Remove state events from /_synapse/admin/v1/rooms/<room_id>/context/<…

…event_id>

Real-world tests show that this API is too slow (and timeouts) because serialization
of state events can be extremely slow when there are too many state events, e.g.
in irc rooms.

Signed-off-by: David Teller <davidt@element.io>

changelog.d/9615.removal

@@ -0,0 +1 @@
+Remove state events from /_synapse/admin/v1/rooms/<room_id>/context/<event_id> for performance reasons.

docs/admin_api/rooms.md

@@ -606,6 +606,8 @@ GET /_synapse/admin/v1/rooms/<room_id>/context/<event_id>
 
 This API mimmicks [GET /_matrix/client/r0/rooms/{roomId}/context/{eventId}](https://matrix.org/docs/spec/client_server/r0.6.1#get-matrix-client-r0-rooms-roomid-context-eventid). Please refer to the link for all details on parameters and reseponse.
 
+The main difference is that this call does NOT return state events, for performance reasons.
+
 Example response:
 
 ```json
@@ -673,43 +675,5 @@ Example response:
     }
   ],
   "start": "t27-54_2_0_2",
-  "state": [
-    {
-      "content": {
-        "creator": "@example:example.org",
-        "room_version": "1",
-        "m.federate": true,
-        "predecessor": {
-          "event_id": "$something:example.org",
-          "room_id": "!oldroom:example.org"
-        }
-      },
-      "type": "m.room.create",
-      "event_id": "$143273582443PhrSn:example.org",
-      "room_id": "!636q39766251:example.com",
-      "sender": "@example:example.org",
-      "origin_server_ts": 1432735824653,
-      "unsigned": {
-        "age": 1234
-      },
-      "state_key": ""
-    },
-    {
-      "content": {
-        "membership": "join",
-        "avatar_url": "mxc://example.org/SEsfnsuifSDFSSEF",
-        "displayname": "Alice Margatroid"
-      },
-      "type": "m.room.member",
-      "event_id": "$143273582443PhrSn:example.org",
-      "room_id": "!636q39766251:example.com",
-      "sender": "@example:example.org",
-      "origin_server_ts": 1432735824653,
-      "unsigned": {
-        "age": 1234
-      },
-      "state_key": "@alice:example.org"
-    }
-  ]
 }
 ```

synapse/rest/admin/rooms.py

@@ -684,8 +684,5 @@ async def on_GET(
         results["events_after"] = await self._event_serializer.serialize_events(
             results["events_after"], time_now
         )
-        results["state"] = await self._event_serializer.serialize_events(
-            results["state"], time_now
-        )
 
         return 200, results