Don't 500 when trying to exchange a revoked 3PID invite

changelog.d/6147.bugfix

@@ -0,0 +1 @@
+Don't 500 when trying to exchange a revoked 3PID invite.

synapse/handlers/federation.py

@@ -2570,7 +2570,7 @@ def on_exchange_third_party_invite_request(self, room_id, event_dict):
         )
 
         try:
-            self.auth.check_from_context(room_version, event, context)
+            yield self.auth.check_from_context(room_version, event, context)
         except AuthError as e:
             logger.warn("Denying third party invite %r because %s", event, e)
             raise e
@@ -2599,8 +2599,21 @@ def add_display_name_to_third_party_invite(
                 original_invite_id, allow_none=True
             )
         if original_invite:
-            display_name = original_invite.content["display_name"]
-            event_dict["content"]["third_party_invite"]["display_name"] = display_name
+            # If the m.room.third_party_invite event's content is empty, it means the
+            # invite has been revoked.
+            if original_invite.content:
+                display_name = original_invite.content["display_name"]
+                event_dict["content"]["third_party_invite"][
+                    "display_name"
+                ] = display_name
+            else:
+                # Don't discard or raise an error here because that's not the right place
+                # to do auth checks. The auth check will fail on this invite because we
+                # won't be able to fetch public keys from the m.room.third_party_invite
+                # event's content (because it's empty).
+                logger.info(
+                    "Found invite event for third_party_invite but it has been revoked"
+                )
         else:
             logger.info(
                 "Could not find invite event for third_party_invite: %r", event_dict

tests/handlers/test_federation.py

@@ -0,0 +1,81 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from synapse.api.constants import EventTypes
+from synapse.api.errors import AuthError, Codes
+from synapse.rest import admin
+from synapse.rest.client.v1 import login, room
+
+from tests import unittest
+
+
+class FederationTestCase(unittest.HomeserverTestCase):
+    servlets = [
+        admin.register_servlets,
+        login.register_servlets,
+        room.register_servlets,
+    ]
+
+    def make_homeserver(self, reactor, clock):
+        hs = self.setup_test_homeserver(http_client=None)
+        self.handler = hs.get_handlers().federation_handler
+        self.store = hs.get_datastore()
+        return hs
+
+    def test_exchange_revoked_invite(self):
+        user_id = self.register_user("kermit", "test")
+        tok = self.login("kermit", "test")
+
+        room_id = self.helper.create_room_as(room_creator=user_id, tok=tok)
+
+        # Send a 3PID invite event with an empty body so it's considered as a revoked one.
+        invite_token = "sometoken"
+        self.helper.send_state(
+            room_id=room_id,
+            event_type=EventTypes.ThirdPartyInvite,
+            state_key=invite_token,
+            body={},
+            tok=tok,
+        )
+
+        d = self.handler.on_exchange_third_party_invite_request(
+            room_id=room_id,
+            event_dict={
+                "type": EventTypes.Member,
+                "room_id": room_id,
+                "sender": user_id,
+                "state_key": "@someone:example.org",
+                "content": {
+                    "membership": "invite",
+                    "third_party_invite": {
+                        "display_name": "alice",
+                        "signed": {
+                            "mxid": "@alice:localhost",
+                            "token": invite_token,
+                            "signatures": {
+                                "magic.forest": {
+                                    "ed25519:3": "fQpGIW1Snz+pwLZu6sTy2aHy/DYWWTspTJRPyNp0PKkymfIsNffysMl6ObMMFdIJhk6g6pwlIqZ54rxo8SLmAg"
+                                }
+                            },
+                        },
+                    },
+                },
+            },
+        )
+
+        failure = self.get_failure(d, AuthError).value
+
+        self.assertEqual(failure.code, 403, failure)
+        self.assertEqual(failure.errcode, Codes.FORBIDDEN, failure)
+        self.assertEqual(failure.msg, "You are not invited to this room.")