  explicit HandshakeCallback(
      ReadCallbackBase* rcb,
      ExpectType expect = EXPECT_SUCCESS)
      : state(STATE_WAITING), rcb_(rcb), expect_(expect) {}
  explicit HandshakeCallback(
      ReadCallbackBase* rcb,
      ExpectType expect = EXPECT_SUCCESS)
      : state(STATE_WAITING), rcb_(rcb), expect_(expect) {}