Use BestBlock for chain state serialization (and somewhat parallelize init)

lightning-background-processor/src/lib.rs

@@ -53,9 +53,9 @@ use lightning::routing::utxo::UtxoLookup;
 use lightning::sign::{
 	ChangeDestinationSource, ChangeDestinationSourceSync, EntropySource, OutputSpender,
 };
-#[cfg(not(c_bindings))]
-use lightning::util::async_poll::MaybeSend;
 use lightning::util::logger::Logger;
+#[cfg(not(c_bindings))]
+use lightning::util::native_async::MaybeSend;
 use lightning::util::persist::{
 	KVStore, KVStoreSync, KVStoreSyncWrapper, CHANNEL_MANAGER_PERSISTENCE_KEY,
 	CHANNEL_MANAGER_PERSISTENCE_PRIMARY_NAMESPACE, CHANNEL_MANAGER_PERSISTENCE_SECONDARY_NAMESPACE,

lightning-block-sync/src/async_poll.rs

@@ -0,0 +1 @@
+../../lightning/src/util/async_poll.rs

lightning-block-sync/src/lib.rs

@@ -16,9 +16,11 @@
 #![deny(rustdoc::broken_intra_doc_links)]
 #![deny(rustdoc::private_intra_doc_links)]
 #![deny(missing_docs)]
-#![deny(unsafe_code)]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 
+extern crate alloc;
+extern crate core;
+
 #[cfg(any(feature = "rest-client", feature = "rpc-client"))]
 pub mod http;
 
@@ -42,6 +44,9 @@ mod test_utils;
 #[cfg(any(feature = "rest-client", feature = "rpc-client"))]
 mod utils;
 
+#[allow(unused)]
+mod async_poll;
+
 use crate::poll::{ChainTip, Poll, ValidatedBlockHeader};
 
 use bitcoin::block::{Block, Header};
@@ -170,18 +175,13 @@ pub enum BlockData {
 /// sources for the best chain tip. During this process it detects any chain forks, determines which
 /// constitutes the best chain, and updates the listener accordingly with any blocks that were
 /// connected or disconnected since the last poll.
-///
-/// Block headers for the best chain are maintained in the parameterized cache, allowing for a
-/// custom cache eviction policy. This offers flexibility to those sensitive to resource usage.
-/// Hence, there is a trade-off between a lower memory footprint and potentially increased network
-/// I/O as headers are re-fetched during fork detection.
-pub struct SpvClient<'a, P: Poll, C: Cache, L: Deref>
+pub struct SpvClient<P: Poll, L: Deref>
 where
 	L::Target: chain::Listen,
 {
 	chain_tip: ValidatedBlockHeader,
 	chain_poller: P,
-	chain_notifier: ChainNotifier<'a, C, L>,
+	chain_notifier: ChainNotifier<HeaderCache, L>,
 }
 
 /// The `Cache` trait defines behavior for managing a block header cache, where block headers are
@@ -194,37 +194,86 @@ where
 /// Implementations may define how long to retain headers such that it's unlikely they will ever be
 /// needed to disconnect a block.  In cases where block sources provide access to headers on stale
 /// forks reliably, caches may be entirely unnecessary.
-pub trait Cache {
+pub(crate) trait Cache {
 	/// Retrieves the block header keyed by the given block hash.
 	fn look_up(&self, block_hash: &BlockHash) -> Option<&ValidatedBlockHeader>;
 
+	/// Inserts the given block header during a find_difference operation, implying it might not be
+	/// the best header.
+	fn insert_during_diff(&mut self, block_hash: BlockHash, block_header: ValidatedBlockHeader);
+
 	/// Called when a block has been connected to the best chain to ensure it is available to be
 	/// disconnected later if needed.
 	fn block_connected(&mut self, block_hash: BlockHash, block_header: ValidatedBlockHeader);
 
-	/// Called when a block has been disconnected from the best chain. Once disconnected, a block's
-	/// header is no longer needed and thus can be removed.
-	fn block_disconnected(&mut self, block_hash: &BlockHash) -> Option<ValidatedBlockHeader>;
+	/// Called when blocks have been disconnected from the best chain. Only the fork point
+	/// (best comon ancestor) is provided.
+	///
+	/// Once disconnected, a block's header is no longer needed and thus can be removed.
+	fn blocks_disconnected(&mut self, fork_point: &ValidatedBlockHeader);
+}
+
+/// The maximum number of [`ValidatedBlockHeader`]s stored in a [`HeaderCache`].
+pub const HEADER_CACHE_LIMIT: u32 = 6 * 24 * 7;
+
+/// Bounded cache of block headers keyed by block hash.
+///
+/// Retains only the latest [`HEADER_CACHE_LIMIT`] block headers based on height.
+pub struct HeaderCache(std::collections::HashMap<BlockHash, ValidatedBlockHeader>);
+
+impl HeaderCache {
+	/// Creates a new empty header cache.
+	pub fn new() -> Self {
+		Self(std::collections::HashMap::new())
+	}
 }
 
