dbus - register object to remote on interface NULL

I have to deal with a binary blob dbus service/server which I need to connect to via dbus (session).

The introspection of the interface is as following (obtained via gdbus-codegen). We register a function to the remote so we get notified if a message has been received by the remote which is called message_handler. That happens as a response on a send_message command which I pass via dbus, but that works (and is thus not shown).

In a java example it is done via

dbus_connection.exportObject("/", new DBusInterfaceDerivedClassFoo());

and shows in bustle as (no interface) message_handler and everything works as expected.

In the bare logs say <none> instead of (no interface).

According to gdbus-monitor - interface `<none>` this is caused by the fact that gdbus-monitor detects interface being NULL

How to register/export a object with interface equal NULL using GDBus?

Things tried so far marked as comments in the code:

Code chunk:

static gchar iface_xml[] = 
"<node name='/'>"
" <interface name='bar.long.long.name.rxobj'>"
"  <method name='message_handler' >"
"   <arg type='s' direction='in'/>"
"  </method>"
"  <method name=isRemote' >"
"   <arg type='b' direction='out'/>"
"  </method>"
" </interface>"
" <interface name='org.freedesktop.DBus.Introspectable'>"
"  <method name='Introspect'>"
"   <arg type='s' direction='out'/>"
"  </method>"
" </interface>"
" <interface name='org.freedesktop.DBus.Peer'>"
"  <method name='Ping'>"
"  </method>"
" </interface>"
"</node>";

GError *error = NULL;

GDBusConnection *con = g_bus_get_sync (G_BUS_TYPE_SESSION, NULL, &error);
g_assert (!error);

GDBusNodeInfo *node_info = g_dbus_node_info_new_for_xml (iface_xml, &error);
// also tried ...de_info = NULL; // - crash, see below
g_assert (!error);

GDBusInterfaceInfo *interface_info = g_dbus_node_info_lookup_interface (node_info,
                              "bar.long.long.name.rxobj");
// also tried ...okup_interface (node_info, NULL); - obviously wrong
g_assert (interface_info);

guint id = g_dbus_connection_register_object (con,
                  (const gchar*)"/",

             // also tried node_info->interfaces[0]
             // also tried "" - crash
             // also tried "\0" - crash
             // also tried NULL - assert failure
                  interface_info,

                  &vtable, /*we never enter any of the callbacks*/
                  NULL,/*user_data*/
                  (GDestroyNotify)NULL,
                  &error);
g_assert (!error);

GMainLoop *loop = g_main_loop_new (...);
g_main_loop_run (loop);
...

No matter of what I commented out I never even entered the callbacks specified in vtable.

Thanks in advance for any tips.

Additional info: The remote uses qtdbus as far as I can say if that does matter.

It is not about exporting the interface on NULL interface (not covered by the spec), but about the service/server actually handling such a call properly.

This was not yet implemented in gdbus, filed a bug (including patch) https://bugzilla.gnome.org/show_bug.cgi?id=706675