https://bugs.kde.org/show_bug.cgi?id=498985
Bug ID: 498985
Summary: Introspecting desktop portal requests hangs
Classification: Plasma
Product: xdg-desktop-portal-kde
Version: 6.2.5
Platform: Fedora RPMs
OS: Linux
Status: REPORTED
Severity: minor
Priority: NOR
Component: general
Assignee: plasma-b...@kde.org
Reporter: d...@natulte.net
CC: aleix...@kde.org
Target Milestone: ---
SUMMARY
DBus objects under /org/freedesktop/portal/desktop/request cannot be
introspected. The org.freedesktop.DBus.Introspectable.Introspect RPC hangs for
ever. This breaks dbus tools that scan the bus for objects and their APIs.
I've reproduced this with the D-Bus client library I'm writing, D-Spy (GUI
debugger) and the upstream dbus-send(1) tool.
STEPS TO REPRODUCE
1. Do something that creates a portal request. I ran Firefox in a flatpak and
played a video, which triggers an inhibit portal request.
2. Run: dbus-send --session --dest=org.freedesktop.impl.portal.desktop.kde
--type=method_call --print-reply /org/freedesktop/portal/desktop/request
org.freedesktop.DBus.Introspectable.Introspect
3. In the response, look for the child node object, and continue traversing
down the object tree until you reach a request object. For example, in my case,
the inhibit request object looks like:
/org/freedesktop/portal/desktop/request/1_61/t/2275739744
3. Run: dbus-send --session --dest=org.freedesktop.impl.portal.desktop.kde
--type=method_call --print-reply REQUEST_PATH_HERE
org.freedesktop.DBus.Introspectable.Introspect
OBSERVED RESULT
The introspection request never gets a response, it just hangs until the object
is destroyed (e.g. in my repro case, by pausing the video playback which
deletes the inhibit request).
EXPECTED RESULT
The introspection request should succeed or fail promptly, not hang for ever.
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Fedora Linux 41 (kernel 6.12.9-200.fc41.x86_64, x86_64,
wayland session)
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.1
DBus implementation: dbus-broker v36
ADDITIONAL INFORMATION
I am not at all familiar with KDE source code and conventions, but I traced the
misbehaving D-Bus object to
https://github.com/KDE/xdg-desktop-portal-kde/blob/master/src/request.cpp ,
which I notice has a custom introspect implementation that returns a raw XML
string snippet. I don't see anything obviously wrong with the implementation,
assuming that QDBus actually calls the method when appropriate.
I see that Request::handleMessage returns true unconditionally for all method
calls, even for calls that it doesn't handle. If QDBus first offers the
introspection request to handleMessage before falling back to introspect, that
would explain the hang. IIUC, returning true without responding to method calls
tells QDBus that this message has been consumed and that it should not do
anything else. That would match the behavior I'm observing.
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