Miniscule FTP protocol

Flow of events

The client and server now take turns exchanging messages, with the client making a request and the server sending a response.

Request/Response syntax

Request/Response semantics

1. LST To request a list of available files, the client sends the six characters "LST <CR><LF>". In response, the server first sends the "LST " code (including exactly one space character), followed immediately by a two-byte big-endian integer indicating the number of bytes in the listing. Note that this two-byte integer is not an ASCII representation of an integer, but rather a 16-bit unsigned binary integer. Finally, the server sends the listing itself.
2. GET To request a file, the client send the "GET " code followed by the name of the requested file, followed by <CR><LF>. In response, the server sends the "FIL " code followed by a two-byte integer indicating the number of bytes in the file, followed by the file.
3. BYE To close the connection, the client sends the six characters "BYE <CR><LF>". The server sends no reply.
4. ERR If the server is unable to comply with the client's request, it sends back the "ERR " code followed by a three-uppercase-letter error type, followed by "<CR><LF>". At present, the only error types allowed are BFL (this "bad file" error occurs when the client asks for a file the server cannot or is unwilling to send) and HUH, which should be sent any other time the server can't figure out what to do.