Pipe channel node information through to `forward_broadcast_msg`

diff --git a/lightning-net-tokio/src/lib.rs b/lightning-net-tokio/src/lib.rs
index 068f77a..cf66311 100644
--- a/lightning-net-tokio/src/lib.rs
+++ b/lightning-net-tokio/src/lib.rs
@@ -660,8 +660,8 @@ mod tests {
 		}
 		fn handle_channel_update(
 			&self, _their_node_id: Option<PublicKey>, _msg: &ChannelUpdate,
-		) -> Result<bool, LightningError> {
-			Ok(false)
+		) -> Result<Option<(NodeId, NodeId)>, LightningError> {
+			Ok(None)
 		}
 		fn get_next_channel_announcement(
 			&self, _starting_point: u64,
diff --git a/lightning/src/ln/msgs.rs b/lightning/src/ln/msgs.rs
index a3483f8..36069b7 100644
--- a/lightning/src/ln/msgs.rs
+++ b/lightning/src/ln/msgs.rs
@@ -2199,13 +2199,13 @@ pub trait RoutingMessageHandler: BaseMessageHandler {
 	fn handle_channel_announcement(
 		&self, their_node_id: Option<PublicKey>, msg: &ChannelAnnouncement,
 	) -> Result<bool, LightningError>;
-	/// Handle an incoming `channel_update` message, returning true if it should be forwarded on,
-	/// `false` or returning an `Err` otherwise.
+	/// Handle an incoming `channel_update` message, returning the node IDs of the channel
+	/// participants if the message should be forwarded on, `None` or returning an `Err` otherwise.
 	///
 	/// If `their_node_id` is `None`, the message was generated by our own local node.
 	fn handle_channel_update(
 		&self, their_node_id: Option<PublicKey>, msg: &ChannelUpdate,
-	) -> Result<bool, LightningError>;
+	) -> Result<Option<(NodeId, NodeId)>, LightningError>;
 	/// Gets channel announcements and updates required to dump our routing table to a remote node,
 	/// starting at the `short_channel_id` indicated by `starting_point` and including announcements
 	/// for a single channel.
diff --git a/lightning/src/ln/peer_handler.rs b/lightning/src/ln/peer_handler.rs
index 796497c..d0a3a74 100644
--- a/lightning/src/ln/peer_handler.rs
+++ b/lightning/src/ln/peer_handler.rs
@@ -157,8 +157,8 @@ impl RoutingMessageHandler for IgnoringMessageHandler {
 	}
 	fn handle_channel_update(
 		&self, _their_node_id: Option<PublicKey>, _msg: &msgs::ChannelUpdate,
-	) -> Result<bool, LightningError> {
-		Ok(false)
+	) -> Result<Option<(NodeId, NodeId)>, LightningError> {
+		Ok(None)
 	}
 	fn get_next_channel_announcement(
 		&self, _starting_point: u64,
@@ -611,6 +611,19 @@ where
 	pub send_only_message_handler: SM,
 }
 
+/// A gossip message to be forwarded to all peers.
+enum BroadcastGossipMessage {
+	ChannelAnnouncement(msgs::ChannelAnnouncement),
+	NodeAnnouncement(msgs::NodeAnnouncement),
+	ChannelUpdate {
+		msg: msgs::ChannelUpdate,
+		/// One of the two channel endpoints.
+		node_id_1: NodeId,
+		/// One of the two channel endpoints.
+		node_id_2: NodeId,
+	},
+}
+
 /// Provides an object which can be used to send data to and which uniquely identifies a connection
 /// to a remote host. You will need to be able to generate multiple of these which meet Eq and
 /// implement Hash to meet the PeerManager API.
@@ -2045,10 +2058,7 @@ where
 		message: wire::Message<
 			<<CMH as Deref>::Target as wire::CustomMessageReader>::CustomMessage,
 		>,
-	) -> Result<
-		Option<wire::Message<<<CMH as Deref>::Target as wire::CustomMessageReader>::CustomMessage>>,
-		MessageHandlingError,
-	> {
+	) -> Result<Option<BroadcastGossipMessage>, MessageHandlingError> {
 		let their_node_id = peer_lock
 			.their_node_id
 			.expect("We know the peer's public key by the time we receive messages")
@@ -2390,10 +2400,7 @@ where
 			<<CMH as Deref>::Target as wire::CustomMessageReader>::CustomMessage,
 		>,
 		their_node_id: PublicKey, logger: &WithContext<'a, L>,
-	) -> Result<
-		Option<wire::Message<<<CMH as Deref>::Target as wire::CustomMessageReader>::CustomMessage>>,
-		MessageHandlingError,
-	> {
+	) -> Result<Option<BroadcastGossipMessage>, MessageHandlingError> {
 		if is_gossip_msg(message.type_id()) {
 			log_gossip!(logger, "Received message {:?} from {}", message, their_node_id);
 		} else {
@@ -2575,7 +2582,7 @@ where
 					.handle_channel_announcement(Some(their_node_id), &msg)
 					.map_err(|e| -> MessageHandlingError { e.into() })?
 				{
-					should_forward = Some(wire::Message::ChannelAnnouncement(msg));
+					should_forward = Some(BroadcastGossipMessage::ChannelAnnouncement(msg));
 				}
 				self.update_gossip_backlogged();
 			},
@@ -2585,7 +2592,7 @@ where
 					.handle_node_announcement(Some(their_node_id), &msg)
 					.map_err(|e| -> MessageHandlingError { e.into() })?
 				{
-					should_forward = Some(wire::Message::NodeAnnouncement(msg));
+					should_forward = Some(BroadcastGossipMessage::NodeAnnouncement(msg));
 				}
 				self.update_gossip_backlogged();
 			},
@@ -2594,11 +2601,12 @@ where
 				chan_handler.handle_channel_update(their_node_id, &msg);
 
