What's the right way to call xcb_connect_to_display_with_auth_info() given a Xauthority file?

[Uli Schlachter]

Hi,

Am 17.10.2014 um 14:55 schrieb Laércio de Sousa:
[...]
> I would like to establish this connection without having to set environment
> variable XAUTHORITY. I know there's a funcion in XCB API called
> xcb_connect_to_display_with_auth_info() which receives a
> xcb_auth_info_t struct,
> but I have absolutely no idea of how to build this struct given a
> Xauthority file path.
> 
> How could I do it?
> Thanks in advance!
[...]

I never used this myself, but you could just look into xcb's source code to
figure out how xcb_connect() gets its auth info.

xcb_connect() just calls xcb_connect_with_auth_info() with NULL for the auth
information. This function then uses _xcb_get_auth_info() to get the
xcb_auth_info_t structure:

http://cgit.freedesktop.org/xcb/libxcb/tree/src/xcb_util.c?id=382d306d6c44a9ece5551c210a932773b5cb94a5#n521

The function _xcb_get_auth_info() does some dances to get a Xauth*, then copies
some information from it into the xcb_auth_info_t and calls compute_auth():

http://cgit.freedesktop.org/xcb/libxcb/tree/src/xcb_auth.c?id=382d306d6c44a9ece5551c210a932773b5cb94a5#n344

This function mostly shuffles some bytes around (does anyone use XDM AUTH?, I
guess the AUTH_MC1 case should suffice for 90% of people):

http://cgit.freedesktop.org/xcb/libxcb/tree/src/xcb_auth.c?id=382d306d6c44a9ece5551c210a932773b5cb94a5#n187

Since you just have a Xauthority file path, you could use XauReadAuth() to read
the FILE*. That gives you an Xauth* structure which you can hopefully use in the
same way that libxcb uses it.

Cheers,
Uli
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