Expand chain::Listen trivially to accept filtered block data

The `chain::Listen` interface provides a block-connection-based
alternative to the `chain::Confirm` interface, which supports
providing transaction data at a time separate from the block
connection time.

For users who are downloading the full headers tree (e.g. from a
node over the Bitcoin P2P protocol) but who are not downloading
full blocks (e.g. because they're using BIP 157/158 filtering)
there is no API that matches exactly their event stream -
`chain::Listen` requries full blocks for each block,
`chain::Confirm` requires breaking each connection event into two
calls.

Given its incredibly trivial to take a `TransactionData` in
addition to a `Block` in `chain::Listen` we do so here, adding a
default-implementation `block_connected` which simply creates the
`TransactionData`, which ultimately all of the `chain::Listen`
implementations currently do anyway.

Closes #1128.

Author: TheBlueMatt

lightning-block-sync/src/init.rs

@@ -4,7 +4,7 @@
 use crate::{BlockSource, BlockSourceResult, Cache, ChainNotifier};
 use crate::poll::{ChainPoller, Validate, ValidatedBlockHeader};
 
-use bitcoin::blockdata::block::{Block, BlockHeader};
+use bitcoin::blockdata::block::BlockHeader;
 use bitcoin::hash_types::BlockHash;
 use bitcoin::network::constants::Network;
 
@@ -203,7 +203,7 @@ impl<'a, C: Cache> Cache for ReadOnlyCache<'a, C> {
 struct DynamicChainListener<'a, L: chain::Listen + ?Sized>(&'a L);
 
 impl<'a, L: chain::Listen + ?Sized> chain::Listen for DynamicChainListener<'a, L> {
-	fn block_connected(&self, _block: &Block, _height: u32) {
+	fn filtered_block_connected(&self, _header: &BlockHeader, _txdata: &chain::transaction::TransactionData, _height: u32) {
 		unreachable!()
 	}
 
@@ -216,10 +216,10 @@ impl<'a, L: chain::Listen + ?Sized> chain::Listen for DynamicChainListener<'a, L
 struct ChainListenerSet<'a, L: chain::Listen + ?Sized>(Vec<(u32, &'a L)>);
 
 impl<'a, L: chain::Listen + ?Sized> chain::Listen for ChainListenerSet<'a, L> {
-	fn block_connected(&self, block: &Block, height: u32) {
+	fn filtered_block_connected(&self, header: &BlockHeader, txdata: &chain::transaction::TransactionData, height: u32) {
 		for (starting_height, chain_listener) in self.0.iter() {
 			if height > *starting_height {
-				chain_listener.block_connected(block, height);
+				chain_listener.filtered_block_connected(header, txdata, height);
 			}
 		}
 	}

lightning-block-sync/src/test_utils.rs

@@ -166,7 +166,7 @@ impl BlockSource for Blockchain {
 pub struct NullChainListener;
 
 impl chain::Listen for NullChainListener {
-	fn block_connected(&self, _block: &Block, _height: u32) {}
+	fn filtered_block_connected(&self, _header: &BlockHeader, _txdata: &chain::transaction::TransactionData, _height: u32) {}
 	fn block_disconnected(&self, _header: &BlockHeader, _height: u32) {}
 }
 
@@ -195,13 +195,13 @@ impl MockChainListener {
 }
 
 impl chain::Listen for MockChainListener {
-	fn block_connected(&self, block: &Block, height: u32) {
+	fn filtered_block_connected(&self, header: &BlockHeader, _txdata: &chain::transaction::TransactionData, height: u32) {
 		match self.expected_blocks_connected.borrow_mut().pop_front() {
 			None => {
-				panic!("Unexpected block connected: {:?}", block.block_hash());
+				panic!("Unexpected block connected: {:?}", header.block_hash());
 			},
 			Some(expected_block) => {
-				assert_eq!(block.block_hash(), expected_block.header.block_hash());
+				assert_eq!(header.block_hash(), expected_block.header.block_hash());
 				assert_eq!(height, expected_block.height);
 			},
 		}

lightning/src/chain/chainmonitor.rs

@@ -23,7 +23,7 @@
 //! events. The remote server would make use of [`ChainMonitor`] for block processing and for
 //! servicing [`ChannelMonitor`] updates from the client.
 
-use bitcoin::blockdata::block::{Block, BlockHeader};
+use bitcoin::blockdata::block::BlockHeader;
 use bitcoin::hash_types::Txid;
 
 use chain;
@@ -501,9 +501,7 @@ where
 	L::Target: Logger,
 	P::Target: Persist<ChannelSigner>,
 {
-	fn block_connected(&self, block: &Block, height: u32) {
-		let header = &block.header;
-		let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
+	fn filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
 		log_debug!(self.logger, "New best block {} at height {} provided via block_connected", header.block_hash(), height);
 		self.process_chain_data(header, Some(height), &txdata, |monitor, txdata| {
 			monitor.block_connected(

lightning/src/chain/channelmonitor.rs

@@ -20,7 +20,7 @@
 //! security-domain-separated system design, you should consider having multiple paths for
 //! ChannelMonitors to get out of the HSM and onto monitoring devices.
 
