Obtener objeto de ruta de GetResponseEvent

Estoy implementando un RequestListener class per the instructions at How to register a new Request Format and Mime Type.

I would like to access the metadata from the routes.yml file (I believe I need a Symfony\Component\Routing\Route object) for the current request so that I can see what formats the current route permits.

How can I obtain this object? Doing var_dump($event); die; resulted in a 600+ MB response.