31 October 1977
FTP Extension: XSEN
This note describes an extension to the File Transfer Protocol which provides for "sending" a message to a logged-in user, as well as variants for mailing it normally whether the user is logged in or not.
Several systems have a SEND command or program which sends a message directly to a user's terminal. On the SAIL (SU-AI) and ITS (MIT-(AI/ML/MC/DMS)) systems the concept has been broadened to allow SEND'ing to users on other network sites; to support this, three new FTP commands were added which have a syntax identical to the existing MAIL command. For reference, the latter is:
MAIL <SP> <recipient name> <CRLF>
If accepted, returns 350 reply and considers all succeeding lines to be the message text, terminated by a line containing only a period, upon which a 256 completion reply is returned. Various errors are possible.
The new commands, with their special replies, are:
XSEN -- Send to terminal.
Returns 453 failure reply if the addressee is refusing or not logged in.
XSEM -- Send, Mail if can't.
Returns 009 notification reply if message cannot be SENT.
XMAS -- Mail And Send. (couldn't resist this one)
No special replies.
Note that for XSEM and XMAS, it is the mailing which determines success, not the SENDing, although XSEM as implemented uses a 009 reply (in addition to the normal success/failure code) to indicate that because the SEND failed, an attempt is being made to mail the message instead. There are no corresponding variants for MLFL, since messages transmitted in this way are generally short, and neither I nor Brian Harvey (implementing respectively the ITS and SAIL servers) wanted to bother.