-/// Unbounded cache of block headers keyed by block hash.
-pub type UnboundedCache = std::collections::HashMap<BlockHash, ValidatedBlockHeader>;
+impl Cache for HeaderCache {
+	fn look_up(&self, block_hash: &BlockHash) -> Option<&ValidatedBlockHeader> {
+		self.0.get(block_hash)
+	}
+
+	fn insert_during_diff(&mut self, block_hash: BlockHash, block_header: ValidatedBlockHeader) {
+		self.0.insert(block_hash, block_header);
+
+		// Remove headers older than our newest header minus a week.
+		let best_height = self.0.iter().map(|(_, header)| header.height).max().unwrap_or(0);
+		let cutoff_height = best_height.saturating_sub(HEADER_CACHE_LIMIT);
+		self.0.retain(|_, header| header.height >= cutoff_height);
+	}
+
+	fn block_connected(&mut self, block_hash: BlockHash, block_header: ValidatedBlockHeader) {
+		self.0.insert(block_hash, block_header);
+
+		// Remove headers older than a week.
+		let cutoff_height = block_header.height.saturating_sub(HEADER_CACHE_LIMIT);
+		self.0.retain(|_, header| header.height >= cutoff_height);
+	}
+
+	fn blocks_disconnected(&mut self, fork_point: &ValidatedBlockHeader) {
+		self.0.retain(|_, block_info| block_info.height <= fork_point.height);
+	}
+}
 
-impl Cache for UnboundedCache {
+impl Cache for &mut HeaderCache {
 	fn look_up(&self, block_hash: &BlockHash) -> Option<&ValidatedBlockHeader> {
-		self.get(block_hash)
+		self.0.get(block_hash)
+	}
+
+	fn insert_during_diff(&mut self, block_hash: BlockHash, block_header: ValidatedBlockHeader) {
+		(*self).insert_during_diff(block_hash, block_header);
 	}
 
 	fn block_connected(&mut self, block_hash: BlockHash, block_header: ValidatedBlockHeader) {
-		self.insert(block_hash, block_header);
+		(*self).block_connected(block_hash, block_header);
 	}
 
-	fn block_disconnected(&mut self, block_hash: &BlockHash) -> Option<ValidatedBlockHeader> {
-		self.remove(block_hash)
+	fn blocks_disconnected(&mut self, fork_point: &ValidatedBlockHeader) {
+		self.0.retain(|_, block_info| block_info.height <= fork_point.height);
 	}
 }
 
-impl<'a, P: Poll, C: Cache, L: Deref> SpvClient<'a, P, C, L>
+impl<P: Poll, L: Deref> SpvClient<P, L>
 where
 	L::Target: chain::Listen,
 {
@@ -239,7 +288,7 @@ where
 	///
 	/// [`poll_best_tip`]: SpvClient::poll_best_tip
 	pub fn new(
-		chain_tip: ValidatedBlockHeader, chain_poller: P, header_cache: &'a mut C,
+		chain_tip: ValidatedBlockHeader, chain_poller: P, header_cache: HeaderCache,
 		chain_listener: L,
 	) -> Self {
 		let chain_notifier = ChainNotifier { header_cache, chain_listener };
@@ -293,15 +342,15 @@ where
 /// Notifies [listeners] of blocks that have been connected or disconnected from the chain.
 ///
 /// [listeners]: lightning::chain::Listen
-pub struct ChainNotifier<'a, C: Cache, L: Deref>
+pub(crate) struct ChainNotifier<C: Cache, L: Deref>
 where
 	L::Target: chain::Listen,
 {
 	/// Cache for looking up headers before fetching from a block source.
-	header_cache: &'a mut C,
+	pub(crate) header_cache: C,
 
 	/// Listener that will be notified of connected or disconnected blocks.
-	chain_listener: L,
+	pub(crate) chain_listener: L,
 }
 
 /// Changes made to the chain between subsequent polls that transformed it from having one chain tip
@@ -315,14 +364,11 @@ struct ChainDifference {
 	/// If there are any disconnected blocks, this is where the chain forked.
 	common_ancestor: ValidatedBlockHeader,
 
