Merge pull request #791 from jkczyz/2021-01-spv-client

SPV client utility for syncing a lightning node

Author: TheBlueMatt

lightning-block-sync/src/init.rs

@@ -0,0 +1,351 @@
+use crate::{BlockSource, BlockSourceResult, Cache, ChainNotifier};
+use crate::poll::{ChainPoller, Validate, ValidatedBlockHeader};
+
+use bitcoin::blockdata::block::{Block, BlockHeader};
+use bitcoin::hash_types::BlockHash;
+use bitcoin::network::constants::Network;
+
+use lightning::chain;
+
+/// 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`]. For example:
+///
+/// ```
+/// use bitcoin::hash_types::BlockHash;
+/// use bitcoin::network::constants::Network;
+///
+/// use lightning::chain;
+/// use lightning::chain::Watch;
+/// use lightning::chain::chainmonitor::ChainMonitor;
+/// use lightning::chain::channelmonitor;
+/// use lightning::chain::channelmonitor::ChannelMonitor;
+/// use lightning::chain::chaininterface::BroadcasterInterface;
+/// use lightning::chain::chaininterface::FeeEstimator;
+/// use lightning::chain::keysinterface;
+/// use lightning::chain::keysinterface::KeysInterface;
+/// use lightning::ln::channelmanager::ChannelManager;
+/// use lightning::ln::channelmanager::ChannelManagerReadArgs;
+/// use lightning::util::config::UserConfig;
+/// use lightning::util::logger::Logger;
+/// use lightning::util::ser::ReadableArgs;
+///
+/// use lightning_block_sync::*;
+///
+/// use std::cell::RefCell;
+/// use std::io::Cursor;
+///
+/// async fn init_sync<
+/// 	B: BlockSource,
+/// 	K: KeysInterface<Signer = S>,
+/// 	S: keysinterface::Sign,
+/// 	T: BroadcasterInterface,
+/// 	F: FeeEstimator,
+/// 	L: Logger,
+/// 	C: chain::Filter,
+/// 	P: channelmonitor::Persist<S>,
+/// >(
+/// 	block_source: &mut B,
+/// 	chain_monitor: &ChainMonitor<S, &C, &T, &F, &L, &P>,
+/// 	config: UserConfig,
+/// 	keys_manager: &K,
+/// 	tx_broadcaster: &T,
+/// 	fee_estimator: &F,
+/// 	logger: &L,
+/// 	persister: &P,
+/// ) {
+/// 	// Read a serialized channel monitor paired with the block hash when it was persisted.
+/// 	let serialized_monitor = "...";
+/// 	let (monitor_block_hash, mut monitor) = <(BlockHash, ChannelMonitor<S>)>::read(
+/// 		&mut Cursor::new(&serialized_monitor), keys_manager).unwrap();
+///
+/// 	// Read the channel manager paired with the block hash when it was persisted.
+/// 	let serialized_manager = "...";
+/// 	let (manager_block_hash, mut manager) = {
+/// 		let read_args = ChannelManagerReadArgs::new(
+/// 			keys_manager,
+/// 			fee_estimator,
+/// 			chain_monitor,
+/// 			tx_broadcaster,
+/// 			logger,
+/// 			config,
+/// 			vec![&mut monitor],
+/// 		);
+/// 		<(BlockHash, ChannelManager<S, &ChainMonitor<S, &C, &T, &F, &L, &P>, &T, &K, &F, &L>)>::read(
+/// 			&mut Cursor::new(&serialized_manager), read_args).unwrap()
+/// 	};
+///
+/// 	// Synchronize any channel monitors and the channel manager to be on the best block.
+/// 	let mut cache = UnboundedCache::new();
+/// 	let mut monitor_listener = (RefCell::new(monitor), &*tx_broadcaster, &*fee_estimator, &*logger);
+/// 	let listeners = vec![
+/// 		(monitor_block_hash, &mut monitor_listener as &mut dyn chain::Listen),
+/// 		(manager_block_hash, &mut manager as &mut dyn chain::Listen),
+/// 	];
+/// 	let chain_tip = init::synchronize_listeners(
+/// 		block_source, Network::Bitcoin, &mut cache, listeners).await.unwrap();
+///
+/// 	// Allow the chain monitor to watch any channels.
+/// 	let monitor = monitor_listener.0.into_inner();
+/// 	chain_monitor.watch_channel(monitor.get_funding_txo().0, monitor);
+///
+/// 	// Create an SPV client to notify the chain monitor and channel manager of block events.
+/// 	let chain_poller = poll::ChainPoller::new(block_source, Network::Bitcoin);
+/// 	let mut chain_listener = (chain_monitor, &manager);
+/// 	let spv_client = SpvClient::new(chain_tip, chain_poller, &mut cache, &chain_listener);
