount::ZERO,
+                untrusted_pending: Amount::ZERO,
+                confirmed: Amount::from_sat(50000),
+            },
+        },
+    ];
+
+    for scenario in scenarios {
+        let (tx_graph, spk_index, exp_tx_ids) = init_graph(scenario.tx_templates.iter());
+
+        let txs = tx_graph
+            .list_canonical_txs(&local_chain, chain_tip)
+            .map(|tx| tx.tx_node.txid)
+            .collect::<BTreeSet<_>>();
+        let exp_txs = scenario
+            .exp_chain_txs
+            .iter()
+            .map(|txid| *exp_tx_ids.get(txid).expect("txid must exist"))
+            .collect::<BTreeSet<_>>();
+        assert_eq!(
+            txs, exp_txs,
+            "\n[{}] 'list_canonical_txs' failed",
+            scenario.name
+        );
+
+        let txouts = tx_graph
+            .filter_chain_txouts(
+                &local_chain,
+                chain_tip,
+                spk_index.outpoints().iter().cloned(),
+            )
+            .map(|(_, full_txout)| full_txout.outpoint)
+            .collect::<BTreeSet<_>>();
+        let exp_txouts = scenario
+            .exp_chain_txouts
+            .iter()
+            .map(|(txid, vout)| OutPoint {
+                txid: *exp_tx_ids.get(txid).expect("txid must exist"),
+                vout: *vout,
+            })
+            .collect::<BTreeSet<_>>();
+        assert_eq!(
+            txouts, exp_txouts,
+            "\n[{}] 'filter_chain_txouts' failed",
+            scenario.name
+        );
+
+        let utxos = tx_graph
+            .filter_chain_unspents(
+                &local_chain,
+                chain_tip,
+                spk_index.outpoints().iter().cloned(),
+            )
+            .map(|(_, full_txout)| full_txout.outpoint)
+            .collect::<BTreeSet<_>>();
+        let exp_utxos = scenario
+            .exp_unspents
+            .iter()
+            .map(|(txid, vout)| OutPoint {
+                txid: *exp_tx_ids.get(txid).expect("txid must exist"),
+                vout: *vout,
+            })
+            .collect::<BTreeSet<_>>();
+        assert_eq!(
+            utxos, exp_utxos,
+            "\n[{}] 'filter_chain_unspents' failed",
+            scenario.name
+        );
+
+        let balance = tx_graph.balance(
+            &local_chain,
+            chain_tip,
+            spk_index.outpoints().iter().cloned(),
+            |_, spk: ScriptBuf| spk_index.index_of_spk(spk).is_some(),
+        );
+        assert_eq!(
+            balance, scenario.exp_balance,
+            "\n[{}] 'balance' failed",
+            scenario.name
+        );
+    }
+}

crates/electrum/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "bdk_electrum"
+version = "0.16.0"
+edition = "2021"
+homepage = "https://bitcoindevkit.org"
+repository = "https://github.com/bitcoindevkit/bdk"
+documentation = "https://docs.rs/bdk_electrum"
+description = "Fetch data from electrum in the form BDK accepts"
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bdk_chain = { path = "../chain", version = "0.17.0" }
+electrum-client = { version = "0.20" }
+#rustls = { version = "=0.21.1", optional = true, features = ["dangerous_configuration"] }
+
+[dev-dependencies]
+bdk_testenv = { path = "../testenv", default-features = false }

crates/electrum/README.md

@@ -0,0 +1,7 @@
+# BDK Electrum
+
+BDK Electrum extends [`electrum-client`] to update [`bdk_chain`] structures
+from an Electrum server.
+
+[`electrum-client`]: https://docs.rs/electrum-client/
+[`bdk_chain`]: https://docs.rs/bdk-chain/

crates/electrum/src/bdk_electrum_client.rs

@@ -0,0 +1,491 @@
+use bdk_chain::{
+    bitcoin::{block::Header, BlockHash, OutPoint, ScriptBuf, Transaction, Txid},
+    collections::{BTreeMap, HashMap},
+    local_chain::CheckPoint,
+    spk_client::{FullScanRequest, FullScanResult, SyncRequest, SyncResult},
+    tx_graph::TxGraph,
+    Anchor, BlockId, ConfirmationBlockTime,
+};
+use electrum_client::{ElectrumApi, Error, HeaderNotification};
+use std::{
+    collections::BTreeSet,
+    sync::{Arc, Mutex},
+};
+
+/// We include a chain suffix of a certain length for the purpose of robustness.
+const CHAIN_SUFFIX_LENGTH: u32 = 8;
+
+/// Wrapper around an [`electrum_client::ElectrumApi`] which includes an internal in-memory
+/// transaction cache to avoid re-fetching already downloaded transactions.
+#[derive(Debug)]
+pub struct BdkElectrumClient<E> {
+    /// The internal [`electrum_client::ElectrumApi`]
+    pub inner: E,
+    /// The transaction cache
+    tx_cache: Mutex<HashMap<Txid, Arc<Transaction>>>,
+    /// The header cache
+    block_header_cache: Mutex<HashMap<u32, Header>>,
+}
+
+impl<E: ElectrumApi> BdkElectrumClient<E> {
+    /// Creates a new bdk client from a [`electrum_client::ElectrumApi`]
+    pub fn new(client: E) -> Self {
+        Self {
+            inner: client,
+            tx_cache: Default::default(),
+            block_header_cache: Default::default(),
+        }
+    }
+
+    /// Inserts transactions into the transaction cache so that the client will not fetch these
+    /// transactions.
+    pub fn populate_tx_cache<A>(&self, tx_graph: impl AsRef<TxGraph<A>>) {
+        let txs = tx_graph
+            .as_ref()
+            .full_txs()
+            .map(|tx_node| (tx_node.txid, tx_node.tx));
+
+        let mut tx_cache = self.tx_cache.lock().unwrap();
+        for (txid, tx) in txs {
+            tx_cache.insert(txid, tx);
+        }
+    }
+
+    /// Fetch transaction of given `txid`.
+    ///
+    /// If it hits the cache it will return the cached version and avoid making the request.
+    pub fn fetch_tx(&self, txid: Txid) -> Result<Arc<Transaction>, Error> {
+        let tx_cache = self.tx_cache.lock().unwrap();
+
+        if let Some(tx) = tx_cache.get(&txid) {
+            return Ok(Arc::clone(tx));
+        }
+
+        drop(tx_cache);
+
+        let tx = Arc::new(self.inner.transaction_get(&txid)?);
+
+        self.tx_cache.lock().unwrap().insert(txid, Arc::clone(&tx));
+
+        Ok(tx)
+    }
+
+    /// Fetch block header of given `height`.
+    ///
+    /// If it hits the cache it will return the cached version and avoid making the request.
+    fn fetch_header(&self, height: u32) -> Result<Header, Error> {
+        let block_header_cache = self.block_header_cache.lock().unwrap();
+
+        if let Some(header) = block_header_cache.get(&height) {
+            return Ok(*header);
+        }
+
+        drop(block_header_cache);
+
+        self.update_header(height)
+    }
+
+    /// Update a block header at given `height`. Returns the updated header.
+    fn update_header(&self, height: u32) -> Result<Header, Error> {
+        let header = self.inner.block_header(height as usize)?;
+
+        self.block_header_cache
+            .lock()
+            .unwrap()
+            .insert(height, header);
+
+        Ok(header)
+    }
+
+    /// Broadcasts a transaction to the network.
+    ///
+    /// This is a re-export of [`ElectrumApi::transaction_broadcast`].
+    pub fn transaction_broadcast(&self, tx: &Transaction) -> Result<Txid, Error> {
+        self.inner.transaction_broadcast(tx)
+    }
+
+    /// Full scan the keychain scripts specified with the blockchain (via an Electrum client) and
+    /// returns updates for [`bdk_chain`] data structures.
+    ///
+    /// - `request`: struct with data required to perform a spk-based blockchain client full scan,
+    ///              see [`FullScanRequest`]
+    /// - `stop_gap`: the full scan for each keychain stops after a gap of script pubkeys with no
+    ///              associated transactions
+    /// - `batch_size`: specifies the max number of script pubkeys to request for in a single batch
+    ///              request
+    /// - `fetch_prev_txouts`: specifies whether or not we want previous `TxOut`s for fee
+    pub fn full_scan<K: Ord + Clone>(
+        &self,
+        request: FullScanRequest<K>,
+        stop_gap: usize,
+        batch_size: usize,
+        fetch_prev_txouts: bool,
+    ) -> Result<FullScanResult<K>, Error> {
+        let (tip, latest_blocks) =
+            fetch_tip_and_latest_blocks(&self.inner, request.chain_tip.clone())?;
+        let mut graph_update = TxGraph::<ConfirmationBlockTime>::default();
+        let mut last_active_indices = BTreeMap::<K, u32>::new();
+
+        for (keychain, spks) in request.spks_by_keychain {
+            if let Some(last_active_index) =
+                self.populate_with_spks(&mut graph_update, spks, stop_gap, batch_size)?
+            {
+                last_active_indices.insert(keychain, last_active_index);
+            }
+        }
+
+        let chain_update = chain_update(tip, &latest_blocks, graph_update.all_anchors())?;
+
+        // Fetch previous `TxOut`s for fee calculation if flag is enabled.
+        if fetch_prev_txouts {
+            self.fetch_prev_txout(&mut graph_update)?;
+        }
+
+        Ok(FullScanResult {
+            graph_update,
+            chain_update,
+            last_active_indices,
+        })
+    }
+
+    /// Sync a set of scripts with the blockchain (via an Electrum client) for the data specified
+    /// and returns updates for [`bdk_chain`] data structures.
+    ///
+    /// - `request`: struct with data required to perform a spk-based blockchain client sync,
+    ///              see [`SyncRequest`]
+    /// - `batch_size`: specifies the max number of script pubkeys to request for in a single batch
+    ///              request
+    /// - `fetch_prev_txouts`: specifies whether or not we want previous `TxOut`s for fee
+    ///              calculation
+    ///
+    /// If the scripts to sync are unknown, such as when restoring or importing a keychain that
+    /// may include scripts that have been used, use [`full_scan`] with the keychain.
+    ///
+    /// [`full_scan`]: Self::full_scan
+    pub fn sync(
+        &self,
+        request: SyncRequest,
+        batch_size: usize,
+        fetch_prev_txouts: bool,
+    ) -> Result<SyncResult, Error> {
+        let full_scan_req = FullScanRequest::from_chain_tip(request.chain_tip.clone())
+            .set_spks_for_keychain((), request.spks.enumerate().map(|(i, spk)| (i as u32, spk)));
+        let mut full_scan_res = self.full_scan(full_scan_req, usize::MAX, batch_size, false)?;
+        let (tip, latest_blocks) =
+            fetch_tip_and_latest_blocks(&self.inner, request.chain_tip.clone())?;
+
+        self.populate_with_txids(&mut full_scan_res.graph_update, request.txids)?;
+        self.populate_with_outpoints(&mut full_scan_res.graph_update, request.outpoints)?;
+
+        let chain_update = chain_update(
+            tip,
+            &latest_blocks,
+            full_scan_res.graph_update.all_anchors(),
+        )?;
+
+        // Fetch previous `TxOut`s for fee calculation if flag is enabled.
+        if fetch_prev_txouts {
+            self.fetch_prev_txout(&mut full_scan_res.graph_update)?;
+        }
+
+        Ok(SyncResult {
+            chain_update,
+            graph_update: full_scan_res.graph_update,
+        })
+    }
+
+    /// Populate the `graph_update` with transactions/anchors associated with the given `spks`.
+    ///
+    /// Transactions that contains an output with requested spk, or spends form an output with
+    /// requested spk will be added to `graph_update`. Anchors of the aforementioned transactions are
+    /// also included.
+    fn populate_with_spks(
+        &self,
+        graph_update: &mut TxGraph<ConfirmationBlockTime>,
+        mut spks: impl Iterator<Item = (u32, ScriptBuf)>,
+        stop_gap: usize,
+        batch_size: usize,
+    ) -> Result<Option<u32>, Error> {
+        let mut unused_spk_count = 0_usize;
+        let mut last_active_index = Option::<u32>::None;
+
+        loop {
+            let spks = (0..batch_size)
+                .map_while(|_| spks.next())
+                .collect::<Vec<_>>();
+            if spks.is_empty() {
+                return Ok(last_active_index);
+            }
+
+            let spk_histories = self
+                .inner
+                .batch_script_get_history(spks.iter().map(|(_, s)| s.as_script()))?;
+
+            for ((spk_index, _spk), spk_history) in spks.into_iter().zip(spk_histories) {
+                if spk_history.is_empty() {
+                    unused_spk_count = unused_spk_count.saturating_add(1);
+                    if unused_spk_count >= stop_gap {
+                        return Ok(last_active_index);
+                    }
+                    continue;
+                } else {
+                    last_active_index = Some(spk_index);
+                    unused_spk_count = 0;
+                }
+
+                for tx_res in spk_history {
+                    let _ = graph_update.insert_tx(self.fetch_tx(tx_res.tx_hash)?);
+                    self.validate_merkle_for_anchor(graph_update, tx_res.tx_hash, tx_res.height)?;
+                }
+            }
+        }
+    }
+
+    /// Populate the `graph_update` with associated transactions/anchors of `outpoints`.
+    ///
+    /// Transactions in which the outpoint resides, and transactions that spend from the outpoint are
+    /// included. Anchors of the aforementioned transactions are included.
+    fn populate_with_outpoints(
+        &self,
+        graph_update: &mut TxGraph<ConfirmationBlockTime>,
+        outpoints: impl IntoIterator<Item = OutPoint>,
+    ) -> Result<(), Error> {
+        for outpoint in outpoints {
+            let op_txid = outpoint.txid;
+            let op_tx = self.fetch_tx(op_txid)?;
+            let op_txout = match op_tx.output.get(outpoint.vout as usize) {
+                Some(txout) => txout,
+                None => continue,
+            };
+            debug_assert_eq!(op_tx.compute_txid(), op_txid);
+
+            // attempt to find the following transactions (alongside their chain positions), and
+            // add to our sparsechain `update`:
+            let mut has_residing = false; // tx in which the outpoint resides
+            let mut has_spending = false; // tx that spends the outpoint
+            for res in self.inner.script_get_history(&op_txout.script_pubkey)? {
+                if has_residing && has_spending {
+                    break;
+                }
+
+                if !has_residing && res.tx_hash == op_txid {
+                    has_residing = true;
+                    let _ = graph_update.insert_tx(Arc::clone(&op_tx));
+                    self.validate_merkle_for_anchor(graph_update, res.tx_hash, res.height)?;
+                }
+
+                if !has_spending && res.tx_hash != op_txid {
+                    let res_tx = self.fetch_tx(res.tx_hash)?;
+                    // we exclude txs/anchors that do not spend our specified outpoint(s)
+                    has_spending = res_tx
+                        .input
+                        .iter()
+                        .any(|txin| txin.previous_output == outpoint);
+                    if !has_spending {
+                        continue;
+                    }
+                    let _ = graph_update.insert_tx(Arc::clone(&res_tx));
+                    self.validate_merkle_for_anchor(graph_update, res.tx_hash, res.height)?;
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Populate the `graph_update` with transactions/anchors of the provided `txids`.
+    fn populate_with_txids(
+        &self,
+        graph_update: &mut TxGraph<ConfirmationBlockTime>,
+        txids: impl IntoIterator<Item = Txid>,
+    ) -> Result<(), Error> {
+        for txid in txids {
+            let tx = match self.fetch_tx(txid) {
+                Ok(tx) => tx,
+                Err(electrum_client::Error::Protocol(_)) => continue,
+                Err(other_err) => return Err(other_err),
+            };
+
+            let spk = tx
+                .output
+                .first()
+                .map(|txo| &txo.script_pubkey)
+                .expect("tx must have an output");
+
+            // because of restrictions of the Electrum API, we have to use the `script_get_history`
+            // call to get confirmation status of our transaction
+            if let Some(r) = self
+                .inner
+                .script_get_history(spk)?
+                .into_iter()
+                .find(|r| r.tx_hash == txid)
+            {
+                self.validate_merkle_for_anchor(graph_update, txid, r.height)?;
+            }
+
+            let _ = graph_update.insert_tx(tx);
+        }
+        Ok(())
+    }
+
+    // Helper function which checks if a transaction is confirmed by validating the merkle proof.
+    // An anchor is inserted if the transaction is validated to be in a confirmed block.
+    fn validate_merkle_for_anchor(
+        &self,
+        graph_update: &mut TxGraph<ConfirmationBlockTime>,
+        txid: Txid,
+        confirmation_height: i32,
+    ) -> Result<(), Error> {
+        if let Ok(merkle_res) = self
+            .inner
+            .transaction_get_merkle(&txid, confirmation_height as usize)
+        {
+            let mut header = self.fetch_header(merkle_res.block_height as u32)?;
+            let mut is_confirmed_tx = electrum_client::utils::validate_merkle_proof(
+                &txid,
+                &header.merkle_root,
+                &merkle_res,
+            );
+
+            // Merkle validation will fail if the header in `block_header_cache` is outdated, so we
+            // want to check if there is a new header and validate against the new one.
+            if !is_confirmed_tx {
+                header = self.update_header(merkle_res.block_height as u32)?;
+                is_confirmed_tx = electrum_client::utils::validate_merkle_proof(
+                    &txid,
+                    &header.merkle_root,
+                    &merkle_res,
+                );
+            }
+
+            if is_confirmed_tx {
+                let _ = graph_update.insert_anchor(
+                    txid,
+                    ConfirmationBlockTime {
+                        confirmation_time: header.time as u64,
+                        block_id: BlockId {
+                            height: merkle_res.block_height as u32,
+                            hash: header.block_hash(),
+                        },
+                    },
+                );
+            }
+        }
+        Ok(())
+    }
+
+    // Helper function which fetches the `TxOut`s of our relevant transactions' previous transactions,
+    // which we do not have by default. This data is needed to calculate the transaction fee.
+    fn fetch_prev_txout(
+        &self,
+        graph_update: &mut TxGraph<ConfirmationBlockTime>,
+    ) -> Result<(), Error> {
+        let full_txs: Vec<Arc<Transaction>> =
+            graph_update.full_txs().map(|tx_node| tx_node.tx).collect();
+        for tx in full_txs {
+            for vin in &tx.input {
+                let outpoint = vin.previous_output;
+                let vout = outpoint.vout;
+                let prev_tx = self.fetch_tx(outpoint.txid)?;
+                let txout = prev_tx.output[vout as usize].clone();
+                let _ = graph_update.insert_txout(outpoint, txout);
+            }
+        }
+        Ok(())
+    }
+}
+
+/// Return a [`CheckPoint`] of the latest tip, that connects with `prev_tip`. The latest blocks are
+/// fetched to construct checkpoint updates with the proper [`BlockHash`] in case of re-org.
+fn fetch_tip_and_latest_blocks(
+    client: &impl ElectrumApi,
+    prev_tip: CheckPoint,
+) -> Result<(CheckPoint, BTreeMap<u32, BlockHash>), Error> {
+    let HeaderNotification { height, .. } = client.block_headers_subscribe()?;
+    let new_tip_height = height as u32;
+
+    // If electrum returns a tip height that is lower than our previous tip, then checkpoints do
+    // not need updating. We just return the previous tip and use that as the point of agreement.
+    if new_tip_height < prev_tip.height() {
+        return Ok((prev_tip, BTreeMap::new()));
+    }
+
+    // Atomically fetch the latest `CHAIN_SUFFIX_LENGTH` count of blocks from Electrum. We use this
+    // to construct our checkpoint update.
+    let mut new_blocks = {
+        let start_height = new_tip_height.saturating_sub(CHAIN_SUFFIX_LENGTH - 1);
+        let hashes = client
+            .block_headers(start_height as _, CHAIN_SUFFIX_LENGTH as _)?
+            .headers
+            .into_iter()
+            .map(|h| h.block_hash());
+        (start_height..).zip(hashes).collect::<BTreeMap<u32, _>>()
+    };
+
+    // Find the "point of agreement" (if any).
+    let agreement_cp = {
+        let mut agreement_cp = Option::<CheckPoint>::None;
+        for cp in prev_tip.iter() {
+            let cp_block = cp.block_id();
+            let hash = match new_blocks.get(&cp_block.height) {
+                Some(&hash) => hash,
+                None => {
+                    assert!(
+                        new_tip_height >= cp_block.height,
+                        "already checked that electrum's tip cannot be smaller"
+                    );
+                    let hash = client.block_header(cp_block.height as _)?.block_hash();
+                    new_blocks.insert(cp_block.height, hash);
+                    hash
+                }
+            };
+            if hash == cp_block.hash {
+                agreement_cp = Some(cp);
+                break;
+            }
+        }
+        agreement_cp
+    };
+
+    let agreement_height = agreement_cp.as_ref().map(CheckPoint::height);
+
+    let new_tip = new_blocks
+        .iter()
+        // Prune `new_blocks` to only include blocks that are actually new.
+        .filter(|(height, _)| Some(*<&u32>::clone(height)) > agreement_height)
+        .map(|(height, hash)| BlockId {
+            height: *height,
+            hash: *hash,
+        })
+        .fold(agreement_cp, |prev_cp, block| {
+            Some(match prev_cp {
+                Some(cp) => cp.push(block).expect("must extend checkpoint"),
+                None => CheckPoint::new(block),
+            })
+        })
+        .expect("must have at least one checkpoint");
+
+    Ok((new_tip, new_blocks))
+}
+
+// Add a corresponding checkpoint per anchor height if it does not yet exist. Checkpoints should not
+// surpass `latest_blocks`.
+fn chain_update<A: Anchor>(
+    mut tip: CheckPoint,
+    latest_blocks: &BTreeMap<u32, BlockHash>,
+    anchors: &BTreeSet<(A, Txid)>,
+) -> Result<CheckPoint, Error> {
+    for anchor in anchors {
+        let height = anchor.0.anchor_block().height;
+
+        // Checkpoint uses the `BlockHash` from `latest_blocks` so that the hash will be consistent
+        // in case of a re-org.
+        if tip.get(height).is_none() && height <= tip.height() {
+            let hash = match latest_blocks.get(&height) {
+                Some(&hash) => hash,
+                None => anchor.0.anchor_block().hash,
+            };
+            tip = tip.insert(BlockId { hash, height });
+        }
+    }
+    Ok(tip)
+}

crates/electrum/src/lib.rs

@@ -0,0 +1,22 @@
+//! This crate is used for updating structures of [`bdk_chain`] with data from an Electrum server.
+//!
+//! The two primary methods are [`BdkElectrumClient::sync`] and [`BdkElectrumClient::full_scan`]. In most cases
+//! [`BdkElectrumClient::sync`] is used to sync the transaction histories of scripts that the application
+//! cares about, for example the scripts for all the receive addresses of a Wallet's keychain that it
+//! has shown a user. [`BdkElectrumClient::full_scan`] is meant to be used when importing or restoring a
+//! keychain where the range of possibly used scripts is not known. In this case it is necessary to
+//! scan all keychain scripts until a number (the "stop gap") of unused scripts is discovered. For a
+//! sync or full scan the user receives relevant blockchain data and output updates for
+//! [`bdk_chain`].
+//!
+//! Refer to [`example_electrum`] for a complete example.
+//!
+//! [`example_electrum`]: https://github.com/bitcoindevkit/bdk/tree/master/example-crates/example_electrum
+
+#![warn(missing_docs)]
+
+mod bdk_electrum_client;
+pub use bdk_electrum_client::*;
+
+pub use bdk_chain;
+pub use electrum_client;

crates/electrum/tests/test_electrum.rs

@@ -0,0 +1,437 @@
+use bdk_chain::{
+    bitcoin::{hashes::Hash, Address, Amount, ScriptBuf, Txid, WScriptHash},
+    local_chain::LocalChain,
+    spk_client::{FullScanRequest, SyncRequest},
+    spk_txout::SpkTxOutIndex,
+    Balance, ConfirmationBlockTime, IndexedTxGraph,
+};
+use bdk_electrum::BdkElectrumClient;
+use bdk_testenv::{anyhow, bitcoincore_rpc::RpcApi, TestEnv};
+use std::collections::{BTreeSet, HashSet};
+use std::str::FromStr;
+
+fn get_balance(
+    recv_chain: &LocalChain,
+    recv_graph: &IndexedTxGraph<ConfirmationBlockTime, SpkTxOutIndex<()>>,
+) -> anyhow::Result<Balance> {
+    let chain_tip = recv_chain.tip().block_id();
+    let outpoints = recv_graph.index.outpoints().clone();
+    let balance = recv_graph
+        .graph()
+        .balance(recv_chain, chain_tip, outpoints, |_, _| true);
+    Ok(balance)
+}
+
+#[test]
+pub fn test_update_tx_graph_without_keychain() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+    let electrum_client = electrum_client::Client::new(env.electrsd.electrum_url.as_str())?;
+    let client = BdkElectrumClient::new(electrum_client);
+
+    let receive_address0 =
+        Address::from_str("bcrt1qc6fweuf4xjvz4x3gx3t9e0fh4hvqyu2qw4wvxm")?.assume_checked();
+    let receive_address1 =
+        Address::from_str("bcrt1qfjg5lv3dvc9az8patec8fjddrs4aqtauadnagr")?.assume_checked();
+
+    let misc_spks = [
+        receive_address0.script_pubkey(),
+        receive_address1.script_pubkey(),
+    ];
+
+    let _block_hashes = env.mine_blocks(101, None)?;
+    let txid1 = env.bitcoind.client.send_to_address(
+        &receive_address1,
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let txid2 = env.bitcoind.client.send_to_address(
+        &receive_address0,
+        Amount::from_sat(20000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    env.mine_blocks(1, None)?;
+    env.wait_until_electrum_sees_block()?;
+
+    // use a full checkpoint linked list (since this is not what we are testing)
+    let cp_tip = env.make_checkpoint_tip();
+
+    let sync_update = {
+        let request = SyncRequest::from_chain_tip(cp_tip.clone()).set_spks(misc_spks);
+        client.sync(request, 1, true)?
+    };
+
+    assert!(
+        {
+            let update_cps = sync_update
+                .chain_update
+                .iter()
+                .map(|cp| cp.block_id())
+                .collect::<BTreeSet<_>>();
+            let superset_cps = cp_tip
+                .iter()
+                .map(|cp| cp.block_id())
+                .collect::<BTreeSet<_>>();
+            superset_cps.is_superset(&update_cps)
+        },
+        "update should not alter original checkpoint tip since we already started with all checkpoints",
+    );
+
+    let graph_update = sync_update.graph_update;
+    // Check to see if we have the floating txouts available from our two created transactions'
+    // previous outputs in order to calculate transaction fees.
+    for tx in graph_update.full_txs() {
+        // Retrieve the calculated fee from `TxGraph`, which will panic if we do not have the
+        // floating txouts available from the transactions' previous outputs.
+        let fee = graph_update.calculate_fee(&tx.tx).expect("Fee must exist");
+
+        // Retrieve the fee in the transaction data from `bitcoind`.
+        let tx_fee = env
+            .bitcoind
+            .client
+            .get_transaction(&tx.txid, None)
+            .expect("Tx must exist")
+            .fee
+            .expect("Fee must exist")
+            .abs()
+            .to_unsigned()
+            .expect("valid `Amount`");
+
+        // Check that the calculated fee matches the fee from the transaction data.
+        assert_eq!(fee, tx_fee);
+    }
+
+    let mut graph_update_txids: Vec<Txid> = graph_update.full_txs().map(|tx| tx.txid).collect();
+    graph_update_txids.sort();
+    let mut expected_txids = vec![txid1, txid2];
+    expected_txids.sort();
+    assert_eq!(graph_update_txids, expected_txids);
+
+    Ok(())
+}
+
+/// Test the bounds of the address scan depending on the `stop_gap`.
+#[test]
+pub fn test_update_tx_graph_stop_gap() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+    let electrum_client = electrum_client::Client::new(env.electrsd.electrum_url.as_str())?;
+    let client = BdkElectrumClient::new(electrum_client);
+    let _block_hashes = env.mine_blocks(101, None)?;
+
+    // Now let's test the gap limit. First of all get a chain of 10 addresses.
+    let addresses = [
+        "bcrt1qj9f7r8r3p2y0sqf4r3r62qysmkuh0fzep473d2ar7rcz64wqvhssjgf0z4",
+        "bcrt1qmm5t0ch7vh2hryx9ctq3mswexcugqe4atkpkl2tetm8merqkthas3w7q30",
+        "bcrt1qut9p7ej7l7lhyvekj28xknn8gnugtym4d5qvnp5shrsr4nksmfqsmyn87g",
+        "bcrt1qqz0xtn3m235p2k96f5wa2dqukg6shxn9n3txe8arlrhjh5p744hsd957ww",
+        "bcrt1q9c0t62a8l6wfytmf2t9lfj35avadk3mm8g4p3l84tp6rl66m48sqrme7wu",
+        "bcrt1qkmh8yrk2v47cklt8dytk8f3ammcwa4q7dzattedzfhqzvfwwgyzsg59zrh",
+        "bcrt1qvgrsrzy07gjkkfr5luplt0azxtfwmwq5t62gum5jr7zwcvep2acs8hhnp2",
+        "bcrt1qw57edarcg50ansq8mk3guyrk78rk0fwvrds5xvqeupteu848zayq549av8",
+        "bcrt1qvtve5ekf6e5kzs68knvnt2phfw6a0yjqrlgat392m6zt9jsvyxhqfx67ef",
+        "bcrt1qw03ddumfs9z0kcu76ln7jrjfdwam20qtffmkcral3qtza90sp9kqm787uk",
+    ];
+    let addresses: Vec<_> = addresses
+        .into_iter()
+        .map(|s| Address::from_str(s).unwrap().assume_checked())
+        .collect();
+    let spks: Vec<_> = addresses
+        .iter()
+        .enumerate()
+        .map(|(i, addr)| (i as u32, addr.script_pubkey()))
+        .collect();
+
+    // Then receive coins on the 4th address.
+    let txid_4th_addr = env.bitcoind.client.send_to_address(
+        &addresses[3],
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    env.mine_blocks(1, None)?;
+    env.wait_until_electrum_sees_block()?;
+
+    // use a full checkpoint linked list (since this is not what we are testing)
+    let cp_tip = env.make_checkpoint_tip();
+
+    // A scan with a stop_gap of 3 won't find the transaction, but a scan with a gap limit of 4
+    // will.
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 3, 1, false)?
+    };
+    assert!(full_scan_update.graph_update.full_txs().next().is_none());
+    assert!(full_scan_update.last_active_indices.is_empty());
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 4, 1, false)?
+    };
+    assert_eq!(
+        full_scan_update
+            .graph_update
+            .full_txs()
+            .next()
+            .unwrap()
+            .txid,
+        txid_4th_addr
+    );
+    assert_eq!(full_scan_update.last_active_indices[&0], 3);
+
+    // Now receive a coin on the last address.
+    let txid_last_addr = env.bitcoind.client.send_to_address(
+        &addresses[addresses.len() - 1],
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    env.mine_blocks(1, None)?;
+    env.wait_until_electrum_sees_block()?;
+
+    // A scan with gap limit 5 won't find the second transaction, but a scan with gap limit 6 will.
+    // The last active indice won't be updated in the first case but will in the second one.
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 5, 1, false)?
+    };
+    let txs: HashSet<_> = full_scan_update
+        .graph_update
+        .full_txs()
+        .map(|tx| tx.txid)
+        .collect();
+    assert_eq!(txs.len(), 1);
+    assert!(txs.contains(&txid_4th_addr));
+    assert_eq!(full_scan_update.last_active_indices[&0], 3);
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 6, 1, false)?
+    };
+    let txs: HashSet<_> = full_scan_update
+        .graph_update
+        .full_txs()
+        .map(|tx| tx.txid)
+        .collect();
+    assert_eq!(txs.len(), 2);
+    assert!(txs.contains(&txid_4th_addr) && txs.contains(&txid_last_addr));
+    assert_eq!(full_scan_update.last_active_indices[&0], 9);
+
+    Ok(())
+}
+
+/// Ensure that [`ElectrumExt`] can sync properly.
+///
+/// 1. Mine 101 blocks.
+/// 2. Send a tx.
+/// 3. Mine extra block to confirm sent tx.
+/// 4. Check [`Balance`] to ensure tx is confirmed.
+#[test]
+fn scan_detects_confirmed_tx() -> anyhow::Result<()> {
+    const SEND_AMOUNT: Amount = Amount::from_sat(10_000);
+
+    let env = TestEnv::new()?;
+    let electrum_client = electrum_client::Client::new(env.electrsd.electrum_url.as_str())?;
+    let client = BdkElectrumClient::new(electrum_client);
+
+    // Setup addresses.
+    let addr_to_mine = env
+        .bitcoind
+        .client
+        .get_new_address(None, None)?
+        .assume_checked();
+    let spk_to_track = ScriptBuf::new_p2wsh(&WScriptHash::all_zeros());
+    let addr_to_track = Address::from_script(&spk_to_track, bdk_chain::bitcoin::Network::Regtest)?;
+
+    // Setup receiver.
+    let (mut recv_chain, _) = LocalChain::from_genesis_hash(env.bitcoind.client.get_block_hash(0)?);
+    let mut recv_graph = IndexedTxGraph::<ConfirmationBlockTime, _>::new({
+        let mut recv_index = SpkTxOutIndex::default();
+        recv_index.insert_spk((), spk_to_track.clone());
+        recv_index
+    });
+
+    // Mine some blocks.
+    env.mine_blocks(101, Some(addr_to_mine))?;
+
+    // Create transaction that is tracked by our receiver.
+    env.send(&addr_to_track, SEND_AMOUNT)?;
+
+    // Mine a block to confirm sent tx.
+    env.mine_blocks(1, None)?;
+
+    // Sync up to tip.
+    env.wait_until_electrum_sees_block()?;
+    let update = client.sync(
+        SyncRequest::from_chain_tip(recv_chain.tip()).chain_spks(core::iter::once(spk_to_track)),
+        5,
+        true,
+    )?;
+
+    let _ = recv_chain
+        .apply_update(update.chain_update)
+        .map_err(|err| anyhow::anyhow!("LocalChain update error: {:?}", err))?;
+    let _ = recv_graph.apply_update(update.graph_update);
+
+    // Check to see if tx is confirmed.
+    assert_eq!(
+        get_balance(&recv_chain, &recv_graph)?,
+        Balance {
+            confirmed: SEND_AMOUNT,
+            ..Balance::default()
+        },
+    );
+
+    for tx in recv_graph.graph().full_txs() {
+        // Retrieve the calculated fee from `TxGraph`, which will panic if we do not have the
+        // floating txouts available from the transaction's previous outputs.
+        let fee = recv_graph
+            .graph()
+            .calculate_fee(&tx.tx)
+            .expect("fee must exist");
+
+        // Retrieve the fee in the transaction data from `bitcoind`.
+        let tx_fee = env
+            .bitcoind
+            .client
+            .get_transaction(&tx.txid, None)
+            .expect("Tx must exist")
+            .fee
+            .expect("Fee must exist")
+            .abs()
+            .to_unsigned()
+            .expect("valid `Amount`");
+
+        // Check that the calculated fee matches the fee from the transaction data.
+        assert_eq!(fee, tx_fee);
+    }
+
+    Ok(())
+}
+
+/// Ensure that confirmed txs that are reorged become unconfirmed.
+///
+/// 1. Mine 101 blocks.
+/// 2. Mine 8 blocks with a confirmed tx in each.
+/// 3. Perform 8 separate reorgs on each block with a confirmed tx.
+/// 4. Check [`Balance`] after each reorg to ensure unconfirmed amount is correct.
+#[test]
+fn tx_can_become_unconfirmed_after_reorg() -> anyhow::Result<()> {
+    const REORG_COUNT: usize = 8;
+    const SEND_AMOUNT: Amount = Amount::from_sat(10_000);
+
+    let env = TestEnv::new()?;
+    let electrum_client = electrum_client::Client::new(env.electrsd.electrum_url.as_str())?;
+    let client = BdkElectrumClient::new(electrum_client);
+
+    // Setup addresses.
+    let addr_to_mine = env
+        .bitcoind
+        .client
+        .get_new_address(None, None)?
+        .assume_checked();
+    let spk_to_track = ScriptBuf::new_p2wsh(&WScriptHash::all_zeros());
+    let addr_to_track = Address::from_script(&spk_to_track, bdk_chain::bitcoin::Network::Regtest)?;
+
+    // Setup receiver.
+    let (mut recv_chain, _) = LocalChain::from_genesis_hash(env.bitcoind.client.get_block_hash(0)?);
+    let mut recv_graph = IndexedTxGraph::<ConfirmationBlockTime, _>::new({
+        let mut recv_index = SpkTxOutIndex::default();
+        recv_index.insert_spk((), spk_to_track.clone());
+        recv_index
+    });
+
+    // Mine some blocks.
+    env.mine_blocks(101, Some(addr_to_mine))?;
+
+    // Create transactions that are tracked by our receiver.
+    let mut txids = vec![];
+    let mut hashes = vec![];
+    for _ in 0..REORG_COUNT {
+        txids.push(env.send(&addr_to_track, SEND_AMOUNT)?);
+        hashes.extend(env.mine_blocks(1, None)?);
+    }
+
+    // Sync up to tip.
+    env.wait_until_electrum_sees_block()?;
+    let update = client.sync(
+        SyncRequest::from_chain_tip(recv_chain.tip()).chain_spks([spk_to_track.clone()]),
+        5,
+        false,
+    )?;
+
+    let _ = recv_chain
+        .apply_update(update.chain_update)
+        .map_err(|err| anyhow::anyhow!("LocalChain update error: {:?}", err))?;
+    let _ = recv_graph.apply_update(update.graph_update.clone());
+
+    // Retain a snapshot of all anchors before reorg process.
+    let initial_anchors = update.graph_update.all_anchors();
+    let anchors: Vec<_> = initial_anchors.iter().cloned().collect();
+    assert_eq!(anchors.len(), REORG_COUNT);
+    for i in 0..REORG_COUNT {
+        let (anchor, txid) = anchors[i];
+        assert_eq!(anchor.block_id.hash, hashes[i]);
+        assert_eq!(txid, txids[i]);
+    }
+
+    // Check if initial balance is correct.
+    assert_eq!(
+        get_balance(&recv_chain, &recv_graph)?,
+        Balance {
+            confirmed: SEND_AMOUNT * REORG_COUNT as u64,
+            ..Balance::default()
+        },
+        "initial balance must be correct",
+    );
+
+    // Perform reorgs with different depths.
+    for depth in 1..=REORG_COUNT {
+        env.reorg_empty_blocks(depth)?;
+
+        env.wait_until_electrum_sees_block()?;
+        let update = client.sync(
+            SyncRequest::from_chain_tip(recv_chain.tip()).chain_spks([spk_to_track.clone()]),
+            5,
+            false,
+        )?;
+
+        let _ = recv_chain
+            .apply_update(update.chain_update)
+            .map_err(|err| anyhow::anyhow!("LocalChain update error: {:?}", err))?;
+
+        // Check that no new anchors are added during current reorg.
+        assert!(initial_anchors.is_superset(update.graph_update.all_anchors()));
+        let _ = recv_graph.apply_update(update.graph_update);
+
+        assert_eq!(
+            get_balance(&recv_chain, &recv_graph)?,
+            Balance {
+                confirmed: SEND_AMOUNT * (REORG_COUNT - depth) as u64,
+                ..Balance::default()
+            },
+            "reorg_count: {}",
+            depth,
+        );
+    }
+
+    Ok(())
+}

