diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index a6d54ee4b8..dafcfa89fb 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -88,6 +88,10 @@ if TYPE_CHECKING:
logger = logging.getLogger(__name__)
+# Logging for https://github.com/matrix-org/matrix-spec/issues/1209 and
+# https://github.com/element-hq/synapse/issues/16940
+client_state_desync_logger = logging.getLogger("synapse.client_state_desync_debug")
+
# Counts the number of times we returned a non-empty sync. `type` is one of
# "initial_sync", "full_state_sync" or "incremental_sync", `lazy_loaded` is
# "true" or "false" depending on if the request asked for lazy loaded members or
@@ -1214,6 +1218,12 @@ class SyncHandler:
previous_timeline_end={},
lazy_load_members=lazy_load_members,
)
+
+ if client_state_desync_logger.isEnabledFor(logging.DEBUG):
+ await self._log_client_state_desync(
+ room_id, None, state_ids, timeline_state, lazy_load_members
+ )
+
return state_ids
async def _compute_state_delta_for_incremental_sync(
@@ -1359,6 +1369,15 @@ class SyncHandler:
lazy_load_members=lazy_load_members,
)
+ if client_state_desync_logger.isEnabledFor(logging.DEBUG):
+ await self._log_client_state_desync(
+ room_id,
+ since_token,
+ state_ids,
+ timeline_state,
+ lazy_load_members,
+ )
+
return state_ids
async def _find_missing_partial_state_memberships(
@@ -1475,6 +1494,125 @@ class SyncHandler:
return additional_state_ids
+ async def _log_client_state_desync(
+ self,
+ room_id: str,
+ since_token: Optional[StreamToken],
+ sync_response_state_state: StateMap[str],
+ sync_response_timeline_state: StateMap[str],
+ lazy_load_members: bool,
+ ) -> None:
+ """
+ Logging to see how often the client's state gets out of sync with the
+ actual current state of the room.
+
+ There are few different potential failure modes here:
+
+ * State resolution can cause changes in the state of the room that don't
+ directly correspond to events with the corresponding (type, state_key).
+ https://github.com/matrix-org/matrix-spec/issues/1209 discusses this in
+ more detail.
+
+ * Even where there is an event that causes a given state change, Synapse
+ may not serve it to the client, since it works on state at specific points
+ in the DAG, rather than "current state".
+ See https://github.com/element-hq/synapse/issues/16940.
+
+ * Lazy-loading adds more complexity, as it means that events that would
+ normally be served via the `state` part of an incremental sync are filtered
+ out.
+
+ To try to get a handle on this, let's put ourselves in the shoes of a client,
+ and compare the state they will calculate against the actual current state.
+ """
+ # We only care about membership events.
+ state_filter = StateFilter.from_types(types=(("m.room.member", None),))
+
+ if since_token is None:
+ if lazy_load_members:
+ # For initial syncs with lazy-loading enabled, there's not too much
+ # concern here. We know the client will do a `/members` query before
+ # doing any encryption, so what sync returns isn't too important.
+ #
+ # (Of course, then `/members` might also return an incomplete list, but
+ # that's a separate problem.)
+ return
+
+ # For regular initial syncs, compare the returned response with the actual
+ # current state.
+ client_calculated_state = {}
+ client_calculated_state.update(sync_response_state_state)
+ client_calculated_state.update(sync_response_timeline_state)
+ else:
+ # For an incremental (gappy or otherwise) sync, let's assume the client has
+ # a complete membership list as of the last sync (or rather, at
+ # `since_token`, which is the closest approximation we have to it
+ # right now), and see what they would calculate as the current state given
+ # this sync update.
+
+ client_calculated_state = dict(
+ await self.get_state_at(
+ room_id,
+ stream_position=since_token,
+ state_filter=state_filter,
+ await_full_state=False,
+ )
+ )
+ client_calculated_state.update(sync_response_state_state)
+ client_calculated_state.update(sync_response_timeline_state)
+
+ current_state = await self._state_storage_controller.get_current_state_ids(
+ room_id, state_filter=state_filter, await_full_state=False
+ )
+ missing_users = await self._calculate_missing_members(
+ current_state, client_calculated_state
+ )
+ if missing_users:
+ client_state_desync_logger.debug(
+ "client state discrepancy in incremental sync in room %s: missing users %s",
+ room_id,
+ missing_users,
+ )
+
+ async def _calculate_missing_members(
+ self,
+ actual_state: StateMap[str],
+ client_calculated_state: StateMap[str],
+ ) -> List[str]:
+ """Helper for `_log_client_state_desync`: calculates the difference in
+ joined members between two state maps.
+
+ Returns:
+ A list of user IDs
+ """
+ missing_users = []
+
+ async def event_id_to_membership(event_id: Optional[str]) -> Optional[str]:
+ if event_id is None:
+ return None
+ event = await self.store.get_event(event_id, allow_none=True)
+ if event is None:
+ return "MISSING_EVENT"
+ return event.membership
+
+ # Check for joined members in the actual state that are missing or have a
+ # different membership in the actual state.
+ for (event_type, state_key), actual_event_id in actual_state.items():
+ if event_type != EventTypes.Member:
+ continue
+
+ calculated_event_id = client_calculated_state.get((event_type, state_key))
+ if calculated_event_id != actual_event_id:
+ actual_membership = event_id_to_membership(actual_event_id)
+ calculated_membership = event_id_to_membership(calculated_event_id)
+ if (
+ actual_membership == Membership.JOIN
+ and calculated_membership != Membership.JOIN
+ ):
+ missing_users.append(state_key)
+
+ return missing_users
+
async def unread_notifs_for_room_id(
self, room_id: str, sync_config: SyncConfig
) -> RoomNotifCounts:
|
