fails to acquire lock if `WAYLAND_DISPLAY` contains a `/`

[uninsane]

$ slurp
failed to open lock file
$ XDG_RUNTIME_DIR=$XDG_RUNTIME_DIR/$(dirname $WAYLAND_DISPLAY) WAYLAND_DISPLAY=$(basename $WAYLAND_DISPLAY) slurp
# (works)

relevant environment:

$ env | egrep 'WAY|XDG_'
SWAYSOCK=/run/user/colin/sway/sway-ipc.sock
WAYLAND_DISPLAY=wl/wayland-1
XDG_CURRENT_DESKTOP=sway
XDG_DATA_DIRS=/etc/profiles/per-user/colin/share:/run/current-system/sw/share
XDG_RUNTIME_DIR=/run/user/colin
XDG_SESSION_TYPE=wayland
XDG_CONFIG_DIRS=/etc/xdg:/etc/profiles/per-user/colin/etc/xdg:/run/current-system/sw/etc/xdg
XDG_CACHE_DIR=/home/colin/.cache
XDG_DESKTOP_DIR=/home/colin/.xdg/Desktop
XDG_DOCUMENTS_DIR=/home/colin/dev
XDG_DOWNLOAD_DIR=/home/colin/tmp
XDG_MUSIC_DIR=/home/colin/Music
XDG_PHOTOS_DIR=/home/colin/Pictures/Photos
XDG_PICTURES_DIR=/home/colin/Pictures
XDG_PUBLICSHARE_DIR=/home/colin/.xdg/Public
XDG_SCREENSHOTS_DIR=/home/colin/Pictures/Screenshots
XDG_TEMPLATES_DIR=/home/colin/.xdg/Templates
XDG_VIDEOS_DIR=/home/colin/Videos

particularly:

$ echo WAYLAND_DISPLAY
wl/wayland-1
$ tree $XDG_RUNTIME_DIR
/run/user/colin
├── chg
├── dbus
│   └── bus
├── keyring
│   └── control
├── pipewire
│   ├── pipewire-0
│   ├── pipewire-0.lock
│   ├── pipewire-0-manager
│   └── pipewire-0-manager.lock
├── pulse
│   ├── native
│   └── pid
├── ssh-agent
│   └── agent
├── sway
│   └── sway-ipc.sock
└── wl
    ├── slurp-wayland-1.lock
    ├── wayland-1
    └── wayland-1.lock

(that $XDG_RUNTIME_DIR/wl/slurp-wayland-1.lock file was created only as part of the 2nd slurp invocation, with XDG_RUNTIME_DIR and WAYLAND_DISPLAY modified as appropriate -- not by the bare slurp call which failed).

[uninsane]

// file: lock.c
bool get_lockfile_path(char path[MAX_PATH_SIZE]) {
	char *runtime_dir = getenv("XDG_RUNTIME_DIR");
	if (!runtime_dir) {
		// Use the /tmp directory if we couldn't get a normal runtime dir
		runtime_dir = "/tmp";
	}
	char *display = getenv("WAYLAND_DISPLAY");
	if (!display) {
		fprintf(stderr, "No wayland session found\n");
		return false;
	}

	if (snprintf(path, MAX_PATH_SIZE, "%s/slurp-%s.lock", runtime_dir, display) >= MAX_PATH_SIZE) {
		fprintf(stderr, "lockfile path was too long\n");
		return false;
	}

	return true;
}

bool acquire_lock() {
	char lockfile[MAX_PATH_SIZE];
	if (!get_lockfile_path(lockfile)) {
		return false;
	}
	// Open the lock file for write, creating with user read/write if necessary
	int fd = open(lockfile, O_WRONLY|O_CREAT, 00600);
	if (fd == -1) {
		fprintf(stderr, "failed to open lock file\n");
		return false;
	}
	if (flock(fd, LOCK_EX|LOCK_NB)) {
		fprintf(stderr, "another slurp process is running for this wayland session\n");
		return false;
	}
	return true;
}

get_lockfile_path yields a path like /run/user/colin/slurp-wl/wayland-0.lock. although slurp opens that with O_CREAT, that doesn't work because the outer directory -- /run/user/colin/slurp-wl/ -- doesn't exist.

[uninsane]

perhaps the sensible thing is to just match wayland's own socket construction logic more closely and avoid the "directory doesn't exist" edgecase: i.e. use a lock path of ${XDG_RUNTIME_DIR}/${WAYLAND_DISPLAY}.slurp.lock instead of ${XDG_RUNTIME_DIR}/slurp-${WAYLAND_DISPLAY}.lock.

[tmccombs]

That wouldn't solve the problem.

/ Isn't allowed in filenames, because it is the path separator.

We would need to replace any / with some other character, like "-".