bug#66667: [PATCH] Socket forwarding in emacsclient --tramp-prefix example

[Peter Oliver <p.d.oliver@mavit.org.uk>]

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On Sat, 21 Oct 2023, Michael Albinus wrote:

> Think about routers, NAS systems, and alike, which aren't upgraded over
> years.

You’re right about these kinds of systems, of course, but the old example already left a lot as an exercise for the reader: it assumes that you’d suitably configured server-port and server-use-tcp, then somehow made ~/.emacs.d/server/server accessible to the client.  Deciding on a suitable ssh -R argument for TCP forwarding doesn’t seem like the hardest part.

So, I’m not certain that one and a half examples is better than one complete example, but, anyway, here’s an updated patch.

-- 
Peter Oliver

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From 067a516fa2d0020170b97602d93eb9f589086d01 Mon Sep 17 00:00:00 2001
From: Peter Oliver <git@mavit.org.uk>
Date: Sat, 21 Oct 2023 15:55:03 +0100
Subject: [PATCH] Socket forwarding in emacsclient --tramp-prefix example
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Previously, the emacsclient --tramp-prefix documentation suggested
using it in conjunction with a forwarded TCP port.  However, OpenSSH
has supported forwarding sockets since version 6.7 (released 2014), so
let’s suggest that instead.  Sockets require less manual configuration
than ports, are less likely to clash, and are more secure, so will be
a better choice for the majority of people looking to set up this
facility for the first time.

* doc/emacs/misc.texi (emacsclient Options): Suggest forwarding sockets.
---
 doc/emacs/misc.texi | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/doc/emacs/misc.texi b/doc/emacs/misc.texi
index a05b7f6c6ea..df206b00dcc 100644
--- a/doc/emacs/misc.texi
+++ b/doc/emacs/misc.texi
@@ -2158,8 +2158,9 @@ emacsclient Options
 Set the prefix to add to filenames for Emacs to locate files on remote
 machines (@pxref{Remote Files}) using TRAMP (@pxref{Top, The Tramp
 Manual,, tramp, The Tramp Manual}).  This is mostly useful in
-combination with using the Emacs server over TCP (@pxref{TCP Emacs
-server}).  By ssh-forwarding the listening port and making the
+combination with using the Emacs server from a remote host.  By
+ssh-forwarding the listening socket, or ssh-forwarding the listening
+port @pxref{TCP Emacs server} and making the
 @var{server-file} available on a remote machine, programs on the
 remote machine can use @command{emacsclient} as the value for the
 @env{EDITOR} and similar environment variables, but instead of talking
@@ -2171,16 +2172,28 @@ emacsclient Options
 effect as using the @samp{-T} option.  If both are specified, the
 command-line option takes precedence.
 
-For example, assume two hosts, @samp{local} and @samp{remote}, and
-that the local Emacs listens on tcp port 12345.  Assume further that
+For example, assume two hosts, @samp{local} and @samp{remote}.
+
+@example
+local$ ssh -R "/tmp/emacs-%r.socket":"$@{XDG_RUNTIME_DIR:-$@{TMPDIR:-/tmp@}/emacs%i@}$@{XDG_RUNTIME_DIR:+/emacs@}/server" remote
+remote$ export EMACS_SOCKET_NAME=/tmp/emacs-$USER.socket
+remote$ export EMACSCLIENT_TRAMP=/ssh:remote:
+remote$ export EDITOR=emacsclient
+remote$ $EDITOR /tmp/foo.txt #Should open in local emacs.
+@end example
+
+If you are using a platform that does not have Unix domain sockets
+(i.e., MS-Windows), or SSH implementations that are not able to
+forward them (e.g., OpenSSH before version 6.7), you can forward a TCP
+port instead.  In this example, assume that the local Emacs listens on
+tcp port 12345.  Assume further that
 @file{/home} is on a shared file system, so that the server file
 @file{~/.emacs.d/server/server} is readable on both hosts.
 
 @example
 local$ ssh -R12345:localhost:12345 remote
-remote$ export EDITOR="emacsclient \
-        --server-file=server \
-        --tramp=/ssh:remote:"
+remote$ export EMACSCLIENT_TRAMP=/ssh:remote:
+remote$ export EDITOR=emacsclient
 remote$ $EDITOR /tmp/foo.txt #Should open in local emacs.
 @end example
 
-- 
2.41.0