gdbus-monitor - interface `<none>`

Question

Has the interface <none> in the gdbus-monitor output a special meaning?

What API call is required to create such a message using GDbus (g_dbus_connection_register_object does not allow to pass NULL as GDBusInterfaceInfo * and that seems to be the only to register a object to a path)

related: dbus - register object to remote on interface NULL

Answer 1

Looking into dbus-monitor's source code shows that it occures as soon as DBUS_EXPORT const char * dbus_message_get_interface ( DBusMessage * message ) returns NULL (which is valid!, but not according to the spec which requires minimum one . and two name chunks!! EDIT: A noteable exception are method calls which do not require the interface field of a message to be set http://dbus.freedesktop.org/doc/dbus-specification.html#message-protocol-types).

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g_dbus_message_new_method_call (...) allows interface_ to be null. But that still only solves half the problems (sender). The receiver method seems to not exist for interface_s being NULL.

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Turns out it is a bug, I did a source code investigation and filed a bug (including fix) https://bugzilla.gnome.org/show_bug.cgi?id=706675

Answer 2

client needs to know the interface name while subscribing g_dbus_connection_signal_subscribe to any signal else it will listen to all interfaces hence inefficient. Interface is required to bind methods and signals in single entity mentioned in server introspection xml file.