xwayland: Allow to retrieve startup-id via _NET_STARTUP_INFO

A launchee notifies with a "remove"¹ message when done starting up.
Catch these and forward to the compositor. This allows the compositor to
end the startup sequence that might have been started by another
protocol like xdg-activation.

We don't handle other messages since we expect the launcher to use a
wayland protocol like xdg-activation.

While `_NET_STARTUP_ID` helps to associate toplevels with startup-ids
this signals the end of the startup sequence.

1) https://specifications.freedesktop.org/startup-notification-spec/startup-notification-latest.txt

include/wlr/xwayland.h

@@ -72,6 +72,7 @@ struct wlr_xwayland {
 	struct {
 		struct wl_signal ready;
 		struct wl_signal new_surface;
+		struct wl_signal remove_startup_info;
 	} events;
 
 	/**
@@ -232,6 +233,11 @@ struct wlr_xwayland_move_event {
 	struct wlr_xwayland_surface *surface;
 };
 
+struct wlr_xwayland_remove_startup_info_event  {
+	const char *id;
+	xcb_window_t window;
+};
+
 struct wlr_xwayland_resize_event {
 	struct wlr_xwayland_surface *surface;
 	uint32_t edges;

include/xwayland/xwm.h

@@ -56,6 +56,8 @@ enum atom_name {
 	TIMESTAMP,
 	DELETE,
 	NET_STARTUP_ID,
+	NET_STARTUP_INFO,
+	NET_STARTUP_INFO_BEGIN,
 	NET_WM_WINDOW_TYPE_NORMAL,
 	NET_WM_WINDOW_TYPE_UTILITY,
 	NET_WM_WINDOW_TYPE_TOOLTIP,
@@ -113,6 +115,7 @@ struct wlr_xwm {
 	// Surfaces in bottom-to-top stacking order, for _NET_CLIENT_LIST_STACKING
 	struct wl_list surfaces_in_stack_order; // wlr_xwayland_surface::stack_link
 	struct wl_list unpaired_surfaces; // wlr_xwayland_surface::unpaired_link
+	struct wl_list pending_startup_ids; // pending_startup_id
 
 	struct wlr_drag *drag;
 	struct wlr_xwayland_surface *drag_focus;

xwayland/xwayland.c

@@ -81,6 +81,7 @@ struct wlr_xwayland *wlr_xwayland_create(struct wl_display *wl_display,
 
 	wl_signal_init(&xwayland->events.new_surface);
 	wl_signal_init(&xwayland->events.ready);
+	wl_signal_init(&xwayland->events.remove_startup_info);
 
 	struct wlr_xwayland_server_options options = {
 		.lazy = lazy,

xwayland/xwm.c

@@ -61,6 +61,8 @@ const char *const atom_map[ATOM_LAST] = {
 	[TIMESTAMP] = "TIMESTAMP",
 	[DELETE] = "DELETE",
 	[NET_STARTUP_ID] = "_NET_STARTUP_ID",
+	[NET_STARTUP_INFO] = "_NET_STARTUP_INFO",
+	[NET_STARTUP_INFO_BEGIN] = "_NET_STARTUP_INFO_BEGIN",
 	[NET_WM_WINDOW_TYPE_NORMAL] = "_NET_WM_WINDOW_TYPE_NORMAL",
 	[NET_WM_WINDOW_TYPE_UTILITY] = "_NET_WM_WINDOW_TYPE_UTILITY",
 	[NET_WM_WINDOW_TYPE_TOOLTIP] = "_NET_WM_WINDOW_TYPE_TOOLTIP",
@@ -89,6 +91,14 @@ const char *const atom_map[ATOM_LAST] = {
 	[NET_CLIENT_LIST_STACKING] = "_NET_CLIENT_LIST_STACKING",
 };
 
+#define STARTUP_INFO_REMOVE_PREFIX "remove: ID="
+struct pending_startup_id {
+	char *msg;
+	size_t len;
+	xcb_window_t window;
+	struct wl_list link;
+};
+
 static const struct wlr_surface_role xwayland_surface_role;
 
 bool wlr_surface_is_xwayland_surface(struct wlr_surface *surface) {
@@ -1361,6 +1371,73 @@ static void xwm_handle_net_active_window_message(struct wlr_xwm *xwm,
 	wlr_signal_emit_safe(&surface->events.request_activate, surface);
 }
 
