Use bus_watch_namespace() for more robust monitoring of mpris players appearing or disappearing on the bus.

Approved by Charles Kerr, PS Jenkins bot.

1 files changed, 349 insertions, 0 deletions

diff --git a/src/bus-watch-namespace.c b/src/bus-watch-namespace.c
new file mode 100644
index 0000000..f20905c
--- /dev/null
+++ b/src/bus-watch-namespace.c
@@ -0,0 +1,349 @@
+/*
+ * Copyright 2013 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * Author: Lars Uebernickel <lars.uebernickel@canonical.com>
+ */
+
+#include <gio/gio.h>
+#include <string.h>
+#include "bus-watch-namespace.h"
+
+typedef struct
+{
+  guint                     id;
+  gchar                    *name_space;
+  GBusNameAppearedCallback  appeared_handler;
+  GBusNameVanishedCallback  vanished_handler;
+  gpointer                  user_data;
+  GDestroyNotify            user_data_destroy;
+
+  GDBusConnection          *connection;
+  GCancellable             *cancellable;
+  GHashTable               *names;
+  guint                     subscription_id;
+} NamespaceWatcher;
+
+typedef struct
+{
+  NamespaceWatcher *watcher;
+  gchar            *name;
+} GetNameOwnerData;
+
+static guint namespace_watcher_next_id;
+static GHashTable *namespace_watcher_watchers;
+
+static void
+namespace_watcher_stop (gpointer data)
+{
+  NamespaceWatcher *watcher = data;
+
+  g_cancellable_cancel (watcher->cancellable);
+  g_object_unref (watcher->cancellable);
+
+  if (watcher->subscription_id)
+    g_dbus_connection_signal_unsubscribe (watcher->connection, watcher->subscription_id);
+
+  if (watcher->vanished_handler)
+    {
+      GHashTableIter it;
+      const gchar *name;
+
+      g_hash_table_iter_init (&it, watcher->names);
+      while (g_hash_table_iter_next (&it, (gpointer *) &name, NULL))
+        watcher->vanished_handler (watcher->connection, name, watcher->user_data);
+    }
+
+  if (watcher->user_data_destroy)
+    watcher->user_data_destroy (watcher->user_data);
+
+  if (watcher->connection)
+    {
+      g_signal_handlers_disconnect_by_func (watcher->connection, namespace_watcher_stop, watcher);
+      g_object_unref (watcher->connection);
+    }
+
+  g_hash_table_unref (watcher->names);
+
+  g_hash_table_remove (namespace_watcher_watchers, GUINT_TO_POINTER (watcher->id));
+  if (g_hash_table_size (namespace_watcher_watchers) == 0)
+    g_clear_pointer (&namespace_watcher_watchers, g_hash_table_destroy);
+
+  g_free (watcher->name_space);
+
+  g_free (watcher);
+}
+
+static void
+namespace_watcher_name_appeared (NamespaceWatcher *watcher,
+                                 const gchar      *name,
+                                 const gchar      *owner)
+{
+  /* There's a race between NameOwnerChanged signals arriving and the
+   * ListNames/GetNameOwner sequence returning, so this function might
+   * be called more than once for the same name. To ensure that
+   * appeared_handler is only called once for each name, it is only
+   * called when inserting the name into watcher->names (each name is
+   * only inserted once there).
