Be more careful which errors we send back over the C-S API

We really shouldn't be sending all CodeMessageExceptions back over the C-S API;
it will include things like 401s which we shouldn't proxy.

That means that we need to explicitly turn a few HttpResponseExceptions into
SynapseErrors in the federation layer.

The effect of the latter is that the matrix errcode will get passed through
correctly to calling clients, which might help with some of the random
M_UNKNOWN errors when trying to join rooms.

synapse/api/errors.py

@@ -69,9 +69,6 @@ class CodeMessageException(RuntimeError):
         self.code = code
         self.msg = msg
 
-    def error_dict(self):
-        return cs_error(self.msg)
-
 
 class MatrixCodeMessageException(CodeMessageException):
     """An error from a general matrix endpoint, eg. from a proxied Matrix API call.
@@ -308,14 +305,6 @@ class LimitExceededError(SynapseError):
         )
 
 
-def cs_exception(exception):
-    if isinstance(exception, CodeMessageException):
-        return exception.error_dict()
-    else:
-        logger.error("Unknown exception type: %s", type(exception))
-        return {}
-
-
 def cs_error(msg, code=Codes.UNKNOWN, **kwargs):
     """ Utility method for constructing an error response for client-server
     interactions.

synapse/federation/federation_client.py

@@ -488,7 +488,7 @@ class FederationClient(FederationBase):
             The [Deferred] result of callback, if it succeeds
 
         Raises:
-            CodeMessageException if the chosen remote server returns a 300/400 code.
+            SynapseError if the chosen remote server returns a 300/400 code.
 
             RuntimeError if no servers were reachable.
         """
@@ -504,9 +504,9 @@ class FederationClient(FederationBase):
                     "Failed to %s via %s: %s",
                     description, destination, e,
                 )
-            except CodeMessageException as e:
+            except HttpResponseException as e:
                 if not 500 <= e.code < 600:
-                    raise
+                    raise SynapseError.from_http_response_exception(e)
                 else:
                     logger.warn(
                         "Failed to %s via %s: %i %s",
@@ -543,7 +543,7 @@ class FederationClient(FederationBase):
             Deferred: resolves to a tuple of (origin (str), event (object))
             where origin is the remote homeserver which generated the event.
 
-            Fails with a ``CodeMessageException`` if the chosen remote server
+            Fails with a ``SynapseError`` if the chosen remote server
             returns a 300/400 code.
 
             Fails with a ``RuntimeError`` if no servers were reachable.
@@ -599,7 +599,7 @@ class FederationClient(FederationBase):
             giving the serer the event was sent to, ``state`` (?) and
             ``auth_chain``.
 
-            Fails with a ``CodeMessageException`` if the chosen remote server
+            Fails with a ``SynapseError`` if the chosen remote server
             returns a 300/400 code.
 
             Fails with a ``RuntimeError`` if no servers were reachable.
@@ -673,12 +673,17 @@ class FederationClient(FederationBase):
     @defer.inlineCallbacks
     def send_invite(self, destination, room_id, event_id, pdu):
         time_now = self._clock.time_msec()
+        try:
             code, content = yield self.transport_layer.send_invite(
                 destination=destination,
                 room_id=room_id,
                 event_id=event_id,
                 content=pdu.get_pdu_json(time_now),
             )
+        except HttpResponseException as e:
+            if e.code == 403:
+                raise SynapseError.from_http_response_exception(e)
+            raise
 
         pdu_dict = content["event"]
 
@@ -709,7 +714,7 @@ class FederationClient(FederationBase):
         Return:
             Deferred: resolves to None.
 
-            Fails with a ``CodeMessageException`` if the chosen remote server
+            Fails with a ``SynapseError`` if the chosen remote server
             returns a 300/400 code.
 
             Fails with a ``RuntimeError`` if no servers were reachable.

synapse/http/server.py

@@ -36,7 +36,6 @@ from synapse.api.errors import (
     Codes,
     SynapseError,
     UnrecognizedRequestError,
-    cs_exception,
 )
 from synapse.http.request_metrics import requests_counter
 from synapse.util.caches import intern_dict
@@ -77,16 +76,13 @@ def wrap_json_request_handler(h):
     def wrapped_request_handler(self, request):
         try:
             yield h(self, request)
-        except CodeMessageException as e:
+        except SynapseError as e:
             code = e.code
-            if isinstance(e, SynapseError):
             logger.info(
                 "%s SynapseError: %s - %s", request, code, e.msg
             )
-            else:
-                logger.exception(e)
             respond_with_json(
-                request, code, cs_exception(e), send_cors=True,
+                request, code, e.error_dict(), send_cors=True,
                 pretty_print=_request_user_agent_is_curl(request),
             )