(PECL gupnp >= 0.1.0)
gupnp_service_info_get_introspection — Get resource introspection of service
Get resource introspection of service or register callback if corresponding parameter was passed.
proxyA service proxy identifier.
callback
       The callback function to be called when introspection object is ready.
       Typically, callback function takes on three parameters. The introspection 
       parameter's identifier being the first, error parameter's message 
       being the second, and the arg is third.
      
arg
       User data for callback. 
      
Return true if callback function was defined. Return introspection identifier if callback function was omited.
Issues E_WARNING with not valid callback function.