Fix channel manager race panic

The race:
- (1) If a channel manager is starting for the first time, it gets its
  initial block hash by calling BlockSource::get_blockchain_info() and
  constructing a BestBlock out of that.
- (2) During the initial chain sync, if chain_tip.is_none() then the
  best chain_tip is retrieved using
  lightning_block_sync::init::validate_best_block_header() which
  similarly uses BlockSource::get_best_block()
- If blocks were mined between (1) and (2), the channel manager’s block
  hash will be at a lower height than that of the block hash contained
  inside the chain_tip fed to the SpvClient. Suppose that this results
  in the channel manager being at block 1 and the SpvClient being at
  block 2. Once block 3 comes in and the SpvClient detects it via
  poll_best_tip(), the SpvClient computes the ChainDifference between
  its saved chain_tip value and block 3, concluding that it just needs
  to connect block 3. However, when Listen::filtered_block_connected is
  called using the data in block 3, the channel manager panics with
  “Blocks must be connected in chain-order - the connected header must
  build on the last connected header” - because block 3’s prev block
  hash is block 2’s block hash, rather than block 1’s block hash which
  the channel manager expects

This commit fixes it by removing the fresh channel manager's query to
the block source, instead deriving its best block from the validated
block header using a new `.to_best_block()` method.

Author: MaxFangX

src/main.rs

@@ -17,7 +17,7 @@ use lightning::chain;
 use lightning::chain::chaininterface::{BroadcasterInterface, ConfirmationTarget, FeeEstimator};
 use lightning::chain::keysinterface::{InMemorySigner, KeysInterface, KeysManager, Recipient};
 use lightning::chain::{chainmonitor, ChannelMonitorUpdateStatus};
-use lightning::chain::{BestBlock, Filter, Watch};
+use lightning::chain::{Filter, Watch};
 use lightning::ln::channelmanager;
 use lightning::ln::channelmanager::{
 	ChainParameters, ChannelManagerReadArgs, SimpleArcChannelManager,
@@ -458,7 +458,12 @@ async fn start_ldk() {
 	// Step 7: Read ChannelMonitor state from disk
 	let mut channelmonitors = persister.read_channelmonitors(keys_manager.clone()).unwrap();
 
-	// Step 8: Initialize the ChannelManager
+	// Step 8: Poll for the best chain tip, which may be used by the channel manager & spv client
+	let polled_chain_tip = init::validate_best_block_header(bitcoind_client.as_ref())
+		.await
+		.expect("Failed to fetch best block header and best block");
+
+	// Step 9: Initialize the ChannelManager
 	let mut user_config = UserConfig::default();
 	user_config.channel_handshake_limits.force_announced_channel_preference = false;
 	let mut restarting_node = true;
@@ -481,15 +486,11 @@ async fn start_ldk() {
 		} else {
 			// We're starting a fresh node.
 			restarting_node = false;
-			let getinfo_resp = bitcoind_client.get_blockchain_info().await;
-
-			let chain_params = ChainParameters {
-				network: args.network,
-				best_block: BestBlock::new(
-					getinfo_resp.latest_blockhash,
-					getinfo_resp.latest_height as u32,
-				),
-			};
+
+			let polled_best_block = polled_chain_tip.to_best_block();
+			let polled_best_block_hash = polled_best_block.block_hash();
+			let chain_params =
+				ChainParameters { network: args.network, best_block: polled_best_block };
 			let fresh_channel_manager = channelmanager::ChannelManager::new(
 				fee_estimator.clone(),
 				chain_monitor.clone(),
@@ -499,11 +500,11 @@ async fn start_ldk() {
 				user_config,
 				chain_params,
 			);
-			(getinfo_resp.latest_blockhash, fresh_channel_manager)
+			(polled_best_block_hash, fresh_channel_manager)
 		}
 	};
 
