Generate shutdown script at channel close

When a shutdown script is omitted from open_channel or accept_channel,
it must be provided when sending shutdown. Generate the shutdown script
at channel closing time in this case rather at channel opening.

This requires producing a ChannelMonitorUpdate with the shutdown script
since it is no longer known at ChannelMonitor creation.

Author: jkczyz

lightning/src/chain/channelmonitor.rs

@@ -438,6 +438,9 @@ pub(crate) enum ChannelMonitorUpdateStep {
 		/// think we've fallen behind!
 		should_broadcast: bool,
 	},
+	ShutdownScript {
+		scriptpubkey: Script,
+	},
 }
 
 impl_writeable_tlv_based_enum!(ChannelMonitorUpdateStep,
@@ -461,6 +464,9 @@ impl_writeable_tlv_based_enum!(ChannelMonitorUpdateStep,
 	(4, ChannelForceClosed) => {
 		(0, should_broadcast, required),
 	},
+	(5, ShutdownScript) => {
+		(0, scriptpubkey, required),
+	},
 ;);
 
 /// A ChannelMonitor handles chain events (blocks connected and disconnected) and generates
@@ -1437,7 +1443,13 @@ impl<Signer: Sign> ChannelMonitorImpl<Signer> {
 						// shouldn't print the scary warning above.
 						log_info!(logger, "Channel off-chain state closed after we broadcasted our latest commitment transaction.");
 					}
-				}
+				},
+				ChannelMonitorUpdateStep::ShutdownScript { scriptpubkey } => {
+					log_trace!(logger, "Updating ChannelMonitor with shutdown script");
+					if let Some(shutdown_script) = self.shutdown_script.replace(scriptpubkey.clone()) {
+						panic!("Attempted to replace shutdown script {} with {}", shutdown_script, scriptpubkey);
+					}
+				},
 			}
 		}
 		self.latest_update_id = updates.update_id;

lightning/src/ln/chanmon_update_fail_tests.rs

@@ -2369,3 +2369,66 @@ fn test_reconnect_dup_htlc_claims() {
 	do_test_reconnect_dup_htlc_claims(HTLCStatusAtDupClaim::HoldingCell, true);
 	do_test_reconnect_dup_htlc_claims(HTLCStatusAtDupClaim::Cleared, true);
 }
+
+#[test]
+fn test_temporary_error_during_shutdown() {
+	// Test that temporary failures when updating the monitor's shutdown script do not prevent
+	// cooperative close.
+	let mut config = test_default_channel_config();
+	config.channel_options.commit_upfront_shutdown_pubkey = false;
+
+	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, &[Some(config), Some(config)]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	let (_, _, channel_id, funding_tx) = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known());
+
+	*nodes[0].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::TemporaryFailure));
+	*nodes[1].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::TemporaryFailure));
+	close_channel(&nodes[0], &nodes[1], &channel_id, funding_tx, false);
+	check_added_monitors!(nodes[0], 1);
+	check_added_monitors!(nodes[1], 1);
+}
+
+#[test]
+fn test_permanent_error_during_sending_shutdown() {
+	// Test that permanent failures when updating the monitor's shutdown script result in a force
+	// close when initiating a cooperative close.
+	let mut config = test_default_channel_config();
+	config.channel_options.commit_upfront_shutdown_pubkey = false;
+
+	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, &[Some(config), None]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	let channel_id = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known()).2;
+	*nodes[0].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::PermanentFailure));
+
+	assert!(nodes[0].node.close_channel(&channel_id).is_ok());
+	check_closed_broadcast!(nodes[0], true);
+	check_added_monitors!(nodes[0], 2);
+}
+
+#[test]
+fn test_permanent_error_during_handling_shutdown() {
+	// Test that permanent failures when updating the monitor's shutdown script result in a force
+	// close when handling a cooperative close.
+	let mut config = test_default_channel_config();
+	config.channel_options.commit_upfront_shutdown_pubkey = false;
+
+	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, Some(config)]);
+	let mut nodes = create_network(2, &node_cfgs, &node_chanmgrs);
+
+	let channel_id = create_announced_chan_between_nodes(&nodes, 0, 1, InitFeatures::known(), InitFeatures::known()).2;
+	*nodes[1].chain_monitor.update_ret.lock().unwrap() = Some(Err(ChannelMonitorUpdateErr::PermanentFailure));
+
+	assert!(nodes[0].node.close_channel(&channel_id).is_ok());
+	let 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(), &InitFeatures::known(), &shutdown);
+	check_closed_broadcast!(nodes[1], true);
+	check_added_monitors!(nodes[1], 2);
+}