Do an early return when the two sets of auth events are the same.

Author: richvdh

synapse/handlers/federation_event.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import collections
 import itertools
 import logging
 from http import HTTPStatus
@@ -1536,6 +1537,14 @@ async def _check_event_auth(
         calculated_auth_event_ids = self._event_auth_handler.compute_auth_events(
             event, prev_state_ids, for_verification=True
         )
+
+        # if those are the same, we're done here.
+        if collections.Counter(event.auth_event_ids()) == collections.Counter(
+            calculated_auth_event_ids
+        ):
+            return context
+
+        # otherwise, re-run the auth checks based on what we calculated.
         calculated_auth_events = await self._store.get_events_as_list(
             calculated_auth_event_ids
         )