Utility for syncing a set of chain listeners

Add a utility for syncing a set of chain listeners to a common chain
tip. Required to use before creating an SpvClient when the chain
listener used with the client is actually a set of listeners each of
which may have had left off at a different block. This would occur when
the listeners had been persisted individually at different frequencies
(e.g., a ChainMonitor's individual ChannelMonitors).

lightning-block-sync/src/init.rs

@@ -0,0 +1,267 @@
+use crate::{BlockSource, BlockSourceResult, Cache, ChainListener, ChainNotifier};
+use crate::poll::{ChainPoller, Validate, ValidatedBlockHeader};
+
+use bitcoin::blockdata::block::{Block, BlockHeader};
+use bitcoin::hash_types::BlockHash;
+use bitcoin::network::constants::Network;
+
+/// Performs a one-time sync of chain listeners using a single *trusted* block source, bringing each
+/// listener's view of the chain from its paired block hash to `block_source`'s best chain tip.
+///
+/// Upon success, the returned header can be used to initialize [`SpvClient`]. In the case of
+/// failure, each listener may be left at a different block hash than the one it was originally
+/// paired with.
+///
+/// Useful during startup to bring the [`ChannelManager`] and each [`ChannelMonitor`] in sync before
+/// switching to [`SpvClient`].
+///
+/// [`SpvClient`]: ../struct.SpvClient.html
+/// [`ChannelManager`]: ../../lightning/ln/channelmanager/struct.ChannelManager.html
+/// [`ChannelMonitor`]: ../../lightning/chain/channelmonitor/struct.ChannelMonitor.html
+pub async fn sync_listeners<B: BlockSource, C: Cache>(
+	block_source: &mut B,
+	network: Network,
+	header_cache: &mut C,
+	mut chain_listeners: Vec<(BlockHash, &mut dyn ChainListener)>,
+) -> BlockSourceResult<ValidatedBlockHeader> {
+	let (best_block_hash, best_block_height) = block_source.get_best_block().await?;
+	let new_header = block_source
+		.get_header(&best_block_hash, best_block_height).await?
+		.validate(best_block_hash)?;
+
+	// Fetch the header for the block hash paired with each listener.
+	let mut chain_listeners_with_old_headers = Vec::new();
+	for (old_block, chain_listener) in chain_listeners.drain(..) {
+		let old_header = match header_cache.look_up(&old_block) {
+			Some(header) => *header,
+			None => block_source
+				.get_header(&old_block, None).await?
+				.validate(old_block)?
+		};
+		chain_listeners_with_old_headers.push((old_header, chain_listener))
+	}
+
+	// Find differences and disconnect blocks for each listener individually.
+	let mut chain_poller = ChainPoller::new(block_source, network);
+	let mut chain_listeners_at_height = Vec::new();
+	let mut most_common_ancestor = None;
+	let mut most_connected_blocks = Vec::new();
+	for (old_header, chain_listener) in chain_listeners_with_old_headers.drain(..) {
+		// Disconnect any stale blocks, but keep them in the cache for the next iteration.
+		let header_cache = &mut ReadOnlyCache(header_cache);
+		let mut chain_notifier = ChainNotifier { header_cache };
+		let difference =
+			chain_notifier.find_difference(new_header, &old_header, &mut chain_poller).await?;
+		chain_notifier.disconnect_blocks(
+			difference.disconnected_blocks,
+			&mut DynamicChainListener(chain_listener),
+		);
+
+		// Keep track of the most common ancestor and all blocks connected across all listeners.
+		chain_listeners_at_height.push((difference.common_ancestor.height, chain_listener));
+		if difference.connected_blocks.len() > most_connected_blocks.len() {
+			most_common_ancestor = Some(difference.common_ancestor);
+			most_connected_blocks = difference.connected_blocks;
+		}
+	}
+
+	// Connect new blocks for all listeners at once to avoid re-fetching blocks.
+	if let Some(common_ancestor) = most_common_ancestor {
+		let mut chain_notifier = ChainNotifier { header_cache };
+		let mut chain_listener = ChainListenerSet(chain_listeners_at_height);
+		chain_notifier.connect_blocks(
+			common_ancestor,
+			most_connected_blocks,
+			&mut chain_poller,
+			&mut chain_listener,
+		).await.or_else(|(e, _)| Err(e))?;
+	}
+
+	Ok(new_header)
+}
+
+/// A wrapper to make a cache read-only.