crates/esplora/Cargo.toml

@@ -0,0 +1,34 @@
+[package]
+name = "bdk_esplora"
+version = "0.16.0"
+edition = "2021"
+homepage = "https://bitcoindevkit.org"
+repository = "https://github.com/bitcoindevkit/bdk"
+documentation = "https://docs.rs/bdk_esplora"
+description = "Fetch data from esplora in the form that accepts"
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bdk_chain = { path = "../chain", version = "0.17.0", default-features = false }
+esplora-client = { version = "0.8.0", default-features = false }
+async-trait = { version = "0.1.66", optional = true }
+futures = { version = "0.3.26", optional = true }
+
+bitcoin = { version = "0.32.0", optional = true, default-features = false }
+miniscript = { version = "12.0.0", optional = true, default-features = false }
+
+[dev-dependencies]
+bdk_testenv = { path = "../testenv", default-features = false }
+tokio = { version = "1", features = ["rt", "rt-multi-thread", "macros"] }
+
+[features]
+default = ["std", "async-https", "blocking-https-rustls"]
+std = ["bdk_chain/std", "miniscript?/std"]
+async = ["async-trait", "futures", "esplora-client/async"]
+async-https = ["async", "esplora-client/async-https"]
+async-https-rustls = ["async", "esplora-client/async-https-rustls"]
+blocking = ["esplora-client/blocking"]
+blocking-https-rustls = ["esplora-client/blocking-https-rustls"]

crates/esplora/README.md

@@ -0,0 +1,36 @@
+# BDK Esplora
+
+BDK Esplora extends [`esplora-client`] to update [`bdk_chain`] structures
+from an Esplora server.
+
+## Usage
+
+There are two versions of the extension trait (blocking and async).
+
+For blocking-only:
+```toml
+bdk_esplora = { version = "0.3", features = ["blocking"] }
+```
+
+For async-only:
+```toml
+bdk_esplora = { version = "0.3", features = ["async"] }
+```
+
+For async-only (with https):
+```toml
+bdk_esplora = { version = "0.3", features = ["async-https"] }
+```
+
+To use the extension traits:
+```rust
+// for blocking
+use bdk_esplora::EsploraExt;
+// for async
+// use bdk_esplora::EsploraAsyncExt;
+```
+
+For full examples, refer to [`example-crates/wallet_esplora_blocking`](https://github.com/bitcoindevkit/bdk/tree/master/example-crates/wallet_esplora_blocking) and [`example-crates/wallet_esplora_async`](https://github.com/bitcoindevkit/bdk/tree/master/example-crates/wallet_esplora_async).
+
+[`esplora-client`]: https://docs.rs/esplora-client/
+[`bdk_chain`]: https://docs.rs/bdk-chain/

crates/esplora/src/async_ext.rs

@@ -0,0 +1,590 @@
+use std::collections::BTreeSet;
+
+use async_trait::async_trait;
+use bdk_chain::spk_client::{FullScanRequest, FullScanResult, SyncRequest, SyncResult};
+use bdk_chain::{
+    bitcoin::{BlockHash, OutPoint, ScriptBuf, TxOut, Txid},
+    collections::BTreeMap,
+    local_chain::CheckPoint,
+    BlockId, ConfirmationBlockTime, TxGraph,
+};
+use bdk_chain::{Anchor, Indexed};
+use esplora_client::{Amount, TxStatus};
+use futures::{stream::FuturesOrdered, TryStreamExt};
+
+use crate::anchor_from_status;
+
+/// [`esplora_client::Error`]
+type Error = Box<esplora_client::Error>;
+
+/// Trait to extend the functionality of [`esplora_client::AsyncClient`].
+///
+/// Refer to [crate-level documentation] for more.
+///
+/// [crate-level documentation]: crate
+#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
+#[cfg_attr(not(target_arch = "wasm32"), async_trait)]
+pub trait EsploraAsyncExt {
+    /// Scan keychain scripts for transactions against Esplora, returning an update that can be
+    /// applied to the receiving structures.
+    ///
+    /// - `request`: struct with data required to perform a spk-based blockchain client full scan,
+    ///              see [`FullScanRequest`]
+    ///
+    /// The full scan for each keychain stops after a gap of `stop_gap` script pubkeys with no
+    /// associated transactions. `parallel_requests` specifies the max number of HTTP requests to
+    /// make in parallel.
+    ///
+    /// ## Note
+    ///
+    /// `stop_gap` is defined as "the maximum number of consecutive unused addresses".
+    /// For example, with a `stop_gap` of  3, `full_scan` will keep scanning
+    /// until it encounters 3 consecutive script pubkeys with no associated transactions.
+    ///
+    /// This follows the same approach as other Bitcoin-related software,
+    /// such as [Electrum](https://electrum.readthedocs.io/en/latest/faq.html#what-is-the-gap-limit),
+    /// [BTCPay Server](https://docs.btcpayserver.org/FAQ/Wallet/#the-gap-limit-problem),
+    /// and [Sparrow](https://www.sparrowwallet.com/docs/faq.html#ive-restored-my-wallet-but-some-of-my-funds-are-missing).
+    ///
+    /// A `stop_gap` of 0 will be treated as a `stop_gap` of 1.
+    async fn full_scan<K: Ord + Clone + Send>(
+        &self,
+        request: FullScanRequest<K>,
+        stop_gap: usize,
+        parallel_requests: usize,
+    ) -> Result<FullScanResult<K>, Error>;
+
+    /// Sync a set of scripts with the blockchain (via an Esplora client) for the data
+    /// specified and return a [`TxGraph`].
+    ///
+    /// - `request`: struct with data required to perform a spk-based blockchain client sync, see
+    ///              [`SyncRequest`]
+    ///
+    /// If the scripts to sync are unknown, such as when restoring or importing a keychain that
+    /// may include scripts that have been used, use [`full_scan`] with the keychain.
+    ///
+    /// [`full_scan`]: EsploraAsyncExt::full_scan
+    async fn sync(
+        &self,
+        request: SyncRequest,
+        parallel_requests: usize,
+    ) -> Result<SyncResult, Error>;
+}
+
+#[cfg_attr(target_arch = "wasm32", async_trait(?Send))]
+#[cfg_attr(not(target_arch = "wasm32"), async_trait)]
+impl EsploraAsyncExt for esplora_client::AsyncClient {
+    async fn full_scan<K: Ord + Clone + Send>(
+        &self,
+        request: FullScanRequest<K>,
+        stop_gap: usize,
+        parallel_requests: usize,
+    ) -> Result<FullScanResult<K>, Error> {
+        let latest_blocks = fetch_latest_blocks(self).await?;
+        let (graph_update, last_active_indices) = full_scan_for_index_and_graph(
+            self,
+            request.spks_by_keychain,
+            stop_gap,
+            parallel_requests,
+        )
+        .await?;
+        let chain_update = chain_update(
+            self,
+            &latest_blocks,
+            &request.chain_tip,
+            graph_update.all_anchors(),
+        )
+        .await?;
+        Ok(FullScanResult {
+            chain_update,
+            graph_update,
+            last_active_indices,
+        })
+    }
+
+    async fn sync(
+        &self,
+        request: SyncRequest,
+        parallel_requests: usize,
+    ) -> Result<SyncResult, Error> {
+        let latest_blocks = fetch_latest_blocks(self).await?;
+        let graph_update = sync_for_index_and_graph(
+            self,
+            request.spks,
+            request.txids,
+            request.outpoints,
+            parallel_requests,
+        )
+        .await?;
+        let chain_update = chain_update(
+            self,
+            &latest_blocks,
+            &request.chain_tip,
+            graph_update.all_anchors(),
+        )
+        .await?;
+        Ok(SyncResult {
+            chain_update,
+            graph_update,
+        })
+    }
+}
+
+/// Fetch latest blocks from Esplora in an atomic call.
+///
+/// We want to do this before fetching transactions and anchors as we cannot fetch latest blocks AND
+/// transactions atomically, and the checkpoint tip is used to determine last-scanned block (for
+/// block-based chain-sources). Therefore it's better to be conservative when setting the tip (use
+/// an earlier tip rather than a later tip) otherwise the caller may accidentally skip blocks when
+/// alternating between chain-sources.
+async fn fetch_latest_blocks(
+    client: &esplora_client::AsyncClient,
+) -> Result<BTreeMap<u32, BlockHash>, Error> {
+    Ok(client
+        .get_blocks(None)
+        .await?
+        .into_iter()
+        .map(|b| (b.time.height, b.id))
+        .collect())
+}
+
+/// Used instead of [`esplora_client::BlockingClient::get_block_hash`].
+///
+/// This first checks the previously fetched `latest_blocks` before fetching from Esplora again.
+async fn fetch_block(
+    client: &esplora_client::AsyncClient,
+    latest_blocks: &BTreeMap<u32, BlockHash>,
+    height: u32,
+) -> Result<Option<BlockHash>, Error> {
+    if let Some(&hash) = latest_blocks.get(&height) {
+        return Ok(Some(hash));
+    }
+
+    // We avoid fetching blocks higher than previously fetched `latest_blocks` as the local chain
+    // tip is used to signal for the last-synced-up-to-height.
+    let &tip_height = latest_blocks
+        .keys()
+        .last()
+        .expect("must have atleast one entry");
+    if height > tip_height {
+        return Ok(None);
+    }
+
+    Ok(Some(client.get_block_hash(height).await?))
+}
+
+/// Create the [`local_chain::Update`].
+///
+/// We want to have a corresponding checkpoint per anchor height. However, checkpoints fetched
+/// should not surpass `latest_blocks`.
+async fn chain_update<A: Anchor>(
+    client: &esplora_client::AsyncClient,
+    latest_blocks: &BTreeMap<u32, BlockHash>,
+    local_tip: &CheckPoint,
+    anchors: &BTreeSet<(A, Txid)>,
+) -> Result<CheckPoint, Error> {
+    let mut point_of_agreement = None;
+    let mut conflicts = vec![];
+    for local_cp in local_tip.iter() {
+        let remote_hash = match fetch_block(client, latest_blocks, local_cp.height()).await? {
+            Some(hash) => hash,
+            None => continue,
+        };
+        if remote_hash == local_cp.hash() {
+            point_of_agreement = Some(local_cp.clone());
+            break;
+        } else {
+            // it is not strictly necessary to include all the conflicted heights (we do need the
+            // first one) but it seems prudent to make sure the updated chain's heights are a
+            // superset of the existing chain after update.
+            conflicts.push(BlockId {
+                height: local_cp.height(),
+                hash: remote_hash,
+            });
+        }
+    }
+
+    let mut tip = point_of_agreement.expect("remote esplora should have same genesis block");
+
+    tip = tip
+        .extend(conflicts.into_iter().rev())
+        .expect("evicted are in order");
+
+    for anchor in anchors {
+        let height = anchor.0.anchor_block().height;
+        if tip.get(height).is_none() {
+            let hash = match fetch_block(client, latest_blocks, height).await? {
+                Some(hash) => hash,
+                None => continue,
+            };
+            tip = tip.insert(BlockId { height, hash });
+        }
+    }
+
+    // insert the most recent blocks at the tip to make sure we update the tip and make the update
+    // robust.
+    for (&height, &hash) in latest_blocks.iter() {
+        tip = tip.insert(BlockId { height, hash });
+    }
+
+    Ok(tip)
+}
+
+/// This performs a full scan to get an update for the [`TxGraph`] and
+/// [`KeychainTxOutIndex`](bdk_chain::indexer::keychain_txout::KeychainTxOutIndex).
+async fn full_scan_for_index_and_graph<K: Ord + Clone + Send>(
+    client: &esplora_client::AsyncClient,
+    keychain_spks: BTreeMap<
+        K,
+        impl IntoIterator<IntoIter = impl Iterator<Item = Indexed<ScriptBuf>> + Send> + Send,
+    >,
+    stop_gap: usize,
+    parallel_requests: usize,
+) -> Result<(TxGraph<ConfirmationBlockTime>, BTreeMap<K, u32>), Error> {
+    type TxsOfSpkIndex = (u32, Vec<esplora_client::Tx>);
+    let parallel_requests = Ord::max(parallel_requests, 1);
+    let mut graph = TxGraph::<ConfirmationBlockTime>::default();
+    let mut last_active_indexes = BTreeMap::<K, u32>::new();
+
+    for (keychain, spks) in keychain_spks {
+        let mut spks = spks.into_iter();
+        let mut last_index = Option::<u32>::None;
+        let mut last_active_index = Option::<u32>::None;
+
+        loop {
+            let handles = spks
+                .by_ref()
+                .take(parallel_requests)
+                .map(|(spk_index, spk)| {
+                    let client = client.clone();
+                    async move {
+                        let mut last_seen = None;
+                        let mut spk_txs = Vec::new();
+                        loop {
+                            let txs = client.scripthash_txs(&spk, last_seen).await?;
+                            let tx_count = txs.len();
+                            last_seen = txs.last().map(|tx| tx.txid);
+                            spk_txs.extend(txs);
+                            if tx_count < 25 {
+                                break Result::<_, Error>::Ok((spk_index, spk_txs));
+                            }
+                        }
+                    }
+                })
+                .collect::<FuturesOrdered<_>>();
+
+            if handles.is_empty() {
+                break;
+            }
+
+            for (index, txs) in handles.try_collect::<Vec<TxsOfSpkIndex>>().await? {
+                last_index = Some(index);
+                if !txs.is_empty() {
+                    last_active_index = Some(index);
+                }
+                for tx in txs {
+                    let _ = graph.insert_tx(tx.to_tx());
+                    if let Some(anchor) = anchor_from_status(&tx.status) {
+                        let _ = graph.insert_anchor(tx.txid, anchor);
+                    }
+
+                    let previous_outputs = tx.vin.iter().filter_map(|vin| {
+                        let prevout = vin.prevout.as_ref()?;
+                        Some((
+                            OutPoint {
+                                txid: vin.txid,
+                                vout: vin.vout,
+                            },
+                            TxOut {
+                                script_pubkey: prevout.scriptpubkey.clone(),
+                                value: Amount::from_sat(prevout.value),
+                            },
+                        ))
+                    });
+
+                    for (outpoint, txout) in previous_outputs {
+                        let _ = graph.insert_txout(outpoint, txout);
+                    }
+                }
+            }
+
+            let last_index = last_index.expect("Must be set since handles wasn't empty.");
+            let gap_limit_reached = if let Some(i) = last_active_index {
+                last_index >= i.saturating_add(stop_gap as u32)
+            } else {
+                last_index + 1 >= stop_gap as u32
+            };
+            if gap_limit_reached {
+                break;
+            }
+        }
+
+        if let Some(last_active_index) = last_active_index {
+            last_active_indexes.insert(keychain, last_active_index);
+        }
+    }
+
+    Ok((graph, last_active_indexes))
+}
+
+async fn sync_for_index_and_graph(
+    client: &esplora_client::AsyncClient,
+    misc_spks: impl IntoIterator<IntoIter = impl Iterator<Item = ScriptBuf> + Send> + Send,
+    txids: impl IntoIterator<IntoIter = impl Iterator<Item = Txid> + Send> + Send,
+    outpoints: impl IntoIterator<IntoIter = impl Iterator<Item = OutPoint> + Send> + Send,
+    parallel_requests: usize,
+) -> Result<TxGraph<ConfirmationBlockTime>, Error> {
+    let mut graph = full_scan_for_index_and_graph(
+        client,
+        [(
+            (),
+            misc_spks
+                .into_iter()
+                .enumerate()
+                .map(|(i, spk)| (i as u32, spk)),
+        )]
+        .into(),
+        usize::MAX,
+        parallel_requests,
+    )
+    .await
+    .map(|(g, _)| g)?;
+
+    let mut txids = txids.into_iter();
+    loop {
+        let handles = txids
+            .by_ref()
+            .take(parallel_requests)
+            .filter(|&txid| graph.get_tx(txid).is_none())
+            .map(|txid| {
+                let client = client.clone();
+                async move { client.get_tx_status(&txid).await.map(|s| (txid, s)) }
+            })
+            .collect::<FuturesOrdered<_>>();
+
+        if handles.is_empty() {
+            break;
+        }
+
+        for (txid, status) in handles.try_collect::<Vec<(Txid, TxStatus)>>().await? {
+            if let Some(anchor) = anchor_from_status(&status) {
+                let _ = graph.insert_anchor(txid, anchor);
+            }
+        }
+    }
+
+    for op in outpoints.into_iter() {
+        if graph.get_tx(op.txid).is_none() {
+            if let Some(tx) = client.get_tx(&op.txid).await? {
+                let _ = graph.insert_tx(tx);
+            }
+            let status = client.get_tx_status(&op.txid).await?;
+            if let Some(anchor) = anchor_from_status(&status) {
+                let _ = graph.insert_anchor(op.txid, anchor);
+            }
+        }
+
+        if let Some(op_status) = client.get_output_status(&op.txid, op.vout as _).await? {
+            if let Some(txid) = op_status.txid {
+                if graph.get_tx(txid).is_none() {
+                    if let Some(tx) = client.get_tx(&txid).await? {
+                        let _ = graph.insert_tx(tx);
+                    }
+                    let status = client.get_tx_status(&txid).await?;
+                    if let Some(anchor) = anchor_from_status(&status) {
+                        let _ = graph.insert_anchor(txid, anchor);
+                    }
+                }
+            }
+        }
+    }
+
+    Ok(graph)
+}
+
+#[cfg(test)]
+mod test {
+    use std::{collections::BTreeSet, time::Duration};
+
+    use bdk_chain::{
+        bitcoin::{hashes::Hash, Txid},
+        local_chain::LocalChain,
+        BlockId,
+    };
+    use bdk_testenv::{anyhow, bitcoincore_rpc::RpcApi, TestEnv};
+    use esplora_client::Builder;
+
+    use crate::async_ext::{chain_update, fetch_latest_blocks};
+
+    macro_rules! h {
+        ($index:literal) => {{
+            bdk_chain::bitcoin::hashes::Hash::hash($index.as_bytes())
+        }};
+    }
+
+    /// Ensure that update does not remove heights (from original), and all anchor heights are included.
+    #[tokio::test]
+    pub async fn test_finalize_chain_update() -> anyhow::Result<()> {
+        struct TestCase<'a> {
+            name: &'a str,
+            /// Initial blockchain height to start the env with.
+            initial_env_height: u32,
+            /// Initial checkpoint heights to start with.
+            initial_cps: &'a [u32],
+            /// The final blockchain height of the env.
+            final_env_height: u32,
+            /// The anchors to test with: `(height, txid)`. Only the height is provided as we can fetch
+            /// the blockhash from the env.
+            anchors: &'a [(u32, Txid)],
+        }
+
+        let test_cases = [
+            TestCase {
+                name: "chain_extends",
+                initial_env_height: 60,
+                initial_cps: &[59, 60],
+                final_env_height: 90,
+                anchors: &[],
+            },
+            TestCase {
+                name: "introduce_older_heights",
+                initial_env_height: 50,
+                initial_cps: &[10, 15],
+                final_env_height: 50,
+                anchors: &[(11, h!("A")), (14, h!("B"))],
+            },
+            TestCase {
+                name: "introduce_older_heights_after_chain_extends",
+                initial_env_height: 50,
+                initial_cps: &[10, 15],
+                final_env_height: 100,
+                anchors: &[(11, h!("A")), (14, h!("B"))],
+            },
+        ];
+
+        for (i, t) in test_cases.into_iter().enumerate() {
+            println!("[{}] running test case: {}", i, t.name);
+
+            let env = TestEnv::new()?;
+            let base_url = format!("http://{}", &env.electrsd.esplora_url.clone().unwrap());
+            let client = Builder::new(base_url.as_str()).build_async()?;
+
+            // set env to `initial_env_height`
+            if let Some(to_mine) = t
+                .initial_env_height
+                .checked_sub(env.make_checkpoint_tip().height())
+            {
+                env.mine_blocks(to_mine as _, None)?;
+            }
+            while client.get_height().await? < t.initial_env_height {
+                std::thread::sleep(Duration::from_millis(10));
+            }
+
+            // craft initial `local_chain`
+            let local_chain = {
+                let (mut chain, _) = LocalChain::from_genesis_hash(env.genesis_hash()?);
+                // force `chain_update_blocking` to add all checkpoints in `t.initial_cps`
+                let anchors = t
+                    .initial_cps
+                    .iter()
+                    .map(|&height| -> anyhow::Result<_> {
+                        Ok((
+                            BlockId {
+                                height,
+                                hash: env.bitcoind.client.get_block_hash(height as _)?,
+                            },
+                            Txid::all_zeros(),
+                        ))
+                    })
+                    .collect::<anyhow::Result<BTreeSet<_>>>()?;
+                let update = chain_update(
+                    &client,
+                    &fetch_latest_blocks(&client).await?,
+                    &chain.tip(),
+                    &anchors,
+                )
+                .await?;
+                chain.apply_update(update)?;
+                chain
+            };
+            println!("local chain height: {}", local_chain.tip().height());
+
+            // extend env chain
+            if let Some(to_mine) = t
+                .final_env_height
+                .checked_sub(env.make_checkpoint_tip().height())
+            {
+                env.mine_blocks(to_mine as _, None)?;
+            }
+            while client.get_height().await? < t.final_env_height {
+                std::thread::sleep(Duration::from_millis(10));
+            }
+
+            // craft update
+            let update = {
+                let anchors = t
+                    .anchors
+                    .iter()
+                    .map(|&(height, txid)| -> anyhow::Result<_> {
+                        Ok((
+                            BlockId {
+                                height,
+                                hash: env.bitcoind.client.get_block_hash(height as _)?,
+                            },
+                            txid,
+                        ))
+                    })
+                    .collect::<anyhow::Result<_>>()?;
+                chain_update(
+                    &client,
+                    &fetch_latest_blocks(&client).await?,
+                    &local_chain.tip(),
+                    &anchors,
+                )
+                .await?
+            };
+
+            // apply update
+            let mut updated_local_chain = local_chain.clone();
+            updated_local_chain.apply_update(update)?;
+            println!(
+                "updated local chain height: {}",
+                updated_local_chain.tip().height()
+            );
+
+            assert!(
+                {
+                    let initial_heights = local_chain
+                        .iter_checkpoints()
+                        .map(|cp| cp.height())
+                        .collect::<BTreeSet<_>>();
+                    let updated_heights = updated_local_chain
+                        .iter_checkpoints()
+                        .map(|cp| cp.height())
+                        .collect::<BTreeSet<_>>();
+                    updated_heights.is_superset(&initial_heights)
+                },
+                "heights from the initial chain must all be in the updated chain",
+            );
+
+            assert!(
+                {
+                    let exp_anchor_heights = t
+                        .anchors
+                        .iter()
+                        .map(|(h, _)| *h)
+                        .chain(t.initial_cps.iter().copied())
+                        .collect::<BTreeSet<_>>();
+                    let anchor_heights = updated_local_chain
+                        .iter_checkpoints()
+                        .map(|cp| cp.height())
+                        .collect::<BTreeSet<_>>();
+                    anchor_heights.is_superset(&exp_anchor_heights)
+                },
+                "anchor heights must all be in updated chain",
+            );
+        }
+
+        Ok(())
+    }
+}