+static void pending_startup_id_destroy(struct pending_startup_id *pending) {
+	wl_list_remove(&pending->link);
+	free(pending->msg);
+	free(pending);
+}
+
+static void xwm_handle_net_startup_info_message(struct wlr_xwm *xwm,
+		xcb_client_message_event_t *ev) {
+	struct pending_startup_id *pending, *curr = NULL;
+	wl_list_for_each(pending, &xwm->pending_startup_ids, link) {
+		if (pending->window == ev->window) {
+			curr = pending;
+			break;
+		}
+	}
+
+	char *start;
+	size_t buf_len = sizeof(ev->data);
+	if (curr) {
+		curr->msg = realloc(curr->msg, curr->len + buf_len);
+		if (!curr->msg) {
+			pending_startup_id_destroy(curr);
+			return;
+		}
+		start = curr->msg + curr->len;
+		curr->len += buf_len;
+	} else {
+		curr = calloc(1, sizeof(struct pending_startup_id));
+		if (!curr)
+			return;
+		curr->window = ev->window;
+		curr->msg = malloc(buf_len);
+		if (!curr->msg) {
+			free(curr);
+			return;
+		}
+		start = curr->msg;
+		curr->len = buf_len;
+		wl_list_insert(&xwm->pending_startup_ids, &curr->link);
+	}
+
+	char *id = NULL;
+	const char *data = (const char *)ev->data.data8;
+	for (size_t i = 0; i < buf_len; i++) {
+		start[i] = data[i];
+		if (start[i] == '\0') {
+			if (strncmp(curr->msg, STARTUP_INFO_REMOVE_PREFIX,
+					strlen(STARTUP_INFO_REMOVE_PREFIX)) == 0 &&
+					strlen(curr->msg) > strlen(STARTUP_INFO_REMOVE_PREFIX)) {
+				id = curr->msg + strlen(STARTUP_INFO_REMOVE_PREFIX);
+				break;
+			} else {
+				wlr_log(WLR_ERROR, "Unhandled message '%s'\n", curr->msg);
+				pending_startup_id_destroy(curr);
+				return;
+			}
+		}
+	}
+
+	if (id) {
+		struct wlr_xwayland_remove_startup_info_event data = { id, ev->window };
+		wlr_log(WLR_DEBUG, "Got startup id: %s", id);
+		wlr_signal_emit_safe(&xwm->xwayland->events.remove_startup_info, &data);
+		pending_startup_id_destroy(curr);
+	}
+}
+
 static void xwm_handle_wm_change_state_message(struct wlr_xwm *xwm,
 		xcb_client_message_event_t *ev) {
 	struct wlr_xwayland_surface *xsurface = lookup_surface(xwm, ev->window);
@@ -1399,6 +1476,9 @@ static void xwm_handle_client_message(struct wlr_xwm *xwm,
 		xwm_handle_wm_protocols_message(xwm, ev);
 	} else if (ev->type == xwm->atoms[NET_ACTIVE_WINDOW]) {
 		xwm_handle_net_active_window_message(xwm, ev);
+	} else if (ev->type == xwm->atoms[NET_STARTUP_INFO] ||
+			ev->type == xwm->atoms[NET_STARTUP_INFO_BEGIN]) {
+		xwm_handle_net_startup_info_message(xwm, ev);
 	} else if (ev->type == xwm->atoms[WM_CHANGE_STATE]) {
 		xwm_handle_wm_change_state_message(xwm, ev);
 	} else if (!xwm_handle_selection_client_message(xwm, ev)) {
@@ -1718,6 +1798,11 @@ void xwm_destroy(struct wlr_xwm *xwm) {
 	wl_list_remove(&xwm->compositor_destroy.link);
 	xcb_disconnect(xwm->xcb_conn);
 
+	struct pending_startup_id *pending, *next;
+	wl_list_for_each_safe(pending, next, &xwm->pending_startup_ids, link) {
+		pending_startup_id_destroy(pending);
+	}
+
 	xwm->xwayland->xwm = NULL;
 	free(xwm);
 }
@@ -1958,6 +2043,7 @@ struct wlr_xwm *xwm_create(struct wlr_xwayland *xwayland, int wm_fd) {
 	wl_list_init(&xwm->surfaces);
 	wl_list_init(&xwm->surfaces_in_stack_order);
 	wl_list_init(&xwm->unpaired_surfaces);
+	wl_list_init(&xwm->pending_startup_ids);
 	xwm->ping_timeout = 10000;
 
 	xwm->xcb_conn = xcb_connect_to_fd(wm_fd, NULL);