Work around LND bug 6039

lightning/src/events/mod.rs

@@ -1501,6 +1501,7 @@ impl MaybeReadable for Event {
 /// broadcast to most peers).
 /// These events are handled by PeerManager::process_events if you are using a PeerManager.
 #[derive(Clone, Debug)]
+#[cfg_attr(test, derive(PartialEq))]
 pub enum MessageSendEvent {
 	/// Used to indicate that we've accepted a channel open and should send the accept_channel
 	/// message provided to the given peer.

lightning/src/ln/channel.rs

@@ -3811,6 +3811,17 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 		}
 	}
 
+	/// Gets the `Shutdown` message we should send our peer on reconnect, if any.
+	pub fn get_outbound_shutdown(&self) -> Option<msgs::Shutdown> {
+		if self.context.channel_state & (ChannelState::LocalShutdownSent as u32) != 0 {
+			assert!(self.context.shutdown_scriptpubkey.is_some());
+			Some(msgs::Shutdown {
+				channel_id: self.context.channel_id,
+				scriptpubkey: self.get_closing_scriptpubkey(),
+			})
+		} else { None }
+	}
+
 	/// May panic if some calls other than message-handling calls (which will all Err immediately)
 	/// have been called between remove_uncommitted_htlcs_and_mark_paused and this call.
 	///
@@ -3877,13 +3888,7 @@ impl<Signer: WriteableEcdsaChannelSigner> Channel<Signer> {
 		self.context.channel_state &= !(ChannelState::PeerDisconnected as u32);
 		self.context.sent_message_awaiting_response = None;
 
-		let shutdown_msg = if self.context.channel_state & (ChannelState::LocalShutdownSent as u32) != 0 {
-			assert!(self.context.shutdown_scriptpubkey.is_some());
-			Some(msgs::Shutdown {
-				channel_id: self.context.channel_id,
-				scriptpubkey: self.get_closing_scriptpubkey(),
-			})
-		} else { None };
+		let shutdown_msg = self.get_outbound_shutdown();
 
 		let announcement_sigs = self.get_announcement_sigs(node_signer, genesis_block_hash, user_config, best_block.height(), logger);
 

lightning/src/ln/channelmanager.rs

@@ -7489,6 +7489,46 @@ where
 	fn handle_error(&self, counterparty_node_id: &PublicKey, msg: &msgs::ErrorMessage) {
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
 
+		match &msg.data as &str {
+			"cannot co-op close channel w/ active htlcs"|
+			"link failed to shutdown" =>
+			{
+				// LND hasn't properly handled shutdown messages ever, and force-closes any time we
+				// send one while HTLCs are still present. The issue is tracked at
+				// https://github.com/lightningnetwork/lnd/issues/6039 and has had multiple patches
+				// to fix it but none so far have managed to land upstream. The issue appears to be
+				// very low priority for the LND team despite being marked "P1".
+				// We're not going to bother handling this in a sensible way, instead simply
+				// repeating the Shutdown message on repeat until morale improves.
+				if msg.channel_id != [0; 32] {
+					let per_peer_state = self.per_peer_state.read().unwrap();
+					let peer_state_mutex_opt = per_peer_state.get(counterparty_node_id);
+					if peer_state_mutex_opt.is_none() { return; }
+					let mut peer_state = peer_state_mutex_opt.unwrap().lock().unwrap();
+					if let Some(chan) = peer_state.channel_by_id.get(&msg.channel_id) {
+						if let Some(msg) = chan.get_outbound_shutdown() {
+							peer_state.pending_msg_events.push(events::MessageSendEvent::SendShutdown {
+								node_id: *counterparty_node_id,
+								msg,
+							});
+						}
+						peer_state.pending_msg_events.push(events::MessageSendEvent::HandleError {
+							node_id: *counterparty_node_id,
+							action: msgs::ErrorAction::SendWarningMessage {
+								msg: msgs::WarningMessage {
+									channel_id: msg.channel_id,
+									data: "You appear to be exhibiting LND bug 6039, we'll keep sending you shutdown messages until you handle them correctly".to_owned()
+								},
+								log_level: Level::Trace,
+							}
+						});
+					}
+				}
+				return;
+			}
+			_ => {}
+		}
+
 		if msg.channel_id == [0; 32] {
 			let channel_ids: Vec<[u8; 32]> = {
 				let per_peer_state = self.per_peer_state.read().unwrap();

lightning/src/ln/msgs.rs

@@ -1144,7 +1144,7 @@ enum EncodingType {
 }
 
 /// Used to put an error message in a [`LightningError`].
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum ErrorAction {
 	/// The peer took some action which made us think they were useless. Disconnect them.
 	DisconnectPeer {

lightning/src/ln/shutdown_tests.rs

@@ -198,6 +198,61 @@ fn expect_channel_shutdown_state_with_htlc() {
 	assert!(nodes[0].node.list_channels().is_empty());
 }
 