crates/esplora/src/blocking_ext.rs

@@ -0,0 +1,785 @@
+use std::collections::BTreeSet;
+use std::thread::JoinHandle;
+
+use bdk_chain::collections::BTreeMap;
+use bdk_chain::spk_client::{FullScanRequest, FullScanResult, SyncRequest, SyncResult};
+use bdk_chain::{
+    bitcoin::{Amount, BlockHash, OutPoint, ScriptBuf, TxOut, Txid},
+    local_chain::CheckPoint,
+    BlockId, ConfirmationBlockTime, TxGraph,
+};
+use bdk_chain::{Anchor, Indexed};
+use esplora_client::TxStatus;
+
+use crate::anchor_from_status;
+
+/// [`esplora_client::Error`]
+pub type Error = Box<esplora_client::Error>;
+
+/// Trait to extend the functionality of [`esplora_client::BlockingClient`].
+///
+/// Refer to [crate-level documentation] for more.
+///
+/// [crate-level documentation]: crate
+pub trait EsploraExt {
+    /// Scan keychain scripts for transactions against Esplora, returning an update that can be
+    /// applied to the receiving structures.
+    ///
+    /// - `request`: struct with data required to perform a spk-based blockchain client full scan,
+    ///              see [`FullScanRequest`]
+    ///
+    /// The full scan for each keychain stops after a gap of `stop_gap` script pubkeys with no
+    /// associated transactions. `parallel_requests` specifies the max number of HTTP requests to
+    /// make in parallel.
+    ///
+    /// ## Note
+    ///
+    /// `stop_gap` is defined as "the maximum number of consecutive unused addresses".
+    /// For example, with a `stop_gap` of  3, `full_scan` will keep scanning
+    /// until it encounters 3 consecutive script pubkeys with no associated transactions.
+    ///
+    /// This follows the same approach as other Bitcoin-related software,
+    /// such as [Electrum](https://electrum.readthedocs.io/en/latest/faq.html#what-is-the-gap-limit),
+    /// [BTCPay Server](https://docs.btcpayserver.org/FAQ/Wallet/#the-gap-limit-problem),
+    /// and [Sparrow](https://www.sparrowwallet.com/docs/faq.html#ive-restored-my-wallet-but-some-of-my-funds-are-missing).
+    ///
+    /// A `stop_gap` of 0 will be treated as a `stop_gap` of 1.
+    fn full_scan<K: Ord + Clone>(
+        &self,
+        request: FullScanRequest<K>,
+        stop_gap: usize,
+        parallel_requests: usize,
+    ) -> Result<FullScanResult<K>, Error>;
+
+    /// Sync a set of scripts with the blockchain (via an Esplora client) for the data
+    /// specified and return a [`TxGraph`].
+    ///
+    /// - `request`: struct with data required to perform a spk-based blockchain client sync, see
+    ///              [`SyncRequest`]
+    ///
+    /// If the scripts to sync are unknown, such as when restoring or importing a keychain that
+    /// may include scripts that have been used, use [`full_scan`] with the keychain.
+    ///
+    /// [`full_scan`]: EsploraExt::full_scan
+    fn sync(&self, request: SyncRequest, parallel_requests: usize) -> Result<SyncResult, Error>;
+}
+
+impl EsploraExt for esplora_client::BlockingClient {
+    fn full_scan<K: Ord + Clone>(
+        &self,
+        request: FullScanRequest<K>,
+        stop_gap: usize,
+        parallel_requests: usize,
+    ) -> Result<FullScanResult<K>, Error> {
+        let latest_blocks = fetch_latest_blocks(self)?;
+        let (graph_update, last_active_indices) = full_scan_for_index_and_graph_blocking(
+            self,
+            request.spks_by_keychain,
+            stop_gap,
+            parallel_requests,
+        )?;
+        let chain_update = chain_update(
+            self,
+            &latest_blocks,
+            &request.chain_tip,
+            graph_update.all_anchors(),
+        )?;
+        Ok(FullScanResult {
+            chain_update,
+            graph_update,
+            last_active_indices,
+        })
+    }
+
+    fn sync(&self, request: SyncRequest, parallel_requests: usize) -> Result<SyncResult, Error> {
+        let latest_blocks = fetch_latest_blocks(self)?;
+        let graph_update = sync_for_index_and_graph_blocking(
+            self,
+            request.spks,
+            request.txids,
+            request.outpoints,
+            parallel_requests,
+        )?;
+        let chain_update = chain_update(
+            self,
+            &latest_blocks,
+            &request.chain_tip,
+            graph_update.all_anchors(),
+        )?;
+        Ok(SyncResult {
+            chain_update,
+            graph_update,
+        })
+    }
+}
+
+/// Fetch latest blocks from Esplora in an atomic call.
+///
+/// We want to do this before fetching transactions and anchors as we cannot fetch latest blocks AND
+/// transactions atomically, and the checkpoint tip is used to determine last-scanned block (for
+/// block-based chain-sources). Therefore it's better to be conservative when setting the tip (use
+/// an earlier tip rather than a later tip) otherwise the caller may accidentally skip blocks when
+/// alternating between chain-sources.
+fn fetch_latest_blocks(
+    client: &esplora_client::BlockingClient,
+) -> Result<BTreeMap<u32, BlockHash>, Error> {
+    Ok(client
+        .get_blocks(None)?
+        .into_iter()
+        .map(|b| (b.time.height, b.id))
+        .collect())
+}
+
+/// Used instead of [`esplora_client::BlockingClient::get_block_hash`].
+///
+/// This first checks the previously fetched `latest_blocks` before fetching from Esplora again.
+fn fetch_block(
+    client: &esplora_client::BlockingClient,
+    latest_blocks: &BTreeMap<u32, BlockHash>,
+    height: u32,
+) -> Result<Option<BlockHash>, Error> {
+    if let Some(&hash) = latest_blocks.get(&height) {
+        return Ok(Some(hash));
+    }
+
+    // We avoid fetching blocks higher than previously fetched `latest_blocks` as the local chain
+    // tip is used to signal for the last-synced-up-to-height.
+    let &tip_height = latest_blocks
+        .keys()
+        .last()
+        .expect("must have atleast one entry");
+    if height > tip_height {
+        return Ok(None);
+    }
+
+    Ok(Some(client.get_block_hash(height)?))
+}
+
+/// Create the [`local_chain::Update`].
+///
+/// We want to have a corresponding checkpoint per anchor height. However, checkpoints fetched
+/// should not surpass `latest_blocks`.
+fn chain_update<A: Anchor>(
+    client: &esplora_client::BlockingClient,
+    latest_blocks: &BTreeMap<u32, BlockHash>,
+    local_tip: &CheckPoint,
+    anchors: &BTreeSet<(A, Txid)>,
+) -> Result<CheckPoint, Error> {
+    let mut point_of_agreement = None;
+    let mut conflicts = vec![];
+    for local_cp in local_tip.iter() {
+        let remote_hash = match fetch_block(client, latest_blocks, local_cp.height())? {
+            Some(hash) => hash,
+            None => continue,
+        };
+        if remote_hash == local_cp.hash() {
+            point_of_agreement = Some(local_cp.clone());
+            break;
+        } else {
+            // it is not strictly necessary to include all the conflicted heights (we do need the
+            // first one) but it seems prudent to make sure the updated chain's heights are a
+            // superset of the existing chain after update.
+            conflicts.push(BlockId {
+                height: local_cp.height(),
+                hash: remote_hash,
+            });
+        }
+    }
+
+    let mut tip = point_of_agreement.expect("remote esplora should have same genesis block");
+
+    tip = tip
+        .extend(conflicts.into_iter().rev())
+        .expect("evicted are in order");
+
+    for anchor in anchors {
+        let height = anchor.0.anchor_block().height;
+        if tip.get(height).is_none() {
+            let hash = match fetch_block(client, latest_blocks, height)? {
+                Some(hash) => hash,
+                None => continue,
+            };
+            tip = tip.insert(BlockId { height, hash });
+        }
+    }
+
+    // insert the most recent blocks at the tip to make sure we update the tip and make the update
+    // robust.
+    for (&height, &hash) in latest_blocks.iter() {
+        tip = tip.insert(BlockId { height, hash });
+    }
+
+    Ok(tip)
+}
+
+/// This performs a full scan to get an update for the [`TxGraph`] and
+/// [`KeychainTxOutIndex`](bdk_chain::indexer::keychain_txout::KeychainTxOutIndex).
+fn full_scan_for_index_and_graph_blocking<K: Ord + Clone>(
+    client: &esplora_client::BlockingClient,
+    keychain_spks: BTreeMap<K, impl IntoIterator<Item = Indexed<ScriptBuf>>>,
+    stop_gap: usize,
+    parallel_requests: usize,
+) -> Result<(TxGraph<ConfirmationBlockTime>, BTreeMap<K, u32>), Error> {
+    type TxsOfSpkIndex = (u32, Vec<esplora_client::Tx>);
+    let parallel_requests = Ord::max(parallel_requests, 1);
+    let mut tx_graph = TxGraph::<ConfirmationBlockTime>::default();
+    let mut last_active_indices = BTreeMap::<K, u32>::new();
+
+    for (keychain, spks) in keychain_spks {
+        let mut spks = spks.into_iter();
+        let mut last_index = Option::<u32>::None;
+        let mut last_active_index = Option::<u32>::None;
+
+        loop {
+            let handles = spks
+                .by_ref()
+                .take(parallel_requests)
+                .map(|(spk_index, spk)| {
+                    std::thread::spawn({
+                        let client = client.clone();
+                        move || -> Result<TxsOfSpkIndex, Error> {
+                            let mut last_seen = None;
+                            let mut spk_txs = Vec::new();
+                            loop {
+                                let txs = client.scripthash_txs(&spk, last_seen)?;
+                                let tx_count = txs.len();
+                                last_seen = txs.last().map(|tx| tx.txid);
+                                spk_txs.extend(txs);
+                                if tx_count < 25 {
+                                    break Ok((spk_index, spk_txs));
+                                }
+                            }
+                        }
+                    })
+                })
+                .collect::<Vec<JoinHandle<Result<TxsOfSpkIndex, Error>>>>();
+
+            if handles.is_empty() {
+                break;
+            }
+
+            for handle in handles {
+                let (index, txs) = handle.join().expect("thread must not panic")?;
+                last_index = Some(index);
+                if !txs.is_empty() {
+                    last_active_index = Some(index);
+                }
+                for tx in txs {
+                    let _ = tx_graph.insert_tx(tx.to_tx());
+                    if let Some(anchor) = anchor_from_status(&tx.status) {
+                        let _ = tx_graph.insert_anchor(tx.txid, anchor);
+                    }
+
+                    let previous_outputs = tx.vin.iter().filter_map(|vin| {
+                        let prevout = vin.prevout.as_ref()?;
+                        Some((
+                            OutPoint {
+                                txid: vin.txid,
+                                vout: vin.vout,
+                            },
+                            TxOut {
+                                script_pubkey: prevout.scriptpubkey.clone(),
+                                value: Amount::from_sat(prevout.value),
+                            },
+                        ))
+                    });
+
+                    for (outpoint, txout) in previous_outputs {
+                        let _ = tx_graph.insert_txout(outpoint, txout);
+                    }
+                }
+            }
+
+            let last_index = last_index.expect("Must be set since handles wasn't empty.");
+            let gap_limit_reached = if let Some(i) = last_active_index {
+                last_index >= i.saturating_add(stop_gap as u32)
+            } else {
+                last_index + 1 >= stop_gap as u32
+            };
+            if gap_limit_reached {
+                break;
+            }
+        }
+
+        if let Some(last_active_index) = last_active_index {
+            last_active_indices.insert(keychain, last_active_index);
+        }
+    }
+
+    Ok((tx_graph, last_active_indices))
+}
+
+fn sync_for_index_and_graph_blocking(
+    client: &esplora_client::BlockingClient,
+    misc_spks: impl IntoIterator<Item = ScriptBuf>,
+    txids: impl IntoIterator<Item = Txid>,
+    outpoints: impl IntoIterator<Item = OutPoint>,
+    parallel_requests: usize,
+) -> Result<TxGraph<ConfirmationBlockTime>, Error> {
+    let (mut tx_graph, _) = full_scan_for_index_and_graph_blocking(
+        client,
+        {
+            let mut keychains = BTreeMap::new();
+            keychains.insert(
+                (),
+                misc_spks
+                    .into_iter()
+                    .enumerate()
+                    .map(|(i, spk)| (i as u32, spk)),
+            );
+            keychains
+        },
+        usize::MAX,
+        parallel_requests,
+    )?;
+
+    let mut txids = txids.into_iter();
+    loop {
+        let handles = txids
+            .by_ref()
+            .take(parallel_requests)
+            .filter(|&txid| tx_graph.get_tx(txid).is_none())
+            .map(|txid| {
+                std::thread::spawn({
+                    let client = client.clone();
+                    move || {
+                        client
+                            .get_tx_status(&txid)
+                            .map_err(Box::new)
+                            .map(|s| (txid, s))
+                    }
+                })
+            })
+            .collect::<Vec<JoinHandle<Result<(Txid, TxStatus), Error>>>>();
+
+        if handles.is_empty() {
+            break;
+        }
+
+        for handle in handles {
+            let (txid, status) = handle.join().expect("thread must not panic")?;
+            if let Some(anchor) = anchor_from_status(&status) {
+                let _ = tx_graph.insert_anchor(txid, anchor);
+            }
+        }
+    }
+
+    for op in outpoints {
+        if tx_graph.get_tx(op.txid).is_none() {
+            if let Some(tx) = client.get_tx(&op.txid)? {
+                let _ = tx_graph.insert_tx(tx);
+            }
+            let status = client.get_tx_status(&op.txid)?;
+            if let Some(anchor) = anchor_from_status(&status) {
+                let _ = tx_graph.insert_anchor(op.txid, anchor);
+            }
+        }
+
+        if let Some(op_status) = client.get_output_status(&op.txid, op.vout as _)? {
+            if let Some(txid) = op_status.txid {
+                if tx_graph.get_tx(txid).is_none() {
+                    if let Some(tx) = client.get_tx(&txid)? {
+                        let _ = tx_graph.insert_tx(tx);
+                    }
+                    let status = client.get_tx_status(&txid)?;
+                    if let Some(anchor) = anchor_from_status(&status) {
+                        let _ = tx_graph.insert_anchor(txid, anchor);
+                    }
+                }
+            }
+        }
+    }
+
+    Ok(tx_graph)
+}
+
+#[cfg(test)]
+mod test {
+    use crate::blocking_ext::{chain_update, fetch_latest_blocks};
+    use bdk_chain::bitcoin::hashes::Hash;
+    use bdk_chain::bitcoin::Txid;
+    use bdk_chain::local_chain::LocalChain;
+    use bdk_chain::BlockId;
+    use bdk_testenv::{anyhow, bitcoincore_rpc::RpcApi, TestEnv};
+    use esplora_client::{BlockHash, Builder};
+    use std::collections::{BTreeMap, BTreeSet};
+    use std::time::Duration;
+
+    macro_rules! h {
+        ($index:literal) => {{
+            bdk_chain::bitcoin::hashes::Hash::hash($index.as_bytes())
+        }};
+    }
+
+    macro_rules! local_chain {
+        [ $(($height:expr, $block_hash:expr)), * ] => {{
+            #[allow(unused_mut)]
+            bdk_chain::local_chain::LocalChain::from_blocks([$(($height, $block_hash).into()),*].into_iter().collect())
+                .expect("chain must have genesis block")
+        }};
+    }
+
+    /// Ensure that update does not remove heights (from original), and all anchor heights are included.
+    #[test]
+    pub fn test_finalize_chain_update() -> anyhow::Result<()> {
+        struct TestCase<'a> {
+            name: &'a str,
+            /// Initial blockchain height to start the env with.
+            initial_env_height: u32,
+            /// Initial checkpoint heights to start with in the local chain.
+            initial_cps: &'a [u32],
+            /// The final blockchain height of the env.
+            final_env_height: u32,
+            /// The anchors to test with: `(height, txid)`. Only the height is provided as we can fetch
+            /// the blockhash from the env.
+            anchors: &'a [(u32, Txid)],
+        }
+
+        let test_cases = [
+            TestCase {
+                name: "chain_extends",
+                initial_env_height: 60,
+                initial_cps: &[59, 60],
+                final_env_height: 90,
+                anchors: &[],
+            },
+            TestCase {
+                name: "introduce_older_heights",
+                initial_env_height: 50,
+                initial_cps: &[10, 15],
+                final_env_height: 50,
+                anchors: &[(11, h!("A")), (14, h!("B"))],
+            },
+            TestCase {
+                name: "introduce_older_heights_after_chain_extends",
+                initial_env_height: 50,
+                initial_cps: &[10, 15],
+                final_env_height: 100,
+                anchors: &[(11, h!("A")), (14, h!("B"))],
+            },
+        ];
+
+        for (i, t) in test_cases.into_iter().enumerate() {
+            println!("[{}] running test case: {}", i, t.name);
+
+            let env = TestEnv::new()?;
+            let base_url = format!("http://{}", &env.electrsd.esplora_url.clone().unwrap());
+            let client = Builder::new(base_url.as_str()).build_blocking();
+
+            // set env to `initial_env_height`
+            if let Some(to_mine) = t
+                .initial_env_height
+                .checked_sub(env.make_checkpoint_tip().height())
+            {
+                env.mine_blocks(to_mine as _, None)?;
+            }
+            while client.get_height()? < t.initial_env_height {
+                std::thread::sleep(Duration::from_millis(10));
+            }
+
+            // craft initial `local_chain`
+            let local_chain = {
+                let (mut chain, _) = LocalChain::from_genesis_hash(env.genesis_hash()?);
+                // force `chain_update_blocking` to add all checkpoints in `t.initial_cps`
+                let anchors = t
+                    .initial_cps
+                    .iter()
+                    .map(|&height| -> anyhow::Result<_> {
+                        Ok((
+                            BlockId {
+                                height,
+                                hash: env.bitcoind.client.get_block_hash(height as _)?,
+                            },
+                            Txid::all_zeros(),
+                        ))
+                    })
+                    .collect::<anyhow::Result<BTreeSet<_>>>()?;
+                let update = chain_update(
+                    &client,
+                    &fetch_latest_blocks(&client)?,
+                    &chain.tip(),
+                    &anchors,
+                )?;
+                chain.apply_update(update)?;
+                chain
+            };
+            println!("local chain height: {}", local_chain.tip().height());
+
+            // extend env chain
+            if let Some(to_mine) = t
+                .final_env_height
+                .checked_sub(env.make_checkpoint_tip().height())
+            {
+                env.mine_blocks(to_mine as _, None)?;
+            }
+            while client.get_height()? < t.final_env_height {
+                std::thread::sleep(Duration::from_millis(10));
+            }
+
+            // craft update
+            let update = {
+                let anchors = t
+                    .anchors
+                    .iter()
+                    .map(|&(height, txid)| -> anyhow::Result<_> {
+                        Ok((
+                            BlockId {
+                                height,
+                                hash: env.bitcoind.client.get_block_hash(height as _)?,
+                            },
+                            txid,
+                        ))
+                    })
+                    .collect::<anyhow::Result<_>>()?;
+                chain_update(
+                    &client,
+                    &fetch_latest_blocks(&client)?,
+                    &local_chain.tip(),
+                    &anchors,
+                )?
+            };
+
+            // apply update
+            let mut updated_local_chain = local_chain.clone();
+            updated_local_chain.apply_update(update)?;
+            println!(
+                "updated local chain height: {}",
+                updated_local_chain.tip().height()
+            );
+
+            assert!(
+                {
+                    let initial_heights = local_chain
+                        .iter_checkpoints()
+                        .map(|cp| cp.height())
+                        .collect::<BTreeSet<_>>();
+                    let updated_heights = updated_local_chain
+                        .iter_checkpoints()
+                        .map(|cp| cp.height())
+                        .collect::<BTreeSet<_>>();
+                    updated_heights.is_superset(&initial_heights)
+                },
+                "heights from the initial chain must all be in the updated chain",
+            );
+
+            assert!(
+                {
+                    let exp_anchor_heights = t
+                        .anchors
+                        .iter()
+                        .map(|(h, _)| *h)
+                        .chain(t.initial_cps.iter().copied())
+                        .collect::<BTreeSet<_>>();
+                    let anchor_heights = updated_local_chain
+                        .iter_checkpoints()
+                        .map(|cp| cp.height())
+                        .collect::<BTreeSet<_>>();
+                    anchor_heights.is_superset(&exp_anchor_heights)
+                },
+                "anchor heights must all be in updated chain",
+            );
+        }
+
+        Ok(())
+    }
+
+    #[test]
+    fn update_local_chain() -> anyhow::Result<()> {
+        const TIP_HEIGHT: u32 = 50;
+
+        let env = TestEnv::new()?;
+        let blocks = {
+            let bitcoind_client = &env.bitcoind.client;
+            assert_eq!(bitcoind_client.get_block_count()?, 1);
+            [
+                (0, bitcoind_client.get_block_hash(0)?),
+                (1, bitcoind_client.get_block_hash(1)?),
+            ]
+            .into_iter()
+            .chain((2..).zip(env.mine_blocks((TIP_HEIGHT - 1) as usize, None)?))
+            .collect::<BTreeMap<_, _>>()
+        };
+        // so new blocks can be seen by Electrs
+        let env = env.reset_electrsd()?;
+        let base_url = format!("http://{}", &env.electrsd.esplora_url.clone().unwrap());
+        let client = Builder::new(base_url.as_str()).build_blocking();
+
+        struct TestCase {
+            name: &'static str,
+            /// Original local chain to start off with.
+            chain: LocalChain,
+            /// Heights of floating anchors. [`chain_update_blocking`] will request for checkpoints
+            /// of these heights.
+            request_heights: &'static [u32],
+            /// The expected local chain result (heights only).
+            exp_update_heights: &'static [u32],
+        }
+
+        let test_cases = [
+            TestCase {
+                name: "request_later_blocks",
+                chain: local_chain![(0, blocks[&0]), (21, blocks[&21])],
+                request_heights: &[22, 25, 28],
+                exp_update_heights: &[21, 22, 25, 28],
+            },
+            TestCase {
+                name: "request_prev_blocks",
+                chain: local_chain![(0, blocks[&0]), (1, blocks[&1]), (5, blocks[&5])],
+                request_heights: &[4],
+                exp_update_heights: &[4, 5],
+            },
+            TestCase {
+                name: "request_prev_blocks_2",
+                chain: local_chain![(0, blocks[&0]), (1, blocks[&1]), (10, blocks[&10])],
+                request_heights: &[4, 6],
+                exp_update_heights: &[4, 6, 10],
+            },
+            TestCase {
+                name: "request_later_and_prev_blocks",
+                chain: local_chain![(0, blocks[&0]), (7, blocks[&7]), (11, blocks[&11])],
+                request_heights: &[8, 9, 15],
+                exp_update_heights: &[8, 9, 11, 15],
+            },
+            TestCase {
+                name: "request_tip_only",
+                chain: local_chain![(0, blocks[&0]), (5, blocks[&5]), (49, blocks[&49])],
+                request_heights: &[TIP_HEIGHT],
+                exp_update_heights: &[49],
+            },
+            TestCase {
+                name: "request_nothing",
+                chain: local_chain![(0, blocks[&0]), (13, blocks[&13]), (23, blocks[&23])],
+                request_heights: &[],
+                exp_update_heights: &[23],
+            },
+            TestCase {
+                name: "request_nothing_during_reorg",
+                chain: local_chain![(0, blocks[&0]), (13, blocks[&13]), (23, h!("23"))],
+                request_heights: &[],
+                exp_update_heights: &[13, 23],
+            },
+            TestCase {
+                name: "request_nothing_during_reorg_2",
+                chain: local_chain![
+                    (0, blocks[&0]),
+                    (21, blocks[&21]),
+                    (22, h!("22")),
+                    (23, h!("23"))
+                ],
+                request_heights: &[],
+                exp_update_heights: &[21, 22, 23],
+            },
+            TestCase {
+                name: "request_prev_blocks_during_reorg",
+                chain: local_chain![
+                    (0, blocks[&0]),
+                    (21, blocks[&21]),
+                    (22, h!("22")),
+                    (23, h!("23"))
+                ],
+                request_heights: &[17, 20],
+                exp_update_heights: &[17, 20, 21, 22, 23],
+            },
+            TestCase {
+                name: "request_later_blocks_during_reorg",
+                chain: local_chain![
+                    (0, blocks[&0]),
+                    (9, blocks[&9]),
+                    (22, h!("22")),
+                    (23, h!("23"))
+                ],
+                request_heights: &[25, 27],
+                exp_update_heights: &[9, 22, 23, 25, 27],
+            },
+            TestCase {
+                name: "request_later_blocks_during_reorg_2",
+                chain: local_chain![(0, blocks[&0]), (9, h!("9"))],
+                request_heights: &[10],
+                exp_update_heights: &[0, 9, 10],
+            },
+            TestCase {
+                name: "request_later_and_prev_blocks_during_reorg",
+                chain: local_chain![(0, blocks[&0]), (1, blocks[&1]), (9, h!("9"))],
+                request_heights: &[8, 11],
+                exp_update_heights: &[1, 8, 9, 11],
+            },
+        ];
+
+        for (i, t) in test_cases.into_iter().enumerate() {
+            println!("Case {}: {}", i, t.name);
+            let mut chain = t.chain;
+
+            let mock_anchors = t
+                .request_heights
+                .iter()
+                .map(|&h| {
+                    let anchor_blockhash: BlockHash = bdk_chain::bitcoin::hashes::Hash::hash(
+                        &format!("hash_at_height_{}", h).into_bytes(),
+                    );
+                    let txid: Txid = bdk_chain::bitcoin::hashes::Hash::hash(
+                        &format!("txid_at_height_{}", h).into_bytes(),
+                    );
+                    let anchor = BlockId {
+                        height: h,
+                        hash: anchor_blockhash,
+                    };
+                    (anchor, txid)
+                })
+                .collect::<BTreeSet<_>>();
+            let chain_update = chain_update(
+                &client,
+                &fetch_latest_blocks(&client)?,
+                &chain.tip(),
+                &mock_anchors,
+            )?;
+
+            let update_blocks = chain_update
+                .iter()
+                .map(|cp| cp.block_id())
+                .collect::<BTreeSet<_>>();
+
+            let exp_update_blocks = t
+                .exp_update_heights
+                .iter()
+                .map(|&height| {
+                    let hash = blocks[&height];
+                    BlockId { height, hash }
+                })
+                .chain(
+                    // Electrs Esplora `get_block` call fetches 10 blocks which is included in the
+                    // update
+                    blocks
+                        .range(TIP_HEIGHT - 9..)
+                        .map(|(&height, &hash)| BlockId { height, hash }),
+                )
+                .collect::<BTreeSet<_>>();
+
+            assert!(
+                update_blocks.is_superset(&exp_update_blocks),
+                "[{}:{}] unexpected update",
+                i,
+                t.name
+            );
+
+            let _ = chain
+                .apply_update(chain_update)
+                .unwrap_or_else(|err| panic!("[{}:{}] update failed to apply: {}", i, t.name, err));
+
+            // all requested heights must exist in the final chain
+            for height in t.request_heights {
+                let exp_blockhash = blocks.get(height).expect("block must exist in bitcoind");
+                assert_eq!(
+                    chain.get(*height).map(|cp| cp.hash()),
+                    Some(*exp_blockhash),
+                    "[{}:{}] block {}:{} must exist in final chain",
+                    i,
+                    t.name,
+                    height,
+                    exp_blockhash
+                );
+            }
+        }
+
+        Ok(())
+    }
+}

crates/esplora/src/lib.rs

@@ -0,0 +1,49 @@
+#![doc = include_str!("../README.md")]
+
+//! This crate is used for updating structures of [`bdk_chain`] with data from an Esplora server.
+//!
+//! The two primary methods are [`EsploraExt::sync`] and [`EsploraExt::full_scan`]. In most cases
+//! [`EsploraExt::sync`] is used to sync the transaction histories of scripts that the application
+//! cares about, for example the scripts for all the receive addresses of a Wallet's keychain that it
+//! has shown a user. [`EsploraExt::full_scan`] is meant to be used when importing or restoring a
+//! keychain where the range of possibly used scripts is not known. In this case it is necessary to
+//! scan all keychain scripts until a number (the "stop gap") of unused scripts is discovered. For a
+//! sync or full scan the user receives relevant blockchain data and output updates for [`bdk_chain`]
+//! via a new [`TxGraph`] to be appended to any existing [`TxGraph`] data.
+//!
+//! Refer to [`example_esplora`] for a complete example.
+//!
+//! [`TxGraph`]: bdk_chain::tx_graph::TxGraph
+//! [`example_esplora`]: https://github.com/bitcoindevkit/bdk/tree/master/example-crates/example_esplora
+
+use bdk_chain::{BlockId, ConfirmationBlockTime};
+use esplora_client::TxStatus;
+
+pub use esplora_client;
+
+#[cfg(feature = "blocking")]
+mod blocking_ext;
+#[cfg(feature = "blocking")]
+pub use blocking_ext::*;
+
+#[cfg(feature = "async")]
+mod async_ext;
+#[cfg(feature = "async")]
+pub use async_ext::*;
+
+fn anchor_from_status(status: &TxStatus) -> Option<ConfirmationBlockTime> {
+    if let TxStatus {
+        block_height: Some(height),
+        block_hash: Some(hash),
+        block_time: Some(time),
+        ..
+    } = status.clone()
+    {
+        Some(ConfirmationBlockTime {
+            block_id: BlockId { height, hash },
+            confirmation_time: time,
+        })
+    } else {
+        None
+    }
+}

crates/esplora/tests/async_ext.rs

@@ -0,0 +1,231 @@
+use bdk_chain::spk_client::{FullScanRequest, SyncRequest};
+use bdk_esplora::EsploraAsyncExt;
+use esplora_client::{self, Builder};
+use std::collections::{BTreeSet, HashSet};
+use std::str::FromStr;
+use std::thread::sleep;
+use std::time::Duration;
+
+use bdk_chain::bitcoin::{Address, Amount, Txid};
+use bdk_testenv::{anyhow, bitcoincore_rpc::RpcApi, TestEnv};
+
+#[tokio::test]
+pub async fn test_update_tx_graph_without_keychain() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+    let base_url = format!("http://{}", &env.electrsd.esplora_url.clone().unwrap());
+    let client = Builder::new(base_url.as_str()).build_async()?;
+
+    let receive_address0 =
+        Address::from_str("bcrt1qc6fweuf4xjvz4x3gx3t9e0fh4hvqyu2qw4wvxm")?.assume_checked();
+    let receive_address1 =
+        Address::from_str("bcrt1qfjg5lv3dvc9az8patec8fjddrs4aqtauadnagr")?.assume_checked();
+
+    let misc_spks = [
+        receive_address0.script_pubkey(),
+        receive_address1.script_pubkey(),
+    ];
+
+    let _block_hashes = env.mine_blocks(101, None)?;
+    let txid1 = env.bitcoind.client.send_to_address(
+        &receive_address1,
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let txid2 = env.bitcoind.client.send_to_address(
+        &receive_address0,
+        Amount::from_sat(20000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let _block_hashes = env.mine_blocks(1, None)?;
+    while client.get_height().await.unwrap() < 102 {
+        sleep(Duration::from_millis(10))
+    }
+
+    // use a full checkpoint linked list (since this is not what we are testing)
+    let cp_tip = env.make_checkpoint_tip();
+
+    let sync_update = {
+        let request = SyncRequest::from_chain_tip(cp_tip.clone()).set_spks(misc_spks);
+        client.sync(request, 1).await?
+    };
+
+    assert!(
+        {
+            let update_cps = sync_update
+                .chain_update
+                .iter()
+                .map(|cp| cp.block_id())
+                .collect::<BTreeSet<_>>();
+            let superset_cps = cp_tip
+                .iter()
+                .map(|cp| cp.block_id())
+                .collect::<BTreeSet<_>>();
+            superset_cps.is_superset(&update_cps)
+        },
+        "update should not alter original checkpoint tip since we already started with all checkpoints",
+    );
+
+    let graph_update = sync_update.graph_update;
+    // Check to see if we have the floating txouts available from our two created transactions'
+    // previous outputs in order to calculate transaction fees.
+    for tx in graph_update.full_txs() {
+        // Retrieve the calculated fee from `TxGraph`, which will panic if we do not have the
+        // floating txouts available from the transactions' previous outputs.
+        let fee = graph_update.calculate_fee(&tx.tx).expect("Fee must exist");
+
+        // Retrieve the fee in the transaction data from `bitcoind`.
+        let tx_fee = env
+            .bitcoind
+            .client
+            .get_transaction(&tx.txid, None)
+            .expect("Tx must exist")
+            .fee
+            .expect("Fee must exist")
+            .abs()
+            .to_unsigned()
+            .expect("valid `Amount`");
+
+        // Check that the calculated fee matches the fee from the transaction data.
+        assert_eq!(fee, tx_fee);
+    }
+
+    let mut graph_update_txids: Vec<Txid> = graph_update.full_txs().map(|tx| tx.txid).collect();
+    graph_update_txids.sort();
+    let mut expected_txids = vec![txid1, txid2];
+    expected_txids.sort();
+    assert_eq!(graph_update_txids, expected_txids);
+    Ok(())
+}
+
+/// Test the bounds of the address scan depending on the `stop_gap`.
+#[tokio::test]
+pub async fn test_async_update_tx_graph_stop_gap() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+    let base_url = format!("http://{}", &env.electrsd.esplora_url.clone().unwrap());
+    let client = Builder::new(base_url.as_str()).build_async()?;
+    let _block_hashes = env.mine_blocks(101, None)?;
+
+    // Now let's test the gap limit. First of all get a chain of 10 addresses.
+    let addresses = [
+        "bcrt1qj9f7r8r3p2y0sqf4r3r62qysmkuh0fzep473d2ar7rcz64wqvhssjgf0z4",
+        "bcrt1qmm5t0ch7vh2hryx9ctq3mswexcugqe4atkpkl2tetm8merqkthas3w7q30",
+        "bcrt1qut9p7ej7l7lhyvekj28xknn8gnugtym4d5qvnp5shrsr4nksmfqsmyn87g",
+        "bcrt1qqz0xtn3m235p2k96f5wa2dqukg6shxn9n3txe8arlrhjh5p744hsd957ww",
+        "bcrt1q9c0t62a8l6wfytmf2t9lfj35avadk3mm8g4p3l84tp6rl66m48sqrme7wu",
+        "bcrt1qkmh8yrk2v47cklt8dytk8f3ammcwa4q7dzattedzfhqzvfwwgyzsg59zrh",
+        "bcrt1qvgrsrzy07gjkkfr5luplt0azxtfwmwq5t62gum5jr7zwcvep2acs8hhnp2",
+        "bcrt1qw57edarcg50ansq8mk3guyrk78rk0fwvrds5xvqeupteu848zayq549av8",
+        "bcrt1qvtve5ekf6e5kzs68knvnt2phfw6a0yjqrlgat392m6zt9jsvyxhqfx67ef",
+        "bcrt1qw03ddumfs9z0kcu76ln7jrjfdwam20qtffmkcral3qtza90sp9kqm787uk",
+    ];
+    let addresses: Vec<_> = addresses
+        .into_iter()
+        .map(|s| Address::from_str(s).unwrap().assume_checked())
+        .collect();
+    let spks: Vec<_> = addresses
+        .iter()
+        .enumerate()
+        .map(|(i, addr)| (i as u32, addr.script_pubkey()))
+        .collect();
+
+    // Then receive coins on the 4th address.
+    let txid_4th_addr = env.bitcoind.client.send_to_address(
+        &addresses[3],
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let _block_hashes = env.mine_blocks(1, None)?;
+    while client.get_height().await.unwrap() < 103 {
+        sleep(Duration::from_millis(10))
+    }
+
+    // use a full checkpoint linked list (since this is not what we are testing)
+    let cp_tip = env.make_checkpoint_tip();
+
+    // A scan with a gap limit of 3 won't find the transaction, but a scan with a gap limit of 4
+    // will.
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 3, 1).await?
+    };
+    assert!(full_scan_update.graph_update.full_txs().next().is_none());
+    assert!(full_scan_update.last_active_indices.is_empty());
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 4, 1).await?
+    };
+    assert_eq!(
+        full_scan_update
+            .graph_update
+            .full_txs()
+            .next()
+            .unwrap()
+            .txid,
+        txid_4th_addr
+    );
+    assert_eq!(full_scan_update.last_active_indices[&0], 3);
+
+    // Now receive a coin on the last address.
+    let txid_last_addr = env.bitcoind.client.send_to_address(
+        &addresses[addresses.len() - 1],
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let _block_hashes = env.mine_blocks(1, None)?;
+    while client.get_height().await.unwrap() < 104 {
+        sleep(Duration::from_millis(10))
+    }
+
+    // A scan with gap limit 5 won't find the second transaction, but a scan with gap limit 6 will.
+    // The last active indice won't be updated in the first case but will in the second one.
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 5, 1).await?
+    };
+    let txs: HashSet<_> = full_scan_update
+        .graph_update
+        .full_txs()
+        .map(|tx| tx.txid)
+        .collect();
+    assert_eq!(txs.len(), 1);
+    assert!(txs.contains(&txid_4th_addr));
+    assert_eq!(full_scan_update.last_active_indices[&0], 3);
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 6, 1).await?
+    };
+    let txs: HashSet<_> = full_scan_update
+        .graph_update
+        .full_txs()
+        .map(|tx| tx.txid)
+        .collect();
+    assert_eq!(txs.len(), 2);
+    assert!(txs.contains(&txid_4th_addr) && txs.contains(&txid_last_addr));
+    assert_eq!(full_scan_update.last_active_indices[&0], 9);
+
+    Ok(())
+}

