Some software think that clipboard daemon is not running

[joonas-fi]

xfce4-screenshooter shows "Copy to the clipboard" button only if it thinks a clipboard manager is running (screenshot is with xfce4-clipman running):

When I'm running $ ./clipcatd --no-daemon (with default config from README, also running with daemonized didn't change a thing) this clipboard button is not showing in xfce4-screenshooter (source code).

The above line calls https://developer.gnome.org/gdk3/stable/GdkDisplay.html#gdk-display-supports-clipboard-persistence which is documented as:

Returns whether the speicifed display supports clipboard persistance; i.e. if it’s possible to store the clipboard data after an application has quit. On X11 this checks if a clipboard daemon is running.

I'm on X11. Copy/pastes are showing up in clipcatd log and things are running just fine, am able to copy/paste images etc. but for some reason Gnome-based software doesn't recognize there's a clipboard manager running. I haven't dug deeper to understand what their heuristics are.

[joonas-fi]

I had lots of trouble finding that function from GDK source code (GitHub search returned no results for gdk_display_supports_clipboard_persistence, but it's there allright), but I found something good: https://github.com/GNOME/gtk/commit/06c4bb44b139f2ed40b70c0303836e1e8558e8d9#diff-6ab4fcfe66397619d5843c2bb1ac48094eb7dba764739979a7b36dc217b06ff8R1096

[joonas-fi]

I used this code snippet (in Go):

func debugClipboardManager() error {
	X, err := xgb.NewConn()
	if err != nil {
		return err
	}
	defer X.Close()

	atomName := "CLIPBOARD_MANAGER"
	clipboardManagerAtom, err := xproto.InternAtom(X, true, uint16(len(atomName)), atomName).Reply()
	if err != nil {
		return err
	}

	clipboardManagerOwnerWindow, err := xproto.GetSelectionOwner(X, clipboardManagerAtom.Atom).Reply()
	if err != nil {
		return err
	}

	fmt.Printf("owner window: %d\n", clipboardManagerOwnerWindow.Owner)

	return nil
}

When no clipboard manager is running:

owner window: 0

When xfce4-clipman is running:

owner window: 192937998

When clipcatd is running:

owner window: 0