docs: def unpack(cls, msg, client, server, request_id):
          """Parse message and return an `OpInsert`.
  
          Takes the client message as bytes, the client and server socket objects,
          and the client request id.
          """
          flags, = _UNPACK_INT(msg[:4])
          namespace, pos = _get_c_string(msg, 4)
          docs = bson.decode_all(msg[pos:], CODEC_OPTIONS)
          return cls(*docs, namespace=namespace, flags=flags, _client=client,
                     request_id=request_id, _server=server)