issue #615: route a dead message to recipients when no reply is expected

mitogen/core.py

@@ -2112,8 +2112,8 @@ class MitogenProtocol(Protocol):
             return False
 
         if msg_len > self._router.max_message_size:
-            LOG.error('Maximum message size exceeded (got %d, max %d)',
-                      msg_len, self._router.max_message_size)
+            LOG.error('%r: Maximum message size exceeded (got %d, max %d)',
+                      self, msg_len, self._router.max_message_size)
             self.stream.on_disconnect(broker)
             return False
 
@@ -3191,28 +3191,55 @@ class Router(object):
             fn(Message.dead(self.respondent_disconnect_msg))
             del self._handle_map[handle]
 
-    def _maybe_send_dead(self, msg, reason, *args):
+    def _maybe_send_dead(self, unreachable, msg, reason, *args):
+        """
+        Send a dead message to either the original sender or the intended
+        recipient of `msg`, if the original sender was expecting a reply
+        (because its `reply_to` was set), otherwise assume the message is a
+        reply of some sort, and send the dead message to the original
+        destination.
+
+        :param bool unreachable:
+            If :data:`True`, the recipient is known to be dead or routing
+            failed due to a security precaution, so don't attempt to fallback
+            to sending the dead message to the recipient if the original sender
+            did not include a reply address.
+        :param mitogen.core.Message msg:
+            Message that triggered the dead message.
+        :param str reason:
+            Human-readable error reason.
+        :param tuple args:
+            Elements to interpolate with `reason`.
+        """
         if args:
             reason %= args
         LOG.debug('%r: %r is dead: %r', self, msg, reason)
         if msg.reply_to and not msg.is_dead:
             msg.reply(Message.dead(reason=reason), router=self)
+        elif not unreachable:
+            self._async_route(
+                Message.dead(
+                    dst_id=msg.dst_id,
+                    handle=msg.handle,
+                    reason=reason,
+                )
+            )
 
     def _invoke(self, msg, stream):
         # IOLOG.debug('%r._invoke(%r)', self, msg)
         try:
             persist, fn, policy, respondent = self._handle_map[msg.handle]
         except KeyError:
-            self._maybe_send_dead(msg, reason=self.invalid_handle_msg)
+            self._maybe_send_dead(True, msg, reason=self.invalid_handle_msg)
             return
 
         if respondent and not (msg.is_dead or
                                msg.src_id == respondent.context_id):
-            self._maybe_send_dead(msg, 'reply from unexpected context')
+            self._maybe_send_dead(True, msg, 'reply from unexpected context')
             return
 
         if policy and not policy(msg, stream):
-            self._maybe_send_dead(msg, self.refused_msg)
+            self._maybe_send_dead(True, msg, self.refused_msg)
             return
 
         if not persist:
@@ -3240,7 +3267,7 @@ class Router(object):
         _vv and IOLOG.debug('%r._async_route(%r, %r)', self, msg, in_stream)
 
         if len(msg.data) > self.max_message_size:
-            self._maybe_send_dead(msg, self.too_large_msg % (
+            self._maybe_send_dead(False, msg, self.too_large_msg % (
                 self.max_message_size,
             ))
             return
@@ -3275,14 +3302,14 @@ class Router(object):
             out_stream = self._stream_by_id.get(mitogen.parent_id)
 
         if out_stream is None:
-            self._maybe_send_dead(msg, self.no_route_msg,
+            self._maybe_send_dead(True, msg, self.no_route_msg,
                                   msg.dst_id, mitogen.context_id)
             return
 
         if in_stream and self.unidirectional and not \
                 (in_stream.protocol.is_privileged or
                  out_stream.protocol.is_privileged):
-            self._maybe_send_dead(msg, self.unidirectional_msg,
+            self._maybe_send_dead(True, msg, self.unidirectional_msg,
                 in_stream.protocol.remote_id,
                 out_stream.protocol.remote_id,
                 mitogen.context_id)

tests/router_test.py

@@ -11,6 +11,7 @@ import mitogen.core
 import mitogen.master
 import mitogen.parent
 import mitogen.utils
+from mitogen.core import b
 
 try:
     import Queue
@@ -258,6 +259,23 @@ class MessageSizeTest(testlib.BrokerMixin, testlib.TestCase):
 
         self.assertTrue(expect in logs.stop())
 
+    def test_remote_dead_message(self):
+        # Router should send dead message to original recipient when reply_to
+        # is unset.
+        router = self.klass(broker=self.broker, max_message_size=4096)
+
+        # Try function call. Receiver should be woken by a dead message sent by
+        # router due to message size exceeded.
+        child = router.local()
+        recv = mitogen.core.Receiver(router)
+
+        recv.to_sender().send(b('x') * 4097)
+        e = self.assertRaises(mitogen.core.ChannelError,
+            lambda: recv.get().unpickle()
+        )
+        expect = router.too_large_msg % (4096,)
+        self.assertEquals(e.args[0], expect)
+
     def test_remote_configured(self):
         router = self.klass(broker=self.broker, max_message_size=64*1024)
         remote = router.local()
@@ -510,7 +528,7 @@ class ShutdownTest(testlib.RouterMixin, testlib.TestCase):
             mitogen.context_id,
         ))
 
-    def test_disconnet_all(self):
+    def test_disconnect_all(self):
         l1 = self.router.local()
         l2 = self.router.local()