This callback is used to generate custom contents published with the
#epc_publisher_add_handler function. The arguments passed are the same as
passed to #epc_publisher_add_handler. The #EpcPublisher will decrease the
reference count of the returned buffer after deliving it. It's valid to
return %NULL in situations were no contents can be generated.
This callback is used to generate custom contents published with the #epc_publisher_add_handler function. The arguments passed are the same as passed to #epc_publisher_add_handler. The #EpcPublisher will decrease the reference count of the returned buffer after deliving it. It's valid to return %NULL in situations were no contents can be generated.