Merge bitcoindevkit/bdk#758: Add HWI example in docs

1437e1ecfe Add the hardware_signer example (Daniela Brozzoni)
1a71eb1f47 Update the hardwaresigner module documentation (Daniela Brozzoni)
0695e9fb3e Bump HWI to 0.2.3 (Daniela Brozzoni)
a4a43ea860 Re-export HWI if the hardware-signer feature is set (Daniela Brozzoni)

Pull request description:

  ### Description

  ### Notes to the reviewers

  ### Changelog notice

  - bdk re-exports the `hwi` create when the feature `hardware-signer` is on
  - Add `examples/hardware_signer.rs`

  ### 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

ACKs for top commit:
  afilini:
    ACK 1437e1ecfe

Tree-SHA512: 181f4d14dce11e19497fbf30e0af8de21c2c210d37129d7d879ed5670ed09a25be1c8d371389c431e18df9e76870cf5e4afe7b29a6c05fe59b3e1816bc8cf673

examples/hardware_signer.rs

@@ -0,0 +1,103 @@
+use bdk::bitcoin::{Address, Network};
+use bdk::blockchain::{Blockchain, ElectrumBlockchain};
+use bdk::database::MemoryDatabase;
+use bdk::hwi::{types::HWIChain, HWIClient};
+use bdk::signer::SignerOrdering;
+use bdk::wallet::{hardwaresigner::HWISigner, AddressIndex};
+use bdk::{FeeRate, KeychainKind, SignOptions, SyncOptions, Wallet};
+use electrum_client::Client;
+use std::str::FromStr;
+use std::sync::Arc;
+
+// This example shows how to sync a wallet, create a transaction, sign it
+// and broadcast it using an external hardware wallet.
+// The hardware wallet must be connected to the computer and unlocked before
+// running the example. Also, the `hwi` python package should be installed
+// and available in the environment.
+//
+// To avoid loss of funds, consider using an hardware wallet simulator:
+// * Coldcard: https://github.com/Coldcard/firmware
+// * Ledger: https://github.com/LedgerHQ/speculos
+// * Trezor: https://docs.trezor.io/trezor-firmware/core/emulator/index.html
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    println!("Hold tight, I'm connecting to your hardware wallet...");
+
+    // Listing all the available hardware wallet devices...
+    let devices = HWIClient::enumerate()?;
+    let first_device = devices
+        .first()
+        .expect("No devices found. Either plug in a hardware wallet, or start a simulator.");
+    // ...and creating a client out of the first one
+    let client = HWIClient::get_client(first_device, true, HWIChain::Test)?;
+    println!("Look what I found, a {}!", first_device.model);
+
+    // Getting the HW's public descriptors
+    let descriptors = client.get_descriptors(None)?;
+    println!(
+        "The hardware wallet's descriptor is: {}",
+        descriptors.receive[0]
+    );
+
+    // Creating a custom signer from the device
+    let custom_signer = HWISigner::from_device(first_device, HWIChain::Test)?;
+    let mut wallet = Wallet::new(
+        &descriptors.receive[0],
+        Some(&descriptors.internal[0]),
+        Network::Testnet,
+        MemoryDatabase::default(),
+    )?;
+
+    // Adding the hardware signer to the BDK wallet
+    wallet.add_signer(
+        KeychainKind::External,
+        SignerOrdering(200),
+        Arc::new(custom_signer),
+    );
+
+    // create client for Blockstream's testnet electrum server
+    let blockchain =
+        ElectrumBlockchain::from(Client::new("ssl://electrum.blockstream.info:60002")?);
+
+    println!("Syncing the wallet...");
+    wallet.sync(&blockchain, SyncOptions::default())?;
+
+    // get deposit address
+    let deposit_address = wallet.get_address(AddressIndex::New)?;
+
+    let balance = wallet.get_balance()?;
+    println!("Wallet balances in SATs: {}", balance);
+
+    if balance.get_total() < 10000 {
+        println!(
+            "Send some sats from the u01.net testnet faucet to address '{addr}'.\nFaucet URL: https://bitcoinfaucet.uo1.net/?to={addr}",
+            addr = deposit_address.address
+        );
+        return Ok(());
+    }
+
+    let return_address = Address::from_str("tb1ql7w62elx9ucw4pj5lgw4l028hmuw80sndtntxt")?;
+    let (mut psbt, _details) = {
+        let mut builder = wallet.build_tx();
+        builder
+            .drain_wallet()
+            .drain_to(return_address.script_pubkey())
+            .enable_rbf()
+            .fee_rate(FeeRate::from_sat_per_vb(5.0));
+        builder.finish()?
+    };
+
+    // `sign` will call the hardware wallet asking for a signature
+    assert!(
+        wallet.sign(&mut psbt, SignOptions::default())?,
+        "The hardware wallet couldn't finalize the transaction :("
+    );
+
+    println!("Let's broadcast your tx...");
+    let raw_transaction = psbt.extract_tx();
+    let txid = raw_transaction.txid();
+
+    blockchain.broadcast(&raw_transaction)?;
+    println!("Transaction broadcasted! TXID: {txid}.\nExplorer URL: https://mempool.space/testnet/tx/{txid}", txid = txid);
+
+    Ok(())
+}