+   */
+  if (g_hash_table_contains (watcher->names, name))
+    return;
+
+  g_hash_table_add (watcher->names, g_strdup (name));
+
+  if (watcher->appeared_handler)
+    watcher->appeared_handler (watcher->connection, name, owner, watcher->user_data);
+}
+
+static void
+namespace_watcher_name_vanished (NamespaceWatcher *watcher,
+                                 const gchar      *name)
+{
+  if (g_hash_table_remove (watcher->names, name) && watcher->vanished_handler)
+    watcher->vanished_handler (watcher->connection, name, watcher->user_data);
+}
+
+static gboolean
+dbus_name_has_namespace (const gchar *name,
+                         const gchar *name_space)
+{
+  gint len_name;
+  gint len_namespace;
+
+  len_name = strlen (name);
+  len_namespace = strlen (name_space);
+
+  if (len_name < len_namespace)
+    return FALSE;
+
+  if (memcmp (name_space, name, len_namespace) != 0)
+    return FALSE;
+
+  return len_namespace == len_name || name[len_namespace] == '.';
+}
+
+static void
+name_owner_changed (GDBusConnection *connection,
+                    const gchar     *sender_name,
+                    const gchar     *object_path,
+                    const gchar     *interface_name,
+                    const gchar     *signal_name,
+                    GVariant        *parameters,
+                    gpointer         user_data)
+{
+  NamespaceWatcher *watcher = user_data;
+  const gchar *name;
+  const gchar *old_owner;
+  const gchar *new_owner;
+
+  g_variant_get (parameters, "(&s&s&s)", &name, &old_owner, &new_owner);
+
+  if (old_owner[0] != '\0')
+    namespace_watcher_name_vanished (watcher, name);
+
+  if (new_owner[0] != '\0')
+    namespace_watcher_name_appeared (watcher, name, new_owner);
+}
+
+static void
+got_name_owner (GObject      *object,
+                GAsyncResult *result,
+                gpointer      user_data)
+{
+  GetNameOwnerData *data = user_data;
+  GError *error = NULL;
+  GVariant *reply;
+  const gchar *owner;
+
+  reply = g_dbus_connection_call_finish (G_DBUS_CONNECTION (object), result, &error);
+
+  if (g_error_matches (error, G_IO_ERROR, G_IO_ERROR_CANCELLED))
+    {
+      g_error_free (error);
+      goto out;
+    }
+
+  if (reply == NULL)
+    {
+      if (!g_error_matches (error, G_DBUS_ERROR, G_DBUS_ERROR_NAME_HAS_NO_OWNER))
+        g_warning ("bus_watch_namespace: error calling org.freedesktop.DBus.GetNameOwner: %s", error->message);
+      g_error_free (error);
+      goto out;
+    }
+
+  g_variant_get (reply, "(&s)", &owner);
+  namespace_watcher_name_appeared (data->watcher, data->name, owner);
+
+  g_variant_unref (reply);
+
+out:
+  g_free (data->name);
+  g_slice_free (GetNameOwnerData, data);
+}
+
+static void
+names_listed (GObject      *object,
+              GAsyncResult *result,
+              gpointer      user_data)
+{
+  NamespaceWatcher *watcher;
+  GError *error = NULL;
+  GVariant *reply;
+  GVariantIter *iter;
+  const gchar *name;
+
+  reply = g_dbus_connection_call_finish (G_DBUS_CONNECTION (object), result, &error);
+
+  if (g_error_matches (error, G_IO_ERROR, G_IO_ERROR_CANCELLED))
+    {
+      g_error_free (error);
+      return;
+    }
+
+  watcher = user_data;
+
+  if (reply == NULL)
+    {
+      g_warning ("bus_watch_namespace: error calling org.freedesktop.DBus.ListNames: %s", error->message);
+      g_error_free (error);
+      return;
+    }
+
+  g_variant_get (reply, "(as)", &iter);
+  while (g_variant_iter_next (iter, "&s", &name))
+    {
+      if (dbus_name_has_namespace (name, watcher->name_space))
+        {
+          GetNameOwnerData *data = g_slice_new (GetNameOwnerData);
+          data->watcher = watcher;
+          data->name = g_strdup (name);
+          g_dbus_connection_call (watcher->connection, "org.freedesktop.DBus", "/",
+                                  "org.freedesktop.DBus", "GetNameOwner",
+                                  g_variant_new ("(s)", name), G_VARIANT_TYPE ("(s)"),
