code: func ReadClientData(rw io.ReadWriter) ([]byte, ws.OpCode, error) {
  	return ReadData(rw, ws.StateServerSide)
  }
docs: // ReadClientData reads next data message from rw, considering that caller
  // represents server side. It is a shortcut for ReadData(rw, ws.StateServerSide).
  //
  // Note this may handle and write control frames into the writer part of a
  // given io.ReadWriter.