+/// }
+/// ```
+///
+/// [`SpvClient`]: ../struct.SpvClient.html
+/// [`ChannelManager`]: ../../lightning/ln/channelmanager/struct.ChannelManager.html
+/// [`ChannelMonitor`]: ../../lightning/chain/channelmonitor/struct.ChannelMonitor.html
+pub async fn synchronize_listeners<B: BlockSource, C: Cache>(
+	block_source: &mut B,
+	network: Network,
+	header_cache: &mut C,
+	mut chain_listeners: Vec<(BlockHash, &mut dyn chain::Listen)>,
+) -> BlockSourceResult<ValidatedBlockHeader> {
+	let (best_block_hash, best_block_height) = block_source.get_best_block().await?;
+	let best_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_hash, chain_listener) in chain_listeners.drain(..) {
+		let old_header = match header_cache.look_up(&old_block_hash) {
+			Some(header) => *header,
+			None => block_source
+				.get_header(&old_block_hash, None).await?
+				.validate(old_block_hash)?
+		};
+		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 (common_ancestor, connected_blocks) = {
+			let chain_listener = &DynamicChainListener(chain_listener);
+			let mut chain_notifier = ChainNotifier { header_cache, chain_listener };
+			let difference =
+				chain_notifier.find_difference(best_header, &old_header, &mut chain_poller).await?;
+			chain_notifier.disconnect_blocks(difference.disconnected_blocks);
+			(difference.common_ancestor, difference.connected_blocks)
+		};
+
+		// Keep track of the most common ancestor and all blocks connected across all listeners.
+		chain_listeners_at_height.push((common_ancestor.height, chain_listener));
+		if connected_blocks.len() > most_connected_blocks.len() {
+			most_common_ancestor = Some(common_ancestor);
+			most_connected_blocks = connected_blocks;
+		}
+	}
+
+	// Connect new blocks for all listeners at once to avoid re-fetching blocks.
+	if let Some(common_ancestor) = most_common_ancestor {
+		let chain_listener = &ChainListenerSet(chain_listeners_at_height);
+		let mut chain_notifier = ChainNotifier { header_cache, chain_listener };
+		chain_notifier.connect_blocks(common_ancestor, most_connected_blocks, &mut chain_poller)
+			.await.or_else(|(e, _)| Err(e))?;
+	}
+
+	Ok(best_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 chain::Listen);
+
+impl<'a> chain::Listen for DynamicChainListener<'a> {
+	fn block_connected(&self, _block: &Block, _height: u32) {
+		unreachable!()
+	}
+
+	fn block_disconnected(&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 chain::Listen)>);
+
+impl<'a> chain::Listen for ChainListenerSet<'a> {
+	fn block_connected(&self, block: &Block, height: u32) {
+		for (starting_height, chain_listener) in self.0.iter() {
+			if height > *starting_height {
+				chain_listener.block_connected(block, height);
+			}
+		}
+	}
+
+	fn block_disconnected(&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 chain::Listen),
+			(chain.at_height(2).block_hash, &mut listener_2 as &mut dyn chain::Listen),
+			(chain.at_height(3).block_hash, &mut listener_3 as &mut dyn chain::Listen),
+		];
+		let mut cache = chain.header_cache(0..=4);
+		match synchronize_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 chain::Listen),
+			(fork_chain_2.tip().block_hash, &mut listener_2 as &mut dyn chain::Listen),
+			(fork_chain_3.tip().block_hash, &mut listener_3 as &mut dyn chain::Listen),
+		];
+		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 synchronize_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 chain::Listen),
+			(fork_chain_2.tip().block_hash, &mut listener_2 as &mut dyn chain::Listen),
+			(fork_chain_3.tip().block_hash, &mut listener_3 as &mut dyn chain::Listen),
+		];
+		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 synchronize_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 chain::Listen)];
+		let mut cache = fork_chain.header_cache(2..=2);
+		match synchronize_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),
+		}
+	}
+}