  explicit WriteCallbackBase(SendMsgParamsCallbackBase* mcb = nullptr)
      : state(STATE_WAITING),
        bytesWritten(0),
        exception(AsyncSocketException::UNKNOWN, "none"),
        mcb_(mcb) {}
  explicit WriteCallbackBase(SendMsgParamsCallbackBase* mcb = nullptr)
      : state(STATE_WAITING),
        bytesWritten(0),
        exception(AsyncSocketException::UNKNOWN, "none"),
        mcb_(mcb) {}