crates/esplora/tests/blocking_ext.rs

@@ -0,0 +1,232 @@
+use bdk_chain::spk_client::{FullScanRequest, SyncRequest};
+use bdk_esplora::EsploraExt;
+use esplora_client::{self, Builder};
+use std::collections::{BTreeSet, HashSet};
+use std::str::FromStr;
+use std::thread::sleep;
+use std::time::Duration;
+
+use bdk_chain::bitcoin::{Address, Amount, Txid};
+use bdk_testenv::{anyhow, bitcoincore_rpc::RpcApi, TestEnv};
+
+#[test]
+pub fn test_update_tx_graph_without_keychain() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+    let base_url = format!("http://{}", &env.electrsd.esplora_url.clone().unwrap());
+    let client = Builder::new(base_url.as_str()).build_blocking();
+
+    let receive_address0 =
+        Address::from_str("bcrt1qc6fweuf4xjvz4x3gx3t9e0fh4hvqyu2qw4wvxm")?.assume_checked();
+    let receive_address1 =
+        Address::from_str("bcrt1qfjg5lv3dvc9az8patec8fjddrs4aqtauadnagr")?.assume_checked();
+
+    let misc_spks = [
+        receive_address0.script_pubkey(),
+        receive_address1.script_pubkey(),
+    ];
+
+    let _block_hashes = env.mine_blocks(101, None)?;
+    let txid1 = env.bitcoind.client.send_to_address(
+        &receive_address1,
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let txid2 = env.bitcoind.client.send_to_address(
+        &receive_address0,
+        Amount::from_sat(20000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let _block_hashes = env.mine_blocks(1, None)?;
+    while client.get_height().unwrap() < 102 {
+        sleep(Duration::from_millis(10))
+    }
+
+    // use a full checkpoint linked list (since this is not what we are testing)
+    let cp_tip = env.make_checkpoint_tip();
+
+    let sync_update = {
+        let request = SyncRequest::from_chain_tip(cp_tip.clone()).set_spks(misc_spks);
+        client.sync(request, 1)?
+    };
+
+    assert!(
+        {
+            let update_cps = sync_update
+                .chain_update
+                .iter()
+                .map(|cp| cp.block_id())
+                .collect::<BTreeSet<_>>();
+            let superset_cps = cp_tip
+                .iter()
+                .map(|cp| cp.block_id())
+                .collect::<BTreeSet<_>>();
+            superset_cps.is_superset(&update_cps)
+        },
+        "update should not alter original checkpoint tip since we already started with all checkpoints",
+    );
+
+    let graph_update = sync_update.graph_update;
+    // Check to see if we have the floating txouts available from our two created transactions'
+    // previous outputs in order to calculate transaction fees.
+    for tx in graph_update.full_txs() {
+        // Retrieve the calculated fee from `TxGraph`, which will panic if we do not have the
+        // floating txouts available from the transactions' previous outputs.
+        let fee = graph_update.calculate_fee(&tx.tx).expect("Fee must exist");
+
+        // Retrieve the fee in the transaction data from `bitcoind`.
+        let tx_fee = env
+            .bitcoind
+            .client
+            .get_transaction(&tx.txid, None)
+            .expect("Tx must exist")
+            .fee
+            .expect("Fee must exist")
+            .abs()
+            .to_unsigned()
+            .expect("valid `Amount`");
+
+        // Check that the calculated fee matches the fee from the transaction data.
+        assert_eq!(fee, tx_fee);
+    }
+
+    let mut graph_update_txids: Vec<Txid> = graph_update.full_txs().map(|tx| tx.txid).collect();
+    graph_update_txids.sort();
+    let mut expected_txids = vec![txid1, txid2];
+    expected_txids.sort();
+    assert_eq!(graph_update_txids, expected_txids);
+
+    Ok(())
+}
+
+/// Test the bounds of the address scan depending on the `stop_gap`.
+#[test]
+pub fn test_update_tx_graph_stop_gap() -> anyhow::Result<()> {
+    let env = TestEnv::new()?;
+    let base_url = format!("http://{}", &env.electrsd.esplora_url.clone().unwrap());
+    let client = Builder::new(base_url.as_str()).build_blocking();
+    let _block_hashes = env.mine_blocks(101, None)?;
+
+    // Now let's test the gap limit. First of all get a chain of 10 addresses.
+    let addresses = [
+        "bcrt1qj9f7r8r3p2y0sqf4r3r62qysmkuh0fzep473d2ar7rcz64wqvhssjgf0z4",
+        "bcrt1qmm5t0ch7vh2hryx9ctq3mswexcugqe4atkpkl2tetm8merqkthas3w7q30",
+        "bcrt1qut9p7ej7l7lhyvekj28xknn8gnugtym4d5qvnp5shrsr4nksmfqsmyn87g",
+        "bcrt1qqz0xtn3m235p2k96f5wa2dqukg6shxn9n3txe8arlrhjh5p744hsd957ww",
+        "bcrt1q9c0t62a8l6wfytmf2t9lfj35avadk3mm8g4p3l84tp6rl66m48sqrme7wu",
+        "bcrt1qkmh8yrk2v47cklt8dytk8f3ammcwa4q7dzattedzfhqzvfwwgyzsg59zrh",
+        "bcrt1qvgrsrzy07gjkkfr5luplt0azxtfwmwq5t62gum5jr7zwcvep2acs8hhnp2",
+        "bcrt1qw57edarcg50ansq8mk3guyrk78rk0fwvrds5xvqeupteu848zayq549av8",
+        "bcrt1qvtve5ekf6e5kzs68knvnt2phfw6a0yjqrlgat392m6zt9jsvyxhqfx67ef",
+        "bcrt1qw03ddumfs9z0kcu76ln7jrjfdwam20qtffmkcral3qtza90sp9kqm787uk",
+    ];
+    let addresses: Vec<_> = addresses
+        .into_iter()
+        .map(|s| Address::from_str(s).unwrap().assume_checked())
+        .collect();
+    let spks: Vec<_> = addresses
+        .iter()
+        .enumerate()
+        .map(|(i, addr)| (i as u32, addr.script_pubkey()))
+        .collect();
+
+    // Then receive coins on the 4th address.
+    let txid_4th_addr = env.bitcoind.client.send_to_address(
+        &addresses[3],
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let _block_hashes = env.mine_blocks(1, None)?;
+    while client.get_height().unwrap() < 103 {
+        sleep(Duration::from_millis(10))
+    }
+
+    // use a full checkpoint linked list (since this is not what we are testing)
+    let cp_tip = env.make_checkpoint_tip();
+
+    // A scan with a stop_gap of 3 won't find the transaction, but a scan with a gap limit of 4
+    // will.
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 3, 1)?
+    };
+    assert!(full_scan_update.graph_update.full_txs().next().is_none());
+    assert!(full_scan_update.last_active_indices.is_empty());
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 4, 1)?
+    };
+    assert_eq!(
+        full_scan_update
+            .graph_update
+            .full_txs()
+            .next()
+            .unwrap()
+            .txid,
+        txid_4th_addr
+    );
+    assert_eq!(full_scan_update.last_active_indices[&0], 3);
+
+    // Now receive a coin on the last address.
+    let txid_last_addr = env.bitcoind.client.send_to_address(
+        &addresses[addresses.len() - 1],
+        Amount::from_sat(10000),
+        None,
+        None,
+        None,
+        None,
+        Some(1),
+        None,
+    )?;
+    let _block_hashes = env.mine_blocks(1, None)?;
+    while client.get_height().unwrap() < 104 {
+        sleep(Duration::from_millis(10))
+    }
+
+    // A scan with gap limit 5 won't find the second transaction, but a scan with gap limit 6 will.
+    // The last active indice won't be updated in the first case but will in the second one.
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 5, 1)?
+    };
+    let txs: HashSet<_> = full_scan_update
+        .graph_update
+        .full_txs()
+        .map(|tx| tx.txid)
+        .collect();
+    assert_eq!(txs.len(), 1);
+    assert!(txs.contains(&txid_4th_addr));
+    assert_eq!(full_scan_update.last_active_indices[&0], 3);
+    let full_scan_update = {
+        let request =
+            FullScanRequest::from_chain_tip(cp_tip.clone()).set_spks_for_keychain(0, spks.clone());
+        client.full_scan(request, 6, 1)?
+    };
+    let txs: HashSet<_> = full_scan_update
+        .graph_update
+        .full_txs()
+        .map(|tx| tx.txid)
+        .collect();
+    assert_eq!(txs.len(), 2);
+    assert!(txs.contains(&txid_4th_addr) && txs.contains(&txid_last_addr));
+    assert_eq!(full_scan_update.last_active_indices[&0], 9);
+
+    Ok(())
+}

crates/file_store/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "bdk_file_store"
+version = "0.14.0"
+edition = "2021"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/bitcoindevkit/bdk"
+documentation = "https://docs.rs/bdk_file_store"
+description = "A simple append-only flat file database for persisting bdk_chain data."
+keywords = ["bitcoin", "persist", "persistence", "bdk", "file"]
+authors = ["Bitcoin Dev Kit Developers"]
+readme = "README.md"
+
+[dependencies]
+bdk_chain = { path = "../chain", version = "0.17.0", features = [ "serde", "miniscript" ] }
+bincode = { version = "1" }
+serde = { version = "1", features = ["derive"] }
+
+[dev-dependencies]
+tempfile = "3"

crates/file_store/README.md

@@ -0,0 +1,7 @@
+# BDK File Store
+
+This is a simple append-only flat file database for persisting [`bdk_chain`] changesets.
+
+The main structure is [`Store`] which works with any [`bdk_chain`] based changesets to persist data into a flat file.
+
+[`bdk_chain`]:https://docs.rs/bdk_chain/latest/bdk_chain/

crates/file_store/src/entry_iter.rs

@@ -0,0 +1,108 @@
+use bincode::Options;
+use std::{
+    fs::File,
+    io::{self, BufReader, Seek},
+    marker::PhantomData,
+};
+
+use crate::bincode_options;
+
+/// Iterator over entries in a file store.
+///
+/// Reads and returns an entry each time [`next`] is called. If an error occurs while reading the
+/// iterator will yield a `Result::Err(_)` instead and then `None` for the next call to `next`.
+///
+/// [`next`]: Self::next
+pub struct EntryIter<'t, T> {
+    /// Buffered reader around the file
+    db_file: BufReader<&'t mut File>,
+    finished: bool,
+    /// The file position for the first read of `db_file`.
+    start_pos: Option<u64>,
+    types: PhantomData<T>,
+}
+
+impl<'t, T> EntryIter<'t, T> {
+    pub fn new(start_pos: u64, db_file: &'t mut File) -> Self {
+        Self {
+            db_file: BufReader::new(db_file),
+            start_pos: Some(start_pos),
+            finished: false,
+            types: PhantomData,
+        }
+    }
+}
+
+impl<'t, T> Iterator for EntryIter<'t, T>
+where
+    T: serde::de::DeserializeOwned,
+{
+    type Item = Result<T, IterError>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.finished {
+            return None;
+        }
+        (|| {
+            if let Some(start) = self.start_pos.take() {
+                self.db_file.seek(io::SeekFrom::Start(start))?;
+            }
+
+            let pos_before_read = self.db_file.stream_position()?;
+            match bincode_options().deserialize_from(&mut self.db_file) {
+                Ok(changeset) => Ok(Some(changeset)),
+                Err(e) => {
+                    self.finished = true;
+                    let pos_after_read = self.db_file.stream_position()?;
+                    // allow unexpected EOF if 0 bytes were read
+                    if let bincode::ErrorKind::Io(inner) = &*e {
+                        if inner.kind() == io::ErrorKind::UnexpectedEof
+                            && pos_after_read == pos_before_read
+                        {
+                            return Ok(None);
+                        }
+                    }
+                    self.db_file.seek(io::SeekFrom::Start(pos_before_read))?;
+                    Err(IterError::Bincode(*e))
+                }
+            }
+        })()
+        .transpose()
+    }
+}
+
+impl<'t, T> Drop for EntryIter<'t, T> {
+    fn drop(&mut self) {
+        // This syncs the underlying file's offset with the buffer's position. This way, we
+        // maintain the correct position to start the next read/write.
+        if let Ok(pos) = self.db_file.stream_position() {
+            let _ = self.db_file.get_mut().seek(io::SeekFrom::Start(pos));
+        }
+    }
+}
+
+/// Error type for [`EntryIter`].
+#[derive(Debug)]
+pub enum IterError {
+    /// Failure to read from the file.
+    Io(io::Error),
+    /// Failure to decode data from the file.
+    Bincode(bincode::ErrorKind),
+}
+
+impl core::fmt::Display for IterError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            IterError::Io(e) => write!(f, "io error trying to read entry {}", e),
+            IterError::Bincode(e) => write!(f, "bincode error while reading entry {}", e),
+        }
+    }
+}
+
+impl From<io::Error> for IterError {
+    fn from(value: io::Error) -> Self {
+        IterError::Io(value)
+    }
+}
+
+impl std::error::Error for IterError {}

crates/file_store/src/lib.rs

@@ -0,0 +1,42 @@
+#![doc = include_str!("../README.md")]
+mod entry_iter;
+mod store;
+use std::io;
+
+use bincode::{DefaultOptions, Options};
+pub use entry_iter::*;
+pub use store::*;
+
+pub(crate) fn bincode_options() -> impl bincode::Options {
+    DefaultOptions::new().with_varint_encoding()
+}
+
+/// Error that occurs due to problems encountered with the file.
+#[derive(Debug)]
+pub enum FileError {
+    /// IO error, this may mean that the file is too short.
+    Io(io::Error),
+    /// Magic bytes do not match what is expected.
+    InvalidMagicBytes { got: Vec<u8>, expected: Vec<u8> },
+}
+
+impl core::fmt::Display for FileError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::Io(e) => write!(f, "io error trying to read file: {}", e),
+            Self::InvalidMagicBytes { got, expected } => write!(
+                f,
+                "file has invalid magic bytes: expected={:?} got={:?}",
+                expected, got,
+            ),
+        }
+    }
+}
+
+impl From<io::Error> for FileError {
+    fn from(value: io::Error) -> Self {
+        Self::Io(value)
+    }
+}
+
+impl std::error::Error for FileError {}

crates/file_store/src/store.rs

@@ -0,0 +1,443 @@
+use crate::{bincode_options, EntryIter, FileError, IterError};
+use bdk_chain::Merge;
+use bincode::Options;
+use std::{
+    fmt::{self, Debug},
+    fs::{File, OpenOptions},
+    io::{self, Read, Seek, Write},
+    marker::PhantomData,
+    path::Path,
+};
+
+/// Persists an append-only list of changesets (`C`) to a single file.
+#[derive(Debug)]
+pub struct Store<C>
+where
+    C: Sync + Send,
+{
+    magic_len: usize,
+    db_file: File,
+    marker: PhantomData<C>,
+}
+
+impl<C> Store<C>
+where
+    C: Merge
+        + serde::Serialize
+        + serde::de::DeserializeOwned
+        + core::marker::Send
+        + core::marker::Sync,
+{
+    /// Create a new [`Store`] file in write-only mode; error if the file exists.
+    ///
+    /// `magic` is the prefixed bytes to write to the new file. This will be checked when opening
+    /// the `Store` in the future with [`open`].
+    ///
+    /// [`open`]: Store::open
+    pub fn create_new<P>(magic: &[u8], file_path: P) -> Result<Self, FileError>
+    where
+        P: AsRef<Path>,
+    {
+        if file_path.as_ref().exists() {
+            // `io::Error` is used instead of a variant on `FileError` because there is already a
+            // nightly-only `File::create_new` method
+            return Err(FileError::Io(io::Error::new(
+                io::ErrorKind::Other,
+                "file already exists",
+            )));
+        }
+        let mut f = OpenOptions::new()
+            .create(true)
+            .read(true)
+            .write(true)
+            .truncate(true)
+            .open(file_path)?;
+        f.write_all(magic)?;
+        Ok(Self {
+            magic_len: magic.len(),
+            db_file: f,
+            marker: Default::default(),
+        })
+    }
+
+    /// Open an existing [`Store`].
+    ///
+    /// Use [`create_new`] to create a new `Store`.
+    ///
+    /// # Errors
+    ///
+    /// If the prefixed bytes of the opened file does not match the provided `magic`, the
+    /// [`FileError::InvalidMagicBytes`] error variant will be returned.
+    ///
+    /// [`create_new`]: Store::create_new
+    pub fn open<P>(magic: &[u8], file_path: P) -> Result<Self, FileError>
+    where
+        P: AsRef<Path>,
+    {
+        let mut f = OpenOptions::new().read(true).write(true).open(file_path)?;
+
+        let mut magic_buf = vec![0_u8; magic.len()];
+        f.read_exact(&mut magic_buf)?;
+        if magic_buf != magic {
+            return Err(FileError::InvalidMagicBytes {
+                got: magic_buf,
+                expected: magic.to_vec(),
+            });
+        }
+
+        Ok(Self {
+            magic_len: magic.len(),
+            db_file: f,
+            marker: Default::default(),
+        })
+    }
+
+    /// Attempt to open existing [`Store`] file; create it if the file is non-existent.
+    ///
+    /// Internally, this calls either [`open`] or [`create_new`].
+    ///
+    /// [`open`]: Store::open
+    /// [`create_new`]: Store::create_new
+    pub fn open_or_create_new<P>(magic: &[u8], file_path: P) -> Result<Self, FileError>
+    where
+        P: AsRef<Path>,
+    {
+        if file_path.as_ref().exists() {
+            Self::open(magic, file_path)
+        } else {
+            Self::create_new(magic, file_path)
+        }
+    }
+
+    /// Iterates over the stored changeset from first to last, changing the seek position at each
+    /// iteration.
+    ///
+    /// The iterator may fail to read an entry and therefore return an error. However, the first time
+    /// it returns an error will be the last. After doing so, the iterator will always yield `None`.
+    ///
+    /// **WARNING**: This method changes the write position in the underlying file. You should
+    /// always iterate over all entries until `None` is returned if you want your next write to go
+    /// at the end; otherwise, you will write over existing entries.
+    pub fn iter_changesets(&mut self) -> EntryIter<C> {
+        EntryIter::new(self.magic_len as u64, &mut self.db_file)
+    }
+
+    /// Loads all the changesets that have been stored as one giant changeset.
+    ///
+    /// This function returns the aggregate changeset, or `None` if nothing was persisted.
+    /// If reading or deserializing any of the entries fails, an error is returned that
+    /// consists of all those it was able to read.
+    ///
+    /// You should usually check the error. In many applications, it may make sense to do a full
+    /// wallet scan with a stop-gap after getting an error, since it is likely that one of the
+    /// changesets was unable to read changes of the derivation indices of a keychain.
+    ///
+    /// **WARNING**: This method changes the write position of the underlying file. The next
+    /// changeset will be written over the erroring entry (or the end of the file if none existed).
+    pub fn aggregate_changesets(&mut self) -> Result<Option<C>, AggregateChangesetsError<C>> {
+        let mut changeset = Option::<C>::None;
+        for next_changeset in self.iter_changesets() {
+            let next_changeset = match next_changeset {
+                Ok(next_changeset) => next_changeset,
+                Err(iter_error) => {
+                    return Err(AggregateChangesetsError {
+                        changeset,
+                        iter_error,
+                    })
+                }
+            };
+            match &mut changeset {
+                Some(changeset) => changeset.merge(next_changeset),
+                changeset => *changeset = Some(next_changeset),
+            }
+        }
+        Ok(changeset)
+    }
+
+    /// Append a new changeset to the file and truncate the file to the end of the appended
+    /// changeset.
+    ///
+    /// The truncation is to avoid the possibility of having a valid but inconsistent changeset
+    /// directly after the appended changeset.
+    pub fn append_changeset(&mut self, changeset: &C) -> Result<(), io::Error> {
+        // no need to write anything if changeset is empty
+        if changeset.is_empty() {
+            return Ok(());
+        }
+
+        bincode_options()
+            .serialize_into(&mut self.db_file, changeset)
+            .map_err(|e| match *e {
+                bincode::ErrorKind::Io(error) => error,
+                unexpected_err => panic!("unexpected bincode error: {}", unexpected_err),
+            })?;
+
+        // truncate file after this changeset addition
+        // if this is not done, data after this changeset may represent valid changesets, however
+        // applying those changesets on top of this one may result in an inconsistent state
+        let pos = self.db_file.stream_position()?;
+        self.db_file.set_len(pos)?;
+
+        Ok(())
+    }
+}
+
+/// Error type for [`Store::aggregate_changesets`].
+#[derive(Debug)]
+pub struct AggregateChangesetsError<C> {
+    /// The partially-aggregated changeset.
+    pub changeset: Option<C>,
+
+    /// The error returned by [`EntryIter`].
+    pub iter_error: IterError,
+}
+
+impl<C> std::fmt::Display for AggregateChangesetsError<C> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Display::fmt(&self.iter_error, f)
+    }
+}
+
+impl<C: fmt::Debug> std::error::Error for AggregateChangesetsError<C> {}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    use bincode::DefaultOptions;
+    use std::{
+        collections::BTreeSet,
+        io::{Read, Write},
+        vec::Vec,
+    };
+    use tempfile::NamedTempFile;
+
+    const TEST_MAGIC_BYTES_LEN: usize = 12;
+    const TEST_MAGIC_BYTES: [u8; TEST_MAGIC_BYTES_LEN] =
+        [98, 100, 107, 102, 115, 49, 49, 49, 49, 49, 49, 49];
+
+    type TestChangeSet = BTreeSet<String>;
+
+    /// Check behavior of [`Store::create_new`] and [`Store::open`].
+    #[test]
+    fn construct_store() {
+        let temp_dir = tempfile::tempdir().unwrap();
+        let file_path = temp_dir.path().join("db_file");
+        let _ = Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, &file_path)
+            .expect_err("must not open as file does not exist yet");
+        let _ = Store::<TestChangeSet>::create_new(&TEST_MAGIC_BYTES, &file_path)
+            .expect("must create file");
+        // cannot create new as file already exists
+        let _ = Store::<TestChangeSet>::create_new(&TEST_MAGIC_BYTES, &file_path)
+            .expect_err("must fail as file already exists now");
+        let _ = Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, &file_path)
+            .expect("must open as file exists now");
+    }
+
+    #[test]
+    fn open_or_create_new() {
+        let temp_dir = tempfile::tempdir().unwrap();
+        let file_path = temp_dir.path().join("db_file");
+        let changeset = BTreeSet::from(["hello".to_string(), "world".to_string()]);
+
+        {
+            let mut db = Store::<TestChangeSet>::open_or_create_new(&TEST_MAGIC_BYTES, &file_path)
+                .expect("must create");
+            assert!(file_path.exists());
+            db.append_changeset(&changeset).expect("must succeed");
+        }
+
+        {
+            let mut db = Store::<TestChangeSet>::open_or_create_new(&TEST_MAGIC_BYTES, &file_path)
+                .expect("must recover");
+            let recovered_changeset = db.aggregate_changesets().expect("must succeed");
+            assert_eq!(recovered_changeset, Some(changeset));
+        }
+    }
+
+    #[test]
+    fn new_fails_if_file_is_too_short() {
+        let mut file = NamedTempFile::new().unwrap();
+        file.write_all(&TEST_MAGIC_BYTES[..TEST_MAGIC_BYTES_LEN - 1])
+            .expect("should write");
+
+        match Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, file.path()) {
+            Err(FileError::Io(e)) => assert_eq!(e.kind(), std::io::ErrorKind::UnexpectedEof),
+            unexpected => panic!("unexpected result: {:?}", unexpected),
+        };
+    }
+
+    #[test]
+    fn new_fails_if_magic_bytes_are_invalid() {
+        let invalid_magic_bytes = "ldkfs0000000";
+
+        let mut file = NamedTempFile::new().unwrap();
+        file.write_all(invalid_magic_bytes.as_bytes())
+            .expect("should write");
+
+        match Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, file.path()) {
+            Err(FileError::InvalidMagicBytes { got, .. }) => {
+                assert_eq!(got, invalid_magic_bytes.as_bytes())
+            }
+            unexpected => panic!("unexpected result: {:?}", unexpected),
+        };
+    }
+
+    #[test]
+    fn append_changeset_truncates_invalid_bytes() {
+        // initial data to write to file (magic bytes + invalid data)
+        let mut data = [255_u8; 2000];
+        data[..TEST_MAGIC_BYTES_LEN].copy_from_slice(&TEST_MAGIC_BYTES);
+
+        let changeset = TestChangeSet::from(["one".into(), "two".into(), "three!".into()]);
+
+        let mut file = NamedTempFile::new().unwrap();
+        file.write_all(&data).expect("should write");
+
+        let mut store =
+            Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, file.path()).expect("should open");
+        match store.iter_changesets().next() {
+            Some(Err(IterError::Bincode(_))) => {}
+            unexpected_res => panic!("unexpected result: {:?}", unexpected_res),
+        }
+
+        store.append_changeset(&changeset).expect("should append");
+
+        drop(store);
+
+        let got_bytes = {
+            let mut buf = Vec::new();
+            file.reopen()
+                .unwrap()
+                .read_to_end(&mut buf)
+                .expect("should read");
+            buf
+        };
+
+        let expected_bytes = {
+            let mut buf = TEST_MAGIC_BYTES.to_vec();
+            DefaultOptions::new()
+                .with_varint_encoding()
+                .serialize_into(&mut buf, &changeset)
+                .expect("should encode");
+            buf
+        };
+
+        assert_eq!(got_bytes, expected_bytes);
+    }
+
+    #[test]
+    fn last_write_is_short() {
+        let temp_dir = tempfile::tempdir().unwrap();
+
+        let changesets = [
+            TestChangeSet::from(["1".into()]),
+            TestChangeSet::from(["2".into(), "3".into()]),
+            TestChangeSet::from(["4".into(), "5".into(), "6".into()]),
+        ];
+        let last_changeset = TestChangeSet::from(["7".into(), "8".into(), "9".into()]);
+        let last_changeset_bytes = bincode_options().serialize(&last_changeset).unwrap();
+
+        for short_write_len in 1..last_changeset_bytes.len() - 1 {
+            let file_path = temp_dir.path().join(format!("{}.dat", short_write_len));
+            println!("Test file: {:?}", file_path);
+
+            // simulate creating a file, writing data where the last write is incomplete
+            {
+                let mut db =
+                    Store::<TestChangeSet>::create_new(&TEST_MAGIC_BYTES, &file_path).unwrap();
+                for changeset in &changesets {
+                    db.append_changeset(changeset).unwrap();
+                }
+                // this is the incomplete write
+                db.db_file
+                    .write_all(&last_changeset_bytes[..short_write_len])
+                    .unwrap();
+            }
+
+            // load file again and aggregate changesets
+            // write the last changeset again (this time it succeeds)
+            {
+                let mut db = Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, &file_path).unwrap();
+                let err = db
+                    .aggregate_changesets()
+                    .expect_err("should return error as last read is short");
+                assert_eq!(
+                    err.changeset,
+                    changesets.iter().cloned().reduce(|mut acc, cs| {
+                        Merge::merge(&mut acc, cs);
+                        acc
+                    }),
+                    "should recover all changesets that are written in full",
+                );
+                db.db_file.write_all(&last_changeset_bytes).unwrap();
+            }
+
+            // load file again - this time we should successfully aggregate all changesets
+            {
+                let mut db = Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, &file_path).unwrap();
+                let aggregated_changesets = db
+                    .aggregate_changesets()
+                    .expect("aggregating all changesets should succeed");
+                assert_eq!(
+                    aggregated_changesets,
+                    changesets
+                        .iter()
+                        .cloned()
+                        .chain(core::iter::once(last_changeset.clone()))
+                        .reduce(|mut acc, cs| {
+                            Merge::merge(&mut acc, cs);
+                            acc
+                        }),
+                    "should recover all changesets",
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn write_after_short_read() {
+        let temp_dir = tempfile::tempdir().unwrap();
+
+        let changesets = (0..20)
+            .map(|n| TestChangeSet::from([format!("{}", n)]))
+            .collect::<Vec<_>>();
+        let last_changeset = TestChangeSet::from(["last".into()]);
+
+        for read_count in 0..changesets.len() {
+            let file_path = temp_dir.path().join(format!("{}.dat", read_count));
+            println!("Test file: {:?}", file_path);
+
+            // First, we create the file with all the changesets!
+            let mut db = Store::<TestChangeSet>::create_new(&TEST_MAGIC_BYTES, &file_path).unwrap();
+            for changeset in &changesets {
+                db.append_changeset(changeset).unwrap();
+            }
+            drop(db);
+
+            // We re-open the file and read `read_count` number of changesets.
+            let mut db = Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, &file_path).unwrap();
+            let mut exp_aggregation = db
+                .iter_changesets()
+                .take(read_count)
+                .map(|r| r.expect("must read valid changeset"))
+                .fold(TestChangeSet::default(), |mut acc, v| {
+                    Merge::merge(&mut acc, v);
+                    acc
+                });
+            // We write after a short read.
+            db.append_changeset(&last_changeset)
+                .expect("last write must succeed");
+            Merge::merge(&mut exp_aggregation, last_changeset.clone());
+            drop(db);
+
+            // We open the file again and check whether aggregate changeset is expected.
+            let aggregation = Store::<TestChangeSet>::open(&TEST_MAGIC_BYTES, &file_path)
+                .unwrap()
+                .aggregate_changesets()
+                .expect("must aggregate changesets")
+                .unwrap_or_default();
+            assert_eq!(aggregation, exp_aggregation);
+        }
+    }
+}

crates/hwi/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "bdk_hwi"
+version = "0.4.0"
+edition = "2021"
+homepage = "https://bitcoindevkit.org"
+repository = "https://github.com/bitcoindevkit/bdk"
+description = "Utilities to use bdk with hardware wallets"
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+
+[dependencies]
+bdk_wallet = { path = "../wallet", version = "1.0.0-beta.1" }
+hwi = { version = "0.9.0", features = [ "miniscript"] }

crates/hwi/README.md

@@ -0,0 +1,3 @@
+# BDK HWI Signer
+
+This crate contains `HWISigner`, an implementation of a `TransactionSigner` to be used with hardware wallets.

crates/hwi/src/lib.rs

@@ -0,0 +1,39 @@
+//! HWI Signer
+//!
+//! This crate contains HWISigner, an implementation of a [`TransactionSigner`] to be
+//! used with hardware wallets.
+//! ```no_run
+//! # use bdk_wallet::bitcoin::Network;
+//! # use bdk_wallet::descriptor::Descriptor;
+//! # use bdk_wallet::signer::SignerOrdering;
+//! # use bdk_hwi::HWISigner;
+//! # use bdk_wallet::{KeychainKind, SignOptions, Wallet};
+//! # use hwi::HWIClient;
+//! # use std::sync::Arc;
+//! # use std::str::FromStr;
+//! #
+//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
+//! let mut devices = HWIClient::enumerate()?;
+//! if devices.is_empty() {
+//!     panic!("No devices found!");
+//! }
+//! let first_device = devices.remove(0)?;
+//! let custom_signer = HWISigner::from_device(&first_device, Network::Testnet.into())?;
+//!
+//! # let mut wallet = Wallet::create("", "").network(Network::Testnet).create_wallet_no_persist()?;
+//! #
+//! // Adding the hardware signer to the BDK wallet
+//! wallet.add_signer(
+//!     KeychainKind::External,
+//!     SignerOrdering(200),
+//!     Arc::new(custom_signer),
+//! );
+//!
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! [`TransactionSigner`]: bdk_wallet::signer::TransactionSigner
+
+mod signer;
+pub use signer::*;

crates/hwi/src/signer.rs

@@ -0,0 +1,94 @@
+use bdk_wallet::bitcoin::bip32::Fingerprint;
+use bdk_wallet::bitcoin::secp256k1::{All, Secp256k1};
+use bdk_wallet::bitcoin::Psbt;
+
+use hwi::error::Error;
+use hwi::types::{HWIChain, HWIDevice};
+use hwi::HWIClient;
+
+use bdk_wallet::signer::{SignerCommon, SignerError, SignerId, TransactionSigner};
+
+#[derive(Debug)]
+/// Custom signer for Hardware Wallets
+///
+/// This ignores `sign_options` and leaves the decisions up to the hardware wallet.
+pub struct HWISigner {
+    fingerprint: Fingerprint,
+    client: HWIClient,
+}
+
+impl HWISigner {
+    /// Create a instance from the specified device and chain
+    pub fn from_device(device: &HWIDevice, chain: HWIChain) -> Result<HWISigner, Error> {
+        let client = HWIClient::get_client(device, false, chain)?;
+        Ok(HWISigner {
+            fingerprint: device.fingerprint,
+            client,
+        })
+    }
+}
+
+impl SignerCommon for HWISigner {
+    fn id(&self, _secp: &Secp256k1<All>) -> SignerId {
+        SignerId::Fingerprint(self.fingerprint)
+    }
+}
+
+impl TransactionSigner for HWISigner {
+    fn sign_transaction(
+        &self,
+        psbt: &mut Psbt,
+        _sign_options: &bdk_wallet::SignOptions,
+        _secp: &Secp256k1<All>,
+    ) -> Result<(), SignerError> {
+        psbt.combine(
+            self.client
+                .sign_tx(psbt)
+                .map_err(|e| {
+                    SignerError::External(format!("While signing with hardware wallet: {}", e))
+                })?
+                .psbt,
+        )
+        .expect("Failed to combine HW signed psbt with passed PSBT");
+        Ok(())
+    }
+}
+
+// TODO: re-enable this once we have the `get_funded_wallet` test util
+// #[cfg(test)]
+// mod tests {
+//     #[test]
+//     fn test_hardware_signer() {
+//         use std::sync::Arc;
+//
+//         use bdk_wallet::tests::get_funded_wallet;
+//         use bdk_wallet::signer::SignerOrdering;
+//         use bdk_wallet::bitcoin::Network;
+//         use crate::HWISigner;
+//         use hwi::HWIClient;
+//
+//         let mut devices = HWIClient::enumerate().unwrap();
+//         if devices.is_empty() {
+//             panic!("No devices found!");
+//         }
+//         let device = devices.remove(0).unwrap();
+//         let client = HWIClient::get_client(&device, true, Network::Regtest.into()).unwrap();
+//         let descriptors = client.get_descriptors::<String>(None).unwrap();
+//         let custom_signer = HWISigner::from_device(&device, Network::Regtest.into()).unwrap();
+//
+//         let (mut wallet, _) = get_funded_wallet(&descriptors.internal[0]);
+//         wallet.add_signer(
+//             bdk_wallet::KeychainKind::External,
+//             SignerOrdering(200),
+//             Arc::new(custom_signer),
+//         );
+//
+//         let addr = wallet.get_address(bdk_wallet::AddressIndex::LastUnused);
+//         let mut builder = wallet.build_tx();
+//         builder.drain_to(addr.script_pubkey()).drain_wallet();
+//         let (mut psbt, _) = builder.finish().unwrap();
+//
+//         let finalized = wallet.sign(&mut psbt, Default::default()).unwrap();
+//         assert!(finalized);
+//     }
+// }

crates/testenv/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "bdk_testenv"
+version = "0.7.0"
+edition = "2021"
+rust-version = "1.63"
+homepage = "https://bitcoindevkit.org"
+repository = "https://github.com/bitcoindevkit/bdk"
+documentation = "https://docs.rs/bdk_testenv"
+description = "Testing framework for BDK chain sources."
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bdk_chain = { path = "../chain", version = "0.17", default-features = false }
+electrsd = { version = "0.28.0", features = ["bitcoind_25_0", "esplora_a33e97e1", "legacy"] }
+
+[features]
+default = ["std"]
+std = ["bdk_chain/std"]
+serde = ["bdk_chain/serde"]

crates/testenv/README.md

@@ -0,0 +1,6 @@
+# BDK TestEnv
+
+This crate sets up a regtest environment with a single [`bitcoind`] node
+connected to an [`electrs`] instance. This framework provides the infrastructure
+for testing chain source crates, e.g., [`bdk_chain`], [`bdk_electrum`],
+[`bdk_esplora`], etc.

