[v3 / linux] linuxSystemTray.run panics on `org.freedesktop.Notifications` signals delivered to its dbus channel

[PavelSimonovCiteck]

Description

A Wails v3 app on Linux that uses both a SystemTray and desktop notifications crashes with panic error: runtime error: index out of range [2] with length 2 from linuxSystemTray.run's signal-handling goroutine.

run() adds a single match for org.freedesktop.DBus.NameOwnerChanged so it can re-register the StatusNotifierItem when the watcher restarts, then routes signals through conn.Signal(sc). The handler indexes sig.Body[2] unconditionally:

// v3/pkg/application/systemtray_linux.go:417-419 (master)
// sig.Body has the args, which are [name old_owner new_owner]
if sig.Body[2] != "" {
    s.register()
}

In godbus, conn.Signal(sc) delivers every signal the connection receives, not just the ones matching the per-channel rules. The systray opens dbus.SessionBus(), which returns a process-wide singleton connection — shared with anything else in the app that talks to the session bus. As soon as another part of the app subscribes to a 2-arg signal, it lands in the systray's channel and the unbounded index panics.

defer handlePanic() in the goroutine recovers, but the default panic handler (defaultPanicHandler → globalApplication.fatal) then exits the process — so the user sees the app die.

Same code is on master (systemtray_linux.go:418) and v3.0.0-alpha.78.

To Reproduce

Captured with this instrumentation in linuxSystemTray.run:

case sig := <-sc:
    if sig == nil { return }
    if len(sig.Body) < 3 {
        fmt.Fprintf(os.Stderr,
            "[dbg] short signal: name=%q path=%q sender=%q len=%d body=%#v\n",
            sig.Name, sig.Path, sig.Sender, len(sig.Body), sig.Body)
    }
    if len(sig.Body) >= 3 && sig.Body[2] != "" { s.register() }

Output from a Wails v3 mail client running idle for ~2 minutes:

[dbg] short signal: name="org.freedesktop.Notifications.ActionInvoked"     path="/org/freedesktop/Notifications" sender=":1.45" len=2 body=[]interface{}{0x3d, "default"}
[dbg] short signal: name="org.freedesktop.Notifications.NotificationClosed" path="/org/freedesktop/Notifications" sender=":1.45" len=2 body=[]interface{}{0x3d, 0x2}
[dbg] short signal: name="org.freedesktop.Notifications.NotificationClosed" path="/org/freedesktop/Notifications" sender=":1.45" len=2 body=[]interface{}{0x3e, 0x2}
[dbg] short signal: name="org.freedesktop.Notifications.NotificationClosed" path="/org/freedesktop/Notifications" sender=":1.45" len=2 body=[]interface{}{0x3c, 0x2}
[dbg] short signal: name="org.freedesktop.Notifications.NotificationClosed" path="/org/freedesktop/Notifications" sender=":1.45" len=2 body=[]interface{}{0x3f, 0x2}

org.freedesktop.Notifications.ActionInvoked(u, s) and NotificationClosed(u, u) both have 2-element bodies per the Desktop Notifications spec. The mail client subscribes to them on the session bus to know when its notifications are clicked or auto-dismissed; that subscription causes godbus to start delivering them to every registered Signal() channel, including the systray's.

Repro is therefore: a Wails v3 app that creates a SystemTray AND has any other code on the session bus subscribing to a 2-arg (or 0/1-arg) signal will eventually crash on the first such signal received after startup.

Expected behaviour

The signal-handling goroutine must filter on the signal name (and bounds-check the body) before indexing it. Anything other than org.freedesktop.DBus.NameOwnerChanged should be ignored.

case sig := <-sc:
    if sig == nil { return }
    if sig.Name != "org.freedesktop.DBus.NameOwnerChanged" { continue }
    if len(sig.Body) >= 3 && sig.Body[2] != "" { s.register() }

Screenshots

No response

Attempted Fixes

The patch above stops the crash. Ready to PR.

System Details

Wails:    v3.0.0-alpha.78 (also reproducible on master)
OS:       Ubuntu 24.04 base (Linux Mint 22.x)
Kernel:   Linux 6.17.0-20-generic
DE:       Cinnamon on X11
dbus:     1.14.10-4ubuntu4.1
Go:       go1.26.1 linux/amd64

Additional context

Original crash trace before instrumentation:

panic error: runtime error: index out of range [2] with length 2
runtime.panicBounds64
	at runtime/panic.go:236
runtime.panicBounds
	at runtime/asm_amd64.s:2129
github.com/wailsapp/wails/v3/pkg/application.(*linuxSystemTray).run.func1
	at github.com/wailsapp/wails/v3/pkg/application/systemtray_linux.go:418
runtime.goexit
	at runtime/asm_amd64.s:1771