Add boilerplate for ChannelMessageHandler::advertise_onion_message_support

We want to indicate to implementors of ChannelMessageHandler whether they
should advertise support for onion messages in their broadcasted node
announcements.

To be implemented in ChannelManager in upcoming commit(s).

Author: valentinewallace

lightning-net-tokio/src/lib.rs

@@ -612,6 +612,7 @@ mod tests {
 		}
 		fn handle_channel_reestablish(&self, _their_node_id: &PublicKey, _msg: &ChannelReestablish) {}
 		fn handle_error(&self, _their_node_id: &PublicKey, _msg: &ErrorMessage) {}
+		fn advertise_onion_message_support(&self) {}
 	}
 	impl MessageSendEventsProvider for MsgHandler {
 		fn get_and_clear_pending_msg_events(&self) -> Vec<MessageSendEvent> {

lightning/src/ln/channelmanager.rs

@@ -6235,6 +6235,8 @@ impl<Signer: Sign, M: Deref , T: Deref , K: Deref , F: Deref , L: Deref >
 			let _ = self.force_close_channel_with_peer(&msg.channel_id, counterparty_node_id, Some(&msg.data), true);
 		}
 	}
+
+	fn advertise_onion_message_support(&self) {}
 }
 
 /// Used to signal to the ChannelManager persister that the manager needs to be re-persisted to

lightning/src/ln/msgs.rs

@@ -896,6 +896,9 @@ pub trait ChannelMessageHandler : MessageSendEventsProvider {
 	// Error:
 	/// Handle an incoming error message from the given peer.
 	fn handle_error(&self, their_node_id: &PublicKey, msg: &ErrorMessage);
+
+	/// Advertise onion message forwarding support in broadcasted node announcements.
+	fn advertise_onion_message_support(&self);
 }
 
 /// A trait to describe an object which can receive routing messages.

lightning/src/ln/peer_handler.rs

@@ -201,6 +201,7 @@ impl ChannelMessageHandler for ErroringMessageHandler {
 	fn peer_disconnected(&self, _their_node_id: &PublicKey, _no_connection_possible: bool) {}
 	fn peer_connected(&self, _their_node_id: &PublicKey, _msg: &msgs::Init) {}
 	fn handle_error(&self, _their_node_id: &PublicKey, _msg: &msgs::ErrorMessage) {}
+	fn advertise_onion_message_support(&self) {}
 }
 impl Deref for ErroringMessageHandler {
 	type Target = ErroringMessageHandler;

lightning/src/util/test_utils.rs

@@ -357,6 +357,7 @@ impl msgs::ChannelMessageHandler for TestChannelMessageHandler {
 	fn handle_error(&self, _their_node_id: &PublicKey, msg: &msgs::ErrorMessage) {
 		self.received_msg(wire::Message::Error(msg.clone()));
 	}
+	fn advertise_onion_message_support(&self) {}
 }
 
 impl events::MessageSendEventsProvider for TestChannelMessageHandler {