crates/testenv/src/lib.rs

@@ -0,0 +1,304 @@
+use bdk_chain::{
+    bitcoin::{
+        address::NetworkChecked, block::Header, hash_types::TxMerkleNode, hashes::Hash,
+        secp256k1::rand::random, transaction, Address, Amount, Block, BlockHash, CompactTarget,
+        ScriptBuf, ScriptHash, Transaction, TxIn, TxOut, Txid,
+    },
+    local_chain::CheckPoint,
+    BlockId,
+};
+use bitcoincore_rpc::{
+    bitcoincore_rpc_json::{GetBlockTemplateModes, GetBlockTemplateRules},
+    RpcApi,
+};
+pub use electrsd;
+pub use electrsd::bitcoind;
+pub use electrsd::bitcoind::anyhow;
+pub use electrsd::bitcoind::bitcoincore_rpc;
+pub use electrsd::electrum_client;
+use electrsd::electrum_client::ElectrumApi;
+use std::time::Duration;
+
+/// Struct for running a regtest environment with a single `bitcoind` node with an `electrs`
+/// instance connected to it.
+pub struct TestEnv {
+    pub bitcoind: electrsd::bitcoind::BitcoinD,
+    pub electrsd: electrsd::ElectrsD,
+}
+
+impl TestEnv {
+    /// Construct a new [`TestEnv`] instance with default configurations.
+    pub fn new() -> anyhow::Result<Self> {
+        let bitcoind = match std::env::var_os("BITCOIND_EXE") {
+            Some(bitcoind_path) => electrsd::bitcoind::BitcoinD::new(bitcoind_path),
+            None => {
+                let bitcoind_exe = electrsd::bitcoind::downloaded_exe_path()
+                    .expect(
+                "you need to provide an env var BITCOIND_EXE or specify a bitcoind version feature",
+                );
+                electrsd::bitcoind::BitcoinD::with_conf(
+                    bitcoind_exe,
+                    &electrsd::bitcoind::Conf::default(),
+                )
+            }
+        }?;
+
+        let mut electrsd_conf = electrsd::Conf::default();
+        electrsd_conf.http_enabled = true;
+        let electrsd = match std::env::var_os("ELECTRS_EXE") {
+            Some(env_electrs_exe) => {
+                electrsd::ElectrsD::with_conf(env_electrs_exe, &bitcoind, &electrsd_conf)
+            }
+            None => {
+                let electrs_exe = electrsd::downloaded_exe_path()
+                    .expect("electrs version feature must be enabled");
+                electrsd::ElectrsD::with_conf(electrs_exe, &bitcoind, &electrsd_conf)
+            }
+        }?;
+
+        Ok(Self { bitcoind, electrsd })
+    }
+
+    /// Exposes the [`ElectrumApi`] calls from the Electrum client.
+    pub fn electrum_client(&self) -> &impl ElectrumApi {
+        &self.electrsd.client
+    }
+
+    /// Exposes the [`RpcApi`] calls from [`bitcoincore_rpc`].
+    pub fn rpc_client(&self) -> &impl RpcApi {
+        &self.bitcoind.client
+    }
+
+    // Reset `electrsd` so that new blocks can be seen.
+    pub fn reset_electrsd(mut self) -> anyhow::Result<Self> {
+        let mut electrsd_conf = electrsd::Conf::default();
+        electrsd_conf.http_enabled = true;
+        let electrsd = match std::env::var_os("ELECTRS_EXE") {
+            Some(env_electrs_exe) => {
+                electrsd::ElectrsD::with_conf(env_electrs_exe, &self.bitcoind, &electrsd_conf)
+            }
+            None => {
+                let electrs_exe = electrsd::downloaded_exe_path()
+                    .expect("electrs version feature must be enabled");
+                electrsd::ElectrsD::with_conf(electrs_exe, &self.bitcoind, &electrsd_conf)
+            }
+        }?;
+        self.electrsd = electrsd;
+        Ok(self)
+    }
+
+    /// Mine a number of blocks of a given size `count`, which may be specified to a given coinbase
+    /// `address`.
+    pub fn mine_blocks(
+        &self,
+        count: usize,
+        address: Option<Address>,
+    ) -> anyhow::Result<Vec<BlockHash>> {
+        let coinbase_address = match address {
+            Some(address) => address,
+            None => self
+                .bitcoind
+                .client
+                .get_new_address(None, None)?
+                .assume_checked(),
+        };
+        let block_hashes = self
+            .bitcoind
+            .client
+            .generate_to_address(count as _, &coinbase_address)?;
+        Ok(block_hashes)
+    }
+
+    /// Mine a block that is guaranteed to be empty even with transactions in the mempool.
+    pub fn mine_empty_block(&self) -> anyhow::Result<(usize, BlockHash)> {
+        let bt = self.bitcoind.client.get_block_template(
+            GetBlockTemplateModes::Template,
+            &[GetBlockTemplateRules::SegWit],
+            &[],
+        )?;
+
+        let txdata = vec![Transaction {
+            version: transaction::Version::ONE,
+            lock_time: bdk_chain::bitcoin::absolute::LockTime::from_height(0)?,
+            input: vec![TxIn {
+                previous_output: bdk_chain::bitcoin::OutPoint::default(),
+                script_sig: ScriptBuf::builder()
+                    .push_int(bt.height as _)
+                    // randomn number so that re-mining creates unique block
+                    .push_int(random())
+                    .into_script(),
+                sequence: bdk_chain::bitcoin::Sequence::default(),
+                witness: bdk_chain::bitcoin::Witness::new(),
+            }],
+            output: vec![TxOut {
+                value: Amount::ZERO,
+                script_pubkey: ScriptBuf::new_p2sh(&ScriptHash::all_zeros()),
+            }],
+        }];
+
+        let bits: [u8; 4] = bt
+            .bits
+            .clone()
+            .try_into()
+            .expect("rpc provided us with invalid bits");
+
+        let mut block = Block {
+            header: Header {
+                version: bdk_chain::bitcoin::block::Version::default(),
+                prev_blockhash: bt.previous_block_hash,
+                merkle_root: TxMerkleNode::all_zeros(),
+                time: Ord::max(bt.min_time, std::time::UNIX_EPOCH.elapsed()?.as_secs()) as u32,
+                bits: CompactTarget::from_consensus(u32::from_be_bytes(bits)),
+                nonce: 0,
+            },
+            txdata,
+        };
+
+        block.header.merkle_root = block.compute_merkle_root().expect("must compute");
+
+        for nonce in 0..=u32::MAX {
+            block.header.nonce = nonce;
+            if block.header.target().is_met_by(block.block_hash()) {
+                break;
+            }
+        }
+
+        self.bitcoind.client.submit_block(&block)?;
+        Ok((bt.height as usize, block.block_hash()))
+    }
+
+    /// This method waits for the Electrum notification indicating that a new block has been mined.
+    pub fn wait_until_electrum_sees_block(&self) -> anyhow::Result<()> {
+        self.electrsd.client.block_headers_subscribe()?;
+        let mut delay = Duration::from_millis(64);
+
+        loop {
+            self.electrsd.trigger()?;
+            self.electrsd.client.ping()?;
+            if self.electrsd.client.block_headers_pop()?.is_some() {
+                return Ok(());
+            }
+
+            if delay.as_millis() < 512 {
+                delay = delay.mul_f32(2.0);
+            }
+            std::thread::sleep(delay);
+        }
+    }
+
+    /// Invalidate a number of blocks of a given size `count`.
+    pub fn invalidate_blocks(&self, count: usize) -> anyhow::Result<()> {
+        let mut hash = self.bitcoind.client.get_best_block_hash()?;
+        for _ in 0..count {
+            let prev_hash = self
+                .bitcoind
+                .client
+                .get_block_info(&hash)?
+                .previousblockhash;
+            self.bitcoind.client.invalidate_block(&hash)?;
+            match prev_hash {
+                Some(prev_hash) => hash = prev_hash,
+                None => break,
+            }
+        }
+        Ok(())
+    }
+
+    /// Reorg a number of blocks of a given size `count`.
+    /// Refer to [`TestEnv::mine_empty_block`] for more information.
+    pub fn reorg(&self, count: usize) -> anyhow::Result<Vec<BlockHash>> {
+        let start_height = self.bitcoind.client.get_block_count()?;
+        self.invalidate_blocks(count)?;
+
+        let res = self.mine_blocks(count, None);
+        assert_eq!(
+            self.bitcoind.client.get_block_count()?,
+            start_height,
+            "reorg should not result in height change"
+        );
+        res
+    }
+
+    /// Reorg with a number of empty blocks of a given size `count`.
+    pub fn reorg_empty_blocks(&self, count: usize) -> anyhow::Result<Vec<(usize, BlockHash)>> {
+        let start_height = self.bitcoind.client.get_block_count()?;
+        self.invalidate_blocks(count)?;
+
+        let res = (0..count)
+            .map(|_| self.mine_empty_block())
+            .collect::<Result<Vec<_>, _>>()?;
+        assert_eq!(
+            self.bitcoind.client.get_block_count()?,
+            start_height,
+            "reorg should not result in height change"
+        );
+        Ok(res)
+    }
+
+    /// Send a tx of a given `amount` to a given `address`.
+    pub fn send(&self, address: &Address<NetworkChecked>, amount: Amount) -> anyhow::Result<Txid> {
+        let txid = self
+            .bitcoind
+            .client
+            .send_to_address(address, amount, None, None, None, None, None, None)?;
+        Ok(txid)
+    }
+
+    /// Create a checkpoint linked list of all the blocks in the chain.
+    pub fn make_checkpoint_tip(&self) -> CheckPoint {
+        CheckPoint::from_block_ids((0_u32..).map_while(|height| {
+            self.bitcoind
+                .client
+                .get_block_hash(height as u64)
+                .ok()
+                .map(|hash| BlockId { height, hash })
+        }))
+        .expect("must craft tip")
+    }
+
+    /// Get the genesis hash of the blockchain.
+    pub fn genesis_hash(&self) -> anyhow::Result<BlockHash> {
+        let hash = self.bitcoind.client.get_block_hash(0)?;
+        Ok(hash)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::TestEnv;
+    use electrsd::bitcoind::{anyhow::Result, bitcoincore_rpc::RpcApi};
+
+    /// This checks that reorgs initiated by `bitcoind` is detected by our `electrsd` instance.
+    #[test]
+    fn test_reorg_is_detected_in_electrsd() -> Result<()> {
+        let env = TestEnv::new()?;
+
+        // Mine some blocks.
+        env.mine_blocks(101, None)?;
+        env.wait_until_electrum_sees_block()?;
+        let height = env.bitcoind.client.get_block_count()?;
+        let blocks = (0..=height)
+            .map(|i| env.bitcoind.client.get_block_hash(i))
+            .collect::<Result<Vec<_>, _>>()?;
+
+        // Perform reorg on six blocks.
+        env.reorg(6)?;
+        env.wait_until_electrum_sees_block()?;
+        let reorged_height = env.bitcoind.client.get_block_count()?;
+        let reorged_blocks = (0..=height)
+            .map(|i| env.bitcoind.client.get_block_hash(i))
+            .collect::<Result<Vec<_>, _>>()?;
+
+        assert_eq!(height, reorged_height);
+
+        // Block hashes should not be equal on the six reorged blocks.
+        for (i, (block, reorged_block)) in blocks.iter().zip(reorged_blocks.iter()).enumerate() {
+            match i <= height as usize - 6 {
+                true => assert_eq!(block, reorged_block),
+                false => assert_ne!(block, reorged_block),
+            }
+        }
+
+        Ok(())
+    }
+}

crates/wallet/Cargo.toml

@@ -0,0 +1,58 @@
+[package]
+name = "bdk_wallet"
+homepage = "https://bitcoindevkit.org"
+version = "1.0.0-beta.1"
+repository = "https://github.com/bitcoindevkit/bdk"
+documentation = "https://docs.rs/bdk"
+description = "A modern, lightweight, descriptor-based wallet library"
+keywords = ["bitcoin", "wallet", "descriptor", "psbt"]
+readme = "README.md"
+license = "MIT OR Apache-2.0"
+authors = ["Bitcoin Dev Kit Developers"]
+edition = "2021"
+rust-version = "1.63"
+
+[dependencies]
+rand_core = { version = "0.6.0" }
+miniscript = { version = "12.0.0", features = ["serde"], default-features = false }
+bitcoin = { version = "0.32.0", features = ["serde", "base64"], default-features = false }
+serde = { version = "^1.0", features = ["derive"] }
+serde_json = { version = "^1.0" }
+bdk_chain = { path = "../chain", version = "0.17.0", features = ["miniscript", "serde"], default-features = false }
+bdk_file_store = { path = "../file_store", version = "0.14.0", optional = true }
+
+# Optional dependencies
+bip39 = { version = "2.0", optional = true }
+
+[features]
+default = ["std"]
+std = ["bitcoin/std", "bitcoin/rand-std", "miniscript/std", "bdk_chain/std"]
+compiler = ["miniscript/compiler"]
+all-keys = ["keys-bip39"]
+keys-bip39 = ["bip39"]
+rusqlite = ["bdk_chain/rusqlite"]
+file_store = ["bdk_file_store"]
+
+[dev-dependencies]
+lazy_static = "1.4"
+assert_matches = "1.5.0"
+tempfile = "3"
+bdk_chain = { path = "../chain", features = ["rusqlite"] }
+bdk_wallet = { path = ".", features = ["rusqlite", "file_store"] }
+bdk_file_store = { path = "../file_store" }
+anyhow = "1"
+rand = "^0.8"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[[example]]
+name = "mnemonic_to_descriptors"
+path = "examples/mnemonic_to_descriptors.rs"
+required-features = ["all-keys"]
+
+[[example]]
+name = "miniscriptc"
+path = "examples/compiler.rs"
+required-features = ["compiler"]

crates/wallet/README.md

@@ -0,0 +1,243 @@
+<div align="center">
+  <h1>BDK</h1>
+
+  <img src="https://raw.githubusercontent.com/bitcoindevkit/bdk/master/static/bdk.png" width="220" />
+
+  <p>
+    <strong>A modern, lightweight, descriptor-based wallet library written in Rust!</strong>
+  </p>
+
+  <p>
+    <a href="https://crates.io/crates/bdk_wallet"><img alt="Crate Info" src="https://img.shields.io/crates/v/bdk_wallet.svg"/></a>
+    <a href="https://github.com/bitcoindevkit/bdk/blob/master/LICENSE"><img alt="MIT or Apache-2.0 Licensed" src="https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg"/></a>
+    <a href="https://github.com/bitcoindevkit/bdk/actions?query=workflow%3ACI"><img alt="CI Status" src="https://github.com/bitcoindevkit/bdk/workflows/CI/badge.svg"></a>
+    <a href="https://coveralls.io/github/bitcoindevkit/bdk?branch=master"><img src="https://coveralls.io/repos/github/bitcoindevkit/bdk/badge.svg?branch=master"/></a>
+    <a href="https://docs.rs/bdk_wallet"><img alt="API Docs" src="https://img.shields.io/badge/docs.rs-bdk_wallet-green"/></a>
+    <a href="https://blog.rust-lang.org/2022/08/11/Rust-1.63.0.html"><img alt="Rustc Version 1.63.0+" src="https://img.shields.io/badge/rustc-1.63.0%2B-lightgrey.svg"/></a>
+    <a href="https://discord.gg/d7NkDKm"><img alt="Chat on Discord" src="https://img.shields.io/discord/753336465005608961?logo=discord"></a>
+  </p>
+
+  <h4>
+    <a href="https://bitcoindevkit.org">Project Homepage</a>
+    <span> | </span>
+    <a href="https://docs.rs/bdk_wallet">Documentation</a>
+  </h4>
+</div>
+
+# BDK Wallet
+
+The `bdk_wallet` crate provides the [`Wallet`] type which is a simple, high-level
+interface built from the low-level components of [`bdk_chain`]. `Wallet` is a good starting point
+for many simple applications as well as a good demonstration of how to use the other mechanisms to
+construct a wallet. It has two keychains (external and internal) which are defined by
+[miniscript descriptors][`rust-miniscript`] and uses them to generate addresses. When you give it
+chain data it also uses the descriptors to find transaction outputs owned by them. From there, you
+can create and sign transactions.
+
+For details about the API of `Wallet` see the [module-level documentation][`Wallet`].
+
+## Blockchain data
+
+In order to get blockchain data for `Wallet` to consume, you should configure a client from
+an available chain source. Typically you make a request to the chain source and get a response
+that the `Wallet` can use to update its view of the chain.
+
+**Blockchain Data Sources**
+
+* [`bdk_esplora`]: Grabs blockchain data from Esplora for updating BDK structures.
+* [`bdk_electrum`]: Grabs blockchain data from Electrum for updating BDK structures.
+* [`bdk_bitcoind_rpc`]: Grabs blockchain data from Bitcoin Core for updating BDK structures.
+
+**Examples**
+
+* [`example-crates/wallet_esplora_async`](https://github.com/bitcoindevkit/bdk/tree/master/example-crates/wallet_esplora_async)
+* [`example-crates/wallet_esplora_blocking`](https://github.com/bitcoindevkit/bdk/tree/master/example-crates/wallet_esplora_blocking)
+* [`example-crates/wallet_electrum`](https://github.com/bitcoindevkit/bdk/tree/master/example-crates/wallet_electrum)
+* [`example-crates/wallet_rpc`](https://github.com/bitcoindevkit/bdk/tree/master/example-crates/wallet_rpc)
+
+## Persistence
+
+To persist `Wallet` state data use a data store crate that reads and writes [`ChangeSet`].
+
+**Implementations**
+
+* [`bdk_file_store`]: Stores wallet changes in a simple flat file.
+
+**Example**
+
+<!-- compile_fail because outpoint and txout are fake variables -->
+```rust,no_run
+use bdk_wallet::{bitcoin::Network, KeychainKind, ChangeSet, Wallet};
+
+// Open or create a new file store for wallet data.
+let mut db =
+    bdk_file_store::Store::<ChangeSet>::open_or_create_new(b"magic_bytes", "/tmp/my_wallet.db")
+        .expect("create store");
+
+// Create a wallet with initial wallet data read from the file store.
+let network = Network::Testnet;
+let descriptor = "wpkh(tprv8ZgxMBicQKsPdcAqYBpzAFwU5yxBUo88ggoBqu1qPcHUfSbKK1sKMLmC7EAk438btHQrSdu3jGGQa6PA71nvH5nkDexhLteJqkM4dQmWF9g/84'/1'/0'/0/*)";
+let change_descriptor = "wpkh(tprv8ZgxMBicQKsPdcAqYBpzAFwU5yxBUo88ggoBqu1qPcHUfSbKK1sKMLmC7EAk438btHQrSdu3jGGQa6PA71nvH5nkDexhLteJqkM4dQmWF9g/84'/1'/0'/1/*)";
+let wallet_opt = Wallet::load()
+    .descriptors(descriptor, change_descriptor)
+    .network(network)
+    .load_wallet(&mut db)
+    .expect("wallet");
+let mut wallet = match wallet_opt {
+    Some(wallet) => wallet,
+    None => Wallet::create(descriptor, change_descriptor)
+        .network(network)
+        .create_wallet(&mut db)
+        .expect("wallet"),
+};
+
+// Get a new address to receive bitcoin.
+let receive_address = wallet.reveal_next_address(KeychainKind::External);
+// Persist staged wallet data changes to the file store.
+wallet.persist(&mut db).expect("persist");
+println!("Your new receive address is: {}", receive_address.address);
+```
+
+<!-- ### Sync the balance of a descriptor -->
+
+<!-- ```rust,no_run -->
+<!-- use bdk_wallet::Wallet; -->
+<!-- use bdk_wallet::blockchain::ElectrumBlockchain; -->
+<!-- use bdk_wallet::SyncOptions; -->
+<!-- use bdk_wallet::electrum_client::Client; -->
+<!-- use bdk_wallet::bitcoin::Network; -->
+
+<!-- fn main() -> Result<(), bdk_wallet::Error> { -->
+<!--     let blockchain = ElectrumBlockchain::from(Client::new("ssl://electrum.blockstream.info:60002")?); -->
+<!--     let wallet = Wallet::new( -->
+<!--         "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/0/*)", -->
+<!--         Some("wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/1/*)"), -->
+<!--         Network::Testnet, -->
+<!--     )?; -->
+
+<!--     wallet.sync(&blockchain, SyncOptions::default())?; -->
+
+<!--     println!("Descriptor balance: {} SAT", wallet.balance()?); -->
+
+<!--     Ok(()) -->
+<!-- } -->
+<!-- ``` -->
+<!-- ### Generate a few addresses -->
+
+<!-- ```rust -->
+<!-- use bdk_wallet::Wallet; -->
+<!-- use bdk_wallet::AddressIndex::New; -->
+<!-- use bdk_wallet::bitcoin::Network; -->
+
+<!-- fn main() -> Result<(), bdk_wallet::Error> { -->
+<!--     let wallet = Wallet::new( -->
+<!--         "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/0/*)", -->
+<!--         Some("wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/1/*)"), -->
+<!--         Network::Testnet, -->
+<!--     )?; -->
+
+<!--     println!("Address #0: {}", wallet.get_address(New)); -->
+<!--     println!("Address #1: {}", wallet.get_address(New)); -->
+<!--     println!("Address #2: {}", wallet.get_address(New)); -->
+
+<!--     Ok(()) -->
+<!-- } -->
+<!-- ``` -->
+
+<!-- ### Create a transaction -->
+
+<!-- ```rust,no_run -->
+<!-- use bdk_wallet::{FeeRate, Wallet, SyncOptions}; -->
+<!-- use bdk_wallet::blockchain::ElectrumBlockchain; -->
+
+<!-- use bdk_wallet::electrum_client::Client; -->
+<!-- use bdk_wallet::AddressIndex::New; -->
+
+<!-- use bitcoin::base64; -->
+<!-- use bdk_wallet::bitcoin::consensus::serialize; -->
+<!-- use bdk_wallet::bitcoin::Network; -->
+
+<!-- fn main() -> Result<(), bdk_wallet::Error> { -->
+<!--     let blockchain = ElectrumBlockchain::from(Client::new("ssl://electrum.blockstream.info:60002")?); -->
+<!--     let wallet = Wallet::new( -->
+<!--         "wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/0/*)", -->
+<!--         Some("wpkh([c258d2e4/84h/1h/0h]tpubDDYkZojQFQjht8Tm4jsS3iuEmKjTiEGjG6KnuFNKKJb5A6ZUCUZKdvLdSDWofKi4ToRCwb9poe1XdqfUnP4jaJjCB2Zwv11ZLgSbnZSNecE/1/*)"), -->
+<!--         Network::Testnet, -->
+<!--     )?; -->
+
+<!--     wallet.sync(&blockchain, SyncOptions::default())?; -->
+
+<!--     let send_to = wallet.get_address(New); -->
+<!--     let (psbt, details) = { -->
+<!--         let mut builder = wallet.build_tx(); -->
+<!--         builder -->
+<!--             .add_recipient(send_to.script_pubkey(), 50_000) -->
+<!--             .enable_rbf() -->
+<!--             .do_not_spend_change() -->
+<!--             .fee_rate(FeeRate::from_sat_per_vb(5.0)); -->
+<!--         builder.finish()? -->
+<!--     }; -->
+
+<!--     println!("Transaction details: {:#?}", details); -->
+<!--     println!("Unsigned PSBT: {}", base64::encode(&serialize(&psbt))); -->
+
+<!--     Ok(()) -->
+<!-- } -->
+<!-- ``` -->
+
+<!-- ### Sign a transaction -->
+
+<!-- ```rust,no_run -->
+<!-- use bdk_wallet::{Wallet, SignOptions}; -->
+
+<!-- use bitcoin::base64; -->
+<!-- use bdk_wallet::bitcoin::consensus::deserialize; -->
+<!-- use bdk_wallet::bitcoin::Network; -->
+
+<!-- fn main() -> Result<(), bdk_wallet::Error> { -->
+<!--     let wallet = Wallet::new( -->
+<!--         "wpkh([c258d2e4/84h/1h/0h]tprv8griRPhA7342zfRyB6CqeKF8CJDXYu5pgnj1cjL1u2ngKcJha5jjTRimG82ABzJQ4MQe71CV54xfn25BbhCNfEGGJZnxvCDQCd6JkbvxW6h/0/*)", -->
+<!--         Some("wpkh([c258d2e4/84h/1h/0h]tprv8griRPhA7342zfRyB6CqeKF8CJDXYu5pgnj1cjL1u2ngKcJha5jjTRimG82ABzJQ4MQe71CV54xfn25BbhCNfEGGJZnxvCDQCd6JkbvxW6h/1/*)"), -->
+<!--         Network::Testnet, -->
+<!--     )?; -->
+
+<!--     let psbt = "..."; -->
+<!--     let mut psbt = deserialize(&base64::decode(psbt).unwrap())?; -->
+
+<!--     let _finalized = wallet.sign(&mut psbt, SignOptions::default())?; -->
+
+<!--     Ok(()) -->
+<!-- } -->
+<!-- ``` -->
+
+## Testing
+
+### Unit testing
+
+```bash
+cargo test
+```
+
+# License
+
+Licensed under either of
+
+* Apache License, Version 2.0, ([LICENSE-APACHE](../../LICENSE-APACHE) or <https://www.apache.org/licenses/LICENSE-2.0>)
+* MIT license ([LICENSE-MIT](../../LICENSE-MIT) or <https://opensource.org/licenses/MIT>)
+
+at your option.
+
+# Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally
+submitted for inclusion in the work by you, as defined in the Apache-2.0
+license, shall be dual licensed as above, without any additional terms or
+conditions.
+
+[`Wallet`]: https://docs.rs/bdk_wallet/latest/bdk_wallet/wallet/struct.Wallet.html
+[`bdk_chain`]: https://docs.rs/bdk_chain/latest
+[`bdk_file_store`]: https://docs.rs/bdk_file_store/latest
+[`bdk_electrum`]: https://docs.rs/bdk_electrum/latest
+[`bdk_esplora`]: https://docs.rs/bdk_esplora/latest
+[`bdk_bitcoind_rpc`]: https://docs.rs/bdk_bitcoind_rpc/latest
+[`rust-miniscript`]: https://docs.rs/miniscript/latest/miniscript/index.html

crates/wallet/examples/compiler.rs

@@ -0,0 +1,98 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+extern crate bdk_wallet;
+extern crate bitcoin;
+extern crate miniscript;
+extern crate serde_json;
+
+use std::error::Error;
+use std::str::FromStr;
+
+use bitcoin::Network;
+use miniscript::policy::Concrete;
+use miniscript::Descriptor;
+
+use bdk_wallet::{KeychainKind, Wallet};
+
+/// Miniscript policy is a high level abstraction of spending conditions. Defined in the
+/// rust-miniscript library here  https://docs.rs/miniscript/7.0.0/miniscript/policy/index.html
+/// rust-miniscript provides a `compile()` function that can be used to compile any miniscript policy
+/// into a descriptor. This descriptor then in turn can be used in bdk a fully functioning wallet
+/// can be derived from the policy.
+///
+/// This example demonstrates the interaction between a bdk wallet and miniscript policy.
+
+fn main() -> Result<(), Box<dyn Error>> {
+    // We start with a miniscript policy string
+    let policy_str = "or(
+        10@thresh(4,
+            pk(029ffbe722b147f3035c87cb1c60b9a5947dd49c774cc31e94773478711a929ac0),pk(025f05815e3a1a8a83bfbb03ce016c9a2ee31066b98f567f6227df1d76ec4bd143),pk(025625f41e4a065efc06d5019cbbd56fe8c07595af1231e7cbc03fafb87ebb71ec),pk(02a27c8b850a00f67da3499b60562673dcf5fdfb82b7e17652a7ac54416812aefd),pk(03e618ec5f384d6e19ca9ebdb8e2119e5bef978285076828ce054e55c4daf473e2)
+        ),1@and(
+            older(4209713),
+            thresh(2,
+                pk(03deae92101c790b12653231439f27b8897264125ecb2f46f48278603102573165),pk(033841045a531e1adf9910a6ec279589a90b3b8a904ee64ffd692bd08a8996c1aa),pk(02aebf2d10b040eb936a6f02f44ee82f8b34f5c1ccb20ff3949c2b28206b7c1068)
+            )
+        )
+    )"
+    .replace(&[' ', '\n', '\t'][..], "");
+
+    println!("Compiling policy: \n{}", policy_str);
+
+    // Parse the string as a [`Concrete`] type miniscript policy.
+    let policy = Concrete::<String>::from_str(&policy_str)?;
+
+    // Create a `wsh` type descriptor from the policy.
+    // `policy.compile()` returns the resulting miniscript from the policy.
+    let descriptor = Descriptor::new_wsh(policy.compile()?)?.to_string();
+
+    println!("Compiled into Descriptor: \n{}", descriptor);
+
+    // Do the same for another (internal) keychain
+    let policy_str = "or(
+        10@thresh(2,
+            pk(029ffbe722b147f3035c87cb1c60b9a5947dd49c774cc31e94773478711a929ac0),pk(025f05815e3a1a8a83bfbb03ce016c9a2ee31066b98f567f6227df1d76ec4bd143),pk(025625f41e4a065efc06d5019cbbd56fe8c07595af1231e7cbc03fafb87ebb71ec)
+        ),1@and(
+            pk(03deae92101c790b12653231439f27b8897264125ecb2f46f48278603102573165),
+            older(12960)
+        )
+    )"
+    .replace(&[' ', '\n', '\t'][..], "");
+
+    println!("Compiling internal policy: \n{}", policy_str);
+
+    let policy = Concrete::<String>::from_str(&policy_str)?;
+    let internal_descriptor = Descriptor::new_wsh(policy.compile()?)?.to_string();
+    println!(
+        "Compiled into internal Descriptor: \n{}",
+        internal_descriptor
+    );
+
+    // Create a new wallet from descriptors
+    let mut wallet = Wallet::create(descriptor, internal_descriptor)
+        .network(Network::Regtest)
+        .create_wallet_no_persist()?;
+
+    println!(
+        "First derived address from the descriptor: \n{}",
+        wallet.next_unused_address(KeychainKind::External),
+    );
+
+    // BDK also has it's own `Policy` structure to represent the spending condition in a more
+    // human readable json format.
+    let spending_policy = wallet.policies(KeychainKind::External)?;
+    println!(
+        "The BDK spending policy: \n{}",
+        serde_json::to_string_pretty(&spending_policy)?
+    );
+
+    Ok(())
+}

crates/wallet/examples/mnemonic_to_descriptors.rs

@@ -0,0 +1,59 @@
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+use anyhow::anyhow;
+use bdk_wallet::bitcoin::bip32::DerivationPath;
+use bdk_wallet::bitcoin::secp256k1::Secp256k1;
+use bdk_wallet::bitcoin::Network;
+use bdk_wallet::descriptor;
+use bdk_wallet::descriptor::IntoWalletDescriptor;
+use bdk_wallet::keys::bip39::{Language, Mnemonic, WordCount};
+use bdk_wallet::keys::{GeneratableKey, GeneratedKey};
+use bdk_wallet::miniscript::Tap;
+use std::str::FromStr;
+
+/// This example demonstrates how to generate a mnemonic phrase
+/// using BDK and use that to generate a descriptor string.
+fn main() -> Result<(), anyhow::Error> {
+    let secp = Secp256k1::new();
+
+    // In this example we are generating a 12 words mnemonic phrase
+    // but it is also possible generate 15, 18, 21 and 24 words
+    // using their respective `WordCount` variant.
+    let mnemonic: GeneratedKey<_, Tap> =
+        Mnemonic::generate((WordCount::Words12, Language::English))
+            .map_err(|_| anyhow!("Mnemonic generation error"))?;
+
+    println!("Mnemonic phrase: {}", *mnemonic);
+    let mnemonic_with_passphrase = (mnemonic, None);
+
+    // define external and internal derivation key path
+    let external_path = DerivationPath::from_str("m/86h/1h/0h/0").unwrap();
+    let internal_path = DerivationPath::from_str("m/86h/1h/0h/1").unwrap();
+
+    // generate external and internal descriptor from mnemonic
+    let (external_descriptor, ext_keymap) =
+        descriptor!(tr((mnemonic_with_passphrase.clone(), external_path)))?
+            .into_wallet_descriptor(&secp, Network::Testnet)?;
+    let (internal_descriptor, int_keymap) =
+        descriptor!(tr((mnemonic_with_passphrase, internal_path)))?
+            .into_wallet_descriptor(&secp, Network::Testnet)?;
+
+    println!("tpub external descriptor: {}", external_descriptor);
+    println!("tpub internal descriptor: {}", internal_descriptor);
+    println!(
+        "tprv external descriptor: {}",
+        external_descriptor.to_string_with_secret(&ext_keymap)
+    );
+    println!(
+        "tprv internal descriptor: {}",
+        internal_descriptor.to_string_with_secret(&int_keymap)
+    );
+
+    Ok(())
+}

