"xdg-settings check default-web-browser something.desktop" fails in Kubuntu 22.04: Bad substitution

[Olivier Tilloy]

[Impact]

The firefox snap (default in 22.04) will always report that it thinks it's not the default browser (even when it actually is) for KDE users (this can be seen when browsing to about:preferences).

This is caused by an upstream bug in xdg-utils (using bashisms in KDE-specific functions whereas the default interpreter is dash).

The fix is rather trivial and will visibly improve the UX for those users.

[Test Plan]

In Kubuntu 22.04:
 - make sure firefox isn't your default browser (by changing the setting to a different browser)
 - run the firefox snap, browse to "about:preferences", and observe that firefox claims NOT to be the default browser
 - click the "Set default" button
 - refresh the page (F5)
 - observe that now firefox claims to be the default browser
 - in a terminal, execute `xdg-open https://example.org`, and verify that the page is open in the firefox snap

[Where problems could occur]

The patch is changing KDE-specific functions (check_browser_kde and check_url_scheme_handler_kde), so in theory it shouldn't affect running xdg-utils in any other desktop environment.

If the proposed patch is incorrect, it would affect the functionality of `xdg-settings check default-web-browser` and `xdg-settings check default-url-scheme-handler`, so this is what needs to be thoroughly tested in KDE.

In the event of a regression, these functions wouldn't work as expected (they already don't, so the user wouldn't observe a functional regression, merely the absence of a fix).

[Original description]

I'm reporting this issue from stock Ubuntu, but the problem is observed only in Kubuntu (can be reliably reproduced in a Kubuntu 22.04 VM). The version of xdg-utils is identical.

This problem was initially reported on the snapcraft forum: https://forum.snapcraft.io/t/firefox-wont-set-as-my-default-browser/29708.

    $ xdg-settings check default-web-browser firefox_firefox.desktop
    /usr/bin/xdg-settings: 734: Bad substitution

The offending line is:

    if [ x"!" == x"${browser:0:1}" ]; then

If I modify /usr/bin/xdg-settings in place to set the interpreter to /bin/bash on the first line of the script, the problem goes away.

ProblemType: Bug
DistroRelease: Ubuntu 22.04
Package: xdg-utils 1.1.3-4.1ubuntu1
ProcVersionSignature: Ubuntu 5.15.0-27.28-generic 5.15.30
Uname: Linux 5.15.0-27-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.11-0ubuntu82
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: ubuntu:GNOME
Date: Wed Apr 27 11:21:31 2022
InstallationDate: Installed on 2020-09-16 (587 days ago)
InstallationMedia: Ubuntu 20.10 "Groovy Gorilla" - Alpha amd64 (20200910)
PackageArchitecture: all
SourcePackage: xdg-utils
UpgradeStatus: Upgraded to jammy on 2022-03-19 (38 days ago)

[Lucy Llewellyn (lucyllewy)]

Can you try replacing the line with:

if [ x"!" == x"$(printf %.1s "$browser")" ]; then

and reverting back to dash? I think this might work in most posix shells, without requiring to move to bash.

[Lucy Llewellyn (lucyllewy)]

There is also a similar statement that needs fixing for DASH on line 1090:

if [ x"!" == x"${binary:0:1}" ]; then

[Olivier Tilloy (osomon)]

I suppose that would work (although I haven't actually tested to confirm, but it looks correct and I'm trusting your shell-fu). The real questions are:

 * why is this working in stock Ubuntu (where /bin/sh is also a symlink to dash) and not in Kubuntu?

 * why does the upstream project declare /bin/sh as the default interpreter for xdg-settings, yet use bash-specific string manipulation functions?

[Lucy Llewellyn (lucyllewy)]

Why in stock Ubuntu and not Kubuntu, I think is because the offending code is inside functions that are named as though only KDE is supposed to use them. For example, the default browser break is inside a function named `check_browser_kde()`. There might be some logic to determine that your stock Ubuntu, even if it is currently running a KDE session, supports testing via the gnome code paths: i.e. via `check_browser_gnome()`

With regards to bash specifics inside a project declaring /bin/sh as the interpreter I would guess it is a bug that has crept through without being caught. The upstream project likely wants to remain portable and not rely on BASH so they probably should drop the BASH-isms.

[Olivier Tilloy (osomon)]

Those are good points. I'm a bit baffled that this was not noticed by other users of xdg-settings earlier. Maybe KDE users don't usually rely on it? I'll file an upstream bug.

[Olivier Tilloy (osomon)]

It turns out it's a known issue: https://gitlab.freedesktop.org/xdg/xdg-utils/-/issues/10.

