Add peer_[dis]connected to CustomMessageHandler trait

There's not much reason not to have these methods on the
`CustomMessageHandler` trait, and they can be quite useful, so we
add them here.

Author: TheBlueMatt

lightning-custom-message/src/lib.rs

@@ -288,6 +288,28 @@ macro_rules! composite_custom_message_handler {
 					.collect()
 			}
 
+			fn peer_connected(
+				&self, their_node_id: &$crate::bitcoin::secp256k1::PublicKey,
+				init_msg: &$crate::lightning::ln::msgs::Init, inbound: bool
+			) -> Result<(), ()> {
+				let should_disconnect = false;
+				$(
+					should_disconnect |= self.$field.peer_connected(their_node_id, init_msg, inbound).is_err();
+				)*
+				if should_disconnect {
+					$(
+						self.$field.peer_disconnected(their_node_id).is_err();
+					)*
+					Err(())
+				} else { Ok(()) }
+			}
+
+			fn peer_disconnected(&self, their_node_id: &$crate::bitcoin::secp256k1::PublicKey) {
+				$(
+					self.$field.peer_disconnected(their_node_id)
+				)*
+			}
+
 			fn provided_node_features(&self) -> $crate::lightning::ln::features::NodeFeatures {
 				$crate::lightning::ln::features::NodeFeatures::empty()
 					$(

lightning/src/ln/peer_handler.rs

@@ -68,6 +68,16 @@ pub trait CustomMessageHandler: wire::CustomMessageReader {
 	/// connection to the node exists, then the message is simply not sent.
 	fn get_and_clear_pending_msg(&self) -> Vec<(PublicKey, Self::CustomMessage)>;
 
+	/// Indicates a connection to the peer failed/an existing connection was lost.
+	fn peer_disconnected(&self, their_node_id: &PublicKey);
+
+	/// Handle a peer reconnecting, possibly generating `channel_reestablish` message(s).
+	///
+	/// May return an `Err(())` if the features the peer supports are not sufficient to communicate
+	/// with us. Implementors should be somewhat conservative about doing so, however, as other
+	/// message handlers may still wish to communicate with this peer.
+	fn peer_connected(&self, their_node_id: &PublicKey, msg: &msgs::Init, inbound: bool) -> Result<(), ()>;
+
 	/// Gets the node feature flags which this handler itself supports. All available handlers are
 	/// queried similarly and their feature flags are OR'd together to form the [`NodeFeatures`]
 	/// which are broadcasted in our [`NodeAnnouncement`] message.
@@ -170,6 +180,10 @@ impl CustomMessageHandler for IgnoringMessageHandler {
 
 	fn get_and_clear_pending_msg(&self) -> Vec<(PublicKey, Self::CustomMessage)> { Vec::new() }
 
+	fn peer_disconnected(&self, _: &PublicKey) {}
+
+	fn peer_connected(&self, _: &PublicKey, _: &msgs::Init, _: bool) -> Result<(), ()> { Ok(()) }
+
 	fn provided_node_features(&self) -> NodeFeatures { NodeFeatures::empty() }
 
 	fn provided_init_features(&self, _their_node_id: &PublicKey) -> InitFeatures {
@@ -1549,6 +1563,10 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, OM: Deref, L: Deref, CM
 				log_debug!(self.logger, "Onion Message Handler decided we couldn't communicate with peer {}", log_pubkey!(their_node_id));
 				return Err(PeerHandleError { }.into());
 			}
+			if let Err(()) = self.message_handler.custom_message_handler.peer_connected(&their_node_id, &msg, peer_lock.inbound_connection) {
+				log_debug!(self.logger, "Custom Message Handler decided we couldn't communicate with peer {}", log_pubkey!(their_node_id));
+				return Err(PeerHandleError { }.into());
+			}
 
 			peer_lock.their_features = Some(msg.features);
 			return Ok(None);
@@ -2237,6 +2255,7 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, OM: Deref, L: Deref, CM
 			log_trace!(self.logger, "Disconnecting peer with id {} due to {}", node_id, reason);
 			self.message_handler.chan_handler.peer_disconnected(&node_id);
 			self.message_handler.onion_message_handler.peer_disconnected(&node_id);
+			self.message_handler.custom_message_handler.peer_disconnected(&node_id);
 		}
 		descriptor.disconnect_socket();
 	}
@@ -2259,6 +2278,7 @@ impl<Descriptor: SocketDescriptor, CM: Deref, RM: Deref, OM: Deref, L: Deref, CM
 					if !peer.handshake_complete() { return; }
 					self.message_handler.chan_handler.peer_disconnected(&node_id);
 					self.message_handler.onion_message_handler.peer_disconnected(&node_id);
+					self.message_handler.custom_message_handler.peer_disconnected(&node_id);
 				}
 			}
 		};
@@ -2553,6 +2573,9 @@ mod tests {
 
 		fn get_and_clear_pending_msg(&self) -> Vec<(PublicKey, Self::CustomMessage)> { Vec::new() }
 
+		fn peer_disconnected(&self, _: &PublicKey) {}
+		fn peer_connected(&self, _: &PublicKey, _: &msgs::Init, _: bool) -> Result<(), ()> { Ok(()) }
+
 		fn provided_node_features(&self) -> NodeFeatures { NodeFeatures::empty() }
 
 		fn provided_init_features(&self, _: &PublicKey) -> InitFeatures {