crates/wallet/examples/policy.rs

@@ -0,0 +1,60 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+extern crate bdk_wallet;
+use std::error::Error;
+
+use bdk_wallet::bitcoin::Network;
+use bdk_wallet::descriptor::{policy::BuildSatisfaction, ExtractPolicy, IntoWalletDescriptor};
+use bdk_wallet::signer::SignersContainer;
+
+/// This example describes the use of the BDK's [`bdk_wallet::descriptor::policy`] module.
+///
+/// Policy is higher abstraction representation of the wallet descriptor spending condition.
+/// This is useful to express complex miniscript spending conditions into more human readable form.
+/// The resulting `Policy` structure  can be used to derive spending conditions the wallet is capable
+/// to spend from.
+///
+/// This example demos a Policy output for a 2of2 multisig between between 2 parties, where the wallet holds
+/// one of the Extend Private key.
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let secp = bitcoin::secp256k1::Secp256k1::new();
+
+    // The descriptor used in the example
+    // The form is "wsh(multi(2, <privkey>, <pubkey>))"
+    let desc = "wsh(multi(2,tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/*,tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/*))";
+
+    // Use the descriptor string to derive the full descriptor and a keymap.
+    // The wallet descriptor can be used to create a new bdk_wallet::wallet.
+    // While the `keymap` can be used to create a `SignerContainer`.
+    //
+    // The `SignerContainer` can sign for `PSBT`s.
+    // a `bdk_wallet::Wallet` internally uses these to handle transaction signing.
+    // But they can be used as independent tools also.
+    let (wallet_desc, keymap) = desc.into_wallet_descriptor(&secp, Network::Testnet)?;
+
+    println!("Example Descriptor for policy analysis : {}", wallet_desc);
+
+    // Create the signer with the keymap and descriptor.
+    let signers_container = SignersContainer::build(keymap, &wallet_desc, &secp);
+
+    // Extract the Policy from the given descriptor and signer.
+    // Note that Policy is a wallet specific structure. It depends on the the descriptor, and
+    // what the concerned wallet with a given signer can sign for.
+    let policy = wallet_desc
+        .extract_policy(&signers_container, BuildSatisfaction::None, &secp)?
+        .expect("We expect a policy");
+
+    println!("Derived Policy for the descriptor {:#?}", policy);
+
+    Ok(())
+}

crates/wallet/src/descriptor/checksum.rs

@@ -0,0 +1,147 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Descriptor checksum
+//!
+//! This module contains a re-implementation of the function used by Bitcoin Core to calculate the
+//! checksum of a descriptor
+
+use crate::descriptor::DescriptorError;
+use alloc::string::String;
+
+const INPUT_CHARSET: &[u8] = b"0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
+const CHECKSUM_CHARSET: &[u8] = b"qpzry9x8gf2tvdw0s3jn54khce6mua7l";
+
+fn poly_mod(mut c: u64, val: u64) -> u64 {
+    let c0 = c >> 35;
+    c = ((c & 0x7ffffffff) << 5) ^ val;
+    if c0 & 1 > 0 {
+        c ^= 0xf5dee51989
+    };
+    if c0 & 2 > 0 {
+        c ^= 0xa9fdca3312
+    };
+    if c0 & 4 > 0 {
+        c ^= 0x1bab10e32d
+    };
+    if c0 & 8 > 0 {
+        c ^= 0x3706b1677a
+    };
+    if c0 & 16 > 0 {
+        c ^= 0x644d626ffd
+    };
+
+    c
+}
+
+/// Compute the checksum bytes of a descriptor, excludes any existing checksum in the descriptor string from the calculation
+pub fn calc_checksum_bytes(mut desc: &str) -> Result<[u8; 8], DescriptorError> {
+    let mut c = 1;
+    let mut cls = 0;
+    let mut clscount = 0;
+
+    let mut original_checksum = None;
+    if let Some(split) = desc.split_once('#') {
+        desc = split.0;
+        original_checksum = Some(split.1);
+    }
+
+    for ch in desc.as_bytes() {
+        let pos = INPUT_CHARSET
+            .iter()
+            .position(|b| b == ch)
+            .ok_or(DescriptorError::InvalidDescriptorCharacter(*ch))? as u64;
+        c = poly_mod(c, pos & 31);
+        cls = cls * 3 + (pos >> 5);
+        clscount += 1;
+        if clscount == 3 {
+            c = poly_mod(c, cls);
+            cls = 0;
+            clscount = 0;
+        }
+    }
+    if clscount > 0 {
+        c = poly_mod(c, cls);
+    }
+    (0..8).for_each(|_| c = poly_mod(c, 0));
+    c ^= 1;
+
+    let mut checksum = [0_u8; 8];
+    for j in 0..8 {
+        checksum[j] = CHECKSUM_CHARSET[((c >> (5 * (7 - j))) & 31) as usize];
+    }
+
+    // if input data already had a checksum, check calculated checksum against original checksum
+    if let Some(original_checksum) = original_checksum {
+        if original_checksum.as_bytes() != checksum {
+            return Err(DescriptorError::InvalidDescriptorChecksum);
+        }
+    }
+
+    Ok(checksum)
+}
+
+/// Compute the checksum of a descriptor, excludes any existing checksum in the descriptor string from the calculation
+pub fn calc_checksum(desc: &str) -> Result<String, DescriptorError> {
+    // unsafe is okay here as the checksum only uses bytes in `CHECKSUM_CHARSET`
+    calc_checksum_bytes(desc).map(|b| unsafe { String::from_utf8_unchecked(b.to_vec()) })
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::descriptor::calc_checksum;
+    use assert_matches::assert_matches;
+
+    // test calc_checksum() function; it should return the same value as Bitcoin Core
+    #[test]
+    fn test_calc_checksum() {
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)";
+        assert_eq!(calc_checksum(desc).unwrap(), "tqz0nc62");
+
+        let desc = "pkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/44'/1'/0'/0/*)";
+        assert_eq!(calc_checksum(desc).unwrap(), "lasegmfs");
+    }
+
+    // test calc_checksum() function; it should return the same value as Bitcoin Core even if the
+    // descriptor string includes a checksum hash
+    #[test]
+    fn test_calc_checksum_with_checksum_hash() {
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)#tqz0nc62";
+        assert_eq!(calc_checksum(desc).unwrap(), "tqz0nc62");
+
+        let desc = "pkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/44'/1'/0'/0/*)#lasegmfs";
+        assert_eq!(calc_checksum(desc).unwrap(), "lasegmfs");
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)#tqz0nc26";
+        assert_matches!(
+            calc_checksum(desc),
+            Err(DescriptorError::InvalidDescriptorChecksum)
+        );
+
+        let desc = "pkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/44'/1'/0'/0/*)#lasegmsf";
+        assert_matches!(
+            calc_checksum(desc),
+            Err(DescriptorError::InvalidDescriptorChecksum)
+        );
+    }
+
+    #[test]
+    fn test_calc_checksum_invalid_character() {
+        let sparkle_heart = unsafe { core::str::from_utf8_unchecked(&[240, 159, 146, 150]) };
+        let invalid_desc = format!("wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcL{}fjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)", sparkle_heart);
+
+        assert_matches!(
+            calc_checksum(&invalid_desc),
+            Err(DescriptorError::InvalidDescriptorCharacter(invalid_char)) if invalid_char == sparkle_heart.as_bytes()[0]
+        );
+    }
+}

crates/wallet/src/descriptor/error.rs

@@ -0,0 +1,127 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Descriptor errors
+use core::fmt;
+
+/// Errors related to the parsing and usage of descriptors
+#[derive(Debug, PartialEq)]
+pub enum Error {
+    /// Invalid HD Key path, such as having a wildcard but a length != 1
+    InvalidHdKeyPath,
+    /// The provided descriptor doesn't match its checksum
+    InvalidDescriptorChecksum,
+    /// The descriptor contains hardened derivation steps on public extended keys
+    HardenedDerivationXpub,
+    /// The descriptor contains multipath keys
+    MultiPath,
+    /// Error thrown while working with [`keys`](crate::keys)
+    Key(crate::keys::KeyError),
+    /// Error while extracting and manipulating policies
+    Policy(crate::descriptor::policy::PolicyError),
+
+    /// Invalid byte found in the descriptor checksum
+    InvalidDescriptorCharacter(u8),
+
+    /// BIP32 error
+    Bip32(bitcoin::bip32::Error),
+    /// Error during base58 decoding
+    Base58(bitcoin::base58::Error),
+    /// Key-related error
+    Pk(bitcoin::key::ParsePublicKeyError),
+    /// Miniscript error
+    Miniscript(miniscript::Error),
+    /// Hex decoding error
+    Hex(bitcoin::hex::HexToBytesError),
+    /// The provided wallet descriptors are identical
+    ExternalAndInternalAreTheSame,
+}
+
+impl From<crate::keys::KeyError> for Error {
+    fn from(key_error: crate::keys::KeyError) -> Error {
+        match key_error {
+            crate::keys::KeyError::Miniscript(inner) => Error::Miniscript(inner),
+            crate::keys::KeyError::Bip32(inner) => Error::Bip32(inner),
+            e => Error::Key(e),
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::InvalidHdKeyPath => write!(f, "Invalid HD key path"),
+            Self::InvalidDescriptorChecksum => {
+                write!(f, "The provided descriptor doesn't match its checksum")
+            }
+            Self::HardenedDerivationXpub => write!(
+                f,
+                "The descriptor contains hardened derivation steps on public extended keys"
+            ),
+            Self::MultiPath => write!(
+                f,
+                "The descriptor contains multipath keys, which are not supported yet"
+            ),
+            Self::Key(err) => write!(f, "Key error: {}", err),
+            Self::Policy(err) => write!(f, "Policy error: {}", err),
+            Self::InvalidDescriptorCharacter(char) => {
+                write!(f, "Invalid descriptor character: {}", char)
+            }
+            Self::Bip32(err) => write!(f, "BIP32 error: {}", err),
+            Self::Base58(err) => write!(f, "Base58 error: {}", err),
+            Self::Pk(err) => write!(f, "Key-related error: {}", err),
+            Self::Miniscript(err) => write!(f, "Miniscript error: {}", err),
+            Self::Hex(err) => write!(f, "Hex decoding error: {}", err),
+            Self::ExternalAndInternalAreTheSame => {
+                write!(f, "External and internal descriptors are the same")
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for Error {}
+
+impl From<bitcoin::bip32::Error> for Error {
+    fn from(err: bitcoin::bip32::Error) -> Self {
+        Error::Bip32(err)
+    }
+}
+
+impl From<bitcoin::base58::Error> for Error {
+    fn from(err: bitcoin::base58::Error) -> Self {
+        Error::Base58(err)
+    }
+}
+
+impl From<bitcoin::key::ParsePublicKeyError> for Error {
+    fn from(err: bitcoin::key::ParsePublicKeyError) -> Self {
+        Error::Pk(err)
+    }
+}
+
+impl From<miniscript::Error> for Error {
+    fn from(err: miniscript::Error) -> Self {
+        Error::Miniscript(err)
+    }
+}
+
+impl From<bitcoin::hex::HexToBytesError> for Error {
+    fn from(err: bitcoin::hex::HexToBytesError) -> Self {
+        Error::Hex(err)
+    }
+}
+
+impl From<crate::descriptor::policy::PolicyError> for Error {
+    fn from(err: crate::descriptor::policy::PolicyError) -> Self {
+        Error::Policy(err)
+    }
+}

crates/wallet/src/descriptor/mod.rs

@@ -0,0 +1,916 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Descriptors
+//!
+//! This module contains generic utilities to work with descriptors, plus some re-exported types
+//! from [`miniscript`].
+
+use crate::collections::BTreeMap;
+use alloc::string::String;
+use alloc::vec::Vec;
+
+use bitcoin::bip32::{ChildNumber, DerivationPath, Fingerprint, KeySource, Xpub};
+use bitcoin::{key::XOnlyPublicKey, secp256k1, PublicKey};
+use bitcoin::{psbt, taproot};
+use bitcoin::{Network, TxOut};
+
+use miniscript::descriptor::{
+    DefiniteDescriptorKey, DescriptorMultiXKey, DescriptorSecretKey, DescriptorType,
+    DescriptorXKey, InnerXKey, KeyMap, SinglePubKey, Wildcard,
+};
+pub use miniscript::{
+    Descriptor, DescriptorPublicKey, Legacy, Miniscript, ScriptContext, Segwitv0,
+};
+use miniscript::{ForEachKey, MiniscriptKey, TranslatePk};
+
+use crate::descriptor::policy::BuildSatisfaction;
+
+pub mod checksum;
+#[doc(hidden)]
+pub mod dsl;
+pub mod error;
+pub mod policy;
+pub mod template;
+
+pub use self::checksum::calc_checksum;
+use self::checksum::calc_checksum_bytes;
+pub use self::error::Error as DescriptorError;
+pub use self::policy::Policy;
+use self::template::DescriptorTemplateOut;
+use crate::keys::{IntoDescriptorKey, KeyError};
+use crate::wallet::signer::SignersContainer;
+use crate::wallet::utils::SecpCtx;
+
+/// Alias for a [`Descriptor`] that can contain extended keys using [`DescriptorPublicKey`]
+pub type ExtendedDescriptor = Descriptor<DescriptorPublicKey>;
+
+/// Alias for a [`Descriptor`] that contains extended **derived** keys
+pub type DerivedDescriptor = Descriptor<DefiniteDescriptorKey>;
+
+/// Alias for the type of maps that represent derivation paths in a [`psbt::Input`] or
+/// [`psbt::Output`]
+///
+/// [`psbt::Input`]: bitcoin::psbt::Input
+/// [`psbt::Output`]: bitcoin::psbt::Output
+pub type HdKeyPaths = BTreeMap<secp256k1::PublicKey, KeySource>;
+
+/// Alias for the type of maps that represent taproot key origins in a [`psbt::Input`] or
+/// [`psbt::Output`]
+///
+/// [`psbt::Input`]: bitcoin::psbt::Input
+/// [`psbt::Output`]: bitcoin::psbt::Output
+pub type TapKeyOrigins = BTreeMap<XOnlyPublicKey, (Vec<taproot::TapLeafHash>, KeySource)>;
+
+/// Trait for types which can be converted into an [`ExtendedDescriptor`] and a [`KeyMap`] usable by a wallet in a specific [`Network`]
+pub trait IntoWalletDescriptor {
+    /// Convert to wallet descriptor
+    fn into_wallet_descriptor(
+        self,
+        secp: &SecpCtx,
+        network: Network,
+    ) -> Result<(ExtendedDescriptor, KeyMap), DescriptorError>;
+}
+
+impl IntoWalletDescriptor for &str {
+    fn into_wallet_descriptor(
+        self,
+        secp: &SecpCtx,
+        network: Network,
+    ) -> Result<(ExtendedDescriptor, KeyMap), DescriptorError> {
+        let descriptor = match self.split_once('#') {
+            Some((desc, original_checksum)) => {
+                let checksum = calc_checksum_bytes(desc)?;
+                if original_checksum.as_bytes() != checksum {
+                    return Err(DescriptorError::InvalidDescriptorChecksum);
+                }
+                desc
+            }
+            None => self,
+        };
+
+        ExtendedDescriptor::parse_descriptor(secp, descriptor)?
+            .into_wallet_descriptor(secp, network)
+    }
+}
+
+impl IntoWalletDescriptor for &String {
+    fn into_wallet_descriptor(
+        self,
+        secp: &SecpCtx,
+        network: Network,
+    ) -> Result<(ExtendedDescriptor, KeyMap), DescriptorError> {
+        self.as_str().into_wallet_descriptor(secp, network)
+    }
+}
+
+impl IntoWalletDescriptor for String {
+    fn into_wallet_descriptor(
+        self,
+        secp: &SecpCtx,
+        network: Network,
+    ) -> Result<(ExtendedDescriptor, KeyMap), DescriptorError> {
+        self.as_str().into_wallet_descriptor(secp, network)
+    }
+}
+
+impl IntoWalletDescriptor for ExtendedDescriptor {
+    fn into_wallet_descriptor(
+        self,
+        secp: &SecpCtx,
+        network: Network,
+    ) -> Result<(ExtendedDescriptor, KeyMap), DescriptorError> {
+        (self, KeyMap::default()).into_wallet_descriptor(secp, network)
+    }
+}
+
+impl IntoWalletDescriptor for (ExtendedDescriptor, KeyMap) {
+    fn into_wallet_descriptor(
+        self,
+        secp: &SecpCtx,
+        network: Network,
+    ) -> Result<(ExtendedDescriptor, KeyMap), DescriptorError> {
+        use crate::keys::DescriptorKey;
+
+        struct Translator<'s, 'd> {
+            secp: &'s SecpCtx,
+            descriptor: &'d ExtendedDescriptor,
+            network: Network,
+        }
+
+        impl<'s, 'd> miniscript::Translator<DescriptorPublicKey, String, DescriptorError>
+            for Translator<'s, 'd>
+        {
+            fn pk(&mut self, pk: &DescriptorPublicKey) -> Result<String, DescriptorError> {
+                let secp = &self.secp;
+
+                let (_, _, networks) = if self.descriptor.is_taproot() {
+                    let descriptor_key: DescriptorKey<miniscript::Tap> =
+                        pk.clone().into_descriptor_key()?;
+                    descriptor_key.extract(secp)?
+                } else if self.descriptor.is_witness() {
+                    let descriptor_key: DescriptorKey<miniscript::Segwitv0> =
+                        pk.clone().into_descriptor_key()?;
+                    descriptor_key.extract(secp)?
+                } else {
+                    let descriptor_key: DescriptorKey<miniscript::Legacy> =
+                        pk.clone().into_descriptor_key()?;
+                    descriptor_key.extract(secp)?
+                };
+
+                if networks.contains(&self.network) {
+                    Ok(Default::default())
+                } else {
+                    Err(DescriptorError::Key(KeyError::InvalidNetwork))
+                }
+            }
+            fn sha256(
+                &mut self,
+                _sha256: &<DescriptorPublicKey as MiniscriptKey>::Sha256,
+            ) -> Result<String, DescriptorError> {
+                Ok(Default::default())
+            }
+            fn hash256(
+                &mut self,
+                _hash256: &<DescriptorPublicKey as MiniscriptKey>::Hash256,
+            ) -> Result<String, DescriptorError> {
+                Ok(Default::default())
+            }
+            fn ripemd160(
+                &mut self,
+                _ripemd160: &<DescriptorPublicKey as MiniscriptKey>::Ripemd160,
+            ) -> Result<String, DescriptorError> {
+                Ok(Default::default())
+            }
+            fn hash160(
+                &mut self,
+                _hash160: &<DescriptorPublicKey as MiniscriptKey>::Hash160,
+            ) -> Result<String, DescriptorError> {
+                Ok(Default::default())
+            }
+        }
+
+        // check the network for the keys
+        use miniscript::TranslateErr;
+        match self.0.translate_pk(&mut Translator {
+            secp,
+            network,
+            descriptor: &self.0,
+        }) {
+            Ok(_) => {}
+            Err(TranslateErr::TranslatorErr(e)) => return Err(e),
+            Err(TranslateErr::OuterError(e)) => return Err(e.into()),
+        }
+
+        Ok(self)
+    }
+}
+
+impl IntoWalletDescriptor for DescriptorTemplateOut {
+    fn into_wallet_descriptor(
+        self,
+        _secp: &SecpCtx,
+        network: Network,
+    ) -> Result<(ExtendedDescriptor, KeyMap), DescriptorError> {
+        struct Translator {
+            network: Network,
+        }
+
+        impl miniscript::Translator<DescriptorPublicKey, DescriptorPublicKey, DescriptorError>
+            for Translator
+        {
+            fn pk(
+                &mut self,
+                pk: &DescriptorPublicKey,
+            ) -> Result<DescriptorPublicKey, DescriptorError> {
+                // workaround for xpubs generated by other key types, like bip39: since when the
+                // conversion is made one network has to be chosen, what we generally choose
+                // "mainnet", but then override the set of valid networks to specify that all of
+                // them are valid. here we reset the network to make sure the wallet struct gets a
+                // descriptor with the right network everywhere.
+                let pk = match pk {
+                    DescriptorPublicKey::XPub(ref xpub) => {
+                        let mut xpub = xpub.clone();
+                        xpub.xkey.network = self.network.into();
+
+                        DescriptorPublicKey::XPub(xpub)
+                    }
+                    other => other.clone(),
+                };
+
+                Ok(pk)
+            }
+            miniscript::translate_hash_clone!(
+                DescriptorPublicKey,
+                DescriptorPublicKey,
+                DescriptorError
+            );
+        }
+
+        let (desc, keymap, networks) = self;
+
+        if !networks.contains(&network) {
+            return Err(DescriptorError::Key(KeyError::InvalidNetwork));
+        }
+
+        // fixup the network for keys that need it in the descriptor
+        use miniscript::TranslateErr;
+        let translated = match desc.translate_pk(&mut Translator { network }) {
+            Ok(descriptor) => descriptor,
+            Err(TranslateErr::TranslatorErr(e)) => return Err(e),
+            Err(TranslateErr::OuterError(e)) => return Err(e.into()),
+        };
+        // ...and in the key map
+        let fixed_keymap = keymap
+            .into_iter()
+            .map(|(mut k, mut v)| {
+                match (&mut k, &mut v) {
+                    (DescriptorPublicKey::XPub(xpub), DescriptorSecretKey::XPrv(xprv)) => {
+                        xpub.xkey.network = network.into();
+                        xprv.xkey.network = network.into();
+                    }
+                    (_, DescriptorSecretKey::Single(key)) => {
+                        key.key.network = network.into();
+                    }
+                    _ => {}
+                }
+
+                (k, v)
+            })
+            .collect();
+
+        Ok((translated, fixed_keymap))
+    }
+}
+
+/// Extra checks for [`ExtendedDescriptor`].
+pub(crate) fn check_wallet_descriptor(
+    descriptor: &Descriptor<DescriptorPublicKey>,
+) -> Result<(), DescriptorError> {
+    // Ensure the keys don't contain any hardened derivation steps or hardened wildcards
+    let descriptor_contains_hardened_steps = descriptor.for_any_key(|k| {
+        if let DescriptorPublicKey::XPub(DescriptorXKey {
+            derivation_path,
+            wildcard,
+            ..
+        }) = k
+        {
+            return *wildcard == Wildcard::Hardened
+                || derivation_path.into_iter().any(ChildNumber::is_hardened);
+        }
+
+        false
+    });
+    if descriptor_contains_hardened_steps {
+        return Err(DescriptorError::HardenedDerivationXpub);
+    }
+
+    if descriptor.is_multipath() {
+        return Err(DescriptorError::MultiPath);
+    }
+
+    // Run miniscript's sanity check, which will look for duplicated keys and other potential
+    // issues
+    descriptor.sanity_check()?;
+
+    Ok(())
+}
+
+#[doc(hidden)]
+/// Used internally mainly by the `descriptor!()` and `fragment!()` macros
+pub trait CheckMiniscript<Ctx: miniscript::ScriptContext> {
+    fn check_miniscript(&self) -> Result<(), miniscript::Error>;
+}
+
+impl<Ctx: miniscript::ScriptContext, Pk: miniscript::MiniscriptKey> CheckMiniscript<Ctx>
+    for miniscript::Miniscript<Pk, Ctx>
+{
+    fn check_miniscript(&self) -> Result<(), miniscript::Error> {
+        Ctx::check_global_validity(self)?;
+
+        Ok(())
+    }
+}
+
+/// Trait implemented on [`Descriptor`]s to add a method to extract the spending [`policy`]
+pub trait ExtractPolicy {
+    /// Extract the spending [`policy`]
+    fn extract_policy(
+        &self,
+        signers: &SignersContainer,
+        psbt: BuildSatisfaction,
+        secp: &SecpCtx,
+    ) -> Result<Option<Policy>, DescriptorError>;
+}
+
+pub(crate) trait XKeyUtils {
+    fn root_fingerprint(&self, secp: &SecpCtx) -> Fingerprint;
+}
+
+impl<T> XKeyUtils for DescriptorMultiXKey<T>
+where
+    T: InnerXKey,
+{
+    fn root_fingerprint(&self, secp: &SecpCtx) -> Fingerprint {
+        match self.origin {
+            Some((fingerprint, _)) => fingerprint,
+            None => self.xkey.xkey_fingerprint(secp),
+        }
+    }
+}
+
+impl<T> XKeyUtils for DescriptorXKey<T>
+where
+    T: InnerXKey,
+{
+    fn root_fingerprint(&self, secp: &SecpCtx) -> Fingerprint {
+        match self.origin {
+            Some((fingerprint, _)) => fingerprint,
+            None => self.xkey.xkey_fingerprint(secp),
+        }
+    }
+}
+
+pub(crate) trait DescriptorMeta {
+    fn is_witness(&self) -> bool;
+    fn is_taproot(&self) -> bool;
+    fn get_extended_keys(&self) -> Vec<DescriptorXKey<Xpub>>;
+    fn derive_from_hd_keypaths(
+        &self,
+        hd_keypaths: &HdKeyPaths,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor>;
+    fn derive_from_tap_key_origins(
+        &self,
+        tap_key_origins: &TapKeyOrigins,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor>;
+    fn derive_from_psbt_key_origins(
+        &self,
+        key_origins: BTreeMap<Fingerprint, (&DerivationPath, SinglePubKey)>,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor>;
+    fn derive_from_psbt_input(
+        &self,
+        psbt_input: &psbt::Input,
+        utxo: Option<TxOut>,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor>;
+}
+
+impl DescriptorMeta for ExtendedDescriptor {
+    fn is_witness(&self) -> bool {
+        matches!(
+            self.desc_type(),
+            DescriptorType::Wpkh
+                | DescriptorType::ShWpkh
+                | DescriptorType::Wsh
+                | DescriptorType::ShWsh
+                | DescriptorType::ShWshSortedMulti
+                | DescriptorType::WshSortedMulti
+        )
+    }
+
+    fn is_taproot(&self) -> bool {
+        self.desc_type() == DescriptorType::Tr
+    }
+
+    fn get_extended_keys(&self) -> Vec<DescriptorXKey<Xpub>> {
+        let mut answer = Vec::new();
+
+        self.for_each_key(|pk| {
+            if let DescriptorPublicKey::XPub(xpub) = pk {
+                answer.push(xpub.clone());
+            }
+
+            true
+        });
+
+        answer
+    }
+
+    fn derive_from_psbt_key_origins(
+        &self,
+        key_origins: BTreeMap<Fingerprint, (&DerivationPath, SinglePubKey)>,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor> {
+        // Ensure that deriving `xpub` with `path` yields `expected`
+        let verify_key =
+            |xpub: &DescriptorXKey<Xpub>, path: &DerivationPath, expected: &SinglePubKey| {
+                let derived = xpub
+                    .xkey
+                    .derive_pub(secp, path)
+                    .expect("The path should never contain hardened derivation steps")
+                    .public_key;
+
+                match expected {
+                    SinglePubKey::FullKey(pk) if &PublicKey::new(derived) == pk => true,
+                    SinglePubKey::XOnly(pk) if &XOnlyPublicKey::from(derived) == pk => true,
+                    _ => false,
+                }
+            };
+
+        let mut path_found = None;
+
+        // using `for_any_key` should make this stop as soon as we return `true`
+        self.for_any_key(|key| {
+            if let DescriptorPublicKey::XPub(xpub) = key {
+                // Check if the key matches one entry in our `key_origins`. If it does, `matches()` will
+                // return the "prefix" that matched, so we remove that prefix from the full path
+                // found in `key_origins` and save it in `derive_path`. We expect this to be a derivation
+                // path of length 1 if the key is `wildcard` and an empty path otherwise.
+                let root_fingerprint = xpub.root_fingerprint(secp);
+                let derive_path = key_origins
+                    .get_key_value(&root_fingerprint)
+                    .and_then(|(fingerprint, (path, expected))| {
+                        xpub.matches(&(*fingerprint, (*path).clone()), secp)
+                            .zip(Some((path, expected)))
+                    })
+                    .and_then(|(prefix, (full_path, expected))| {
+                        let derive_path = full_path
+                            .into_iter()
+                            .skip(prefix.into_iter().count())
+                            .cloned()
+                            .collect::<DerivationPath>();
+
+                        // `derive_path` only contains the replacement index for the wildcard, if present, or
+                        // an empty path for fixed descriptors. To verify the key we also need the normal steps
+                        // that come before the wildcard, so we take them directly from `xpub` and then append
+                        // the final index
+                        if verify_key(
+                            xpub,
+                            &xpub.derivation_path.extend(derive_path.clone()),
+                            expected,
+                        ) {
+                            Some(derive_path)
+                        } else {
+                            None
+                        }
+                    });
+
+                match derive_path {
+                    Some(path) if xpub.wildcard != Wildcard::None && path.len() == 1 => {
+                        // Ignore hardened wildcards
+                        if let ChildNumber::Normal { index } = path[0] {
+                            path_found = Some(index);
+                            return true;
+                        }
+                    }
+                    Some(path) if xpub.wildcard == Wildcard::None && path.is_empty() => {
+                        path_found = Some(0);
+                        return true;
+                    }
+                    _ => {}
+                }
+            }
+
+            false
+        });
+
+        path_found.map(|path| {
+            self.at_derivation_index(path)
+                .expect("We ignore hardened wildcards")
+        })
+    }
+
+    fn derive_from_hd_keypaths(
+        &self,
+        hd_keypaths: &HdKeyPaths,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor> {
+        // "Convert" an hd_keypaths map to the format required by `derive_from_psbt_key_origins`
+        let key_origins = hd_keypaths
+            .iter()
+            .map(|(pk, (fingerprint, path))| {
+                (
+                    *fingerprint,
+                    (path, SinglePubKey::FullKey(PublicKey::new(*pk))),
+                )
+            })
+            .collect();
+        self.derive_from_psbt_key_origins(key_origins, secp)
+    }
+
+    fn derive_from_tap_key_origins(
+        &self,
+        tap_key_origins: &TapKeyOrigins,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor> {
+        // "Convert" a tap_key_origins map to the format required by `derive_from_psbt_key_origins`
+        let key_origins = tap_key_origins
+            .iter()
+            .map(|(pk, (_, (fingerprint, path)))| (*fingerprint, (path, SinglePubKey::XOnly(*pk))))
+            .collect();
+        self.derive_from_psbt_key_origins(key_origins, secp)
+    }
+
+    fn derive_from_psbt_input(
+        &self,
+        psbt_input: &psbt::Input,
+        utxo: Option<TxOut>,
+        secp: &SecpCtx,
+    ) -> Option<DerivedDescriptor> {
+        if let Some(derived) = self.derive_from_hd_keypaths(&psbt_input.bip32_derivation, secp) {
+            return Some(derived);
+        }
+        if let Some(derived) = self.derive_from_tap_key_origins(&psbt_input.tap_key_origins, secp) {
+            return Some(derived);
+        }
+        if self.has_wildcard() {
+            // We can't try to bruteforce the derivation index, exit here
+            return None;
+        }
+
+        let descriptor = self.at_derivation_index(0).expect("0 is not hardened");
+        match descriptor.desc_type() {
+            // TODO: add pk() here
+            DescriptorType::Pkh
+            | DescriptorType::Wpkh
+            | DescriptorType::ShWpkh
+            | DescriptorType::Tr
+                if utxo.is_some()
+                    && descriptor.script_pubkey() == utxo.as_ref().unwrap().script_pubkey =>
+            {
+                Some(descriptor)
+            }
+            DescriptorType::Bare | DescriptorType::Sh | DescriptorType::ShSortedMulti
+                if psbt_input.redeem_script.is_some()
+                    && &descriptor.explicit_script().unwrap()
+                        == psbt_input.redeem_script.as_ref().unwrap() =>
+            {
+                Some(descriptor)
+            }
+            DescriptorType::Wsh
+            | DescriptorType::ShWsh
+            | DescriptorType::ShWshSortedMulti
+            | DescriptorType::WshSortedMulti
+                if psbt_input.witness_script.is_some()
+                    && &descriptor.explicit_script().unwrap()
+                        == psbt_input.witness_script.as_ref().unwrap() =>
+            {
+                Some(descriptor)
+            }
+            _ => None,
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use alloc::string::ToString;
+    use core::str::FromStr;
+
+    use assert_matches::assert_matches;
+    use bitcoin::hex::FromHex;
+    use bitcoin::secp256k1::Secp256k1;
+    use bitcoin::{bip32, Psbt};
+    use bitcoin::{NetworkKind, ScriptBuf};
+
+    use super::*;
+    use crate::psbt::PsbtUtils;
+
+    #[test]
+    fn test_derive_from_psbt_input_wpkh_wif() {
+        let descriptor = Descriptor::<DescriptorPublicKey>::from_str(
+            "wpkh(02b4632d08485ff1df2db55b9dafd23347d1c47a457072a1e87be26896549a8737)",
+        )
+        .unwrap();
+        let psbt = Psbt::deserialize(
+            &Vec::<u8>::from_hex(
+                "70736274ff010052010000000162307be8e431fbaff807cdf9cdc3fde44d7402\
+                 11bc8342c31ffd6ec11fe35bcc0100000000ffffffff01328601000000000016\
+                 001493ce48570b55c42c2af816aeaba06cfee1224fae000000000001011fa086\
+                 01000000000016001493ce48570b55c42c2af816aeaba06cfee1224fae010304\
+                 010000000000",
+            )
+            .unwrap(),
+        )
+        .unwrap();
+
+        assert!(descriptor
+            .derive_from_psbt_input(&psbt.inputs[0], psbt.get_utxo_for(0), &Secp256k1::new())
+            .is_some());
+    }
+
+    #[test]
+    fn test_derive_from_psbt_input_pkh_tpub() {
+        let descriptor = Descriptor::<DescriptorPublicKey>::from_str(
+            "pkh([0f056943/44h/0h/0h]tpubDDpWvmUrPZrhSPmUzCMBHffvC3HyMAPnWDSAQNBTnj1iZeJa7BZQEttFiP4DS4GCcXQHezdXhn86Hj6LHX5EDstXPWrMaSneRWM8yUf6NFd/10/*)",
+        )
+        .unwrap();
+        let psbt = Psbt::deserialize(
+            &Vec::<u8>::from_hex(
+                "70736274ff010053010000000145843b86be54a3cd8c9e38444e1162676c00df\
+                 e7964122a70df491ea12fd67090100000000ffffffff01c19598000000000017\
+                 a91432bb94283282f72b2e034709e348c44d5a4db0ef8700000000000100f902\
+                 0000000001010167e99c0eb67640f3a1b6805f2d8be8238c947f8aaf49eb0a9c\
+                 bee6a42c984200000000171600142b29a22019cca05b9c2b2d283a4c4489e1cf\
+                 9f8ffeffffff02a01dced06100000017a914e2abf033cadbd74f0f4c74946201\
+                 decd20d5c43c8780969800000000001976a9148b0fce5fb1264e599a65387313\
+                 3c95478b902eb288ac02473044022015d9211576163fa5b001e84dfa3d44efd9\
+                 86b8f3a0d3d2174369288b2b750906022048dacc0e5d73ae42512fd2b97e2071\
+                 a8d0bce443b390b1fe0b8128fe70ec919e01210232dad1c5a67dcb0116d407e2\
+                 52584228ab7ec00e8b9779d0c3ffe8114fc1a7d2c80600000103040100000022\
+                 0603433b83583f8c4879b329dd08bbc7da935e4cc02f637ff746e05f0466ffb2\
+                 a6a2180f0569432c00008000000080000000800a000000000000000000",
+            )
+            .unwrap(),
+        )
+        .unwrap();
+
+        assert!(descriptor
+            .derive_from_psbt_input(&psbt.inputs[0], psbt.get_utxo_for(0), &Secp256k1::new())
+            .is_some());
+    }
+
+    #[test]
+    fn test_derive_from_psbt_input_wsh() {
+        let descriptor = Descriptor::<DescriptorPublicKey>::from_str(
+            "wsh(and_v(v:pk(03b6633fef2397a0a9de9d7b6f23aef8368a6e362b0581f0f0af70d5ecfd254b14),older(6)))",
+        )
+        .unwrap();
+        let psbt = Psbt::deserialize(
+            &Vec::<u8>::from_hex(
+                "70736274ff01005302000000011c8116eea34408ab6529223c9a176606742207\
+                 67a1ff1d46a6e3c4a88243ea6e01000000000600000001109698000000000017\
+                 a914ad105f61102e0d01d7af40d06d6a5c3ae2f7fde387000000000001012b80\
+                 969800000000002200203ca72f106a72234754890ca7640c43f65d2174e44d33\
+                 336030f9059345091044010304010000000105252103b6633fef2397a0a9de9d\
+                 7b6f23aef8368a6e362b0581f0f0af70d5ecfd254b14ad56b20000",
+            )
+            .unwrap(),
+        )
+        .unwrap();
+
+        assert!(descriptor
+            .derive_from_psbt_input(&psbt.inputs[0], psbt.get_utxo_for(0), &Secp256k1::new())
+            .is_some());
+    }
+
+    #[test]
+    fn test_derive_from_psbt_input_sh() {
+        let descriptor = Descriptor::<DescriptorPublicKey>::from_str(
+            "sh(and_v(v:pk(021403881a5587297818fcaf17d239cefca22fce84a45b3b1d23e836c4af671dbb),after(630000)))",
+        )
+        .unwrap();
+        let psbt = Psbt::deserialize(
+            &Vec::<u8>::from_hex(
+                "70736274ff0100530100000001bc8c13df445dfadcc42afa6dc841f85d22b01d\
+                 a6270ebf981740f4b7b1d800390000000000feffffff01ba9598000000000017\
+                 a91457b148ba4d3e5fa8608a8657875124e3d1c9390887f09c0900000100e002\
+                 0000000001016ba1bbe05cc93574a0d611ec7d93ad0ab6685b28d0cd80e8a82d\
+                 debb326643c90100000000feffffff02809698000000000017a914d9a6e8c455\
+                 8e16c8253afe53ce37ad61cf4c38c487403504cf6100000017a9144044fb6e0b\
+                 757dfc1b34886b6a95aef4d3db137e870247304402202a9b72d939bcde8ba2a1\
+                 e0980597e47af4f5c152a78499143c3d0a78ac2286a602207a45b1df9e93b8c9\
+                 6f09f5c025fe3e413ca4b905fe65ee55d32a3276439a9b8f012102dc1fcc2636\
+                 4da1aa718f03d8d9bd6f2ff410ed2cf1245a168aa3bcc995ac18e0a806000001\
+                 03040100000001042821021403881a5587297818fcaf17d239cefca22fce84a4\
+                 5b3b1d23e836c4af671dbbad03f09c09b10000",
+            )
+            .unwrap(),
+        )
+        .unwrap();
+
+        assert!(descriptor
+            .derive_from_psbt_input(&psbt.inputs[0], psbt.get_utxo_for(0), &Secp256k1::new())
+            .is_some());
+    }
+
+    #[test]
+    fn test_to_wallet_descriptor_fixup_networks() {
+        use crate::keys::{any_network, IntoDescriptorKey};
+
+        let secp = Secp256k1::new();
+
+        let xprv = bip32::Xpriv::from_str("xprv9s21ZrQH143K3c3gF1DUWpWNr2SG2XrG8oYPpqYh7hoWsJy9NjabErnzriJPpnGHyKz5NgdXmq1KVbqS1r4NXdCoKitWg5e86zqXHa8kxyB").unwrap();
+        let path = bip32::DerivationPath::from_str("m/0").unwrap();
+
+        // here `to_descriptor_key` will set the valid networks for the key to only mainnet, since
+        // we are using an "xpub"
+        let key = (xprv, path.clone()).into_descriptor_key().unwrap();
+        // override it with any. this happens in some key conversions, like bip39
+        let key = key.override_valid_networks(any_network());
+
+        // make a descriptor out of it
+        let desc = crate::descriptor!(wpkh(key)).unwrap();
+        // this should convert the key that supports "any_network" to the right network (testnet)
+        let (wallet_desc, keymap) = desc
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .unwrap();
+
+        let mut xprv_testnet = xprv;
+        xprv_testnet.network = NetworkKind::Test;
+
+        let xpub_testnet = bip32::Xpub::from_priv(&secp, &xprv_testnet);
+        let desc_pubkey = DescriptorPublicKey::XPub(DescriptorXKey {
+            xkey: xpub_testnet,
+            origin: None,
+            derivation_path: path,
+            wildcard: Wildcard::Unhardened,
+        });
+
+        assert_eq!(wallet_desc.to_string(), "wpkh(tpubD6NzVbkrYhZ4XtJzoDja5snUjBNQRP5B3f4Hyn1T1x6PVPxzzVjvw6nJx2D8RBCxog9GEVjZoyStfepTz7TtKoBVdkCtnc7VCJh9dD4RAU9/0/*)#a3svx0ha");
+        assert_eq!(
+            keymap
+                .get(&desc_pubkey)
+                .map(|key| key.to_public(&secp).unwrap()),
+            Some(desc_pubkey)
+        );
+    }
+
+    // test IntoWalletDescriptor trait from &str with and without checksum appended
+    #[test]
+    fn test_descriptor_from_str_with_checksum() {
+        let secp = Secp256k1::new();
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)#tqz0nc62"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/2/*)#67ju93jw"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)#67ju93jw"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert_matches!(desc, Err(DescriptorError::InvalidDescriptorChecksum));
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)#67ju93jw"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert_matches!(desc, Err(DescriptorError::InvalidDescriptorChecksum));
+    }
+
+    // test IntoWalletDescriptor trait from &str with keys from right and wrong network
+    #[test]
+    fn test_descriptor_from_str_with_keys_network() {
+        let secp = Secp256k1::new();
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Regtest);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Regtest);
+        assert!(desc.is_ok());
+
+        let desc = "sh(wpkh(02864bb4ad00cefa806098a69e192bbda937494e69eb452b87bb3f20f6283baedb))"
+            .into_wallet_descriptor(&secp, Network::Testnet);
+        assert!(desc.is_ok());
+
+        let desc = "sh(wpkh(02864bb4ad00cefa806098a69e192bbda937494e69eb452b87bb3f20f6283baedb))"
+            .into_wallet_descriptor(&secp, Network::Bitcoin);
+        assert!(desc.is_ok());
+
+        let desc = "wpkh(tprv8ZgxMBicQKsPdpkqS7Eair4YxjcuuvDPNYmKX3sCniCf16tHEVrjjiSXEkFRnUH77yXc6ZcwHHcLNfjdi5qUvw3VDfgYiH5mNsj5izuiu2N/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Bitcoin);
+        assert_matches!(desc, Err(DescriptorError::Key(KeyError::InvalidNetwork)));
+
+        let desc = "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/2/*)"
+            .into_wallet_descriptor(&secp, Network::Bitcoin);
+        assert_matches!(desc, Err(DescriptorError::Key(KeyError::InvalidNetwork)));
+    }
+
+    // test IntoWalletDescriptor trait from the output of the descriptor!() macro
+    #[test]
+    fn test_descriptor_from_str_from_output_of_macro() {
+        let secp = Secp256k1::new();
+
+        let tpub = bip32::Xpub::from_str("tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK").unwrap();
+        let path = bip32::DerivationPath::from_str("m/1/2").unwrap();
+        let key = (tpub, path).into_descriptor_key().unwrap();
+
+        // make a descriptor out of it
+        let desc = crate::descriptor!(wpkh(key)).unwrap();
+
+        let (wallet_desc, _) = desc
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .unwrap();
+        let wallet_desc_str = wallet_desc.to_string();
+        assert_eq!(wallet_desc_str, "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/1/2/*)#67ju93jw");
+
+        let (wallet_desc2, _) = wallet_desc_str
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .unwrap();
+        assert_eq!(wallet_desc, wallet_desc2)
+    }
+
+    #[test]
+    fn test_check_wallet_descriptor() {
+        let secp = Secp256k1::new();
+
+        let descriptor = "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/0'/1/2/*)";
+        let (descriptor, _) = descriptor
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .expect("must parse");
+        let result = check_wallet_descriptor(&descriptor);
+
+        assert_matches!(result, Err(DescriptorError::HardenedDerivationXpub));
+
+        let descriptor = "wpkh(tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/<0;1>/*)";
+        let (descriptor, _) = descriptor
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .expect("must parse");
+        let result = check_wallet_descriptor(&descriptor);
+
+        assert_matches!(result, Err(DescriptorError::MultiPath));
+
+        // repeated pubkeys
+        let descriptor = "wsh(multi(2,tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/0/*,tpubD6NzVbkrYhZ4XHndKkuB8FifXm8r5FQHwrN6oZuWCz13qb93rtgKvD4PQsqC4HP4yhV3tA2fqr2RbY5mNXfM7RxXUoeABoDtsFUq2zJq6YK/0/*))";
+        let (descriptor, _) = descriptor
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .expect("must parse");
+        let result = check_wallet_descriptor(&descriptor);
+
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn test_sh_wsh_sortedmulti_redeemscript() {
+        use miniscript::psbt::PsbtInputExt;
+
+        let secp = Secp256k1::new();
+
+        let descriptor = "sh(wsh(sortedmulti(3,tpubDEsqS36T4DVsKJd9UH8pAKzrkGBYPLEt9jZMwpKtzh1G6mgYehfHt9WCgk7MJG5QGSFWf176KaBNoXbcuFcuadAFKxDpUdMDKGBha7bY3QM/0/*,tpubDF3cpwfs7fMvXXuoQbohXtLjNM6ehwYT287LWtmLsd4r77YLg6MZg4vTETx5MSJ2zkfigbYWu31VA2Z2Vc1cZugCYXgS7FQu6pE8V6TriEH/0/*,tpubDE1SKfcW76Tb2AASv5bQWMuScYNAdoqLHoexw13sNDXwmUhQDBbCD3QAedKGLhxMrWQdMDKENzYtnXPDRvexQPNuDrLj52wAjHhNEm8sJ4p/0/*,tpubDFLc6oXwJmhm3FGGzXkfJNTh2KitoY3WhmmQvuAjMhD8YbyWn5mAqckbxXfm2etM3p5J6JoTpSrMqRSTfMLtNW46poDaEZJ1kjd3csRSjwH/0/*,tpubDEWD9NBeWP59xXmdqSNt4VYdtTGwbpyP8WS962BuqpQeMZmX9Pur14dhXdZT5a7wR1pK6dPtZ9fP5WR493hPzemnBvkfLLYxnUjAKj1JCQV/0/*,tpubDEHyZkkwd7gZWCTgQuYQ9C4myF2hMEmyHsBCCmLssGqoqUxeT3gzohF5uEVURkf9TtmeepJgkSUmteac38FwZqirjApzNX59XSHLcwaTZCH/0/*,tpubDEqLouCekwnMUWN486kxGzD44qVgeyuqHyxUypNEiQt5RnUZNJe386TKPK99fqRV1vRkZjYAjtXGTECz98MCsdLcnkM67U6KdYRzVubeCgZ/0/*)))";
+        let (descriptor, _) = descriptor
+            .into_wallet_descriptor(&secp, Network::Testnet)
+            .unwrap();
+        check_wallet_descriptor(&descriptor).expect("descriptor");
+
+        let descriptor = descriptor.at_derivation_index(0).unwrap();
+
+        let script = ScriptBuf::from_hex("5321022f533b667e2ea3b36e21961c9fe9dca340fbe0af5210173a83ae0337ab20a57621026bb53a98e810bd0ee61a0ed1164ba6c024786d76554e793e202dc6ce9c78c4ea2102d5b8a7d66a41ffdb6f4c53d61994022e886b4f45001fb158b95c9164d45f8ca3210324b75eead2c1f9c60e8adeb5e7009fec7a29afcdb30d829d82d09562fe8bae8521032d34f8932200833487bd294aa219dcbe000b9f9b3d824799541430009f0fa55121037468f8ea99b6c64788398b5ad25480cad08f4b0d65be54ce3a55fd206b5ae4722103f72d3d96663b0ea99b0aeb0d7f273cab11a8de37885f1dddc8d9112adb87169357ae").unwrap();
+
+        let mut psbt_input = psbt::Input::default();
+        psbt_input
+            .update_with_descriptor_unchecked(&descriptor)
+            .unwrap();
+
+        assert_eq!(psbt_input.redeem_script, Some(script.to_p2wsh()));
+        assert_eq!(psbt_input.witness_script, Some(script));
+    }
+}

