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RFC 737 UNKNOWN FTP · MESSAGING

FTP extension: XSEN

Send a message directly to a user's terminal over FTP, or mail it if they are not logged in

On rfc-editor.org ↗
PUBLISHED
October 1977
AUTHORS
K. Harrenstien
STREAM
Legacy
DOI
10.17487/RFC0737

RFC text

Original text · RFC Editor View on rfc-editor.org ↗ 
NWG/RFC# 737                                         KLH 31 Oct 77 42217
Network Working Group                                     K. Harrenstien
Request for Comments: 737                                         SRI-KL
NIC: 42217                                               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.

AI ELI5

On this page
PROBLEMOn some systems, users could send messages directly to someone else's terminal if they were logged in, but this only worked locally. Extending this across the network required new FTP commands.
MECHANISMThe XSEN extension adds three new FTP commands with the same syntax as the existing MAIL command: XSEN (send to terminal only), XSEM (send, mail if can't), and XMAS (mail and send). The server returns different reply codes depending on success and whether the message was sent versus mailed.
EARLY REMOTE MESSAGINGInter-system message sending became possible on systems with the extension, though implementations on ITS and SAIL were limited to short messages and did not extend to MLFL (mail file) mode.

§1Remote Terminal Messaging

Several computers in the network—notably SAIL (SU-AI) and ITS systems at MIT—had a local SEND command that could dispatch a message directly to a user's terminal. RFC 737 extends this idea to the network: three new FTP commands allow sending messages between sites.

The commands have the same syntax as the existing MAIL command, making them familiar to implementors already using FTP for mail.

The RFC adds new commands to FTP so one computer can push a message straight to someone's terminal on another computer.

§2The Three New Commands

XSEN sends a message directly to the recipient's terminal. If the user is not logged in or is refusing messages, the server returns a 453 failure reply.

XSEM (Send, Mail if can't) attempts to send the message to the terminal, but if that fails, it falls back to mailing the message. It returns a 009 notification reply if the send failed but the mail succeeded.

XMAS (Mail And Send) does both: it attempts to send to the terminal and also mails the message, with no special distinction between success modes. The humor in the name was intentional.

XSEN tries to put it on someone's screen. XSEM tries the screen first, then emails it. XMAS does both. Each has different reply codes to say what happened.

§3Implementation Constraints

These commands are designed for short messages only. The RFC notes that neither the ITS nor SAIL implementations provides variants for MLFL (mail file), because the extended messages from MLFL mode are too large for this use case. The design prioritizes simplicity and the interactive, conversational nature of terminal messages over bulk message handling.

These commands work best for quick notes, not long files. That is why they did not add support for the bigger message mode.

§4References

[RFC959]RFC 959Postel, J. and Reynolds, J., "File Transfer Protocol", STD 9, RFC 959, October 1985.October 1985