 				let route_handler = &self.message_handler.route_handler;
-				if route_handler
+				if let Some((node_id_1, node_id_2)) = route_handler
 					.handle_channel_update(Some(their_node_id), &msg)
 					.map_err(|e| -> MessageHandlingError { e.into() })?
 				{
-					should_forward = Some(wire::Message::ChannelUpdate(msg));
+					should_forward =
+						Some(BroadcastGossipMessage::ChannelUpdate { msg, node_id_1, node_id_2 });
 				}
 				self.update_gossip_backlogged();
 			},
@@ -2652,12 +2660,11 @@ where
 	/// unless `allow_large_buffer` is set, in which case the message will be treated as critical
 	/// and delivered no matter the available buffer space.
 	fn forward_broadcast_msg(
-		&self, peers: &HashMap<Descriptor, Mutex<Peer>>,
-		msg: &wire::Message<<<CMH as Deref>::Target as wire::CustomMessageReader>::CustomMessage>,
+		&self, peers: &HashMap<Descriptor, Mutex<Peer>>, msg: &BroadcastGossipMessage,
 		except_node: Option<&PublicKey>, allow_large_buffer: bool,
 	) {
 		match msg {
-			wire::Message::ChannelAnnouncement(ref msg) => {
+			BroadcastGossipMessage::ChannelAnnouncement(ref msg) => {
 				log_gossip!(self.logger, "Sending message to all peers except {:?} or the announced channel's counterparties: {:?}", except_node, msg);
 				let encoded_msg = encode_msg!(msg);
 
@@ -2696,7 +2703,7 @@ where
 					peer.gossip_broadcast_buffer.push_back(encoded_message);
 				}
 			},
-			wire::Message::NodeAnnouncement(ref msg) => {
+			BroadcastGossipMessage::NodeAnnouncement(ref msg) => {
 				log_gossip!(
 					self.logger,
 					"Sending message to all peers except {:?} or the announced node: {:?}",
@@ -2738,7 +2745,7 @@ where
 					peer.gossip_broadcast_buffer.push_back(encoded_message);
 				}
 			},
-			wire::Message::ChannelUpdate(ref msg) => {
+			BroadcastGossipMessage::ChannelUpdate { msg, node_id_1: _, node_id_2: _ } => {
 				log_gossip!(
 					self.logger,
 					"Sending message to all peers except {:?}: {:?}",
@@ -2775,9 +2782,6 @@ where
 					peer.gossip_broadcast_buffer.push_back(encoded_message);
 				}
 			},
-			_ => {
-				debug_assert!(false, "We shouldn't attempt to forward anything but gossip messages")
-			},
 		}
 	}
 
