Bug 521662

Summary:	krfb-virtualmonitor crashes with "zkde_screencast_stream_unstable_v1 has no event 3" after upgrade to KWin 6.7.0
Product:	[Applications] krfb	Reporter:	freeusernamestuff <freeusernamestuff>
Component:	krfb-virtualmonitor	Assignee:	George Goldberg <grundleborg>
Status:	REPORTED ---
Severity:	crash	CC:	antti.savo, kdedev
Priority:	NOR	Keywords:	regression
Version First Reported In:	26.04.2
Target Milestone:	---
Platform:	Fedora RPMs
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description freeusernamestuff@gmail.com 2026-06-18 18:02:46 UTC

***
If you're not sure this is actually a bug or valid feature request, instead post about it at https://discuss.kde.org

If you're reporting a crash, attach a backtrace with debug symbols; see https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports

Please remove this comment after reading and before submitting - thanks!
***

DESCRIPTION
After upgrading KWin from 6.6.4 to 6.7.0, krfb-virtualmonitor crashes immediately with exit code 255. The issue is a Wayland protocol mismatch: KWin 6.7.0 sends event index 3 (serial) on the zkde_screencast_stream_unstable_v1 interface, but krfb's compiled-in protocol definition only knows events 0–2 (created, failed, closed), causing libwayland-client to abort.
Error message (stderr):
interface 'zkde_screencast_stream_unstable_v1' has no event 3

STEPS TO REPRODUCE
1. Run KWin 6.7.0 on a Wayland session (Plasma 6.7.0)
2. Run: krfb-virtualmonitor --resolution 1366x1024 --name "test" --password "test" --port 5901
3. Observe immediate crash with exit code 255

OBSERVED RESULT
Process exits with code 255, no virtual output created

EXPECTED RESULT
Virtual output "test" appears in kscreen-doctor --outputs

SOFTWARE/OS VERSIONS
Operating System: Fedora Linux 44  kernel 7.0.12-201.fc44.x86_64, Wayland session
KDE Plasma Version: 6.6.4
KDE Frameworks Version: 6.25.0 
Qt Version: 6.10.2

Plasma version: 6.7.0
krfb 25.12.3 — crashes (same error)
krfb 26.04.2 — crashes (same error)
KWin 6.6.4-2 — both krfb versions work correctly


ADDITIONAL INFORMATION
Bisect: Confirmed regression between KWin 6.6.4 → 6.7.0. Downgrading KWin to 6.6.4-2 restores functionality immediately without any other changes.

Comment 1 TraceyC 2026-06-18 19:56:13 UTC

Thanks for the crash report, and the troubleshooting, that's very helpful. 

As the message at the top of the summary says, if something crashed, we also need a backtrace of it so we can figure out what's going on. Can you please attach a backtrace of the crash, as detailed in https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports ?

Thanks.

Comment 2 freeusernamestuff@gmail.com 2026-06-19 02:16:09 UTC

We are unable to provide a backtrace through normal means. When attempting to reproduce the crash under gdb, we encountered a separate issue caused by a partial package downgrade on our end (kwin 6.7.0 + kscreenlocker 6.6.4 version mismatch), which prevented kwin_wayland from starting at all. This was not a KWin bug — it was a consequence of our own recovery process.
The SIGABRT source is identifiable from the error message itself: libwayland-client aborts when it receives event index 3 on zkde_screencast_stream_unstable_v1, which is not present in krfb's compiled-in protocol definition. Both krfb 25.12.3 and 26.04.2 are affected identically. We confirmed the regression bisect: KWin 6.6.4 works, KWin 6.7.0 breaks it.
If you can confirm whether event 3 (serial) was added to zkde_screencast_stream_unstable_v1 in KWin 6.7.0, that would pinpoint the exact commit responsible

Comment 3 TraceyC 2026-06-23 21:50:52 UTC

I'm not able to reproduce this with krdp and Plasma built from git-master 
The developers can look further into zkde_screencast_stream_unstable_v1. Thanks for the additional detail there, that's helpful.