Check for duplicate HTLC events having matured

Author: jkczyz

lightning/src/chain/channelmonitor.rs

@@ -2067,31 +2067,56 @@ impl<Signer: Sign> ChannelMonitorImpl<Signer> {
 			claimable_outpoints.append(&mut new_outpoints);
 		}
 
+		// Find which on-chain events have reached their confirmation threshold.
 		let onchain_events_waiting_threshold_conf =
 			self.onchain_events_waiting_threshold_conf.drain(..).collect::<Vec<_>>();
+		let mut onchain_events_reaching_threshold_conf = Vec::new();
 		for entry in onchain_events_waiting_threshold_conf {
 			if entry.has_reached_confirmation_threshold(height) {
-				match entry.event {
-					OnchainEvent::HTLCUpdate { htlc_update } => {
-						log_trace!(logger, "HTLC {} failure update has got enough confirmations to be passed upstream", log_bytes!((htlc_update.1).0));
-						self.pending_monitor_events.push(MonitorEvent::HTLCEvent(HTLCUpdate {
-							payment_hash: htlc_update.1,
-							payment_preimage: None,
-							source: htlc_update.0,
-						}));
-					},
-					OnchainEvent::MaturingOutput { descriptor } => {
-						log_trace!(logger, "Descriptor {} has got enough confirmations to be passed upstream", log_spendable!(descriptor));
-						self.pending_events.push(Event::SpendableOutputs {
-							outputs: vec![descriptor]
-						});
-					}
-				}
+				onchain_events_reaching_threshold_conf.push(entry);
 			} else {
 				self.onchain_events_waiting_threshold_conf.push(entry);
 			}
 		}
 
+		// Used to check for duplicate HTLC resolutions.
+		#[cfg(debug_assertions)]
+		let unconfirmed_htlcs: Vec<_> = self.onchain_events_waiting_threshold_conf
+			.iter()
+			.filter_map(|entry| match &entry.event {
+				OnchainEvent::HTLCUpdate { htlc_update } => Some(htlc_update.0.clone()),
+				OnchainEvent::MaturingOutput { .. } => None,
+			})
+			.collect();
+		#[cfg(debug_assertions)]
+		let mut confirmed_htlcs = Vec::new();
+
+		// Produce actionable events from on-chain events having reached their threshold.
+		for entry in onchain_events_reaching_threshold_conf.drain(..) {
+			match entry.event {
+				OnchainEvent::HTLCUpdate { htlc_update } => {
+					// Check for duplicate HTLC resolutions.
+					debug_assert!(unconfirmed_htlcs.iter().find(|&htlc| htlc == &htlc_update.0).is_none());
+					debug_assert!(confirmed_htlcs.iter().find(|&htlc| htlc == &htlc_update.0).is_none());
+					#[cfg(debug_assertions)]
+					confirmed_htlcs.push(htlc_update.0.clone());
+
+					log_trace!(logger, "HTLC {} failure update has got enough confirmations to be passed upstream", log_bytes!((htlc_update.1).0));
+					self.pending_monitor_events.push(MonitorEvent::HTLCEvent(HTLCUpdate {
+						payment_hash: htlc_update.1,
+						payment_preimage: None,
+						source: htlc_update.0,
+					}));
+				},
+				OnchainEvent::MaturingOutput { descriptor } => {
+					log_trace!(logger, "Descriptor {} has got enough confirmations to be passed upstream", log_spendable!(descriptor));
+					self.pending_events.push(Event::SpendableOutputs {
+						outputs: vec![descriptor]
+					});
+				}
+			}
+		}
+
 		self.onchain_tx_handler.update_claims_view(&txn_matched, claimable_outpoints, Some(height), &&*broadcaster, &&*fee_estimator, &&*logger);
 		self.last_block_hash = block_hash;