@@ -3129,13 +3133,15 @@ where
 						},
 						MessageSendEvent::BroadcastChannelAnnouncement { msg, update_msg } => {
 							log_debug!(self.logger, "Handling BroadcastChannelAnnouncement event in peer_handler for short channel id {}", msg.contents.short_channel_id);
+							let node_id_1 = msg.contents.node_id_1;
+							let node_id_2 = msg.contents.node_id_2;
 							match route_handler.handle_channel_announcement(None, &msg) {
 								Ok(_)
 								| Err(LightningError {
 									action: msgs::ErrorAction::IgnoreDuplicateGossip,
 									..
 								}) => {
-									let forward = wire::Message::ChannelAnnouncement(msg);
+									let forward = BroadcastGossipMessage::ChannelAnnouncement(msg);
 									self.forward_broadcast_msg(
 										peers,
 										&forward,
@@ -3152,7 +3158,11 @@ where
 										action: msgs::ErrorAction::IgnoreDuplicateGossip,
 										..
 									}) => {
-										let forward = wire::Message::ChannelUpdate(msg);
+										let forward = BroadcastGossipMessage::ChannelUpdate {
+											msg,
+											node_id_1,
+											node_id_2,
+										};
 										self.forward_broadcast_msg(
 											peers,
 											&forward,
@@ -3164,7 +3174,7 @@ where
 								}
 							}
 						},
-						MessageSendEvent::BroadcastChannelUpdate { msg, .. } => {
+						MessageSendEvent::BroadcastChannelUpdate { msg, node_id_1, node_id_2 } => {
 							log_debug!(self.logger, "Handling BroadcastChannelUpdate event in peer_handler for contents {:?}", msg.contents);
 							match route_handler.handle_channel_update(None, &msg) {
 								Ok(_)
@@ -3172,7 +3182,11 @@ where
 									action: msgs::ErrorAction::IgnoreDuplicateGossip,
 									..
 								}) => {
-									let forward = wire::Message::ChannelUpdate(msg);
+									let forward = BroadcastGossipMessage::ChannelUpdate {
+										msg,
+										node_id_1,
+										node_id_2,
+									};
 									self.forward_broadcast_msg(
 										peers,
 										&forward,
@@ -3191,7 +3205,7 @@ where
 									action: msgs::ErrorAction::IgnoreDuplicateGossip,
 									..
 								}) => {
-									let forward = wire::Message::NodeAnnouncement(msg);
+									let forward = BroadcastGossipMessage::NodeAnnouncement(msg);
 									self.forward_broadcast_msg(
 										peers,
 										&forward,
@@ -3668,7 +3682,7 @@ where
 		let _ = self.message_handler.route_handler.handle_node_announcement(None, &msg);
 		self.forward_broadcast_msg(
 			&*self.peers.read().unwrap(),
-			&wire::Message::NodeAnnouncement(msg),
+			&BroadcastGossipMessage::NodeAnnouncement(msg),
 			None,
 			true,
 		);
diff --git a/lightning/src/routing/gossip.rs b/lightning/src/routing/gossip.rs
index edd0347..ae317ad 100644
--- a/lightning/src/routing/gossip.rs
+++ b/lightning/src/routing/gossip.rs
@@ -556,9 +556,12 @@ where
 
 	fn handle_channel_update(
 		&self, _their_node_id: Option<PublicKey>, msg: &msgs::ChannelUpdate,
-	) -> Result<bool, LightningError> {
-		self.network_graph.update_channel(msg)?;
-		Ok(msg.contents.excess_data.len() <= MAX_EXCESS_BYTES_FOR_RELAY)
+	) -> Result<Option<(NodeId, NodeId)>, LightningError> {
+		match self.network_graph.update_channel(msg) {
+			Ok(nodes) if msg.contents.excess_data.len() <= MAX_EXCESS_BYTES_FOR_RELAY => Ok(nodes),
+			Ok(_) => Ok(None),
+			Err(e) => Err(e),
+		}
 	}
 
 	fn get_next_channel_announcement(
@@ -2433,7 +2436,11 @@ where
 	///
 	/// If not built with `std`, any updates with a timestamp more than two weeks in the past or
 	/// materially in the future will be rejected.
-	pub fn update_channel(&self, msg: &msgs::ChannelUpdate) -> Result<(), LightningError> {
+	///
+	/// Returns the [`NodeId`]s of both sides of the channel if it was applied.
+	pub fn update_channel(
+		&self, msg: &msgs::ChannelUpdate,
+	) -> Result<Option<(NodeId, NodeId)>, LightningError> {
 		self.update_channel_internal(&msg.contents, Some(&msg), Some(&msg.signature), false)
 	}
 
@@ -2443,9 +2450,11 @@ where
 	///
 	/// If not built with `std`, any updates with a timestamp more than two weeks in the past or
 	/// materially in the future will be rejected.
+	///
+	/// Returns the [`NodeId`]s of both sides of the channel if it was applied.
 	pub fn update_channel_unsigned(
 		&self, msg: &msgs::UnsignedChannelUpdate,
-	) -> Result<(), LightningError> {
+	) -> Result<Option<(NodeId, NodeId)>, LightningError> {
 		self.update_channel_internal(msg, None, None, false)
 	}
 
