A GDBusCapabilityFlags describing what protocol features are supported.
A pointer to a valid binary D-Bus message of out_size bytes generated by message or NULL if error is set. Free with g_free(). [array length=out_size][transfer full]
GException on failure.
Serializes message to a blob. The byte order returned by g_dbus_message_get_byte_order() will be used. Since 2.26