Factor out exception handling in federation_client

Factor out the error handling from make_membership_event, send_join, and
send_leave, so that it can be shared.

synapse/federation/federation_client.py

@@ -48,6 +48,13 @@ sent_queries_counter = Counter("synapse_federation_client_sent_queries", "", ["t
 PDU_RETRY_TIME_MS = 1 * 60 * 1000
 
 
+class InvalidResponseError(RuntimeError):
+    """Helper for _try_destination_list: indicates that the server returned a response
+    we couldn't parse
+    """
+    pass
+
+
 class FederationClient(FederationBase):
     def __init__(self, hs):
         super(FederationClient, self).__init__(hs)
@@ -458,6 +465,61 @@ class FederationClient(FederationBase):
         defer.returnValue(signed_auth)
 
     @defer.inlineCallbacks
+    def _try_destination_list(self, description, destinations, callback):
+        """Try an operation on a series of servers, until it succeeds
+
+        Args:
+            description (unicode): description of the operation we're doing, for logging
+
+            destinations (Iterable[unicode]): list of server_names to try
+
+            callback (callable):  Function to run for each server. Passed a single
+                argument: the server_name to try. May return a deferred.
+
+                If the callback raises a CodeMessageException with a 300/400 code,
+                attempts to perform the operation stop immediately and the exception is
+                reraised.
+
+                Otherwise, if the callback raises an Exception the error is logged and the
+                next server tried. Normally the stacktrace is logged but this is
+                suppressed if the exception is an InvalidResponseError.
+
+        Returns:
+            The [Deferred] result of callback, if it succeeds
+
+        Raises:
+            CodeMessageException if the chosen remote server returns a 300/400 code.
+
+            RuntimeError if no servers were reachable.
+        """
+        for destination in destinations:
+            if destination == self.server_name:
+                continue
+
+            try:
+                res = yield callback(destination)
+                defer.returnValue(res)
+            except InvalidResponseError as e:
+                logger.warn(
+                    "Failed to %s via %s: %s",
+                    description, destination, e,
+                )
+            except CodeMessageException as e:
+                if not 500 <= e.code < 600:
+                    raise
+                else:
+                    logger.warn(
+                        "Failed to %s via %s: %i %s",
+                        description, destination, e.code, e.message,
+                    )
+            except Exception:
+                logger.warn(
+                    "Failed to %s via %s",
+                    description, destination, exc_info=1,
+                )
+
+        raise RuntimeError("Failed to %s via any server", description)
+
     def make_membership_event(self, destinations, room_id, user_id, membership,
                               content={},):
         """
@@ -492,11 +554,9 @@ class FederationClient(FederationBase):
                 "make_membership_event called with membership='%s', must be one of %s" %
                 (membership, ",".join(valid_memberships))
             )
-        for destination in destinations:
-            if destination == self.server_name:
-                continue
 
-            try:
+        @defer.inlineCallbacks
+        def send_request(destination):
             ret = yield self.transport_layer.make_membership_event(
                 destination, room_id, user_id, membership
             )
@@ -518,24 +578,11 @@ class FederationClient(FederationBase):
             defer.returnValue(
                 (destination, ev)
             )
-                break
-            except CodeMessageException as e:
-                if not 500 <= e.code < 600:
-                    raise
-                else:
-                    logger.warn(
-                        "Failed to make_%s via %s: %s",
-                        membership, destination, e.message
-                    )
-            except Exception as e:
-                logger.warn(
-                    "Failed to make_%s via %s: %s",
-                    membership, destination, e.message
+
+        return self._try_destination_list(
+            "make_" + membership, destinations, send_request,
         )
 
-        raise RuntimeError("Failed to send to any server.")
-
-    @defer.inlineCallbacks
     def send_join(self, destinations, pdu):
         """Sends a join event to one of a list of homeservers.
 
@@ -558,11 +605,8 @@ class FederationClient(FederationBase):
             Fails with a ``RuntimeError`` if no servers were reachable.
         """
 
-        for destination in destinations:
-            if destination == self.server_name:
-                continue
-
-            try:
+        @defer.inlineCallbacks
+        def send_request(destination):
             time_now = self._clock.time_msec()
             _, content = yield self.transport_layer.send_join(
                 destination=destination,
@@ -624,21 +668,7 @@ class FederationClient(FederationBase):
                 "auth_chain": signed_auth,
                 "origin": destination,
             })
-            except CodeMessageException as e:
-                if not 500 <= e.code < 600:
-                    raise
-                else:
-                    logger.exception(
-                        "Failed to send_join via %s: %s",
-                        destination, e.message
-                    )
-            except Exception as e:
-                logger.exception(
-                    "Failed to send_join via %s: %s",
-                    destination, e.message
-                )
-
-        raise RuntimeError("Failed to send to any server.")
+        return self._try_destination_list("send_join", destinations, send_request)
 
     @defer.inlineCallbacks
     def send_invite(self, destination, room_id, event_id, pdu):
@@ -663,7 +693,6 @@ class FederationClient(FederationBase):
 
         defer.returnValue(pdu)
 
-    @defer.inlineCallbacks
     def send_leave(self, destinations, pdu):
         """Sends a leave event to one of a list of homeservers.
 
@@ -681,15 +710,12 @@ class FederationClient(FederationBase):
             Deferred: resolves to None.
 
             Fails with a ``CodeMessageException`` if the chosen remote server
-            returns a non-200 code.
+            returns a 300/400 code.
 
             Fails with a ``RuntimeError`` if no servers were reachable.
         """
-        for destination in destinations:
-            if destination == self.server_name:
-                continue
-
-            try:
+        @defer.inlineCallbacks
+        def send_request(destination):
             time_now = self._clock.time_msec()
             _, content = yield self.transport_layer.send_leave(
                 destination=destination,
@@ -700,15 +726,8 @@ class FederationClient(FederationBase):
 
             logger.debug("Got content: %s", content)
             defer.returnValue(None)
-            except CodeMessageException:
-                raise
-            except Exception as e:
-                logger.exception(
-                    "Failed to send_leave via %s: %s",
-                    destination, e.message
-                )
 
-        raise RuntimeError("Failed to send to any server.")
+        return self._try_destination_list("send_leave", destinations, send_request)
 
     def get_public_rooms(self, destination, limit=None, since_token=None,
                          search_filter=None, include_all_networks=False,