FTP extension: XSEN
FTP commands for sending text to a logged-in user or mailing it as a fallback.
Harrenstien, K., "FTP extension: XSEN", RFC 737, DOI 10.17487/RFC0737, October 1977, <https://www.rfc-editor.org/info/rfc737>.
@misc{rfc737,
series = {Request for Comments},
number = 737,
howpublished = {RFC 737},
publisher = {RFC Editor},
doi = {10.17487/RFC0737},
url = {https://www.rfc-editor.org/info/rfc737},
author = {K. Harrenstien},
title = {{FTP extension: XSEN}},
pagetotal = 1,
year = 1977,
month = oct,
} RFC text
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.
ISO Plain Language
On this page
§1Sending to a User's Terminal
Some systems had a SEND command or program that put a message directly on a user's terminal. SAIL and ITS had broadened this idea to reach users at other network sites, and their FTP servers added three commands with the same syntax as the existing MAIL command.
For MAIL, the sender gives a recipient name, then sends message text ending with a line containing only a period. The server returns a completion reply after the message text.
The extension takes a local feature that displays a message on a user's terminal and makes it available through FTP between network sites.
§2XSEN, XSEM and XMAS
XSEN means “Send to terminal.” It returns failure reply 453 if the addressee is not logged in or is refusing messages. XSEM means “Send, Mail if can't”; it returns notification reply 009 if direct sending cannot be done and an attempt is made to mail instead.
XMAS means “Mail And Send” and has no special replies. For XSEM and XMAS, mailing determines success, not direct sending.
XSEN only tries the terminal. XSEM falls back to mail if the user cannot be reached, while XMAS combines mailing and sending.
§3Short Messages Only
The RFC says there are no corresponding variants for MLFL. The author explains that messages sent this way are generally short and that the implementors did not want to add the extra work.
The extension therefore describes command behavior for message text through MAIL-style input, rather than adding the same send options for file-based mail.
The extension does not add MLFL versions of these commands. The authors considered this kind of terminal message generally short enough to use MAIL.