-	/// Blocks that were disconnected from the chain since the last poll.
-	disconnected_blocks: Vec<ValidatedBlockHeader>,
-
 	/// Blocks that were connected to the chain since the last poll.
 	connected_blocks: Vec<ValidatedBlockHeader>,
 }
 
-impl<'a, C: Cache, L: Deref> ChainNotifier<'a, C, L>
+impl<C: Cache, L: Deref> ChainNotifier<C, L>
 where
 	L::Target: chain::Listen,
 {
@@ -338,23 +384,66 @@ where
 		chain_poller: &mut P,
 	) -> Result<(), (BlockSourceError, Option<ValidatedBlockHeader>)> {
 		let difference = self
-			.find_difference(new_header, old_header, chain_poller)
+			.find_difference_from_header(new_header, old_header, chain_poller)
 			.await
 			.map_err(|e| (e, None))?;
-		self.disconnect_blocks(difference.disconnected_blocks);
+		if difference.common_ancestor != *old_header {
+			self.disconnect_blocks(difference.common_ancestor);
+		}
 		self.connect_blocks(difference.common_ancestor, difference.connected_blocks, chain_poller)
 			.await
 	}
 
+	/// Returns the changes needed to produce the chain with `current_header` as its tip from the
+	/// chain with `prev_best_block` as its tip.
+	///
+	/// First resolves `prev_best_block` to a `ValidatedBlockHeader` using the `previous_blocks`
+	/// field as fallback if needed, then finds the common ancestor.
+	async fn find_difference_from_best_block<P: Poll>(
+		&mut self, current_header: ValidatedBlockHeader, prev_best_block: BestBlock,
+		chain_poller: &mut P,
+	) -> BlockSourceResult<ChainDifference> {
+		// Try to resolve the header for the previous best block. First try the block_hash,
+		// then fall back to previous_blocks if that fails.
+		let cur_tip = core::iter::once((0, &prev_best_block.block_hash));
+		let prev_tips =
+			prev_best_block.previous_blocks.iter().enumerate().filter_map(|(idx, hash_opt)| {
+				if let Some(block_hash) = hash_opt {
+					Some((idx as u32 + 1, block_hash))
+				} else {
+					None
+				}
+			});
+		let mut found_header = None;
+		for (height_diff, block_hash) in cur_tip.chain(prev_tips) {
+			if let Some(header) = self.header_cache.look_up(block_hash) {
+				found_header = Some(*header);
+				break;
+			}
+			let height = prev_best_block.height.checked_sub(height_diff).ok_or(
+				BlockSourceError::persistent("BestBlock had more previous_blocks than its height"),
+			)?;
+			if let Ok(header) = chain_poller.get_header(block_hash, Some(height)).await {
+				found_header = Some(header);
+				self.header_cache.insert_during_diff(*block_hash, header);
+				break;
+			}
+		}
+		let found_header = found_header.ok_or_else(|| {
+			BlockSourceError::persistent("could not resolve any block from BestBlock")
+		})?;
+
+		self.find_difference_from_header(current_header, &found_header, chain_poller).await
+	}
+
 	/// Returns the changes needed to produce the chain with `current_header` as its tip from the
 	/// chain with `prev_header` as its tip.
 	///
 	/// Walks backwards from `current_header` and `prev_header`, finding the common ancestor.
-	async fn find_difference<P: Poll>(
+	async fn find_difference_from_header<P: Poll>(
 		&self, current_header: ValidatedBlockHeader, prev_header: &ValidatedBlockHeader,
 		chain_poller: &mut P,
 	) -> BlockSourceResult<ChainDifference> {
-		let mut disconnected_blocks = Vec::new();
 		let mut connected_blocks = Vec::new();
 		let mut current = current_header;
 		let mut previous = *prev_header;
@@ -369,7 +458,6 @@ where
 			let current_height = current.height;
 			let previous_height = previous.height;
 			if current_height <= previous_height {
-				disconnected_blocks.push(previous);
 				previous = self.look_up_previous_header(chain_poller, &previous).await?;
 			}
 			if current_height >= previous_height {
@@ -379,7 +467,7 @@ where
 		}
 
 		let common_ancestor = current;
-		Ok(ChainDifference { common_ancestor, disconnected_blocks, connected_blocks })
+		Ok(ChainDifference { common_ancestor, connected_blocks })
 	}
 
 	/// Returns the previous header for the given header, either by looking it up in the cache or
@@ -394,16 +482,10 @@ where
 	}
 