crates/wallet/src/keys/bip39.rs

@@ -0,0 +1,227 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! BIP-0039
+
+// TODO: maybe write our own implementation of bip39? Seems stupid to have an extra dependency for
+// something that should be fairly simple to re-implement.
+
+use alloc::string::String;
+use bitcoin::bip32;
+use bitcoin::Network;
+
+use miniscript::ScriptContext;
+
+pub use bip39::{Error, Language, Mnemonic};
+
+type Seed = [u8; 64];
+
+/// Type describing entropy length (aka word count) in the mnemonic
+pub enum WordCount {
+    /// 12 words mnemonic (128 bits entropy)
+    Words12 = 128,
+    /// 15 words mnemonic (160 bits entropy)
+    Words15 = 160,
+    /// 18 words mnemonic (192 bits entropy)
+    Words18 = 192,
+    /// 21 words mnemonic (224 bits entropy)
+    Words21 = 224,
+    /// 24 words mnemonic (256 bits entropy)
+    Words24 = 256,
+}
+
+use super::{
+    any_network, DerivableKey, DescriptorKey, ExtendedKey, GeneratableKey, GeneratedKey, KeyError,
+};
+
+fn set_valid_on_any_network<Ctx: ScriptContext>(
+    descriptor_key: DescriptorKey<Ctx>,
+) -> DescriptorKey<Ctx> {
+    // We have to pick one network to build the xprv, but since the bip39 standard doesn't
+    // encode the network, the xprv we create is actually valid everywhere. So we override the
+    // valid networks with `any_network()`.
+    descriptor_key.override_valid_networks(any_network())
+}
+
+/// Type for a BIP39 mnemonic with an optional passphrase
+pub type MnemonicWithPassphrase = (Mnemonic, Option<String>);
+
+#[cfg_attr(docsrs, doc(cfg(feature = "keys-bip39")))]
+impl<Ctx: ScriptContext> DerivableKey<Ctx> for Seed {
+    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
+        Ok(bip32::Xpriv::new_master(Network::Bitcoin, &self[..])?.into())
+    }
+
+    fn into_descriptor_key(
+        self,
+        source: Option<bip32::KeySource>,
+        derivation_path: bip32::DerivationPath,
+    ) -> Result<DescriptorKey<Ctx>, KeyError> {
+        let descriptor_key = self
+            .into_extended_key()?
+            .into_descriptor_key(source, derivation_path)?;
+
+        Ok(set_valid_on_any_network(descriptor_key))
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(feature = "keys-bip39")))]
+impl<Ctx: ScriptContext> DerivableKey<Ctx> for MnemonicWithPassphrase {
+    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
+        let (mnemonic, passphrase) = self;
+        let seed: Seed = mnemonic.to_seed(passphrase.as_deref().unwrap_or(""));
+
+        seed.into_extended_key()
+    }
+
+    fn into_descriptor_key(
+        self,
+        source: Option<bip32::KeySource>,
+        derivation_path: bip32::DerivationPath,
+    ) -> Result<DescriptorKey<Ctx>, KeyError> {
+        let descriptor_key = self
+            .into_extended_key()?
+            .into_descriptor_key(source, derivation_path)?;
+
+        Ok(set_valid_on_any_network(descriptor_key))
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(feature = "keys-bip39")))]
+impl<Ctx: ScriptContext> DerivableKey<Ctx> for (GeneratedKey<Mnemonic, Ctx>, Option<String>) {
+    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
+        let (mnemonic, passphrase) = self;
+        (mnemonic.into_key(), passphrase).into_extended_key()
+    }
+
+    fn into_descriptor_key(
+        self,
+        source: Option<bip32::KeySource>,
+        derivation_path: bip32::DerivationPath,
+    ) -> Result<DescriptorKey<Ctx>, KeyError> {
+        let (mnemonic, passphrase) = self;
+        (mnemonic.into_key(), passphrase).into_descriptor_key(source, derivation_path)
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(feature = "keys-bip39")))]
+impl<Ctx: ScriptContext> DerivableKey<Ctx> for Mnemonic {
+    fn into_extended_key(self) -> Result<ExtendedKey<Ctx>, KeyError> {
+        (self, None).into_extended_key()
+    }
+
+    fn into_descriptor_key(
+        self,
+        source: Option<bip32::KeySource>,
+        derivation_path: bip32::DerivationPath,
+    ) -> Result<DescriptorKey<Ctx>, KeyError> {
+        let descriptor_key = self
+            .into_extended_key()?
+            .into_descriptor_key(source, derivation_path)?;
+
+        Ok(set_valid_on_any_network(descriptor_key))
+    }
+}
+
+#[cfg_attr(docsrs, doc(cfg(feature = "keys-bip39")))]
+impl<Ctx: ScriptContext> GeneratableKey<Ctx> for Mnemonic {
+    type Entropy = [u8; 32];
+
+    type Options = (WordCount, Language);
+    type Error = Option<bip39::Error>;
+
+    fn generate_with_entropy(
+        (word_count, language): Self::Options,
+        entropy: Self::Entropy,
+    ) -> Result<GeneratedKey<Self, Ctx>, Self::Error> {
+        let entropy = &entropy[..(word_count as usize / 8)];
+        let mnemonic = Mnemonic::from_entropy_in(language, entropy)?;
+
+        Ok(GeneratedKey::new(mnemonic, any_network()))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use alloc::string::ToString;
+    use core::str::FromStr;
+
+    use bitcoin::bip32;
+
+    use bip39::{Language, Mnemonic};
+
+    use crate::keys::{any_network, GeneratableKey, GeneratedKey};
+
+    use super::WordCount;
+
+    #[test]
+    fn test_keys_bip39_mnemonic() {
+        let mnemonic =
+            "aim bunker wash balance finish force paper analyst cabin spoon stable organ";
+        let mnemonic = Mnemonic::parse_in(Language::English, mnemonic).unwrap();
+        let path = bip32::DerivationPath::from_str("m/44'/0'/0'/0").unwrap();
+
+        let key = (mnemonic, path);
+        let (desc, keys, networks) = crate::descriptor!(wpkh(key)).unwrap();
+        assert_eq!(desc.to_string(), "wpkh([be83839f/44'/0'/0']xpub6DCQ1YcqvZtSwGWMrwHELPehjWV3f2MGZ69yBADTxFEUAoLwb5Mp5GniQK6tTp3AgbngVz9zEFbBJUPVnkG7LFYt8QMTfbrNqs6FNEwAPKA/0/*)#0r8v4nkv");
+        assert_eq!(keys.len(), 1);
+        assert_eq!(networks.len(), 4);
+    }
+
+    #[test]
+    fn test_keys_bip39_mnemonic_passphrase() {
+        let mnemonic =
+            "aim bunker wash balance finish force paper analyst cabin spoon stable organ";
+        let mnemonic = Mnemonic::parse_in(Language::English, mnemonic).unwrap();
+        let path = bip32::DerivationPath::from_str("m/44'/0'/0'/0").unwrap();
+
+        let key = ((mnemonic, Some("passphrase".into())), path);
+        let (desc, keys, networks) = crate::descriptor!(wpkh(key)).unwrap();
+        assert_eq!(desc.to_string(), "wpkh([8f6cb80c/44'/0'/0']xpub6DWYS8bbihFevy29M4cbw4ZR3P5E12jB8R88gBDWCTCNpYiDHhYWNywrCF9VZQYagzPmsZpxXpytzSoxynyeFr4ZyzheVjnpLKuse4fiwZw/0/*)#h0j0tg5m");
+        assert_eq!(keys.len(), 1);
+        assert_eq!(networks.len(), 4);
+    }
+
+    #[test]
+    fn test_keys_generate_bip39() {
+        let generated_mnemonic: GeneratedKey<_, miniscript::Segwitv0> =
+            Mnemonic::generate_with_entropy(
+                (WordCount::Words12, Language::English),
+                crate::keys::test::TEST_ENTROPY,
+            )
+            .unwrap();
+        assert_eq!(generated_mnemonic.valid_networks, any_network());
+        assert_eq!(
+            generated_mnemonic.to_string(),
+            "primary fetch primary fetch primary fetch primary fetch primary fetch primary fever"
+        );
+
+        let generated_mnemonic: GeneratedKey<_, miniscript::Segwitv0> =
+            Mnemonic::generate_with_entropy(
+                (WordCount::Words24, Language::English),
+                crate::keys::test::TEST_ENTROPY,
+            )
+            .unwrap();
+        assert_eq!(generated_mnemonic.valid_networks, any_network());
+        assert_eq!(generated_mnemonic.to_string(), "primary fetch primary fetch primary fetch primary fetch primary fetch primary fetch primary fetch primary fetch primary fetch primary fetch primary fetch primary foster");
+    }
+
+    #[test]
+    fn test_keys_generate_bip39_random() {
+        let generated_mnemonic: GeneratedKey<_, miniscript::Segwitv0> =
+            Mnemonic::generate((WordCount::Words12, Language::English)).unwrap();
+        assert_eq!(generated_mnemonic.valid_networks, any_network());
+
+        let generated_mnemonic: GeneratedKey<_, miniscript::Segwitv0> =
+            Mnemonic::generate((WordCount::Words24, Language::English)).unwrap();
+        assert_eq!(generated_mnemonic.valid_networks, any_network());
+    }
+}

crates/wallet/src/lib.rs

@@ -0,0 +1,50 @@
+#![doc = include_str!("../README.md")]
+// only enables the `doc_cfg` feature when the `docsrs` configuration attribute is defined
+#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(
+    docsrs,
+    doc(html_logo_url = "https://github.com/bitcoindevkit/bdk/raw/master/static/bdk.png")
+)]
+#![no_std]
+#![warn(missing_docs)]
+
+#[cfg(feature = "std")]
+#[macro_use]
+extern crate std;
+
+#[doc(hidden)]
+#[macro_use]
+pub extern crate alloc;
+pub extern crate bdk_chain as chain;
+#[cfg(feature = "file_store")]
+pub extern crate bdk_file_store as file_store;
+#[cfg(feature = "keys-bip39")]
+pub extern crate bip39;
+pub extern crate bitcoin;
+pub extern crate miniscript;
+pub extern crate serde;
+pub extern crate serde_json;
+
+pub mod descriptor;
+pub mod keys;
+pub mod psbt;
+mod types;
+mod wallet;
+
+pub(crate) use bdk_chain::collections;
+#[cfg(feature = "rusqlite")]
+pub use bdk_chain::rusqlite;
+#[cfg(feature = "rusqlite")]
+pub use bdk_chain::rusqlite_impl;
+pub use descriptor::template;
+pub use descriptor::HdKeyPaths;
+pub use signer;
+pub use signer::SignOptions;
+pub use tx_builder::*;
+pub use types::*;
+pub use wallet::*;
+
+/// Get the version of [`bdk_wallet`](crate) at runtime.
+pub fn version() -> &'static str {
+    env!("CARGO_PKG_VERSION", "unknown")
+}

crates/wallet/src/psbt/mod.rs

@@ -0,0 +1,70 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Additional functions on the `rust-bitcoin` `Psbt` structure.
+
+use alloc::vec::Vec;
+use bitcoin::Amount;
+use bitcoin::FeeRate;
+use bitcoin::Psbt;
+use bitcoin::TxOut;
+
+// TODO upstream the functions here to `rust-bitcoin`?
+
+/// Trait to add functions to extract utxos and calculate fees.
+pub trait PsbtUtils {
+    /// Get the `TxOut` for the specified input index, if it doesn't exist in the PSBT `None` is returned.
+    fn get_utxo_for(&self, input_index: usize) -> Option<TxOut>;
+
+    /// The total transaction fee amount, sum of input amounts minus sum of output amounts, in sats.
+    /// If the PSBT is missing a TxOut for an input returns None.
+    fn fee_amount(&self) -> Option<Amount>;
+
+    /// The transaction's fee rate. This value will only be accurate if calculated AFTER the
+    /// `Psbt` is finalized and all witness/signature data is added to the
+    /// transaction.
+    /// If the PSBT is missing a TxOut for an input returns None.
+    fn fee_rate(&self) -> Option<FeeRate>;
+}
+
+impl PsbtUtils for Psbt {
+    fn get_utxo_for(&self, input_index: usize) -> Option<TxOut> {
+        let tx = &self.unsigned_tx;
+        let input = self.inputs.get(input_index)?;
+
+        match (&input.witness_utxo, &input.non_witness_utxo) {
+            (Some(_), _) => input.witness_utxo.clone(),
+            (_, Some(_)) => input.non_witness_utxo.as_ref().map(|in_tx| {
+                in_tx.output[tx.input[input_index].previous_output.vout as usize].clone()
+            }),
+            _ => None,
+        }
+    }
+
+    fn fee_amount(&self) -> Option<Amount> {
+        let tx = &self.unsigned_tx;
+        let utxos: Option<Vec<TxOut>> = (0..tx.input.len()).map(|i| self.get_utxo_for(i)).collect();
+
+        utxos.map(|inputs| {
+            let input_amount: Amount = inputs.iter().map(|i| i.value).sum();
+            let output_amount: Amount = self.unsigned_tx.output.iter().map(|o| o.value).sum();
+            input_amount
+                .checked_sub(output_amount)
+                .expect("input amount must be greater than output amount")
+        })
+    }
+
+    fn fee_rate(&self) -> Option<FeeRate> {
+        let fee_amount = self.fee_amount();
+        let weight = self.clone().extract_tx().ok()?.weight();
+        fee_amount.map(|fee| fee / weight)
+    }
+}

crates/wallet/src/types.rs

@@ -0,0 +1,135 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+use alloc::boxed::Box;
+use core::convert::AsRef;
+
+use bdk_chain::ConfirmationTime;
+use bitcoin::transaction::{OutPoint, Sequence, TxOut};
+use bitcoin::{psbt, Weight};
+
+use serde::{Deserialize, Serialize};
+
+/// Types of keychains
+#[derive(Serialize, Deserialize, Debug, Clone, Copy, PartialEq, Eq, Hash, Ord, PartialOrd)]
+pub enum KeychainKind {
+    /// External keychain, used for deriving recipient addresses.
+    External = 0,
+    /// Internal keychain, used for deriving change addresses.
+    Internal = 1,
+}
+
+impl KeychainKind {
+    /// Return [`KeychainKind`] as a byte
+    pub fn as_byte(&self) -> u8 {
+        match self {
+            KeychainKind::External => b'e',
+            KeychainKind::Internal => b'i',
+        }
+    }
+}
+
+impl AsRef<[u8]> for KeychainKind {
+    fn as_ref(&self) -> &[u8] {
+        match self {
+            KeychainKind::External => b"e",
+            KeychainKind::Internal => b"i",
+        }
+    }
+}
+
+/// An unspent output owned by a [`Wallet`].
+///
+/// [`Wallet`]: crate::Wallet
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, Hash)]
+pub struct LocalOutput {
+    /// Reference to a transaction output
+    pub outpoint: OutPoint,
+    /// Transaction output
+    pub txout: TxOut,
+    /// Type of keychain
+    pub keychain: KeychainKind,
+    /// Whether this UTXO is spent or not
+    pub is_spent: bool,
+    /// The derivation index for the script pubkey in the wallet
+    pub derivation_index: u32,
+    /// The confirmation time for transaction containing this utxo
+    pub confirmation_time: ConfirmationTime,
+}
+
+/// A [`Utxo`] with its `satisfaction_weight`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct WeightedUtxo {
+    /// The weight of the witness data and `scriptSig` expressed in [weight units]. This is used to
+    /// properly maintain the feerate when adding this input to a transaction during coin selection.
+    ///
+    /// [weight units]: https://en.bitcoin.it/wiki/Weight_units
+    pub satisfaction_weight: Weight,
+    /// The UTXO
+    pub utxo: Utxo,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+/// An unspent transaction output (UTXO).
+pub enum Utxo {
+    /// A UTXO owned by the local wallet.
+    Local(LocalOutput),
+    /// A UTXO owned by another wallet.
+    Foreign {
+        /// The location of the output.
+        outpoint: OutPoint,
+        /// The nSequence value to set for this input.
+        sequence: Option<Sequence>,
+        /// The information about the input we require to add it to a PSBT.
+        // Box it to stop the type being too big.
+        psbt_input: Box<psbt::Input>,
+    },
+}
+
+impl Utxo {
+    /// Get the location of the UTXO
+    pub fn outpoint(&self) -> OutPoint {
+        match &self {
+            Utxo::Local(local) => local.outpoint,
+            Utxo::Foreign { outpoint, .. } => *outpoint,
+        }
+    }
+
+    /// Get the `TxOut` of the UTXO
+    pub fn txout(&self) -> &TxOut {
+        match &self {
+            Utxo::Local(local) => &local.txout,
+            Utxo::Foreign {
+                outpoint,
+                psbt_input,
+                ..
+            } => {
+                if let Some(prev_tx) = &psbt_input.non_witness_utxo {
+                    return &prev_tx.output[outpoint.vout as usize];
+                }
+
+                if let Some(txout) = &psbt_input.witness_utxo {
+                    return txout;
+                }
+
+                unreachable!("Foreign UTXOs will always have one of these set")
+            }
+        }
+    }
+
+    /// Get the sequence number if an explicit sequence number has to be set for this input.
+    pub fn sequence(&self) -> Option<Sequence> {
+        match self {
+            Utxo::Local(_) => None,
+            Utxo::Foreign { sequence, .. } => *sequence,
+        }
+    }
+}

