Function state_snapshots 

async fn state_snapshots(
    services: &Services,
    room_id: &RoomId,
    __arg2: StateSelection<'_>,
    compared: bool,
) -> (Option<ShortStateHash>, Option<(PduCount, ShortStateHash)>)

The room’s current snapshot and the base a delta compares requested state with.

The current snapshot is read before any state key, so a change racing the read is sent again rather than lost. The base is the snapshot the room’s required state was last delivered from, or without one, the snapshot before the first event past the cursor.