Telnet X display location option
A Telnet option that lets a client tell the remote host where the user's X display is.
Marcy, G.A., "Telnet X display location option", RFC 1096, DOI 10.17487/RFC1096, March 1989, <https://www.rfc-editor.org/info/rfc1096>.
@misc{rfc1096,
series = {Request for Comments},
number = 1096,
howpublished = {RFC 1096},
publisher = {RFC Editor},
doi = {10.17487/RFC1096},
url = {https://www.rfc-editor.org/info/rfc1096},
author = {G.A. Marcy},
title = {{Telnet X display location option}},
pagetotal = 3,
year = 1989,
month = mar,
} RFC text
Contents
Network Working Group G. Marcy
Request for Comments: 1096 Carnegie Mellon University
March 1989
Telnet X Display Location Option
Status of This Memo
This RFC specifies a standard for the Internet community. Hosts on
the Internet that transmit the X display location within the Telnet
protocol are expected to adopt and implement this standard.
Distribution of this memo is unlimited.
This standard is modelled on RFC 1079 [1], the telnet terminal speed
option. Much of the text of this document is copied from that RFC.
Motivation
When a user is running the Telnet client under the X window system,
it is useful for the remote Telnet to know the X display location of
that client. For example, the user might wish to start other X
applications from the remote host using the same display location as
the Telnet client. The purpose of this option is to make this
information available through telnet connections.
1. Command Name and Code
X-DISPLAY-LOCATION (XDISPLOC)
Code = 35
2. Command Meanings
IAC WILL X-DISPLAY-LOCATION
Sender is willing to send the X display location in a
subsequent sub-negotiation.
IAC WON'T X-DISPLAY-LOCATION
Sender refuses to send the X display location.
IAC DO X-DISPLAY-LOCATION
Sender is willing to receive the X display location in a
subsequent sub-negotiation.
IAC DON'T X-DISPLAY-LOCATION
Sender refuses to accept the X display location.
IAC SB X-DISPLAY-LOCATION SEND IAC SE
Sender requests receiver to transmit his (the receiver's) X
display location. The code for SEND is 1. (See below.)
IAC SB X-DISPLAY-LOCATION IS ... IAC SE
Sender is stating his X display location. The code for IS is
0. (See below.)
3. Default
WON'T X-DISPLAY-LOCATION
The X display location will not be exchanged.
DON'T X-DISPLAY-LOCATION
The X display location will not be exchanged.
4. Description of the Option
WILL and DO are used only to obtain and grant permission for future
discussion. The actual exchange of status information occurs within
option subcommands (IAC SB X-DISPLAY-LOCATION...).
Once the two hosts have exchanged a WILL and a DO, the sender of the
DO X-DISPLAY-LOCATION is free to request the X display location.
Only the sender of the DO may send requests (IAC SB X-DISPLAY-
LOCATION SEND IAC SE) and only the sender of the WILL may transmit
actual X display location (within an IAC SB X-DISPLAY-LOCATION IS ...
IAC SE command). The X display location may not be sent
spontaneously, but only in response to a request.
The X display location is an NVT ASCII string. This string follows
the normal Unix convention used for the DISPLAY environment variable,
e.g.,
<host>:<dispnum>[.<screennum>]
No extraneous characters such as spaces may be included.
The following is an example of use of the option:
Host1: IAC DO X-DISPLAY-LOCATION
Host2: IAC WILL X-DISPLAY-LOCATION
(Host1 is now free to request status information at any time.)
Host1: IAC SB X-DISPLAY-LOCATION SEND IAC SE
Host2: IAC SB X-DISPLAY-LOCATION IS "SRI-NIC.ARPA:0.0" IAC SE
(This command is 22 octets.)
5. Implementation Suggestions
Since the X display location may not contain a hostname on the client
host, i.e., ":0" or "unix:0.0", the Telnet client will need to modify
the location appropriately before sending it on to the remote Telnet.
Reference
[1] Hedrick, C., "Telnet Terminal Speed Option", RFC 1079,
Rutgers University, December, 1988.
Author's Address:
Glenn A. Marcy
Carnegie Mellon University
School of Computer Science
Pittsburgh, PA 15213-3890
Phone: (412) 268-7669
Email: Glenn.Marcy@CS.CMU.EDU
AI ELI5
On this page
§1Why Share the Display Location
When a user runs the Telnet client under the X window system, the remote Telnet benefits from knowing that client's X display location. The user might want to start other X applications from the remote host on the same display. This option makes that information available through Telnet connections.
It is modelled on the terminal speed option in RFC 1079, and much of its text is copied from that RFC.
If you start a program far away, it needs to know which screen to show up on. This option tells it.
§2Commands and Negotiation
The option is named X-DISPLAY-LOCATION (XDISPLOC) and has code 35. The usual WILL, WON'T, DO and DON'T commands are used. WILL and DO only obtain and grant permission. The default is WON'T and DON'T, so the location is not exchanged unless both sides agree.
After a WILL and a DO, the side that sent DO may ask for the location with IAC SB X-DISPLAY-LOCATION SEND IAC SE (SEND is code 1). Only the sender of the WILL may answer with IAC SB X-DISPLAY-LOCATION IS ... IAC SE (IS is code 0). The location may not be sent spontaneously, only in response to a request.
First both sides agree they will talk about it. Then one asks, "where is your screen?" and the other answers. Nobody blurts it out unasked.
- IAC DO X-DISPLAY-LOCATION
- IAC WILL X-DISPLAY-LOCATION
- IAC SB X-DISPLAY-LOCATION SEND IAC SE
- IAC SB X-DISPLAY-LOCATION IS "SRI-NIC.ARPA:0.0" IAC SE
§3The Location String
The location is an NVT ASCII string in the normal Unix DISPLAY convention: <host>:<dispnum>[.<screennum>]. No extraneous characters, such as spaces, may be included.
The RFC's example has Host2 answer with "SRI-NIC.ARPA:0.0", a command of 22 octets. It also notes that a local location such as :0 or unix:0.0 lacks a hostname, so the Telnet client must modify it appropriately before sending it on.
The answer is a short line of text like an address: which computer, which display, and which screen.