core: add NMDBusTrackObjPath helper

When one D-Bus object exposes (the path of) another D-Bus object,
we want that the path property gets cleared before the other
object gets unexported(). That essentially requires to register
to the "exported-changed" signal.

Add a helper struct NMDBusTrackObjPath to help with this.

src/nm-dbus-utils.c

@@ -207,3 +207,102 @@ nm_dbus_utils_get_paths_for_clist (const CList *lst_head,
 }
 
 /*****************************************************************************/
+
+void
+nm_dbus_track_obj_path_init (NMDBusTrackObjPath *track,
+                             GObject *target,
+                             const GParamSpec *pspec)
+{
+	nm_assert (track);
+	nm_assert (G_IS_OBJECT (target));
+	nm_assert (G_IS_PARAM_SPEC (pspec));
+
+	track->_obj = NULL;
+	track->_notify_target = target;
+	track->_notify_pspec = pspec;
+	track->_notify_signal_id = 0;
+	track->_visible = FALSE;
+}
+
+void
+nm_dbus_track_obj_path_deinit (NMDBusTrackObjPath *track)
+{
+	/* we allow deinit() to be called multiple times (e.g. from
+	 * dispose(), which must be re-entrant). */
+	nm_assert (track);
+	nm_assert (!track->_notify_target || G_IS_OBJECT (track->_notify_target));
+
+	nm_clear_g_signal_handler (track->obj, &track->_notify_signal_id);
+	track->_notify_target = NULL;
+	track->_notify_pspec = NULL;
+	track->_visible = FALSE;
+	nm_clear_g_object (&track->_obj);
+}
+
+void
+nm_dbus_track_obj_path_notify (const NMDBusTrackObjPath *track)
+{
+	nm_assert (track);
+	nm_assert (G_IS_OBJECT (track->_notify_target));
+	nm_assert (G_IS_PARAM_SPEC (track->_notify_pspec));
+
+	g_object_notify_by_pspec (track->_notify_target,
+	                          (GParamSpec *) track->_notify_pspec);
+}
+
+const char *
+nm_dbus_track_obj_path_get (const NMDBusTrackObjPath *track)
+{
+	nm_assert (track);
+	nm_assert (G_IS_OBJECT (track->_notify_target));
+
+	return track->obj && track->visible
+	       ? nm_dbus_object_get_path_still_exported (track->obj)
+	       : NULL;
+}
+
+static void
+_track_obj_exported_changed (NMDBusObject *obj,
+                             NMDBusTrackObjPath *track)
+{
+	nm_dbus_track_obj_path_notify (track);
+}
+
+void
+nm_dbus_track_obj_path_set (NMDBusTrackObjPath *track,
+                            gpointer obj,
+                            gboolean visible)
+{
+	gs_unref_object NMDBusObject *old_obj = NULL;
+	const char *old_path;
+
+	nm_assert (track);
+	nm_assert (G_IS_OBJECT (track->_notify_target));
+
+	g_return_if_fail (!obj || NM_IS_DBUS_OBJECT (obj));
+
+	if (   track->obj == obj
+	    && track->visible == !!visible)
+		return;
+
+	old_path = nm_dbus_track_obj_path_get (track);
+
+	track->_visible = visible;
+
+	if (track->obj != obj) {
+		nm_clear_g_signal_handler (track->obj, &track->_notify_signal_id);
+
+		old_obj = track->obj;
+		track->_obj = nm_g_object_ref (obj);
+
+		if (obj) {
+			track->_notify_signal_id = g_signal_connect (obj,
+			                                             NM_DBUS_OBJECT_EXPORTED_CHANGED,
+			                                             G_CALLBACK (_track_obj_exported_changed),
+			                                             track);
+		}
+	}
+
+	if (!nm_streq0 (old_path, nm_dbus_track_obj_path_get (track)))
+		nm_dbus_track_obj_path_notify (track);
+}

src/nm-dbus-utils.h

@@ -179,4 +179,34 @@ void nm_dbus_utils_g_value_set_object_path_from_hash (GValue *value,
                                                       GHashTable *hash,
                                                       gboolean expect_all_exported);
 
+/*****************************************************************************/
+
+typedef struct {
+	union {
+		gpointer const obj;
+		gpointer _obj;
+	};
+	GObject *_notify_target;
+	const GParamSpec *_notify_pspec;
+	gulong _notify_signal_id;
+	union {
+		const bool visible;
+		bool _visible;
+	};
+} NMDBusTrackObjPath;
+
+void nm_dbus_track_obj_path_init (NMDBusTrackObjPath *track,
+                                  GObject *target,
+                                  const GParamSpec *pspec);
+
+void nm_dbus_track_obj_path_deinit (NMDBusTrackObjPath *track);
+
+void nm_dbus_track_obj_path_notify (const NMDBusTrackObjPath *track);
+
+const char *nm_dbus_track_obj_path_get (const NMDBusTrackObjPath *track);
+
+void nm_dbus_track_obj_path_set (NMDBusTrackObjPath *track,
+                                 gpointer obj,
+                                 gboolean visible);
+
 #endif /* __NM_DBUS_UTILS_H__ */