Re: Questions about XDG_RUNTIME_DIR and server-socket-dir

[Eli Zaretskii <eliz@gnu.org>]

On February 3, 2019 7:21:37 AM GMT+02:00, Phil Sainty <psainty@orcon.net.nz> wrote:
> The recent change to server-socket-dir to use the XDG_RUNTIME_DIR
> environment variable is breaking some of my tooling, so I want to
> understand the matter better.
> 
> The essence of my issue is that, via my wrapper script, a user can
> run multiple independent Emacs instances, including running multiple
> Emacs servers, and it's necessary that I'm not depending on
> --daemon=NAME to differentiate the server sockets in this situation,
> because the user should be able to specify any arbitrary options,
> and should be able to have a non-server instance call (server-start)
> to create a new non-conflicting server with the default server-name.
> 
> At present I automatically establish a distinct TMPDIR for each
> instance, and until Emacs 27 this has worked well: server-socket-dir
> was relative to TMPDIR, and so it didn't matter whether multiple
> servers had a common server-name, as the sockets themselves were in
> different directories.
> 
> With the new behaviour, the socket filenames are all in a common
> directory, and so unless a distinct server-name is specified,
> conflicts occur.
> 
> XDG_RUNTIME_DIR is completely new to me, so I'm uncertain how I should
> fix this.
> 
> I can, of course, create a temporary XDG_RUNTIME_DIR the same way that
> I create a temporary TMPDIR (the new dir is a sub-dir of the original
> dir), which would deal with the conflicts; but as such a change is
> reflected in process-environment inside Emacs, any processes that
> Emacs creates will see the modified XDG_RUNTIME_DIR too, and maybe
> that's not ok?  I'm relatively comfortable with this being the case
> for TMPDIR, but I don't know about XDG_RUNTIME_DIR.  Does that get
> used in ways that rely upon its path never changing?
> 
> If it's not safe to change it, then I think I need a way to specify
> the server-socket-dir via some new environment variable?
> 
> NEWS says that:
> 
> > *** Emacs and emacsclient now default to $XDG_RUNTIME_DIR/emacs
> > as the directory for client/server sockets, if Emacs is running
> > under an X Window System desktop that sets the XDG_RUNTIME_DIR
> > environment variable to indicate where session sockets should go.
> > To get the old, less-secure behavior, you can set the
> > EMACS_SOCKET_NAME environment variable to an appropriate value.
> 
> It appears to me that *only* emacsclient respects the
> EMACS_SOCKET_NAME
> environment variable.  Emacs itself ignores it when establishing the
> socket, as far as I can see.  (This is a current bug?)
> 
> I think EMACS_SOCKET_NAME is, in any case, not suited for my purposes,
> as it represents a combination of server-socket-dir and server-name,
> and the emacsclient option --socket-name overrides it such that
> --socket-name=foo would be looking for foo in the default location,
> even if EMACS_SOCKET_NAME specified a directory.
> 
> Can we perhaps introduce an EMACS_SOCKET_DIR environment variable
> which is respected by both emacs and emacsclient?
> 
> 
> -Phil

The value of server-name can include leading directories, so I think you can already have what you want.  Right?