Мне понравились ответы сервера в протоколе общения клиента с сервером программы cvs:
The possible server responses (each of which is followed by a linefeed) are the following.
I LOVE YOU The authentication is successful. The client proceeds with the cvs protocol itself. I HATE YOU The authentication fails. After sending this response, the server may close the connection. It is up to the server to decide whether to give this response, which is generic, or a more specific response using `E' and/or `error'.