Merge bitcoindevkit/bdk#1453: refactor(electrum) put the tx cache in electrum

2d2656acfa feat(electrum): re-export `transaction_broadcast` method (志宇)
53fa35096f refactor(electrum)!: put the tx cache in electrum (LLFourn)

Pull request description:

  Previously there was a `TxCache` that you passed in as part of the sync request. There are lots of downsides to this:

  1. If the user forgets to do this you cache nothing
  2. where are you meant to keep this cache? The example shows it being recreated every time which seems very suboptimal.
  3. More API and documentation surface area.

  Instead just do a plain old simple cache inside the electrum client. This way at least you only download transactions once. You can pre-populate the cache with a method also and I did this in the examples.

  * [x] This pull request breaks the existing API

ACKs for top commit:
  evanlinjin:
    self-ACK 2d2656acfa
  notmandatory:
    ACK 2d2656acfa

Tree-SHA512: 6c29fd4f99ea5bd66234d5cdaf4b157a192ddd3baacc91076e402d8df0de7010bc482e24895e85fcb2f805ec6d1ce6cdb7654f8f552c90ba75ed35f80a00b856

crates/chain/src/indexed_tx_graph.rs

@@ -352,3 +352,9 @@ pub trait Indexer {
     /// Determines whether the transaction should be included in the index.
     fn is_tx_relevant(&self, tx: &Transaction) -> bool;
 }
+
+impl<A, I> AsRef<TxGraph<A>> for IndexedTxGraph<A, I> {
+    fn as_ref(&self) -> &TxGraph<A> {
+        &self.graph
+    }
+}

crates/chain/src/spk_client.rs

@@ -1,19 +1,12 @@
 //! Helper types for spk-based blockchain clients.
 
 use crate::{
-    collections::{BTreeMap, HashMap},
-    local_chain::CheckPoint,
-    ConfirmationTimeHeightAnchor, TxGraph,
+    collections::BTreeMap, local_chain::CheckPoint, ConfirmationTimeHeightAnchor, TxGraph,
 };
-use alloc::{boxed::Box, sync::Arc, vec::Vec};
-use bitcoin::{OutPoint, Script, ScriptBuf, Transaction, Txid};
+use alloc::{boxed::Box, vec::Vec};
+use bitcoin::{OutPoint, Script, ScriptBuf, Txid};
 use core::{fmt::Debug, marker::PhantomData, ops::RangeBounds};
 
-/// A cache of [`Arc`]-wrapped full transactions, identified by their [`Txid`]s.
-///
-/// This is used by the chain-source to avoid re-fetching full transactions.
-pub type TxCache = HashMap<Txid, Arc<Transaction>>;
-
 /// 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
@@ -24,8 +17,6 @@ pub struct SyncRequest {
     ///
     /// [`LocalChain::tip`]: crate::local_chain::LocalChain::tip
     pub chain_tip: CheckPoint,
-    /// Cache of full transactions, so the chain-source can avoid re-fetching.
-    pub tx_cache: TxCache,
     /// Transactions that spend from or to these indexed script pubkeys.
     pub spks: Box<dyn ExactSizeIterator<Item = ScriptBuf> + Send>,
     /// Transactions with these txids.
@@ -39,36 +30,12 @@ impl SyncRequest {
     pub fn from_chain_tip(cp: CheckPoint) -> Self {
         Self {
             chain_tip: cp,
-            tx_cache: TxCache::new(),
             spks: Box::new(core::iter::empty()),
             txids: Box::new(core::iter::empty()),
             outpoints: Box::new(core::iter::empty()),
         }
     }
 
-    /// Add to the [`TxCache`] held by the request.
-    ///
-    /// This consumes the [`SyncRequest`] and returns the updated one.
-    #[must_use]
-    pub fn cache_txs<T>(mut self, full_txs: impl IntoIterator<Item = (Txid, T)>) -> Self
-    where
-        T: Into<Arc<Transaction>>,
-    {
-        self.tx_cache = full_txs
-            .into_iter()
-            .map(|(txid, tx)| (txid, tx.into()))
-            .collect();
-        self
-    }
-
-    /// Add all transactions from [`TxGraph`] into the [`TxCache`].
-    ///
-    /// This consumes the [`SyncRequest`] and returns the updated one.
-    #[must_use]
-    pub fn cache_graph_txs<A>(self, graph: &TxGraph<A>) -> Self {
-        self.cache_txs(graph.full_txs().map(|tx_node| (tx_node.txid, tx_node.tx)))
-    }
-
     /// Set the [`Script`]s that will be synced against.
     ///
     /// This consumes the [`SyncRequest`] and returns the updated one.
@@ -227,8 +194,6 @@ pub struct FullScanRequest<K> {
     ///
     /// [`LocalChain::tip`]: crate::local_chain::LocalChain::tip
     pub chain_tip: CheckPoint,
-    /// Cache of full transactions, so the chain-source can avoid re-fetching.
-    pub tx_cache: TxCache,
     /// Iterators of script pubkeys indexed by the keychain index.
     pub spks_by_keychain: BTreeMap<K, Box<dyn Iterator<Item = (u32, ScriptBuf)> + Send>>,
 }
@@ -239,34 +204,10 @@ impl<K: Ord + Clone> FullScanRequest<K> {
     pub fn from_chain_tip(chain_tip: CheckPoint) -> Self {
         Self {
             chain_tip,
-            tx_cache: TxCache::new(),
             spks_by_keychain: BTreeMap::new(),
         }
     }
 
-    /// Add to the [`TxCache`] held by the request.
-    ///
-    /// This consumes the [`SyncRequest`] and returns the updated one.
-    #[must_use]
-    pub fn cache_txs<T>(mut self, full_txs: impl IntoIterator<Item = (Txid, T)>) -> Self
-    where
-        T: Into<Arc<Transaction>>,
-    {
-        self.tx_cache = full_txs
-            .into_iter()
-            .map(|(txid, tx)| (txid, tx.into()))
-            .collect();
-        self
-    }
-
-    /// Add all transactions from [`TxGraph`] into the [`TxCache`].
-    ///
-    /// This consumes the [`SyncRequest`] and returns the updated one.
-    #[must_use]
-    pub fn cache_graph_txs<A>(self, graph: &TxGraph<A>) -> Self {
-        self.cache_txs(graph.full_txs().map(|tx_node| (tx_node.txid, tx_node.tx)))
-    }
-
     /// Construct a new [`FullScanRequest`] from a given `chain_tip` and `index`.
     ///
     /// Unbounded script pubkey iterators for each keychain (`K`) are extracted using