I have code where I want to write a file as a result stream. It used to
be that file streams were classes, and implemented InputStream. Now they
are structs.

Which is fine, except...

res.writeBody(stream); // Error, no such overload

OK, so I found asInterface in
by looking at how vibe itself does it. and...

import vibe.d; // don't know the right way module to import?

This works, but I get the message:

Deprecation: vibe.inet.urltransfer.asInterface is not visible from 
module files

Where files is my module. So what is the proper way to do this? I'm
assuming importing vibe.core.internal is probably bad.