+                                  G_DBUS_CALL_FLAGS_NONE, -1, watcher->cancellable,
+                                  got_name_owner, data);
+        }
+    }
+
+  g_variant_iter_free (iter);
+  g_variant_unref (reply);
+}
+
+static void
+connection_closed (GDBusConnection *connection,
+                   gboolean         remote_peer_vanished,
+                   GError          *error,
+                   gpointer         user_data)
+{
+  NamespaceWatcher *watcher = user_data;
+
+  namespace_watcher_stop (watcher);
+}
+
+static void
+got_bus (GObject      *object,
+         GAsyncResult *result,
+         gpointer      user_data)
+{
+  GDBusConnection *connection;
+  NamespaceWatcher *watcher;
+  GError *error = NULL;
+
+  connection = g_bus_get_finish (result, &error);
+
+  if (g_error_matches (error, G_IO_ERROR, G_IO_ERROR_CANCELLED))
+    {
+      g_error_free (error);
+      return;
+    }
+
+  watcher = user_data;
+
+  if (connection == NULL)
+    {
+      namespace_watcher_stop (watcher);
+      return;
+    }
+
+  watcher->connection = connection;
+  g_signal_connect (watcher->connection, "closed", G_CALLBACK (connection_closed), watcher);
+
+  watcher->subscription_id =
+    g_dbus_connection_signal_subscribe (watcher->connection, "org.freedesktop.DBus",
+                                        "org.freedesktop.DBus", "NameOwnerChanged", "/org/freedesktop/DBus",
+                                        watcher->name_space, G_DBUS_SIGNAL_FLAGS_MATCH_ARG0_NAMESPACE,
+                                        name_owner_changed, watcher, NULL);
+
+  g_dbus_connection_call (watcher->connection, "org.freedesktop.DBus", "/",
+                          "org.freedesktop.DBus", "ListNames", NULL, G_VARIANT_TYPE ("(as)"),
+                          G_DBUS_CALL_FLAGS_NONE, -1, watcher->cancellable,
+                          names_listed, watcher);
+}
+
+guint
+bus_watch_namespace (GBusType                  bus_type,
+                     const gchar              *name_space,
+                     GBusNameAppearedCallback  appeared_handler,
+                     GBusNameVanishedCallback  vanished_handler,
+                     gpointer                  user_data,
+                     GDestroyNotify            user_data_destroy)
+{
+  NamespaceWatcher *watcher;
+
+  /* same rules for interfaces and well-known names */
+  g_return_val_if_fail (name_space != NULL && g_dbus_is_interface_name (name_space), 0);
+  g_return_val_if_fail (appeared_handler || vanished_handler, 0);
+
+  watcher = g_new0 (NamespaceWatcher, 1);
+  watcher->id = namespace_watcher_next_id++;
+  watcher->name_space = g_strdup (name_space);
+  watcher->appeared_handler = appeared_handler;
+  watcher->vanished_handler = vanished_handler;
+  watcher->user_data = user_data;
+  watcher->user_data_destroy = user_data_destroy;
+  watcher->cancellable = g_cancellable_new ();
+  watcher->names = g_hash_table_new_full (g_str_hash, g_str_equal, g_free, NULL);
+
+  if (namespace_watcher_watchers == NULL)
+    namespace_watcher_watchers = g_hash_table_new (g_direct_hash, g_direct_equal);
+  g_hash_table_insert (namespace_watcher_watchers, GUINT_TO_POINTER (watcher->id), watcher);
+
+  g_bus_get (bus_type, watcher->cancellable, got_bus, watcher);
+
+  return watcher->id;
+}
+
+void
+bus_unwatch_namespace (guint id)
+{
+  /* namespace_watcher_stop() might have already removed the watcher
+   * with @id in the case of a connection error. Thus, this function
+   * doesn't warn when @id is absent from the hash table.
+   */
+
+  if (namespace_watcher_watchers)
+    {
+      NamespaceWatcher *watcher;
+
+      watcher = g_hash_table_lookup (namespace_watcher_watchers, GUINT_TO_POINTER (id));
+      if (watcher)
+        {
+          /* make sure vanished() is not called as a result of this function */
+          g_hash_table_remove_all (watcher->names);
+
+          namespace_watcher_stop (watcher);
+        }
+    }
+}