Respond with an error when client hasn't got a registered handle

crates/client/src/client.rs

@@ -1235,6 +1235,7 @@ impl Client {
             subscriber
         } else {
             log::info!("unhandled message {}", type_name);
+            self.peer.respond_with_unhandled_message(message).log_err();
             return;
         };
 
@@ -1278,6 +1279,7 @@ impl Client {
                 .detach();
         } else {
             log::info!("unhandled message {}", type_name);
+            self.peer.respond_with_unhandled_message(message).log_err();
         }
     }
 

crates/rpc/src/peer.rs

@@ -494,6 +494,27 @@ impl Peer {
         Ok(())
     }
 
+    pub fn respond_with_unhandled_message(
+        &self,
+        envelope: Box<dyn AnyTypedEnvelope>,
+    ) -> Result<()> {
+        let connection = self.connection_state(envelope.sender_id())?;
+        let response = proto::Error {
+            message: format!("message {} was not handled", envelope.payload_type_name()),
+        };
+        let message_id = connection
+            .next_message_id
+            .fetch_add(1, atomic::Ordering::SeqCst);
+        connection
+            .outgoing_tx
+            .unbounded_send(proto::Message::Envelope(response.into_envelope(
+                message_id,
+                Some(envelope.message_id()),
+                None,
+            )))?;
+        Ok(())
+    }
+
     fn connection_state(&self, connection_id: ConnectionId) -> Result<ConnectionState> {
         let connections = self.connections.read();
         let connection = connections

crates/rpc/src/proto.rs

@@ -42,6 +42,8 @@ pub trait AnyTypedEnvelope: 'static + Send + Sync {
     fn into_any(self: Box<Self>) -> Box<dyn Any + Send + Sync>;
     fn is_background(&self) -> bool;
     fn original_sender_id(&self) -> Option<PeerId>;
+    fn sender_id(&self) -> ConnectionId;
+    fn message_id(&self) -> u32;
 }
 
 pub enum MessagePriority {
@@ -73,6 +75,14 @@ impl<T: EnvelopedMessage> AnyTypedEnvelope for TypedEnvelope<T> {
     fn original_sender_id(&self) -> Option<PeerId> {
         self.original_sender_id
     }
+
+    fn sender_id(&self) -> ConnectionId {
+        self.sender_id
+    }
+
+    fn message_id(&self) -> u32 {
+        self.message_id
+    }
 }
 
 impl PeerId {