@@ -2456,13 +2465,14 @@ where
 	/// If not built with `std`, any updates with a timestamp more than two weeks in the past or
 	/// materially in the future will be rejected.
 	pub fn verify_channel_update(&self, msg: &msgs::ChannelUpdate) -> Result<(), LightningError> {
-		self.update_channel_internal(&msg.contents, Some(&msg), Some(&msg.signature), true)
+		self.update_channel_internal(&msg.contents, Some(&msg), Some(&msg.signature), true)?;
+		Ok(())
 	}
 
 	fn update_channel_internal(
 		&self, msg: &msgs::UnsignedChannelUpdate, full_msg: Option<&msgs::ChannelUpdate>,
 		sig: Option<&secp256k1::ecdsa::Signature>, only_verify: bool,
-	) -> Result<(), LightningError> {
+	) -> Result<Option<(NodeId, NodeId)>, LightningError> {
 		let chan_enabled = msg.channel_flags & (1 << 1) != (1 << 1);
 
 		if msg.chain_hash != self.chain_hash {
@@ -2602,7 +2612,7 @@ where
 		}
 
 		if only_verify {
-			return Ok(());
+			return Ok(None);
 		}
 
 		let mut channels = self.channels.write().unwrap();
@@ -2633,9 +2643,11 @@ where
 			} else {
 				channel.one_to_two = new_channel_info;
 			}
-		}
 
-		Ok(())
+			Ok(Some((channel.node_one, channel.node_two)))
+		} else {
+			Ok(None)
+		}
 	}
 
 	fn remove_channel_in_nodes_callback<RM: FnMut(IndexedMapOccupiedEntry<NodeId, NodeInfo>)>(
@@ -3180,7 +3192,7 @@ pub(crate) mod tests {
 		let valid_channel_update = get_signed_channel_update(|_| {}, node_1_privkey, &secp_ctx);
 		network_graph.verify_channel_update(&valid_channel_update).unwrap();
 		match gossip_sync.handle_channel_update(Some(node_1_pubkey), &valid_channel_update) {
-			Ok(res) => assert!(res),
+			Ok(res) => assert!(res.is_some()),
 			_ => panic!(),
 		};
 
@@ -3202,9 +3214,9 @@ pub(crate) mod tests {
 			node_1_privkey,
 			&secp_ctx,
 		);
-		// Return false because contains excess data
+		// Update is accepted but won't be relayed because contains excess data
 		match gossip_sync.handle_channel_update(Some(node_1_pubkey), &valid_channel_update) {
-			Ok(res) => assert!(!res),
+			Ok(res) => assert!(res.is_none()),
 			_ => panic!(),
 		};
 
diff --git a/lightning/src/routing/test_utils.rs b/lightning/src/routing/test_utils.rs
index ab2b24c..c5c35c9 100644
--- a/lightning/src/routing/test_utils.rs
+++ b/lightning/src/routing/test_utils.rs
@@ -111,7 +111,7 @@ pub(crate) fn update_channel(
 	};
 
 	match gossip_sync.handle_channel_update(Some(node_pubkey), &valid_channel_update) {
-		Ok(res) => assert!(res),
+		Ok(res) => assert!(res.is_some()),
 		Err(e) => panic!("{e:?}")
 	};
 }
diff --git a/lightning/src/util/test_utils.rs b/lightning/src/util/test_utils.rs
index ad8ea22..6e664d3 100644
--- a/lightning/src/util/test_utils.rs
+++ b/lightning/src/util/test_utils.rs
@@ -1522,9 +1522,9 @@ impl msgs::RoutingMessageHandler for TestRoutingMessageHandler {
 	}
 	fn handle_channel_update(
 		&self, _their_node_id: Option<PublicKey>, _msg: &msgs::ChannelUpdate,
-	) -> Result<bool, msgs::LightningError> {
+	) -> Result<Option<(NodeId, NodeId)>, msgs::LightningError> {
 		self.chan_upds_recvd.fetch_add(1, Ordering::AcqRel);
-		Ok(true)
+		Ok(Some((NodeId::from_slice(&[2; 33]).unwrap(), NodeId::from_slice(&[3; 33]).unwrap())))
 	}
 	fn get_next_channel_announcement(
 		&self, starting_point: u64,