-use bitcoin::blockdata::block::{Block, BlockHeader};
+use bitcoin::blockdata::block::BlockHeader;
 use bitcoin::blockdata::transaction::{TxOut,Transaction};
 use bitcoin::blockdata::script::{Script, Builder};
 use bitcoin::blockdata::opcodes;
@@ -3007,9 +3007,8 @@ where
 	F::Target: FeeEstimator,
 	L::Target: Logger,
 {
-	fn block_connected(&self, block: &Block, height: u32) {
-		let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
-		self.0.block_connected(&block.header, &txdata, height, &*self.1, &*self.2, &*self.3);
+	fn filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
+		self.0.block_connected(header, txdata, height, &*self.1, &*self.2, &*self.3);
 	}
 
 	fn block_disconnected(&self, header: &BlockHeader, height: u32) {

lightning/src/chain/mod.rs

@@ -87,9 +87,20 @@ pub trait Access {
 /// sourcing chain data using a block-oriented API should prefer this interface over [`Confirm`].
 /// Such clients fetch the entire header chain whereas clients using [`Confirm`] only fetch headers
 /// when needed.
+///
+/// By using [`Listen::filtered_block_connected`] this interface supports clients fetching the
+/// entire header chain and only blocks with matching transaction data using BIP 157 filters or
+/// other similar filtering.
 pub trait Listen {
+	/// Notifies the listener that a block was added at the given height, with the transaction data
+	/// possibly filtered.
+	fn filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32);
+
 	/// Notifies the listener that a block was added at the given height.
-	fn block_connected(&self, block: &Block, height: u32);
+	fn block_connected(&self, block: &Block, height: u32) {
+		let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
+		self.filtered_block_connected(&block.header, &txdata, height);
+	}
 
 	/// Notifies the listener that a block was removed at the given height.
 	fn block_disconnected(&self, header: &BlockHeader, height: u32);
@@ -355,8 +366,8 @@ pub struct WatchedOutput {
 }
 
 impl<T: Listen> Listen for core::ops::Deref<Target = T> {
-	fn block_connected(&self, block: &Block, height: u32) {
-		(**self).block_connected(block, height);
+	fn filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
+		(**self).filtered_block_connected(header, txdata, height);
 	}
 
 	fn block_disconnected(&self, header: &BlockHeader, height: u32) {
@@ -369,9 +380,9 @@ where
 	T::Target: Listen,
 	U::Target: Listen,
 {
-	fn block_connected(&self, block: &Block, height: u32) {
-		self.0.block_connected(block, height);
-		self.1.block_connected(block, height);
+	fn filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
+		self.0.filtered_block_connected(header, txdata, height);
+		self.1.filtered_block_connected(header, txdata, height);
 	}
 
 	fn block_disconnected(&self, header: &BlockHeader, height: u32) {

lightning/src/ln/channelmanager.rs

@@ -18,7 +18,7 @@
 //! imply it needs to fail HTLCs/payments/channels it manages).
 //!
 
-use bitcoin::blockdata::block::{Block, BlockHeader};
+use bitcoin::blockdata::block::BlockHeader;
 use bitcoin::blockdata::transaction::Transaction;
 use bitcoin::blockdata::constants::genesis_block;
 use bitcoin::network::constants::Network;
@@ -5303,18 +5303,17 @@ where
 	F::Target: FeeEstimator,
 	L::Target: Logger,
 {
-	fn block_connected(&self, block: &Block, height: u32) {
+	fn filtered_block_connected(&self, header: &BlockHeader, txdata: &TransactionData, height: u32) {
 		{
 			let best_block = self.best_block.read().unwrap();
-			assert_eq!(best_block.block_hash(), block.header.prev_blockhash,
+			assert_eq!(best_block.block_hash(), header.prev_blockhash,
 				"Blocks must be connected in chain-order - the connected header must build on the last connected header");
 			assert_eq!(best_block.height(), height - 1,
 				"Blocks must be connected in chain-order - the connected block height must be one greater than the previous height");
 		}
 
-		let txdata: Vec<_> = block.txdata.iter().enumerate().collect();
-		self.transactions_confirmed(&block.header, &txdata, height);
-		self.best_block_updated(&block.header, height);
+		self.transactions_confirmed(header, txdata, height);
+		self.best_block_updated(header, height);
 	}
 
 	fn block_disconnected(&self, header: &BlockHeader, height: u32) {