1 files changed, 25 insertions, 9 deletions
diff --git a/synapse/handlers/search.py b/synapse/handlers/search.py
index 56ed262a1f..ef750d1497 100644
--- a/synapse/handlers/search.py
+++ b/synapse/handlers/search.py
@@ -21,7 +21,7 @@ from unpaddedbase64 import decode_base64, encode_base64
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, Membership
-from synapse.api.errors import SynapseError
+from synapse.api.errors import NotFoundError, SynapseError
 from synapse.api.filtering import Filter
 from synapse.storage.state import StateFilter
 from synapse.visibility import filter_events_for_client
@@ -37,6 +37,7 @@ class SearchHandler(BaseHandler):
         self._event_serializer = hs.get_event_client_serializer()
         self.storage = hs.get_storage()
         self.state_store = self.storage.state
+        self.auth = hs.get_auth()
 
     @defer.inlineCallbacks
     def get_old_rooms_from_upgraded_room(self, room_id):
@@ -53,23 +54,38 @@ class SearchHandler(BaseHandler):
             room_id (str): id of the room to search through.
 
         Returns:
-            Deferred[iterable[unicode]]: predecessor room ids
+            Deferred[iterable[str]]: predecessor room ids
         """
 
         historical_room_ids = []
 
-        while True:
-            predecessor = yield self.store.get_room_predecessor(room_id)
+        # The initial room must have been known for us to get this far
+        predecessor = yield self.store.get_room_predecessor(room_id)
 
-            # If no predecessor, assume we've hit a dead end
+        while True:
             if not predecessor:
+                # We have reached the end of the chain of predecessors
+                break
+
+            if not isinstance(predecessor.get("room_id"), str):
+                # This predecessor object is malformed. Exit here
+                break
+
+            predecessor_room_id = predecessor["room_id"]
+
+            # Don't add it to the list until we have checked that we are in the room
+            try:
+                next_predecessor_room = yield self.store.get_room_predecessor(
+                    predecessor_room_id
+                )
+            except NotFoundError:
+                # The predecessor is not a known room, so we are done here
                 break
 
-            # Add predecessor's room ID
-            historical_room_ids.append(predecessor["room_id"])
+            historical_room_ids.append(predecessor_room_id)
 
-            # Scan through the old room for further predecessors
-            room_id = predecessor["room_id"]
+            # And repeat
+            predecessor = next_predecessor_room
 
         return historical_room_ids