[Launchpad Janitor (janitor)]

This bug was fixed in the package xdg-utils - 1.1.3-4.1ubuntu2

---------------
xdg-utils (1.1.3-4.1ubuntu2) kinetic; urgency=medium

  * Cherry-pick an upstream merge request to remove bashisms from xdg-settings
    (LP: #1970594)
    - debian/source/options
    - debian/patches/upstream-mr-remove-bashisms.patch

 -- Olivier Tilloy <email address hidden> Tue, 03 May 2022 11:16:46 +0200

[Brian Murray (brian-murray)]

Hello Olivier, or anyone else affected,

Accepted xdg-utils into jammy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/xdg-utils/1.1.3-4.1ubuntu1.22.04.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-jammy to verification-done-jammy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-jammy. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Olivier Tilloy (osomon)]

Successfully tested by doing the following:

In a fully up-to-date jammy VM:

    $ sudo apt -y install libkf5config-bin
    $ export XDG_CURRENT_DESKTOP=KDE
    $ export KDE_SESSION_VERSION=5
    $ xdg-settings get default-web-browser
    firefox.desktop
    $ xdg-settings check default-web-browser firefox.desktop
    /usr/bin/xdg-settings: 734: Bad substitution

Then enabled the jammy-proposed pocket and updated xdg-utils to version 1.1.3-4.1ubuntu1.22.04.1:

    $ xdg-settings get default-web-browser
    firefox.desktop
    $ xdg-settings check default-web-browser foobar.desktop
    no
    $ xdg-settings check default-web-browser firefox.desktop
    /usr/bin/xdg-settings: 734: [: x!: unexpected operator
    yes

The result is as expected in all cases. Note the extra "/usr/bin/xdg-settings: 734: [: x!: unexpected operator" on stderr in the last test. This is not expected, but it is harmless as the output on stdout is as expected. I will report a follow-up upstream bug to get that addressed.

[Olivier Tilloy (osomon)]

Reported the "unexpected operator" error here: https://gitlab.freedesktop.org/xdg/xdg-utils/-/merge_requests/52#note_1389020.

[Lucy Llewellyn (lucyllewy)]

I've updated the PR with a fix for this ugly message

[Launchpad Janitor (janitor)]

This bug was fixed in the package xdg-utils - 1.1.3-4.1ubuntu1.22.04.1

---------------
xdg-utils (1.1.3-4.1ubuntu1.22.04.1) jammy; urgency=medium

  * Cherry-pick an upstream merge request to remove bashisms from xdg-settings
    (LP: #1970594)
    - debian/source/options
    - debian/patches/upstream-mr-remove-bashisms.patch

 -- Olivier Tilloy <email address hidden> Tue, 03 May 2022 11:16:46 +0200

[Brian Murray (brian-murray)]

The verification of the Stable Release Update for xdg-utils has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

[Jonas Gamao (yamiyukisenpai)]

Still not fixed for me.

$ kreadconfig5 --file kdeglobals --group General --key BrowserApplication
firefox.desktop

$ xdg-settings check default-web-browser firefox.desktop
/usr/bin/xdg-settings: 734: [: x!: unexpected operator
no

[Lucy Llewellyn (lucyllewy)]

Yamiyukisenpai, that is working correctly. The error message does not impact the functionality of the program. It is merely ugly. There is a patch upstream that fixes this, but it isn't appropriate to SRU this fix.

[Olivier Tilloy (osomon)]

I think what Jonas means is that he's expecting the answer to be "yes", not "no".

Jonas, what is the output of `xdg-settings get default-web-browser` ?

[Elvis Stansvik (elvstone)]

@diddledani The error does have an impact on the Firefox snap running under KDE, which I can only presume does some poor parsing of xdg-settings output (including stderr?) when determining if it is itself the default browser.

BTW, the patch in https://gitlab.freedesktop.org/xdg/xdg-utils/-/merge_requests/52 is wrong (see my comment at https://gitlab.freedesktop.org/xdg/xdg-utils/-/merge_requests/52#note_1488548), use the attached patch instead.

With this, the Firefox snap recognizes itself as the default browser for me.

[Elvis Stansvik (elvstone)]

> [...] which I can only presume does some poor parsing of xdg-settings output (including stderr?) when determining if it is itself the default browser.

I had a look (https://searchfox.org/mozilla-central/source/browser/components/shell/nsGNOMEShellService.cpp#184-204) and it does suppress stderr, but the problem is the non-zero exit status that the error results in. Firefox will only consider itself the default browser if the command exits with 0 exit status *and* prints "yes".

[Lucy Llewellyn (lucyllewy)]

I've updated the MR on the freedesktop gitlab instance. Olivier, it might be worth updating again with a new SRU to include Elvis' further patch?

[Olivier Tilloy (osomon)]

Yes, I have updated the patch in kinetic, and I will SRU it in jammy. This will require using a new bug report though, maybe bug #1967963 ?

[Olivier Tilloy (osomon)]

I am testing in a fully up-to-date Kubuntu 22.04 VM:

    $ xdg-settings check default-web-browser firefox_firefox.desktop
    /usr/bin/xdg-settings: 734: [: x!: unexpected operator
    yes

    $ echo $?
    0

So while the error printed on stderr is misleading, the result printed on stdout is correct, and so is the return code.

I am still going to SRU the updated patch to jammy, as I think it's useful, but it shouldn't impact firefox's checking whether it is the default browser.