Virtual table for handling properties and method calls for a D-Bus interface.
Since 2.38, if you want to handle getting/setting D-Bus properties asynchronously, give null as your
get_property or set_property function. The D-Bus call will be directed to your method_call
function, with the provided interface_name set to "org.freedesktop.DBus.Properties".
Ownership of the DBusMethodInvocation object passed to the method_call
function is transferred to your handler; you must call one of the methods of
DBusMethodInvocation to return a reply (possibly empty), or an error. These
functions also take ownership of the passed-in invocation object, so unless the invocation object has otherwise been referenced, it will
be then be freed. Calling one of these functions may be done within your method_call implementation but it also can be done
at a later point to handle the method asynchronously.
The usual checks on the validity of the calls is performed. For `Get` calls, an error is automatically returned if the property does not exist or the permissions do not allow access. The same checks are performed for `Set` calls, and the provided value is also checked for being the correct type.
For both `Get` and `Set` calls, the DBusMethodInvocation passed to the
method_call handler can be queried with
get_property_info to get a pointer to the DBusPropertyInfo of the property.
If you have readable properties specified in your interface info, you must ensure that you either provide a non-
null get_property() function or provide implementations of both the `Get` and `GetAll`
methods on org.freedesktop.DBus.Properties interface in your method_call function. Note that the required return type of the
`Get` call is `(v)`, not the type of the property. `GetAll` expects a return value of type `a{sv}`.
If you have writable properties specified in your interface info, you must ensure that you either provide a non-
null set_property() function or provide an implementation of the `Set` call. If
implementing the call, you must return the value of type g_variant_type_unit.