Handle outliers in /federation/v1/event

Author: richvdh

synapse/handlers/federation.py

@@ -1029,19 +1029,24 @@ async def get_persisted_pdu(
             event_id, allow_none=True, allow_rejected=True
         )
 
-        if event:
-            in_room = await self._event_auth_handler.check_host_in_room(
-                event.room_id, origin
-            )
-            if not in_room:
-                raise AuthError(403, "Host not in room.")
+        if not event:
+            return None
 
-            events = await filter_events_for_server(self.storage, origin, [event])
-            event = events[0]
-            return event
-        else:
+        if event.internal_metadata.is_outlier():
+            # we can't tell if the requesting server can see this event, since
+            # we don't have the state at that point. Return a 404.
             return None
 
+        in_room = await self._event_auth_handler.check_host_in_room(
+            event.room_id, origin
+        )
+        if not in_room:
+            raise AuthError(403, "Host not in room.")
+
+        events = await filter_events_for_server(self.storage, origin, [event])
+        event = events[0]
+        return event
+
     async def on_get_missing_events(
         self,
         origin: str,