Fix backfill auth events

synapse/handlers/federation.py

@@ -335,18 +335,35 @@ class FederationHandler(BaseHandler):
             state_events.update({s.event_id: s for s in state})
             events_to_state[e_id] = state
 
-        seen_events = yield self.store.have_events(
-            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
+            a_id
+            for event in events + state_events.values() + auth_events.values()
+            for a_id, _ in event.auth_events
+        )
+        auth_events.update({
+            e_id: event_map[e_id] for e_id in required_auth if e_id in event_map
+        })
+        missing_auth = required_auth - set(auth_events)
+        failed_to_fetch = set()
+
+        # Try and fetch any missing auth events from both DB and remote servers.
+        # We repeatedly do this until we stop finding new auth events.
+        while missing_auth - failed_to_fetch:
+            logger.info("Missing auth for backfill: %r", missing_auth)
+            ret_events = yield self.store.get_events(missing_auth - failed_to_fetch)
+            auth_events.update(ret_events)
+
+            required_auth.update(
+                a_id for event in ret_events.values() for a_id, _ in event.auth_events
+            )
+            missing_auth = required_auth - set(auth_events)
+
+            if missing_auth - failed_to_fetch:
+                logger.info(
+                    "Fetching missing auth for backfill: %r",
+                    missing_auth - failed_to_fetch
                 )
 
-        missing_auth = required_auth - set(auth_events)
-        if missing_auth:
-            logger.info("Missing auth for backfill: %r", missing_auth)
                 results = yield defer.gatherResults(
                     [
                         self.replication_layer.get_pdu(
@@ -355,11 +372,21 @@ class FederationHandler(BaseHandler):
                             outlier=True,
                             timeout=10000,
                         )
-                    for event_id in missing_auth
+                        for event_id in missing_auth - failed_to_fetch
                     ],
                     consumeErrors=True
                 ).addErrback(unwrapFirstError)
                 auth_events.update({a.event_id: a for a in results})
+                required_auth.update(
+                    a_id for event in results for a_id, _ in event.auth_events
+                )
+                missing_auth = required_auth - set(auth_events)
+
+                failed_to_fetch = missing_auth - set(auth_events)
+
+        seen_events = yield self.store.have_events(
+            set(auth_events.keys()) | set(state_events.keys())
+        )
 
         ev_infos = []
         for a in auth_events.values():
@@ -372,6 +399,7 @@ class FederationHandler(BaseHandler):
                     (auth_events[a_id].type, auth_events[a_id].state_key):
                     auth_events[a_id]
                     for a_id, _ in a.auth_events
+                    if a_id in auth_events
                 }
             })
 
@@ -383,6 +411,7 @@ class FederationHandler(BaseHandler):
                     (auth_events[a_id].type, auth_events[a_id].state_key):
                     auth_events[a_id]
                     for a_id, _ in event_map[e_id].auth_events
+                    if a_id in auth_events
                 }
             })