Add is_resolving_output in ChannelMonitor

Called in ChannelMonitor block_connected, returning
HTLCUpdate upstream via ManyChannelMonitor to
link htlcs between monitors. Used by ChannelManager to
fulfill/fail htlcs backwards accordingly

If spurrious HTLCUpdate are generated due to block re-scan
and htlc are already LocalRemoved, discard them in
channel get_update_*_htlc

Author: Antoine Riard

src/ln/channel.rs

@@ -1140,10 +1140,22 @@ impl Channel {
 		for (idx, htlc) in self.pending_inbound_htlcs.iter().enumerate() {
 			if htlc.htlc_id == htlc_id_arg {
 				assert_eq!(htlc.payment_hash, payment_hash_calc);
-				if let InboundHTLCState::Committed = htlc.state {
-				} else {
-					debug_assert!(false, "Have an inbound HTLC we tried to claim before it was fully committed to");
-					// Don't return in release mode here so that we can update channel_monitor
+				match htlc.state {
+					InboundHTLCState::Committed => {},
+					InboundHTLCState::LocalRemoved(ref reason) => {
+						// ChannelManager may generate duplicate claims due to HTLC update events from on-chain
+						// ChannelsMonitors during block rescan
+						// TODO: Ideally we'd just drop these
+						if let &InboundHTLCRemovalReason::Fulfill(_) = reason {
+							return Ok((None, None));
+						} else {
+							assert!(false, "Got an update_fulfill for previously-failed HTLC!");
+						}
+					},
+					_ => {
+						debug_assert!(false, "Have an inbound HTLC we tried to claim before it was fully committed to");
+						// Don't return in release mode here so that we can update channel_monitor
+					}
 				}
 				pending_idx = idx;
 				break;
@@ -1226,10 +1238,22 @@ impl Channel {
 		let mut pending_idx = std::usize::MAX;
 		for (idx, htlc) in self.pending_inbound_htlcs.iter().enumerate() {
 			if htlc.htlc_id == htlc_id_arg {
-				if let InboundHTLCState::Committed = htlc.state {
-				} else {
-					debug_assert!(false, "Have an inbound HTLC we tried to fail before it was fully committed to");
-					return Err(ChannelError::Ignore("Unable to find a pending HTLC which matched the given HTLC ID"));
+				match htlc.state {
+					InboundHTLCState::Committed => {},
+					InboundHTLCState::LocalRemoved(ref reason) => {
+						// ChannelManager may generate duplicate claims due to HTLC update events from on-chain
+						// ChannelsMonitors during block rescan
+						// TODO: Ideally we'd just drop these
+						if let &InboundHTLCRemovalReason::Fulfill(_) = reason {
+							assert!(false, "Got an update_fail for previously-fulfilled HTLC!");
+						} else {
+							return Ok(None);
+						}
+					},
+					_ => {
+						debug_assert!(false, "Have an inbound HTLC we tried to claim before it was fully committed to");
+						return Err(ChannelError::Ignore("Unable to find a pending HTLC which matchd the given HTLC ID"));
+					}
 				}
 				pending_idx = idx;
 			}
@@ -1251,7 +1275,9 @@ impl Channel {
 					},
 					&HTLCUpdateAwaitingACK::FailHTLC { htlc_id, .. } => {
 						if htlc_id_arg == htlc_id {
-							debug_assert!(false, "Tried to fail an HTLC that we already had a pending failure for");
+							// ChannelManager may generate duplicate claims due to HTLC update events from on-chain
+							// ChannelsMonitors during block rescan
+							// TODO: Ideally we'd just drop these
 							return Ok(None);
 						}
 					},

src/ln/channelmanager.rs

@@ -679,13 +679,6 @@ impl ChannelManager {
 		for tx in local_txn {
 			self.tx_broadcaster.broadcast_transaction(&tx);
 		}
-		//TODO: We need to have a way where outbound HTLC claims can result in us claiming the
-		//now-on-chain HTLC output for ourselves (and, thereafter, passing the HTLC backwards).
-		//TODO: We need to handle monitoring of pending offered HTLCs which just hit the chain and
-		//may be claimed, resulting in us claiming the inbound HTLCs (and back-failing after
-		//timeouts are hit and our claims confirm).
-		//TODO: In any case, we need to make sure we remove any pending htlc tracking (via
-		//fail_backwards or claim_funds) eventually for all HTLCs that were in the channel
 	}
 
 	/// Force closes a channel, immediately broadcasting the latest local commitment transaction to
@@ -2718,6 +2711,13 @@ impl ChainListener for ChannelManager {
 		for failure in failed_channels.drain(..) {
 			self.finish_force_close_channel(failure);
 		}
+		{
+			for htlc_update in self.monitor.fetch_pending_htlc_updated() {
+				if let Some(preimage) = htlc_update.payment_preimage {
+					self.claim_funds_internal(self.channel_state.lock().unwrap(), htlc_update.source, preimage);
+				}
+			}
+		}
 		self.latest_block_height.store(height as usize, Ordering::Release);
 		*self.last_block_hash.try_lock().expect("block_(dis)connected must not be called in parallel") = header.bitcoin_hash();
 	}