-	// Step 9: Sync ChannelMonitors and ChannelManager to chain tip
+	// Step 10: Sync ChannelMonitors and ChannelManager to chain tip
 	let mut chain_listener_channel_monitors = Vec::new();
 	let mut cache = UnboundedCache::new();
 	let mut chain_tip: Option<poll::ValidatedBlockHeader> = None;
@@ -540,7 +541,7 @@ async fn start_ldk() {
 		);
 	}
 
-	// Step 10: Give ChannelMonitors to ChainMonitor
+	// Step 11: Give ChannelMonitors to ChainMonitor
 	for item in chain_listener_channel_monitors.drain(..) {
 		let channel_monitor = item.1 .0;
 		let funding_outpoint = item.2;
@@ -550,7 +551,7 @@ async fn start_ldk() {
 		);
 	}
 
-	// Step 11: Optional: Initialize the P2PGossipSync
+	// Step 12: Optional: Initialize the P2PGossipSync
 	let genesis = genesis_block(args.network).header.block_hash();
 	let network_graph_path = format!("{}/network_graph", ldk_data_dir.clone());
 	let network_graph =
@@ -561,7 +562,7 @@ async fn start_ldk() {
 		logger.clone(),
 	));
 
-	// Step 12: Initialize the PeerManager
+	// Step 13: Initialize the PeerManager
 	let channel_manager: Arc<ChannelManager> = Arc::new(channel_manager);
 	let onion_messenger: Arc<OnionMessenger> = Arc::new(OnionMessenger::new(
 		Arc::clone(&keys_manager),
@@ -586,7 +587,7 @@ async fn start_ldk() {
 	));
 
 	// ## Running LDK
-	// Step 13: Initialize networking
+	// Step 14: Initialize networking
 
 	let peer_manager_connection_handler = peer_manager.clone();
 	let listening_port = args.ldk_peer_listening_port;
@@ -612,9 +613,9 @@ async fn start_ldk() {
 		}
 	});
 
-	// Step 14: Connect and Disconnect Blocks
+	// Step 15: Connect and Disconnect Blocks
 	if chain_tip.is_none() {
-		chain_tip = Some(init::validate_best_block_header(bitcoind_client.as_ref()).await.unwrap());
+		chain_tip = Some(polled_chain_tip);
 	}
 	let channel_manager_listener = channel_manager.clone();
 	let chain_monitor_listener = chain_monitor.clone();
@@ -631,7 +632,7 @@ async fn start_ldk() {
 		}
 	});
 
-	// Step 15: Handle LDK Events
+	// Step 16: Handle LDK Events
 	let channel_manager_event_listener = channel_manager.clone();
 	let keys_manager_listener = keys_manager.clone();
 	// TODO: persist payment info to disk
@@ -656,15 +657,15 @@ async fn start_ldk() {
 		));
 	};
 
-	// Step 16: Initialize routing ProbabilisticScorer
+	// Step 17: Initialize routing ProbabilisticScorer
 	let scorer_path = format!("{}/scorer", ldk_data_dir.clone());
 	let scorer = Arc::new(Mutex::new(disk::read_scorer(
 		Path::new(&scorer_path),
 		Arc::clone(&network_graph),
 		Arc::clone(&logger),
 	)));
 
-	// Step 17: Create InvoicePayer
+	// Step 18: Create InvoicePayer
 	let router = DefaultRouter::new(
 		network_graph.clone(),
 		logger.clone(),
@@ -679,10 +680,10 @@ async fn start_ldk() {
 		payment::Retry::Timeout(Duration::from_secs(10)),
 	));
 
-	// Step 18: Persist ChannelManager and NetworkGraph
+	// Step 19: Persist ChannelManager and NetworkGraph
 	let persister = Arc::new(FilesystemPersister::new(ldk_data_dir.clone()));
 
-	// Step 19: Background Processing
+	// Step 20: Background Processing
 	let background_processor = BackgroundProcessor::start(
 		persister,
 		invoice_payer.clone(),