xpra shadow raises "Error parsing xdg menu data"

[stdedos]

It feels related to #2153, but no idea if it is. Search returns nothing.

2019-02-25 10:21:05,810 xpra GTK2 shadow version 2.5-r21828 64-bit
2019-02-25 10:21:05,810  running with pid 1055 on Linux Ubuntu 16.04 xenial

[Antoine Martin]

This isn't related to #2153, different menu: this one is your system "start menu" definition.

That's a bug in your distribution. You can reproduce it with:

python2 -c "from xdg.Menu import parse;parse()"

On most distributions this works fine but on Ubuntu this can fail. IIRC, that's because the menu definitions point to a menu file which is missing. (further details can be obtained by running with -d menu)

They shouldn't be shipping a library that cannot be called: either the library should fail more gracefully or they should ensure that their menu definitions do not trigger the problem.

[stdedos]

What if it doesn't fail?

$ python2 -c "from xdg.Menu import parse;parse()"
$ echo $?
0
$

No further debug coming with -d menu :/

[Antoine Martin]

No further debug coming with -d menu :/

Whoops, sorry. Try -d exec. It will honour -d menu as of r21875.

[stdedos]

The error is not "more helpful":

2019-02-25 11:01:11,521 load_xdg_menu_data()
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/xpra/platform/xposix/xdg_helper.py", line 218, in load_xdg_menu_data
    menu = parse()
  File "/usr/lib/python2.7/dist-packages/xdg/Menu.py", line 570, in parse
    raise ParsingError('File not found', "/etc/xdg/menus/%s" % candidate)
ParsingError: ParsingError in file '/etc/xdg/menus/debian-menu.menu', File not found

The file indeed does not exist:

$ ls -lah /etc/xdg/menus/
total 36K
drwxr-xr-x 2 root root 4,0K Φεβ  25 11:02 .
drwxr-xr-x 5 root root 4,0K Αύγ  28 14:46 ..
-rw-r--r-- 1 root root  19K Ιούν 30  2016 gnome-applications.menu
-rw-r--r-- 1 root root 2,8K Φεβ  14  2017 unitycc.menu
-rw-r--r-- 1 root root 3,8K Ιούλ  1  2016 unity-lens-applications.menu

touching does not help xpra either; but the call itself has no issues working either way. I even "changed" the code to verify the call explicitly following the same code path:

$ python2 -c "from xdg.Menu import parse;parse()" ; echo $?
filename
/etc/xdg/menus/gnome-applications.menu
<xml.dom.minidom.Document instance at 0x7ff8d8c1bb00>
0
$

vs

2019-02-25 11:16:23,713 xpra is ready.
filename
/etc/xdg/menus/debian-menu.menu
2019-02-25 11:16:23,812 load_xdg_menu_data()
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/xpra/platform/xposix/xdg_helper.py", line 218, in load_xdg_menu_data
    menu = parse()
  File "/usr/lib/python2.7/dist-packages/xdg/Menu.py", line 583, in parse
    raise ParsingError('Not a valid .menu file', filename)
ParsingError: ParsingError in file '/etc/xdg/menus/debian-menu.menu', Not a valid .menu file
2019-02-25 11:16:23,813 Error parsing xdg menu data:
2019-02-25 11:16:23,813  ParsingError in file '/etc/xdg/menus/debian-menu.menu', Not a valid .menu file
2019-02-25 11:16:23,813  this is either a bug in python-xdg,
2019-02-25 11:16:23,813  or an invalid system menu configuration

No idea why xpra needs to "fallback to default" and the python call itself doesn't.

[Antoine Martin]

It must be related to some environment variable that's going to be different when running under xpra.

[Antoine Martin]

FYI: the problem does occur if you run that python command from within the xpra session. (ie: from an xterm started with --start=xterm.

[stdedos]

Replying to Antoine Martin:

FYI: the problem does occur if you run that python command from within the xpra session. (ie: from an xterm started with --start=xterm.

More debugs show the issue:

#559: candidate = applications.menu
#560: filename = None
2019-02-25 11:16:23,812 load_xdg_menu_data()
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/xpra/platform/xposix/xdg_helper.py", line 218, in load_xdg_menu_data
    menu = parse()
  File "/usr/lib/python2.7/dist-packages/xdg/Menu.py", line 583, in parse
    raise ParsingError('Not a valid .menu file', filename)
ParsingError: ParsingError in file '/etc/xdg/menus/debian-menu.menu', Not a valid .menu file

It seems that "someone" sets XDG_MENU_PREFIX=gnome- on "normal ubuntu 16.04":
​https://gitlab.gnome.org/GNOME/gnome-session/blob/3.8.2.1/gnome-session/main.c#L362

not set in xpra though. Simple
XDG_MENU_PREFIX=gnome- python2 -c "from xdg.Menu import parse;parse()" does the job.

[Antoine Martin]

try without the XDG_MENU_PREFIX first

[Antoine Martin]

Thanks for figuring it out.

That's bogus IMO, here's the spec: ​menu spec which states that For example if a system contains both the GNOME and the KDE desktop environments it can decide to use gnome-applications.menu as the menu layout in GNOME sessions and kde-applications.menu as the menu layout in KDE sessions. To correctly reflect this, it should set the $XDG_MENU_PREFIX environment variable to "gnome-" respectively "kde-".

We're not gnome or KDE, so during server initialization we run the code that reads:

    #we don't want client apps to think these mean anything:
    #(if set, they belong to the desktop the server was started from)

This ticket looks similar to: ​applications.menu file has been renamed to gnome-applications.menu but XDG_MENU_PREFIX is not set: If they decide to only respect specifications, no menu will be found.

Anyway, we will now avoid sanitizing this value, and so we'll keep the "gnome-" prefix even though we're not gnome: r21878.
The patch above would solve it by trying both without and with the prefix, but I don't have time to test it.

[Antoine Martin]

Logging in via ssh does not set the XDG_MENU_PREFIX, so sessions started via ssh will not have the menus. What a mess!

[Antoine Martin]

Should now work as of r21880, even from ssh or a clean environment.

It is now possible to run the code directly for testing:

$ python ./xpra/platform/xposix/xdg_helper.py
* Accessories
  - Comment                       : Desktop accessories
  - Entries
    - About Xfce
      - Categories                : Utility, X-XFCE, Documentation
      - Comment                   : Information about the Xfce Desktop Environment
      - Exec                      : xfce4-about
      - GenericName               : 
      - Hidden                    : False
      - Icon                      : help-about
...