Allow channel message handlers to short circuit

- a message handler can return logical True to prevent subsequent message handlers from running

Examples/Channel.py

@@ -152,7 +152,7 @@ def client_connected(link):
     # Register message types and add callback to channel
     channel = link.get_channel()
     channel.register_message_type(StringMessage)
-    channel.add_message_callback(server_message_received)
+    channel.add_message_handler(server_message_received)
 
 def client_disconnected(link):
     RNS.log("Client disconnected")
@@ -290,7 +290,7 @@ def link_established(link):
     # Register messages and add handler to channel
     channel = link.get_channel()
     channel.register_message_type(StringMessage)
-    channel.add_message_callback(client_message_received)
+    channel.add_message_handler(client_message_received)
 
     # Inform the user that the server is
     # connected

RNS/Channel.py

@@ -150,10 +150,13 @@ class Channel(contextlib.AbstractContextManager):
         return False
 
     def register_message_type(self, message_class: Type[MessageBase]):
+        with self._lock:
             if not issubclass(message_class, MessageBase):
-            raise ChannelException(CEType.ME_INVALID_MSG_TYPE, f"{message_class} is not a subclass of {MessageBase}.")
+                raise ChannelException(CEType.ME_INVALID_MSG_TYPE,
+                                       f"{message_class} is not a subclass of {MessageBase}.")
             if message_class.MSGTYPE is None:
-            raise ChannelException(CEType.ME_INVALID_MSG_TYPE, f"{message_class} has invalid MSGTYPE class attribute.")
+                raise ChannelException(CEType.ME_INVALID_MSG_TYPE,
+                                       f"{message_class} has invalid MSGTYPE class attribute.")
             try:
                 message_class()
             except Exception as ex:
@@ -162,14 +165,17 @@ class Channel(contextlib.AbstractContextManager):
 
             self._message_factories[message_class.MSGTYPE] = message_class
 
-    def add_message_callback(self, callback: MessageCallbackType):
+    def add_message_handler(self, callback: MessageCallbackType):
+        with self._lock:
             if callback not in self._message_callbacks:
                 self._message_callbacks.append(callback)
 
-    def remove_message_callback(self, callback: MessageCallbackType):
+    def remove_message_handler(self, callback: MessageCallbackType):
+        with self._lock:
             self._message_callbacks.remove(callback)
 
     def shutdown(self):
+        with self._lock:
             self._message_callbacks.clear()
             self.clear_rings()
 
@@ -205,19 +211,29 @@ class Channel(contextlib.AbstractContextManager):
                 env.tracked = False
                 self._rx_ring.remove(env)
 
+    def _run_callbacks(self, message: MessageBase):
+        with self._lock:
+            cbs = self._message_callbacks.copy()
+
+        for cb in cbs:
+            try:
+                if cb(message):
+                    return
+            except Exception as ex:
+                RNS.log(f"Channel: Error running message callback: {ex}", RNS.LOG_ERROR)
+
     def receive(self, raw: bytes):
         try:
             envelope = Envelope(outlet=self._outlet, raw=raw)
-            message = envelope.unpack(self._message_factories)
             with self._lock:
+                message = envelope.unpack(self._message_factories)
                 is_new = self.emplace_envelope(envelope, self._rx_ring)
                 self.prune_rx_ring()
             if not is_new:
                 RNS.log("Channel: Duplicate message received", RNS.LOG_DEBUG)
                 return
             RNS.log(f"Message received: {message}", RNS.LOG_DEBUG)
-            for cb in self._message_callbacks:
-                threading.Thread(target=cb, name="Message Callback", args=[message], daemon=True).start()
+            threading.Thread(target=self._run_callbacks, name="Message Callback", args=[message], daemon=True).start()
         except Exception as ex:
             RNS.log(f"Channel: Error receiving data: {ex}")
 

tests/channel.py

@@ -245,13 +245,49 @@ class TestChannel(unittest.TestCase):
         self.assertEqual(MessageState.MSGSTATE_FAILED, packet.state)
         self.assertFalse(envelope.tracked)
 
+    def test_multiple_handler(self):
+        handler1_called = 0
+        handler1_return = True
+        handler2_called = 0
+
+        def handler1(msg: MessageBase):
+            nonlocal handler1_called, handler1_return
+            self.assertIsInstance(msg, MessageTest)
+            handler1_called += 1
+            return handler1_return
+
+        def handler2(msg: MessageBase):
+            nonlocal handler2_called
+            self.assertIsInstance(msg, MessageTest)
+            handler2_called += 1
+
+        message = MessageTest()
+        self.h.channel.register_message_type(MessageTest)
+        self.h.channel.add_message_handler(handler1)
+        self.h.channel.add_message_handler(handler2)
+        envelope = RNS.Channel.Envelope(self.h.outlet, message, sequence=0)
+        raw = envelope.pack()
+        self.h.channel.receive(raw)
+
+        self.assertEqual(1, handler1_called)
+        self.assertEqual(0, handler2_called)
+
+        handler1_return = False
+        envelope = RNS.Channel.Envelope(self.h.outlet, message, sequence=1)
+        raw = envelope.pack()
+        self.h.channel.receive(raw)
+
+        self.assertEqual(2, handler1_called)
+        self.assertEqual(1, handler2_called)
+
+
     def eat_own_dog_food(self, message: MessageBase, checker: typing.Callable[[MessageBase], None]):
         decoded: [MessageBase] = []
 
         def handle_message(message: MessageBase):
             decoded.append(message)
 
-        self.h.channel.add_message_callback(handle_message)
+        self.h.channel.add_message_handler(handle_message)
         self.assertEqual(len(self.h.outlet.packets), 0)
 
         envelope = self.h.channel.send(message)

tests/link.py

@@ -382,7 +382,7 @@ class TestLink(unittest.TestCase):
 
         channel = l1.get_channel()
         channel.register_message_type(MessageTest)
-        channel.add_message_callback(handle_message)
+        channel.add_message_handler(handle_message)
         channel.send(test_message)
 
         time.sleep(0.5)
@@ -466,7 +466,7 @@ def targets(yp=False):
             message.data = message.data + " back"
             channel.send(message)
         channel.register_message_type(MessageTest)
-        channel.add_message_callback(handle_message)
+        channel.add_message_handler(handle_message)
 
     m_rns = RNS.Reticulum("./tests/rnsconfig")
     id1 = RNS.Identity.from_bytes(bytes.fromhex(fixed_keys[0][0]))