+///
+/// Used to prevent losing headers that may be needed to disconnect blocks common to more than one
+/// listener.
+struct ReadOnlyCache<'a, C: Cache>(&'a mut C);
+
+impl<'a, C: Cache> Cache for ReadOnlyCache<'a, C> {
+	fn look_up(&self, block_hash: &BlockHash) -> Option<&ValidatedBlockHeader> {
+		self.0.look_up(block_hash)
+	}
+
+	fn block_connected(&mut self, _block_hash: BlockHash, _block_header: ValidatedBlockHeader) {
+		unreachable!()
+	}
+
+	fn block_disconnected(&mut self, _block_hash: &BlockHash) -> Option<ValidatedBlockHeader> {
+		None
+	}
+}
+
+/// Wrapper for supporting dynamically sized chain listeners.
+struct DynamicChainListener<'a>(&'a mut dyn ChainListener);
+
+impl<'a> ChainListener for DynamicChainListener<'a> {
+	fn block_connected(&mut self, _block: &Block, _height: u32) {
+		unreachable!()
+	}
+
+	fn block_disconnected(&mut self, header: &BlockHeader, height: u32) {
+		self.0.block_disconnected(header, height)
+	}
+}
+
+/// A set of dynamically sized chain listeners, each paired with a starting block height.
+struct ChainListenerSet<'a>(Vec<(u32, &'a mut dyn ChainListener)>);
+
+impl<'a> ChainListener for ChainListenerSet<'a> {
+	fn block_connected(&mut self, block: &Block, height: u32) {
+		for (starting_height, chain_listener) in self.0.iter_mut() {
+			if height > *starting_height {
+				chain_listener.block_connected(block, height);
+			}
+		}
+	}
+
+	fn block_disconnected(&mut self, _header: &BlockHeader, _height: u32) {
+		unreachable!()
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use crate::test_utils::{Blockchain, MockChainListener};
+	use super::*;
+
+	use bitcoin::network::constants::Network;
+
+	#[tokio::test]
+	async fn sync_from_same_chain() {
+		let mut chain = Blockchain::default().with_height(4);
+
+		let mut listener_1 = MockChainListener::new()
+			.expect_block_connected(*chain.at_height(2))
+			.expect_block_connected(*chain.at_height(3))
+			.expect_block_connected(*chain.at_height(4));
+		let mut listener_2 = MockChainListener::new()
+			.expect_block_connected(*chain.at_height(3))
+			.expect_block_connected(*chain.at_height(4));
+		let mut listener_3 = MockChainListener::new()
+			.expect_block_connected(*chain.at_height(4));
+
+		let listeners = vec![
+			(chain.at_height(1).block_hash, &mut listener_1 as &mut dyn ChainListener),
+			(chain.at_height(2).block_hash, &mut listener_2 as &mut dyn ChainListener),
+			(chain.at_height(3).block_hash, &mut listener_3 as &mut dyn ChainListener),
+		];
+		let mut cache = chain.header_cache(0..=4);
+		match sync_listeners(&mut chain, Network::Bitcoin, &mut cache, listeners).await {
+			Ok(header) => assert_eq!(header, chain.tip()),
+			Err(e) => panic!("Unexpected error: {:?}", e),
+		}
+	}
+
+	#[tokio::test]
+	async fn sync_from_different_chains() {
+		let mut main_chain = Blockchain::default().with_height(4);
+		let fork_chain_1 = main_chain.fork_at_height(1);
+		let fork_chain_2 = main_chain.fork_at_height(2);
+		let fork_chain_3 = main_chain.fork_at_height(3);
+
+		let mut listener_1 = MockChainListener::new()
+			.expect_block_disconnected(*fork_chain_1.at_height(4))
+			.expect_block_disconnected(*fork_chain_1.at_height(3))
+			.expect_block_disconnected(*fork_chain_1.at_height(2))
+			.expect_block_connected(*main_chain.at_height(2))
+			.expect_block_connected(*main_chain.at_height(3))
+			.expect_block_connected(*main_chain.at_height(4));
+		let mut listener_2 = MockChainListener::new()
+			.expect_block_disconnected(*fork_chain_2.at_height(4))
+			.expect_block_disconnected(*fork_chain_2.at_height(3))
+			.expect_block_connected(*main_chain.at_height(3))
+			.expect_block_connected(*main_chain.at_height(4));