crates/wallet/src/wallet/changeset.rs

@@ -0,0 +1,209 @@
+use bdk_chain::{
+    indexed_tx_graph, keychain_txout, local_chain, tx_graph, ConfirmationBlockTime, Merge,
+};
+use miniscript::{Descriptor, DescriptorPublicKey};
+
+type IndexedTxGraphChangeSet =
+    indexed_tx_graph::ChangeSet<ConfirmationBlockTime, keychain_txout::ChangeSet>;
+
+/// A changeset for [`Wallet`](crate::Wallet).
+#[derive(Default, Debug, Clone, PartialEq, serde::Deserialize, serde::Serialize)]
+#[non_exhaustive]
+pub struct ChangeSet {
+    /// Descriptor for recipient addresses.
+    pub descriptor: Option<Descriptor<DescriptorPublicKey>>,
+    /// Descriptor for change addresses.
+    pub change_descriptor: Option<Descriptor<DescriptorPublicKey>>,
+    /// Stores the network type of the transaction data.
+    pub network: Option<bitcoin::Network>,
+    /// Changes to the [`LocalChain`](local_chain::LocalChain).
+    pub local_chain: local_chain::ChangeSet,
+    /// Changes to [`TxGraph`](tx_graph::TxGraph).
+    pub tx_graph: tx_graph::ChangeSet<ConfirmationBlockTime>,
+    /// Changes to [`KeychainTxOutIndex`](keychain_txout::KeychainTxOutIndex).
+    pub indexer: keychain_txout::ChangeSet,
+}
+
+impl Merge for ChangeSet {
+    /// Merge another [`ChangeSet`] into itself.
+    fn merge(&mut self, other: Self) {
+        if other.descriptor.is_some() {
+            debug_assert!(
+                self.descriptor.is_none() || self.descriptor == other.descriptor,
+                "descriptor must never change"
+            );
+            self.descriptor = other.descriptor;
+        }
+        if other.change_descriptor.is_some() {
+            debug_assert!(
+                self.change_descriptor.is_none()
+                    || self.change_descriptor == other.change_descriptor,
+                "change descriptor must never change"
+            );
+            self.change_descriptor = other.change_descriptor;
+        }
+        if other.network.is_some() {
+            debug_assert!(
+                self.network.is_none() || self.network == other.network,
+                "network must never change"
+            );
+            self.network = other.network;
+        }
+
+        Merge::merge(&mut self.local_chain, other.local_chain);
+        Merge::merge(&mut self.tx_graph, other.tx_graph);
+        Merge::merge(&mut self.indexer, other.indexer);
+    }
+
+    fn is_empty(&self) -> bool {
+        self.descriptor.is_none()
+            && self.change_descriptor.is_none()
+            && self.network.is_none()
+            && self.local_chain.is_empty()
+            && self.tx_graph.is_empty()
+            && self.indexer.is_empty()
+    }
+}
+
+#[cfg(feature = "rusqlite")]
+impl ChangeSet {
+    /// Schema name for wallet.
+    pub const WALLET_SCHEMA_NAME: &'static str = "bdk_wallet";
+    /// Name of table to store wallet descriptors and network.
+    pub const WALLET_TABLE_NAME: &'static str = "bdk_wallet";
+
+    /// Initialize sqlite tables for wallet schema & table.
+    fn init_wallet_sqlite_tables(
+        db_tx: &chain::rusqlite::Transaction,
+    ) -> chain::rusqlite::Result<()> {
+        let schema_v0: &[&str] = &[&format!(
+            "CREATE TABLE {} ( \
+                id INTEGER PRIMARY KEY NOT NULL CHECK (id = 0), \
+                descriptor TEXT, \
+                change_descriptor TEXT, \
+                network TEXT \
+                ) STRICT;",
+            Self::WALLET_TABLE_NAME,
+        )];
+        crate::rusqlite_impl::migrate_schema(db_tx, Self::WALLET_SCHEMA_NAME, &[schema_v0])
+    }
+
+    /// Recover a [`ChangeSet`] from sqlite database.
+    pub fn from_sqlite(db_tx: &chain::rusqlite::Transaction) -> chain::rusqlite::Result<Self> {
+        Self::init_wallet_sqlite_tables(db_tx)?;
+        use chain::rusqlite::OptionalExtension;
+        use chain::Impl;
+
+        let mut changeset = Self::default();
+
+        let mut wallet_statement = db_tx.prepare(&format!(
+            "SELECT descriptor, change_descriptor, network FROM {}",
+            Self::WALLET_TABLE_NAME,
+        ))?;
+        let row = wallet_statement
+            .query_row([], |row| {
+                Ok((
+                    row.get::<_, Impl<Descriptor<DescriptorPublicKey>>>("descriptor")?,
+                    row.get::<_, Impl<Descriptor<DescriptorPublicKey>>>("change_descriptor")?,
+                    row.get::<_, Impl<bitcoin::Network>>("network")?,
+                ))
+            })
+            .optional()?;
+        if let Some((Impl(desc), Impl(change_desc), Impl(network))) = row {
+            changeset.descriptor = Some(desc);
+            changeset.change_descriptor = Some(change_desc);
+            changeset.network = Some(network);
+        }
+
+        changeset.local_chain = local_chain::ChangeSet::from_sqlite(db_tx)?;
+        changeset.tx_graph = tx_graph::ChangeSet::<_>::from_sqlite(db_tx)?;
+        changeset.indexer = keychain_txout::ChangeSet::from_sqlite(db_tx)?;
+
+        Ok(changeset)
+    }
+
+    /// Persist [`ChangeSet`] to sqlite database.
+    pub fn persist_to_sqlite(
+        &self,
+        db_tx: &chain::rusqlite::Transaction,
+    ) -> chain::rusqlite::Result<()> {
+        Self::init_wallet_sqlite_tables(db_tx)?;
+        use chain::rusqlite::named_params;
+        use chain::Impl;
+
+        let mut descriptor_statement = db_tx.prepare_cached(&format!(
+            "INSERT INTO {}(id, descriptor) VALUES(:id, :descriptor) ON CONFLICT(id) DO UPDATE SET descriptor=:descriptor",
+            Self::WALLET_TABLE_NAME,
+        ))?;
+        if let Some(descriptor) = &self.descriptor {
+            descriptor_statement.execute(named_params! {
+                ":id": 0,
+                ":descriptor": Impl(descriptor.clone()),
+            })?;
+        }
+
+        let mut change_descriptor_statement = db_tx.prepare_cached(&format!(
+            "INSERT INTO {}(id, change_descriptor) VALUES(:id, :change_descriptor) ON CONFLICT(id) DO UPDATE SET change_descriptor=:change_descriptor",
+            Self::WALLET_TABLE_NAME,
+        ))?;
+        if let Some(change_descriptor) = &self.change_descriptor {
+            change_descriptor_statement.execute(named_params! {
+                ":id": 0,
+                ":change_descriptor": Impl(change_descriptor.clone()),
+            })?;
+        }
+
+        let mut network_statement = db_tx.prepare_cached(&format!(
+            "INSERT INTO {}(id, network) VALUES(:id, :network) ON CONFLICT(id) DO UPDATE SET network=:network",
+            Self::WALLET_TABLE_NAME,
+        ))?;
+        if let Some(network) = self.network {
+            network_statement.execute(named_params! {
+                ":id": 0,
+                ":network": Impl(network),
+            })?;
+        }
+
+        self.local_chain.persist_to_sqlite(db_tx)?;
+        self.tx_graph.persist_to_sqlite(db_tx)?;
+        self.indexer.persist_to_sqlite(db_tx)?;
+        Ok(())
+    }
+}
+
+impl From<local_chain::ChangeSet> for ChangeSet {
+    fn from(chain: local_chain::ChangeSet) -> Self {
+        Self {
+            local_chain: chain,
+            ..Default::default()
+        }
+    }
+}
+
+impl From<IndexedTxGraphChangeSet> for ChangeSet {
+    fn from(indexed_tx_graph: IndexedTxGraphChangeSet) -> Self {
+        Self {
+            tx_graph: indexed_tx_graph.tx_graph,
+            indexer: indexed_tx_graph.indexer,
+            ..Default::default()
+        }
+    }
+}
+
+impl From<tx_graph::ChangeSet<ConfirmationBlockTime>> for ChangeSet {
+    fn from(tx_graph: tx_graph::ChangeSet<ConfirmationBlockTime>) -> Self {
+        Self {
+            tx_graph,
+            ..Default::default()
+        }
+    }
+}
+
+impl From<keychain_txout::ChangeSet> for ChangeSet {
+    fn from(indexer: keychain_txout::ChangeSet) -> Self {
+        Self {
+            indexer,
+            ..Default::default()
+        }
+    }
+}

crates/wallet/src/wallet/error.rs

@@ -0,0 +1,260 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Errors that can be thrown by the [`Wallet`](crate::wallet::Wallet)
+
+use crate::descriptor::policy::PolicyError;
+use crate::descriptor::DescriptorError;
+use crate::wallet::coin_selection;
+use crate::{descriptor, KeychainKind};
+use alloc::string::String;
+use bitcoin::{absolute, psbt, Amount, OutPoint, Sequence, Txid};
+use core::fmt;
+
+/// Errors returned by miniscript when updating inconsistent PSBTs
+#[derive(Debug, Clone)]
+pub enum MiniscriptPsbtError {
+    /// Descriptor key conversion error
+    Conversion(miniscript::descriptor::ConversionError),
+    /// Return error type for PsbtExt::update_input_with_descriptor
+    UtxoUpdate(miniscript::psbt::UtxoUpdateError),
+    /// Return error type for PsbtExt::update_output_with_descriptor
+    OutputUpdate(miniscript::psbt::OutputUpdateError),
+}
+
+impl fmt::Display for MiniscriptPsbtError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Conversion(err) => write!(f, "Conversion error: {}", err),
+            Self::UtxoUpdate(err) => write!(f, "UTXO update error: {}", err),
+            Self::OutputUpdate(err) => write!(f, "Output update error: {}", err),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for MiniscriptPsbtError {}
+
+#[derive(Debug)]
+/// Error returned from [`TxBuilder::finish`]
+///
+/// [`TxBuilder::finish`]: crate::wallet::tx_builder::TxBuilder::finish
+pub enum CreateTxError {
+    /// There was a problem with the descriptors passed in
+    Descriptor(DescriptorError),
+    /// There was a problem while extracting and manipulating policies
+    Policy(PolicyError),
+    /// Spending policy is not compatible with this [`KeychainKind`]
+    SpendingPolicyRequired(KeychainKind),
+    /// Requested invalid transaction version '0'
+    Version0,
+    /// Requested transaction version `1`, but at least `2` is needed to use OP_CSV
+    Version1Csv,
+    /// Requested `LockTime` is less than is required to spend from this script
+    LockTime {
+        /// Requested `LockTime`
+        requested: absolute::LockTime,
+        /// Required `LockTime`
+        required: absolute::LockTime,
+    },
+    /// Cannot enable RBF with a `Sequence` >= 0xFFFFFFFE
+    RbfSequence,
+    /// Cannot enable RBF with `Sequence` given a required OP_CSV
+    RbfSequenceCsv {
+        /// Given RBF `Sequence`
+        rbf: Sequence,
+        /// Required OP_CSV `Sequence`
+        csv: Sequence,
+    },
+    /// When bumping a tx the absolute fee requested is lower than replaced tx absolute fee
+    FeeTooLow {
+        /// Required fee absolute value [`Amount`]
+        required: Amount,
+    },
+    /// When bumping a tx the fee rate requested is lower than required
+    FeeRateTooLow {
+        /// Required fee rate
+        required: bitcoin::FeeRate,
+    },
+    /// `manually_selected_only` option is selected but no utxo has been passed
+    NoUtxosSelected,
+    /// Output created is under the dust limit, 546 satoshis
+    OutputBelowDustLimit(usize),
+    /// There was an error with coin selection
+    CoinSelection(coin_selection::Error),
+    /// Cannot build a tx without recipients
+    NoRecipients,
+    /// Partially signed bitcoin transaction error
+    Psbt(psbt::Error),
+    /// In order to use the [`TxBuilder::add_global_xpubs`] option every extended
+    /// key in the descriptor must either be a master key itself (having depth = 0) or have an
+    /// explicit origin provided
+    ///
+    /// [`TxBuilder::add_global_xpubs`]: crate::wallet::tx_builder::TxBuilder::add_global_xpubs
+    MissingKeyOrigin(String),
+    /// Happens when trying to spend an UTXO that is not in the internal database
+    UnknownUtxo,
+    /// Missing non_witness_utxo on foreign utxo for given `OutPoint`
+    MissingNonWitnessUtxo(OutPoint),
+    /// Miniscript PSBT error
+    MiniscriptPsbt(MiniscriptPsbtError),
+}
+
+impl fmt::Display for CreateTxError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Descriptor(e) => e.fmt(f),
+            Self::Policy(e) => e.fmt(f),
+            CreateTxError::SpendingPolicyRequired(keychain_kind) => {
+                write!(f, "Spending policy required: {:?}", keychain_kind)
+            }
+            CreateTxError::Version0 => {
+                write!(f, "Invalid version `0`")
+            }
+            CreateTxError::Version1Csv => {
+                write!(
+                    f,
+                    "TxBuilder requested version `1`, but at least `2` is needed to use OP_CSV"
+                )
+            }
+            CreateTxError::LockTime {
+                requested,
+                required,
+            } => {
+                write!(f, "TxBuilder requested timelock of `{:?}`, but at least `{:?}` is required to spend from this script", required, requested)
+            }
+            CreateTxError::RbfSequence => {
+                write!(f, "Cannot enable RBF with a nSequence >= 0xFFFFFFFE")
+            }
+            CreateTxError::RbfSequenceCsv { rbf, csv } => {
+                write!(
+                    f,
+                    "Cannot enable RBF with nSequence `{:?}` given a required OP_CSV of `{:?}`",
+                    rbf, csv
+                )
+            }
+            CreateTxError::FeeTooLow { required } => {
+                write!(f, "Fee to low: required {}", required.display_dynamic())
+            }
+            CreateTxError::FeeRateTooLow { required } => {
+                write!(
+                    f,
+                    // Note: alternate fmt as sat/vb (ceil) available in bitcoin-0.31
+                    //"Fee rate too low: required {required:#}"
+                    "Fee rate too low: required {} sat/vb",
+                    crate::floating_rate!(required)
+                )
+            }
+            CreateTxError::NoUtxosSelected => {
+                write!(f, "No UTXO selected")
+            }
+            CreateTxError::OutputBelowDustLimit(limit) => {
+                write!(f, "Output below the dust limit: {}", limit)
+            }
+            CreateTxError::CoinSelection(e) => e.fmt(f),
+            CreateTxError::NoRecipients => {
+                write!(f, "Cannot build tx without recipients")
+            }
+            CreateTxError::Psbt(e) => e.fmt(f),
+            CreateTxError::MissingKeyOrigin(err) => {
+                write!(f, "Missing key origin: {}", err)
+            }
+            CreateTxError::UnknownUtxo => {
+                write!(f, "UTXO not found in the internal database")
+            }
+            CreateTxError::MissingNonWitnessUtxo(outpoint) => {
+                write!(f, "Missing non_witness_utxo on foreign utxo {}", outpoint)
+            }
+            CreateTxError::MiniscriptPsbt(err) => {
+                write!(f, "Miniscript PSBT error: {}", err)
+            }
+        }
+    }
+}
+
+impl From<descriptor::error::Error> for CreateTxError {
+    fn from(err: descriptor::error::Error) -> Self {
+        CreateTxError::Descriptor(err)
+    }
+}
+
+impl From<PolicyError> for CreateTxError {
+    fn from(err: PolicyError) -> Self {
+        CreateTxError::Policy(err)
+    }
+}
+
+impl From<MiniscriptPsbtError> for CreateTxError {
+    fn from(err: MiniscriptPsbtError) -> Self {
+        CreateTxError::MiniscriptPsbt(err)
+    }
+}
+
+impl From<psbt::Error> for CreateTxError {
+    fn from(err: psbt::Error) -> Self {
+        CreateTxError::Psbt(err)
+    }
+}
+
+impl From<coin_selection::Error> for CreateTxError {
+    fn from(err: coin_selection::Error) -> Self {
+        CreateTxError::CoinSelection(err)
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for CreateTxError {}
+
+#[derive(Debug)]
+/// Error returned from [`Wallet::build_fee_bump`]
+///
+/// [`Wallet::build_fee_bump`]: super::Wallet::build_fee_bump
+pub enum BuildFeeBumpError {
+    /// Happens when trying to spend an UTXO that is not in the internal database
+    UnknownUtxo(OutPoint),
+    /// Thrown when a tx is not found in the internal database
+    TransactionNotFound(Txid),
+    /// Happens when trying to bump a transaction that is already confirmed
+    TransactionConfirmed(Txid),
+    /// Trying to replace a tx that has a sequence >= `0xFFFFFFFE`
+    IrreplaceableTransaction(Txid),
+    /// Node doesn't have data to estimate a fee rate
+    FeeRateUnavailable,
+}
+
+impl fmt::Display for BuildFeeBumpError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::UnknownUtxo(outpoint) => write!(
+                f,
+                "UTXO not found in the internal database with txid: {}, vout: {}",
+                outpoint.txid, outpoint.vout
+            ),
+            Self::TransactionNotFound(txid) => {
+                write!(
+                    f,
+                    "Transaction not found in the internal database with txid: {}",
+                    txid
+                )
+            }
+            Self::TransactionConfirmed(txid) => {
+                write!(f, "Transaction already confirmed with txid: {}", txid)
+            }
+            Self::IrreplaceableTransaction(txid) => {
+                write!(f, "Transaction can't be replaced with txid: {}", txid)
+            }
+            Self::FeeRateUnavailable => write!(f, "Fee rate unavailable"),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl std::error::Error for BuildFeeBumpError {}

crates/wallet/src/wallet/export.rs

@@ -0,0 +1,366 @@
+// Bitcoin Dev Kit
+// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
+//
+// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
+//
+// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
+// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
+// You may not use this file except in accordance with one or both of these
+// licenses.
+
+//! Wallet export
+//!
+//! This modules implements the wallet export format used by [FullyNoded](https://github.com/Fonta1n3/FullyNoded/blob/10b7808c8b929b171cca537fb50522d015168ac9/Docs/Wallets/Wallet-Export-Spec.md).
+//!
+//! ## Examples
+//!
+//! ### Import from JSON
+//!
+//! ```
+//! # use std::str::FromStr;
+//! # use bitcoin::*;
+//! # use bdk_wallet::export::*;
+//! # use bdk_wallet::*;
+//! let import = r#"{
+//!     "descriptor": "wpkh([c258d2e4\/84h\/1h\/0h]tpubDD3ynpHgJQW8VvWRzQ5WFDCrs4jqVFGHB3vLC3r49XHJSqP8bHKdK4AriuUKLccK68zfzowx7YhmDN8SiSkgCDENUFx9qVw65YyqM78vyVe\/0\/*)",
+//!     "blockheight":1782088,
+//!     "label":"testnet"
+//! }"#;
+//!
+//! let import = FullyNodedExport::from_str(import)?;
+//! let wallet = Wallet::create(
+//!     import.descriptor(),
+//!     import.change_descriptor().expect("change descriptor"),
+//! )
+//! .network(Network::Testnet)
+//! .create_wallet_no_persist()?;
+//! # Ok::<_, Box<dyn std::error::Error>>(())
+//! ```
+//!
+//! ### Export a `Wallet`
+//! ```
+//! # use bitcoin::*;
+//! # use bdk_wallet::export::*;
+//! # use bdk_wallet::*;
+//! let wallet = Wallet::create(
+//!     "wpkh([c258d2e4/84h/1h/0h]tpubDD3ynpHgJQW8VvWRzQ5WFDCrs4jqVFGHB3vLC3r49XHJSqP8bHKdK4AriuUKLccK68zfzowx7YhmDN8SiSkgCDENUFx9qVw65YyqM78vyVe/0/*)",
+//!     "wpkh([c258d2e4/84h/1h/0h]tpubDD3ynpHgJQW8VvWRzQ5WFDCrs4jqVFGHB3vLC3r49XHJSqP8bHKdK4AriuUKLccK68zfzowx7YhmDN8SiSkgCDENUFx9qVw65YyqM78vyVe/1/*)",
+//! )
+//! .network(Network::Testnet)
+//! .create_wallet_no_persist()?;
+//! let export = FullyNodedExport::export_wallet(&wallet, "exported wallet", true).unwrap();
+//!
+//! println!("Exported: {}", export.to_string());
+//! # Ok::<_, Box<dyn std::error::Error>>(())
+//! ```
+
+use alloc::string::String;
+use core::fmt;
+use core::str::FromStr;
+use serde::{Deserialize, Serialize};
+
+use miniscript::descriptor::{ShInner, WshInner};
+use miniscript::{Descriptor, ScriptContext, Terminal};
+
+use crate::types::KeychainKind;
+use crate::wallet::Wallet;
+
+/// Alias for [`FullyNodedExport`]
+#[deprecated(since = "0.18.0", note = "Please use [`FullyNodedExport`] instead")]
+pub type WalletExport = FullyNodedExport;
+
+/// Structure that contains the export of a wallet
+///
+/// For a usage example see [this module](crate::wallet::export)'s documentation.
+#[derive(Debug, Serialize, Deserialize)]
+pub struct FullyNodedExport {
+    descriptor: String,
+    /// Earliest block to rescan when looking for the wallet's transactions
+    pub blockheight: u32,
+    /// Arbitrary label for the wallet
+    pub label: String,
+}
+
+impl fmt::Display for FullyNodedExport {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", serde_json::to_string(self).unwrap())
+    }
+}
+
+impl FromStr for FullyNodedExport {
+    type Err = serde_json::Error;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        serde_json::from_str(s)
+    }
+}
+
+fn remove_checksum(s: String) -> String {
+    s.split_once('#').map(|(a, _)| String::from(a)).unwrap()
+}
+
+impl FullyNodedExport {
+    /// Export a wallet
+    ///
+    /// This function returns an error if it determines that the `wallet`'s descriptor(s) are not
+    /// supported by Bitcoin Core or don't follow the standard derivation paths defined by BIP44
+    /// and others.
+    ///
+    /// If `include_blockheight` is `true`, this function will look into the `wallet`'s database
+    /// for the oldest transaction it knows and use that as the earliest block to rescan.
+    ///
+    /// If the database is empty or `include_blockheight` is false, the `blockheight` field
+    /// returned will be `0`.
+    pub fn export_wallet(
+        wallet: &Wallet,
+        label: &str,
+        include_blockheight: bool,
+    ) -> Result<Self, &'static str> {
+        let descriptor = wallet
+            .public_descriptor(KeychainKind::External)
+            .to_string_with_secret(
+                &wallet
+                    .get_signers(KeychainKind::External)
+                    .as_key_map(wallet.secp_ctx()),
+            );
+        let descriptor = remove_checksum(descriptor);
+        Self::is_compatible_with_core(&descriptor)?;
+
+        let blockheight = if include_blockheight {
+            wallet.transactions().next().map_or(0, |canonical_tx| {
+                match canonical_tx.chain_position {
+                    bdk_chain::ChainPosition::Confirmed(a) => a.block_id.height,
+                    bdk_chain::ChainPosition::Unconfirmed(_) => 0,
+                }
+            })
+        } else {
+            0
+        };
+
+        let export = FullyNodedExport {
+            descriptor,
+            label: label.into(),
+            blockheight,
+        };
+
+        let change_descriptor = {
+            let descriptor = wallet
+                .public_descriptor(KeychainKind::Internal)
+                .to_string_with_secret(
+                    &wallet
+                        .get_signers(KeychainKind::Internal)
+                        .as_key_map(wallet.secp_ctx()),
+                );
+            Some(remove_checksum(descriptor))
+        };
+
+        if export.change_descriptor() != change_descriptor {
+            return Err("Incompatible change descriptor");
+        }
+
+        Ok(export)
+    }
+
+    fn is_compatible_with_core(descriptor: &str) -> Result<(), &'static str> {
+        fn check_ms<Ctx: ScriptContext>(
+            terminal: &Terminal<String, Ctx>,
+        ) -> Result<(), &'static str> {
+            if let Terminal::Multi(_) = terminal {
+                Ok(())
+            } else {
+                Err("The descriptor contains operators not supported by Bitcoin Core")
+            }
+        }
+
+        // pkh(), wpkh(), sh(wpkh()) are always fine, as well as multi() and sortedmulti()
+        match Descriptor::<String>::from_str(descriptor).map_err(|_| "Invalid descriptor")? {
+            Descriptor::Pkh(_) | Descriptor::Wpkh(_) => Ok(()),
+            Descriptor::Sh(sh) => match sh.as_inner() {
+                ShInner::Wpkh(_) => Ok(()),
+                ShInner::SortedMulti(_) => Ok(()),
+                ShInner::Wsh(wsh) => match wsh.as_inner() {
+                    WshInner::SortedMulti(_) => Ok(()),
+                    WshInner::Ms(ms) => check_ms(&ms.node),
+                },
+                ShInner::Ms(ms) => check_ms(&ms.node),
+            },
+            Descriptor::Wsh(wsh) => match wsh.as_inner() {
+                WshInner::SortedMulti(_) => Ok(()),
+                WshInner::Ms(ms) => check_ms(&ms.node),
+            },
+            Descriptor::Tr(_) => Ok(()),
+            _ => Err("The descriptor is not compatible with Bitcoin Core"),
+        }
+    }
+
+    /// Return the external descriptor
+    pub fn descriptor(&self) -> String {
+        self.descriptor.clone()
+    }
+
+    /// Return the internal descriptor, if present
+    pub fn change_descriptor(&self) -> Option<String> {
+        let replaced = self.descriptor.replace("/0/*", "/1/*");
+
+        if replaced != self.descriptor {
+            Some(replaced)
+        } else {
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use core::str::FromStr;
+
+    use crate::std::string::ToString;
+    use bdk_chain::{BlockId, ConfirmationBlockTime};
+    use bitcoin::hashes::Hash;
+    use bitcoin::{transaction, BlockHash, Network, Transaction};
+
+    use super::*;
+    use crate::Wallet;
+
+    fn get_test_wallet(descriptor: &str, change_descriptor: &str, network: Network) -> Wallet {
+        use crate::wallet::Update;
+        use bdk_chain::TxGraph;
+        let mut wallet = Wallet::create(descriptor.to_string(), change_descriptor.to_string())
+            .network(network)
+            .create_wallet_no_persist()
+            .expect("must create wallet");
+        let transaction = Transaction {
+            input: vec![],
+            output: vec![],
+            version: transaction::Version::non_standard(0),
+            lock_time: bitcoin::absolute::LockTime::ZERO,
+        };
+        let txid = transaction.compute_txid();
+        let block_id = BlockId {
+            height: 5000,
+            hash: BlockHash::all_zeros(),
+        };
+        wallet.insert_checkpoint(block_id).unwrap();
+        wallet
+            .insert_checkpoint(BlockId {
+                height: 5001,
+                hash: BlockHash::all_zeros(),
+            })
+            .unwrap();
+        wallet.insert_tx(transaction);
+        let anchor = ConfirmationBlockTime {
+            confirmation_time: 0,
+            block_id,
+        };
+        let mut graph = TxGraph::default();
+        let _ = graph.insert_anchor(txid, anchor);
+        wallet
+            .apply_update(Update {
+                graph,
+                ..Default::default()
+            })
+            .unwrap();
+        wallet
+    }
+
+    #[test]
+    fn test_export_bip44() {
+        let descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/0/*)";
+        let change_descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/1/*)";
+
+        let wallet = get_test_wallet(descriptor, change_descriptor, Network::Bitcoin);
+        let export = FullyNodedExport::export_wallet(&wallet, "Test Label", true).unwrap();
+
+        assert_eq!(export.descriptor(), descriptor);
+        assert_eq!(export.change_descriptor(), Some(change_descriptor.into()));
+        assert_eq!(export.blockheight, 5000);
+        assert_eq!(export.label, "Test Label");
+    }
+
+    #[test]
+    #[should_panic(expected = "Incompatible change descriptor")]
+    fn test_export_no_change() {
+        // The wallet's change descriptor has no wildcard. It should be impossible to
+        // export, because exporting this kind of external descriptor normally implies the
+        // existence of a compatible internal descriptor
+
+        let descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/0/*)";
+        let change_descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/1/0)";
+
+        let wallet = get_test_wallet(descriptor, change_descriptor, Network::Bitcoin);
+        FullyNodedExport::export_wallet(&wallet, "Test Label", true).unwrap();
+    }
+
+    #[test]
+    #[should_panic(expected = "Incompatible change descriptor")]
+    fn test_export_incompatible_change() {
+        // This wallet has a change descriptor, but the derivation path is not in the "standard"
+        // bip44/49/etc format
+
+        let descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/0/*)";
+        let change_descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/50'/0'/1/*)";
+
+        let wallet = get_test_wallet(descriptor, change_descriptor, Network::Bitcoin);
+        FullyNodedExport::export_wallet(&wallet, "Test Label", true).unwrap();
+    }
+
+    #[test]
+    fn test_export_multi() {
+        let descriptor = "wsh(multi(2,\
+                                [73756c7f/48'/0'/0'/2']tpubDCKxNyM3bLgbEX13Mcd8mYxbVg9ajDkWXMh29hMWBurKfVmBfWAM96QVP3zaUcN51HvkZ3ar4VwP82kC8JZhhux8vFQoJintSpVBwpFvyU3/0/*,\
+                                [f9f62194/48'/0'/0'/2']tpubDDp3ZSH1yCwusRppH7zgSxq2t1VEUyXSeEp8E5aFS8m43MknUjiF1bSLo3CGWAxbDyhF1XowA5ukPzyJZjznYk3kYi6oe7QxtX2euvKWsk4/0/*,\
+                                [c98b1535/48'/0'/0'/2']tpubDCDi5W4sP6zSnzJeowy8rQDVhBdRARaPhK1axABi8V1661wEPeanpEXj4ZLAUEoikVtoWcyK26TKKJSecSfeKxwHCcRrge9k1ybuiL71z4a/0/*\
+                          ))";
+        let change_descriptor = "wsh(multi(2,\
+                                       [73756c7f/48'/0'/0'/2']tpubDCKxNyM3bLgbEX13Mcd8mYxbVg9ajDkWXMh29hMWBurKfVmBfWAM96QVP3zaUcN51HvkZ3ar4VwP82kC8JZhhux8vFQoJintSpVBwpFvyU3/1/*,\
+                                       [f9f62194/48'/0'/0'/2']tpubDDp3ZSH1yCwusRppH7zgSxq2t1VEUyXSeEp8E5aFS8m43MknUjiF1bSLo3CGWAxbDyhF1XowA5ukPzyJZjznYk3kYi6oe7QxtX2euvKWsk4/1/*,\
+                                       [c98b1535/48'/0'/0'/2']tpubDCDi5W4sP6zSnzJeowy8rQDVhBdRARaPhK1axABi8V1661wEPeanpEXj4ZLAUEoikVtoWcyK26TKKJSecSfeKxwHCcRrge9k1ybuiL71z4a/1/*\
+                                 ))";
+
+        let wallet = get_test_wallet(descriptor, change_descriptor, Network::Testnet);
+        let export = FullyNodedExport::export_wallet(&wallet, "Test Label", true).unwrap();
+
+        assert_eq!(export.descriptor(), descriptor);
+        assert_eq!(export.change_descriptor(), Some(change_descriptor.into()));
+        assert_eq!(export.blockheight, 5000);
+        assert_eq!(export.label, "Test Label");
+    }
+
+    #[test]
+    fn test_export_tr() {
+        let descriptor = "tr([73c5da0a/86'/0'/0']tprv8fMn4hSKPRC1oaCPqxDb1JWtgkpeiQvZhsr8W2xuy3GEMkzoArcAWTfJxYb6Wj8XNNDWEjfYKK4wGQXh3ZUXhDF2NcnsALpWTeSwarJt7Vc/0/*)";
+        let change_descriptor = "tr([73c5da0a/86'/0'/0']tprv8fMn4hSKPRC1oaCPqxDb1JWtgkpeiQvZhsr8W2xuy3GEMkzoArcAWTfJxYb6Wj8XNNDWEjfYKK4wGQXh3ZUXhDF2NcnsALpWTeSwarJt7Vc/1/*)";
+        let wallet = get_test_wallet(descriptor, change_descriptor, Network::Testnet);
+        let export = FullyNodedExport::export_wallet(&wallet, "Test Label", true).unwrap();
+        assert_eq!(export.descriptor(), descriptor);
+        assert_eq!(export.change_descriptor(), Some(change_descriptor.into()));
+        assert_eq!(export.blockheight, 5000);
+        assert_eq!(export.label, "Test Label");
+    }
+
+    #[test]
+    fn test_export_to_json() {
+        let descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/0/*)";
+        let change_descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/1/*)";
+
+        let wallet = get_test_wallet(descriptor, change_descriptor, Network::Bitcoin);
+        let export = FullyNodedExport::export_wallet(&wallet, "Test Label", true).unwrap();
+
+        assert_eq!(export.to_string(), "{\"descriptor\":\"wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44\'/0\'/0\'/0/*)\",\"blockheight\":5000,\"label\":\"Test Label\"}");
+    }
+
+    #[test]
+    fn test_export_from_json() {
+        let descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/0/*)";
+        let change_descriptor = "wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44'/0'/0'/1/*)";
+
+        let import_str = "{\"descriptor\":\"wpkh(xprv9s21ZrQH143K4CTb63EaMxja1YiTnSEWKMbn23uoEnAzxjdUJRQkazCAtzxGm4LSoTSVTptoV9RbchnKPW9HxKtZumdyxyikZFDLhogJ5Uj/44\'/0\'/0\'/0/*)\",\"blockheight\":5000,\"label\":\"Test Label\"}";
+        let export = FullyNodedExport::from_str(import_str).unwrap();
+
+        assert_eq!(export.descriptor(), descriptor);
+        assert_eq!(export.change_descriptor(), Some(change_descriptor.into()));
+        assert_eq!(export.blockheight, 5000);
+        assert_eq!(export.label, "Test Label");
+    }
+}