multiple bind options for local sockets

[Antoine Martin]

Follow up from #888.

Add a --bind= option, similar to the --bind-tcp option but for unix domain sockets, and eventually named pipes for win32(#389). This would ease the transition to /run: we can just create sockets in both locations by default.

It may also help with containers if we support both a directory form (--bind=dir:$HOME/.xpra) and an absolute path (--bind=socket:/path/to/thesocket.

And maybe this could help with selinux (#815) because we can then pick the socket in its more "proper" location.

[Antoine Martin]

r11485 implements this for unix domain sockets. r11486 adds $UID and $GID path extension (as used for socket-dirs already).

Example:

xpra start \
    --bind=/tmp/
    --bind=/run/user/$UID/xpra/
    --bind=/home/antoine/tmp/tmp/mysocket

Will create:

• the usual socket (the filename of the socket will be generated from the hostname) in the 2 directories specified: /tmp and /run/user/$UID/xpra/
• a socket named /home/antoine/tmp/tmp/mysocket

---

I could have used a more explicit differentiator between socket directories (identified by a trailing slash or if the directory exists already) and explicit filenames ("mysocket"), but I couldn't come up with anything that wasn't ugly.

Note: the sockets created will only be found by clients if they are in one of the directories specified with the socket-dirs option. For backwards compatibility with older clients / servers, you should keep ~/.xpra/ in that list.
Sockets specified using the full filename will not be found, even if they are in a socket-dir that is searched by clients, unless the actual socket filename matches the hostname. (like the automatically generated ones)

@jonathan.underwood: if all your other clients and servers are 0.17 or later, you can now safely change the default socket location to be /var/run/user/$UID/xpra and things should just work.

[Antoine Martin]

See also #1066.

[Antoine Martin]

Fix for "upgrade" server exit in r11722, ideally we should keep track of which server owns which sockets to make we cleanup all the ones that we should cleanup.

[Antoine Martin]

attempt at figuring out the real socket path from the socket file descriptor - does not work..

[jonathan.underwood]

Can confirm that on 0.16.2, starting server like this:

xpra start --start-child=xterm --socket-dir=/run/user/1000/xpra :100

and then simply doing a

xpra --mmap=no  attach ssh:withnail.phys.ucl.ac.uk:100

worked fine. Does that cover what you wanted?

[jonathan.underwood]

Also, I'm not quite clear quite what the --bind is intended to do - in your example (with three paths), is it creating three sockets at the three paths? You talk about 2 sockets, so I am a bit confused.

Aside: I looked for it in the man page (on 0.16.2), and didn't see any mention there.

[Antoine Martin]

jonathan.underwood: no, socket-dir and bind are related, but different things. bind is a 0.17 feature (sorry about the confusion) which allows you to create as many unix domain sockets as you like.
I have edited comment:1 to try to clarify.

[Antoine Martin]

@jonathan.underwood: we have a problem, please see ticket:1129#comment:9

[Antoine Martin]

@afarr: I think we can close this ticket for 0.17 as this works fine (unless you can break it, see comment:1), though things may still change when it comes to the defaults we ship, as per #1129.

[alas]

Uhh... not familiar enough with manually manipulating my sockets to know where to start trying to break it.

I'll go ahead and close and maybe open a new one if I can learn enough to be socket-dangerous at some point in the future.

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/963