Add is_resolving_output in ChannelMonitor

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

If spurrious htlc updates 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 +1140,17 @@ 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(_) => {
+						//TODO (ariard) We may have spurrious HTLC update events from ChannelMonitor due to block re-scan
+						// Should we discard them ?
+						return Ok((None, None));
+					},
+					_ => {
+						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 +1233,17 @@ 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(_) => {
+						//TODO (ariard) We may have spurrious HTLC update events from ChannelMonitor due to block re-scan
+						// Should we discard them ?
+						return Ok(None);
+					},
+					_ => {
+						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;
 			}

src/ln/channelmanager.rs

@@ -624,13 +624,7 @@ 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
@@ -2661,6 +2655,17 @@ impl ChainListener for ChannelManager {
 		for failure in failed_channels.drain(..) {
 			self.finish_force_close_channel(failure);
 		}
+		{
+			let mut channel_state = Some(self.channel_state.lock().unwrap());
+			for (_, payment_preimage, htlc_source) in self.monitor.fetch_pending_htlc_updated() {
+				if let Some(source) = htlc_source {
+					if let Some(preimage) = payment_preimage {
+						if channel_state.is_none() { channel_state = Some(self.channel_state.lock().unwrap());}
+						self.claim_funds_internal(channel_state.take().unwrap(), 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();
 	}
@@ -6064,6 +6069,105 @@ mod tests {
 		assert_eq!(nodes[1].node.list_channels().len(), 0);
 	}
 
+	#[test]
+	fn test_htlc_on_chain_success() {
+		// Test that in case of an unilateral close onchain, we detect the state of output thanks to
+		// ChainWatchInterface and pass the preimage backward accordingly. So here we test that ChannelManager is
+		// broadcasting the right event to other nodes in payment path.
+		// A --------------------> B ----------------------> C (preimage)
+		//    A's commitment tx			C's commitment tx
+		// 	       \				   \
+		// 	   B's preimage tx		 	C's HTLC Success tx
+
+		let nodes = create_network(3);
+
+		// Create some initial channels
+		let chan_1 = create_announced_chan_between_nodes(&nodes, 0, 1);
+		let chan_2 = create_announced_chan_between_nodes(&nodes, 1, 2);
+
+		// Rebalance the network a bit by relaying one payment through all the channels...
+		send_payment(&nodes[0], &vec!(&nodes[1], &nodes[2])[..], 8000000);
+		send_payment(&nodes[0], &vec!(&nodes[1], &nodes[2])[..], 8000000);
+
+		let (payment_preimage, _payment_hash) = route_payment(&nodes[0], &vec!(&nodes[1], &nodes[2]), 3000000);
+		let header = BlockHeader { version: 0x20000000, prev_blockhash: Default::default(), merkle_root: Default::default(), time: 42, bits: 42, nonce: 42};
+
+		// Broadcast legit commitment tx from C on B's chain
+		// Broadcast HTLC Success transation by C on received output from C's commitment tx on B's chain
+		let commitment_tx = nodes[2].node.channel_state.lock().unwrap().by_id.get(&chan_2.2).unwrap().last_local_commitment_txn.clone();
+		nodes[2].node.claim_funds(payment_preimage);
+		{
+			let mut added_monitors = nodes[2].chan_monitor.added_monitors.lock().unwrap();
+			assert_eq!(added_monitors.len(), 1);
+			added_monitors.clear();
+		}
+		let events = nodes[2].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 1);
+		match events[0] {
+			MessageSendEvent::UpdateHTLCs { ref node_id, updates: msgs::CommitmentUpdate { ref update_add_htlcs, ref update_fulfill_htlcs, ref update_fail_htlcs, ref update_fail_malformed_htlcs, .. } } => {
+				assert!(update_add_htlcs.is_empty());
+				assert!(update_fail_htlcs.is_empty());
+				assert!(!update_fulfill_htlcs.is_empty());
+				assert!(update_fail_malformed_htlcs.is_empty());
+				assert_eq!(nodes[1].node.get_our_node_id(), *node_id);
+			},
+			_ => panic!("Unexpected event"),
+		};
+		nodes[2].chain_monitor.block_connected_with_filtering(&Block { header, txdata: vec![commitment_tx[0].clone()]}, 1);
+		let events = nodes[2].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 1);
+		match events[0] {
+			MessageSendEvent::BroadcastChannelUpdate { .. } => {},
+			_ => panic!("Unexpected event"),
+		}
+		let node_txn = nodes[2].tx_broadcaster.txn_broadcasted.lock().unwrap().clone();
+
+		// Verify that B's ChannelManager is able to extract preimage from HTLC Success tx and pass it backward
+		nodes[1].chain_monitor.block_connected_with_filtering(&Block { header, txdata: node_txn}, 1);
+		{
+			let mut added_monitors = nodes[1].chan_monitor.added_monitors.lock().unwrap();
+			assert_eq!(added_monitors.len(), 1);
+			added_monitors.clear();
+		}
+		let events = nodes[1].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 2);
+		match events[0] {
+			MessageSendEvent::BroadcastChannelUpdate { .. } => {},
+			_ => panic!("Unexpected event"),
+		}
+		match events[1] {
+			MessageSendEvent::UpdateHTLCs { ref node_id, updates: msgs::CommitmentUpdate { ref update_add_htlcs, ref update_fail_htlcs, ref update_fulfill_htlcs, ref update_fail_malformed_htlcs, .. } } => {
+				assert!(update_add_htlcs.is_empty());
+				assert!(update_fail_htlcs.is_empty());
+				assert!(!update_fulfill_htlcs.is_empty());
+				assert!(update_fail_malformed_htlcs.is_empty());
+				assert_eq!(nodes[0].node.get_our_node_id(), *node_id);
+			},
+			_ => panic!("Unexpected event"),
+		};
+
+		// Broadcast legit commitment tx from A on B's chain
+		// Broadcast preimage tx by B on offered output from A commitment tx  on A's chain
+		let commitment_tx = nodes[0].node.channel_state.lock().unwrap().by_id.get(&chan_1.2).unwrap().last_local_commitment_txn.clone();
+		nodes[1].chain_monitor.block_connected_with_filtering(&Block { header, txdata: vec![commitment_tx[0].clone()]}, 1);
+		let events = nodes[1].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 1);
+		match events[0] {
+			MessageSendEvent::BroadcastChannelUpdate { .. } => {},
+			_ => panic!("Unexpected event"),
+		}
+		let node_txn = nodes[1].tx_broadcaster.txn_broadcasted.lock().unwrap().clone();
+
+		// Verify that A's ChannelManager is able to extract preimage from preimage tx and pass it backward
+		nodes[0].chain_monitor.block_connected_with_filtering(&Block { header, txdata: node_txn }, 1);
+		let events = nodes[0].node.get_and_clear_pending_msg_events();
+		assert_eq!(events.len(), 1);
+		match events[0] {
+			MessageSendEvent::BroadcastChannelUpdate { .. } => {},
+			_ => panic!("Unexpected event"),
+		}
+	}
+
 	#[test]
 	fn test_htlc_ignore_latest_remote_commitment() {
 		// Test that HTLC transactions spending the latest remote commitment transaction are simply