 	/// Notifies the chain listeners of disconnected blocks.
-	fn disconnect_blocks(&mut self, disconnected_blocks: Vec<ValidatedBlockHeader>) {
-		for header in disconnected_blocks.iter() {
-			if let Some(cached_header) = self.header_cache.block_disconnected(&header.block_hash) {
-				assert_eq!(cached_header, *header);
-			}
-		}
-		if let Some(block) = disconnected_blocks.last() {
-			let fork_point = BestBlock::new(block.header.prev_blockhash, block.height - 1);
-			self.chain_listener.blocks_disconnected(fork_point);
-		}
+	fn disconnect_blocks(&mut self, fork_point: ValidatedBlockHeader) {
+		self.header_cache.blocks_disconnected(&fork_point);
+		let best_block = BestBlock::new(fork_point.block_hash, fork_point.height);
+		self.chain_listener.blocks_disconnected(best_block);
 	}
 
 	/// Notifies the chain listeners of connected blocks.
@@ -447,9 +529,9 @@ mod spv_client_tests {
 		let best_tip = chain.at_height(1);
 
 		let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
-		let mut cache = UnboundedCache::new();
+		let cache = HeaderCache::new();
 		let mut listener = NullChainListener {};
-		let mut client = SpvClient::new(best_tip, poller, &mut cache, &mut listener);
+		let mut client = SpvClient::new(best_tip, poller, cache, &mut listener);
 		match client.poll_best_tip().await {
 			Err(e) => {
 				assert_eq!(e.kind(), BlockSourceErrorKind::Persistent);
@@ -466,9 +548,9 @@ mod spv_client_tests {
 		let common_tip = chain.tip();
 
 		let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
-		let mut cache = UnboundedCache::new();
+		let cache = HeaderCache::new();
 		let mut listener = NullChainListener {};
-		let mut client = SpvClient::new(common_tip, poller, &mut cache, &mut listener);
+		let mut client = SpvClient::new(common_tip, poller, cache, &mut listener);
 		match client.poll_best_tip().await {
 			Err(e) => panic!("Unexpected error: {:?}", e),
 			Ok((chain_tip, blocks_connected)) => {
@@ -486,9 +568,9 @@ mod spv_client_tests {
 		let old_tip = chain.at_height(1);
 
 		let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
-		let mut cache = UnboundedCache::new();
+		let cache = HeaderCache::new();
 		let mut listener = NullChainListener {};
-		let mut client = SpvClient::new(old_tip, poller, &mut cache, &mut listener);
+		let mut client = SpvClient::new(old_tip, poller, cache, &mut listener);
 		match client.poll_best_tip().await {
 			Err(e) => panic!("Unexpected error: {:?}", e),
 			Ok((chain_tip, blocks_connected)) => {
@@ -506,9 +588,9 @@ mod spv_client_tests {
 		let old_tip = chain.at_height(1);
 
 		let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
-		let mut cache = UnboundedCache::new();
+		let cache = HeaderCache::new();
 		let mut listener = NullChainListener {};
-		let mut client = SpvClient::new(old_tip, poller, &mut cache, &mut listener);
+		let mut client = SpvClient::new(old_tip, poller, cache, &mut listener);
 		match client.poll_best_tip().await {
 			Err(e) => panic!("Unexpected error: {:?}", e),
 			Ok((chain_tip, blocks_connected)) => {
@@ -526,9 +608,9 @@ mod spv_client_tests {
 		let old_tip = chain.at_height(1);
 
 		let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
-		let mut cache = UnboundedCache::new();
+		let cache = HeaderCache::new();
 		let mut listener = NullChainListener {};
-		let mut client = SpvClient::new(old_tip, poller, &mut cache, &mut listener);
+		let mut client = SpvClient::new(old_tip, poller, cache, &mut listener);
 		match client.poll_best_tip().await {
 			Err(e) => panic!("Unexpected error: {:?}", e),
 			Ok((chain_tip, blocks_connected)) => {
@@ -547,9 +629,9 @@ mod spv_client_tests {
 		let worse_tip = chain.tip();
 
 		let poller = poll::ChainPoller::new(&mut chain, Network::Testnet);
-		let mut cache = UnboundedCache::new();
+		let cache = HeaderCache::new();
 		let mut listener = NullChainListener {};
-		let mut client = SpvClient::new(best_tip, poller, &mut cache, &mut listener);
+		let mut client = SpvClient::new(best_tip, poller, cache, &mut listener);
 		match client.poll_best_tip().await {
 			Err(e) => panic!("Unexpected error: {:?}", e),
 			Ok((chain_tip, blocks_connected)) => {