Handle the fact we might be missing auth events

synapse/handlers/federation.py

@@ -264,6 +264,7 @@ class FederationHandler(BaseHandler):
                 event_id=e_id
             )
             auth_events.update({a.event_id: a for a in auth})
+            auth_events.update({s.event_id: s for s in state})
             state_events.update({s.event_id: s for s in state})
             events_to_state[e_id] = state
 
@@ -271,6 +272,25 @@ class FederationHandler(BaseHandler):
             set(auth_events.keys()) | set(state_events.keys())
         )
 
+        all_events = events + state_events.values() + auth_events.values()
+        required_auth = set(
+            a_id for event in all_events for a_id, _ in event.auth_events
+        )
+
+        missing_auth = required_auth - set(auth_events)
+        results = yield defer.gatherResults(
+            [
+                self.replication_layer.get_pdu(
+                    [dest],
+                    event_id,
+                    outlier=True,
+                )
+                for event_id in missing_auth
+            ],
+            consumeErrors=True
+        ).addErrback(unwrapFirstError)
+        auth_events.update({a.event_id: a for a in results})
+
         yield defer.gatherResults(
             [
                 self._handle_new_event(
@@ -287,22 +307,6 @@ class FederationHandler(BaseHandler):
             consumeErrors=True,
         ).addErrback(unwrapFirstError)
 
-        yield defer.gatherResults(
-            [
-                self._handle_new_event(
-                    dest, s,
-                    auth_events={
-                        (auth_events[a_id].type, auth_events[a_id].state_key):
-                        auth_events[a_id]
-                        for a_id, _ in s.auth_events
-                    },
-                )
-                for s in state_events.values()
-                if s.event_id not in seen_events
-            ],
-            consumeErrors=True,
-        ).addErrback(unwrapFirstError)
-
         yield defer.gatherResults(
             [
                 self._handle_new_event(