Test + fuzz that Channel{,Monitor} would_broadcast are identical

Author: TheBlueMatt

fuzz/src/chanmon_consistency.rs

@@ -126,6 +126,10 @@ impl channelmonitor::ManyChannelMonitor for TestChannelMonitor {
 		self.update_ret.lock().unwrap().clone()
 	}
 
+	fn get_monitor_would_broadcast(&self, funding_txo: &OutPoint, height: u32) -> bool {
+		self.simple_monitor.get_monitor_would_broadcast(funding_txo, height)
+	}
+
 	fn get_and_clear_pending_htlcs_updated(&self) -> Vec<HTLCUpdate> {
 		return self.simple_monitor.get_and_clear_pending_htlcs_updated();
 	}

lightning/src/ln/channelmanager.rs

@@ -3044,6 +3044,15 @@ impl<ChanSigner: ChannelKeys, M: Deref + Sync + Send, T: Deref + Sync + Send, K:
 						}
 					}
 				}
+				#[cfg(any(test, feature = "fuzztarget"))]
+				if channel.is_funding_initiated() {
+					// In testing/fuzzing, check that the channel's would_broadcast_at_height
+					// implementation is always identical to the ChannelMonitor equivalent.
+					for i in height..height + 144 {
+						assert_eq!(channel.monitor_would_broadcast_at_height(i, &self.logger),
+							self.monitor.get_monitor_would_broadcast(&channel.get_funding_txo().unwrap(), i));
+					}
+				}
 				if channel.is_funding_initiated() && channel.monitor_would_broadcast_at_height(height, &self.logger) {
 					if let Some(short_id) = channel.get_short_channel_id() {
 						short_to_id.remove(&short_id);

lightning/src/ln/channelmonitor.rs

@@ -285,6 +285,11 @@ impl<ChanSigner: ChannelKeys, T: Deref + Sync + Send, F: Deref + Sync + Send, L:
 		}
 	}
 
+	#[cfg(any(test, feature = "fuzztarget"))]
+	fn get_monitor_would_broadcast(&self, funding_txo: &OutPoint, height: u32) -> bool {
+		self.monitors.lock().unwrap().get(funding_txo).unwrap().would_broadcast_at_height(height, &self.logger)
+	}
+
 	fn get_and_clear_pending_htlcs_updated(&self) -> Vec<HTLCUpdate> {
 		let mut pending_htlcs_updated = Vec::new();
 		for chan in self.monitors.lock().unwrap().values_mut() {
@@ -870,6 +875,11 @@ pub trait ManyChannelMonitor: Send + Sync {
 	/// ChannelMonitors via block_connected may result in FUNDS LOSS.
 	fn update_monitor(&self, funding_txo: OutPoint, monitor: ChannelMonitorUpdate) -> Result<(), ChannelMonitorUpdateErr>;
 
+	#[cfg(any(test, feature = "fuzztarget"))]
+	/// Calls would_broadcast_at_height() on the given monitor. Used in testing to check that the
+	/// ChannelMonitor copy can never get out of sync with the Channel copy.
+	fn get_monitor_would_broadcast(&self, funding_txo: &OutPoint, height: u32) -> bool;
+
 	/// Used by ChannelManager to get list of HTLC resolved onchain and which needed to be updated
 	/// with success or failure.
 	///

lightning/src/util/test_utils.rs

@@ -120,6 +120,10 @@ impl<'a> channelmonitor::ManyChannelMonitor for TestChannelMonitor<'a> {
 		ret
 	}
 
+	fn get_monitor_would_broadcast(&self, funding_txo: &OutPoint, height: u32) -> bool {
+		self.simple_monitor.get_monitor_would_broadcast(funding_txo, height)
+	}
+
 	fn get_and_clear_pending_htlcs_updated(&self) -> Vec<HTLCUpdate> {
 		return self.simple_monitor.get_and_clear_pending_htlcs_updated();
 	}