Interface DBusMessageFilterFunction

A filter function is passed a #GDBusMessage and expected to return a #GDBusMessage too. Passive filter functions that don't modify the message can simply return the message object: |[ static GDBusMessage * passive_filter (GDBusConnection *connection GDBusMessage *message, gboolean incoming, gpointer user_data) { // inspect message return message; }

Filter functions that wants to drop a message can simply return %NULL:
|[
static GDBusMessage *
drop_filter (GDBusConnection *connection
             GDBusMessage    *message,
             gboolean         incoming,
             gpointer         user_data)
{
  if (should_drop_message)
    {
      g_object_unref (message);
      message = NULL;
    }
  return message;
}

Finally, a filter function may modify a message by copying it: |[ static GDBusMessage * modifying_filter (GDBusConnection *connection GDBusMessage *message, gboolean incoming, gpointer user_data) { GDBusMessage *copy; GError *error;

error = NULL; copy = g_dbus_message_copy (message, &error); // handle error being set g_object_unref (message);

// modify copy

return copy; }

If the returned #GDBusMessage is different from `message` and cannot
be sent on `connection` (it could use features, such as file
descriptors, not compatible with `connection)`, then a warning is
logged to standard error. Applications can
check this ahead of time using g_dbus_message_to_blob() passing a
#GDBusCapabilityFlags value obtained from `connection`.
@callback 
@param connection A #GDBusConnection.
@param message A locked #GDBusMessage that the filter function takes ownership of.
@param incoming %TRUE if it is a message received from the other peer, %FALSE if it is a message to be sent to the other peer.