To do some pre-verification of received property set messages I need to get the type of the message data and compare it to the type of the property.
When I try to peek the type (using sd_bus_message_peek_type) it returns "v" which is the signature of variant. Is it possible to get the signature of the actual data wrapped in the variant? And how to do that?
A variant is a container so one needs to enter that container to get the actual type.
Entering the container is done with sd_bus_message_enter_container.
Once the container is entered, the next data to read is the variant wrapped value.
Note that the pre-verification step can be done by the call to sd_bus_message_enter_container itself.
The type argument is the type of the property, and if it doesn't match the type of the message data then sd_bus_message_enter_container will return -ENXIO.