UPDATE AFTER ANSWER: the code is now fixed and works look below for correct code
Im trying to post from a perl script (on my server) to my google app engine, and im not
Since you're sending the audio file as the body of the request, not as part of a form, you can access it with self.request.body.
self.request.body
I'm a little confused as to why you're sending an audio file to App Engine just so it can send it to another service, though.