+		let mut listener_3 = MockChainListener::new()
+			.expect_block_disconnected(*fork_chain_3.at_height(4))
+			.expect_block_connected(*main_chain.at_height(4));
+
+		let listeners = vec![
+			(fork_chain_1.tip().block_hash, &mut listener_1 as &mut dyn ChainListener),
+			(fork_chain_2.tip().block_hash, &mut listener_2 as &mut dyn ChainListener),
+			(fork_chain_3.tip().block_hash, &mut listener_3 as &mut dyn ChainListener),
+		];
+		let mut cache = fork_chain_1.header_cache(2..=4);
+		cache.extend(fork_chain_2.header_cache(3..=4));
+		cache.extend(fork_chain_3.header_cache(4..=4));
+		match sync_listeners(&mut main_chain, Network::Bitcoin, &mut cache, listeners).await {
+			Ok(header) => assert_eq!(header, main_chain.tip()),
+			Err(e) => panic!("Unexpected error: {:?}", e),
+		}
+	}
+
+	#[tokio::test]
+	async fn sync_from_overlapping_chains() {
+		let mut main_chain = Blockchain::default().with_height(4);
+		let fork_chain_1 = main_chain.fork_at_height(1);
+		let fork_chain_2 = fork_chain_1.fork_at_height(2);
+		let fork_chain_3 = fork_chain_2.fork_at_height(3);
+
+		let mut listener_1 = MockChainListener::new()
+			.expect_block_disconnected(*fork_chain_1.at_height(4))
+			.expect_block_disconnected(*fork_chain_1.at_height(3))
+			.expect_block_disconnected(*fork_chain_1.at_height(2))
+			.expect_block_connected(*main_chain.at_height(2))
+			.expect_block_connected(*main_chain.at_height(3))
+			.expect_block_connected(*main_chain.at_height(4));
+		let mut listener_2 = MockChainListener::new()
+			.expect_block_disconnected(*fork_chain_2.at_height(4))
+			.expect_block_disconnected(*fork_chain_2.at_height(3))
+			.expect_block_disconnected(*fork_chain_2.at_height(2))
+			.expect_block_connected(*main_chain.at_height(2))
+			.expect_block_connected(*main_chain.at_height(3))
+			.expect_block_connected(*main_chain.at_height(4));
+		let mut listener_3 = MockChainListener::new()
+			.expect_block_disconnected(*fork_chain_3.at_height(4))
+			.expect_block_disconnected(*fork_chain_3.at_height(3))
+			.expect_block_disconnected(*fork_chain_3.at_height(2))
+			.expect_block_connected(*main_chain.at_height(2))
+			.expect_block_connected(*main_chain.at_height(3))
+			.expect_block_connected(*main_chain.at_height(4));
+
+		let listeners = vec![
+			(fork_chain_1.tip().block_hash, &mut listener_1 as &mut dyn ChainListener),
+			(fork_chain_2.tip().block_hash, &mut listener_2 as &mut dyn ChainListener),
+			(fork_chain_3.tip().block_hash, &mut listener_3 as &mut dyn ChainListener),
+		];
+		let mut cache = fork_chain_1.header_cache(2..=4);
+		cache.extend(fork_chain_2.header_cache(3..=4));
+		cache.extend(fork_chain_3.header_cache(4..=4));
+		match sync_listeners(&mut main_chain, Network::Bitcoin, &mut cache, listeners).await {
+			Ok(header) => assert_eq!(header, main_chain.tip()),
+			Err(e) => panic!("Unexpected error: {:?}", e),
+		}
+	}
+
+	#[tokio::test]
+	async fn cache_connected_and_keep_disconnected_blocks() {
+		let mut main_chain = Blockchain::default().with_height(2);
+		let fork_chain = main_chain.fork_at_height(1);
+		let new_tip = main_chain.tip();
+		let old_tip = fork_chain.tip();
+
+		let mut listener = MockChainListener::new()
+			.expect_block_disconnected(*old_tip)
+			.expect_block_connected(*new_tip);
+
+		let listeners = vec![(old_tip.block_hash, &mut listener as &mut dyn ChainListener)];
+		let mut cache = fork_chain.header_cache(2..=2);
+		match sync_listeners(&mut main_chain, Network::Bitcoin, &mut cache, listeners).await {
+			Ok(_) => {
+				assert!(cache.contains_key(&new_tip.block_hash));
+				assert!(cache.contains_key(&old_tip.block_hash));
+			},
+			Err(e) => panic!("Unexpected error: {:?}", e),
+		}
+	}
+}