+#[test]
+fn test_lnd_bug_6039() {
+	// LND sends a nonsense error message any time it gets a shutdown if there are still HTLCs
+	// pending. We currently swallow that error to work around LND's bug #6039. This test emulates
+	// the LND nonsense and ensures we at least kinda handle it.
+	let chanmon_cfgs = create_chanmon_cfgs(2);
+	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+	let chan = create_announced_chan_between_nodes(&nodes, 0, 1);
+
+	let (payment_preimage, payment_hash, _) = route_payment(&nodes[0], &[&nodes[1]], 100_000);
+
+	nodes[0].node.close_channel(&chan.2, &nodes[1].node.get_our_node_id()).unwrap();
+	let node_0_shutdown = get_event_msg!(nodes[0], MessageSendEvent::SendShutdown, nodes[1].node.get_our_node_id());
+	nodes[1].node.handle_shutdown(&nodes[0].node.get_our_node_id(), &node_0_shutdown);
+
+	// Generate an lnd-like error message and check that we respond by simply screaming louder to
+	// see if LND will accept our protocol compliance.
+	let err_msg = msgs::ErrorMessage { channel_id: chan.2, data: "link failed to shutdown".to_string() };
+	nodes[0].node.handle_error(&nodes[1].node.get_our_node_id(), &err_msg);
+	let node_a_responses = nodes[0].node.get_and_clear_pending_msg_events();
+	assert_eq!(node_a_responses[0], MessageSendEvent::SendShutdown {
+			node_id: nodes[1].node.get_our_node_id(),
+			msg: node_0_shutdown,
+		});
+	if let MessageSendEvent::HandleError { action: msgs::ErrorAction::SendWarningMessage { .. }, .. }
+		= node_a_responses[1] {} else { panic!(); }
+
+	let node_1_shutdown = get_event_msg!(nodes[1], MessageSendEvent::SendShutdown, nodes[0].node.get_our_node_id());
+
+	assert!(nodes[0].node.get_and_clear_pending_msg_events().is_empty());
+	assert!(nodes[1].node.get_and_clear_pending_msg_events().is_empty());
+
+	claim_payment(&nodes[0], &[&nodes[1]], payment_preimage);
+
+	// Assume that LND will eventually respond to our Shutdown if we clear all the remaining HTLCs
+	nodes[0].node.handle_shutdown(&nodes[1].node.get_our_node_id(), &node_1_shutdown);
+
+	// ClosingSignNegotion process
+	let node_0_closing_signed = get_event_msg!(nodes[0], MessageSendEvent::SendClosingSigned, nodes[1].node.get_our_node_id());
+	nodes[1].node.handle_closing_signed(&nodes[0].node.get_our_node_id(), &node_0_closing_signed);
+	let node_1_closing_signed = get_event_msg!(nodes[1], MessageSendEvent::SendClosingSigned, nodes[0].node.get_our_node_id());
+	nodes[0].node.handle_closing_signed(&nodes[1].node.get_our_node_id(), &node_1_closing_signed);
+	let (_, node_0_2nd_closing_signed) = get_closing_signed_broadcast!(nodes[0].node, nodes[1].node.get_our_node_id());
+	nodes[1].node.handle_closing_signed(&nodes[0].node.get_our_node_id(), &node_0_2nd_closing_signed.unwrap());
+	let (_, node_1_none) = get_closing_signed_broadcast!(nodes[1].node, nodes[0].node.get_our_node_id());
+	assert!(node_1_none.is_none());
+	check_closed_event!(nodes[0], 1, ClosureReason::CooperativeClosure, [nodes[1].node.get_our_node_id()], 100000);
+	check_closed_event!(nodes[1], 1, ClosureReason::CooperativeClosure, [nodes[0].node.get_our_node_id()], 100000);
+
+	// Shutdown basically removes the channelDetails, testing of shutdowncomplete state unnecessary
+	assert!(nodes[0].node.list_channels().is_empty());
+}
+
 #[test]
 fn expect_channel_shutdown_state_with_force_closure() {
 	// Test sending a shutdown prior to channel_ready after funding generation