Don't use bodyParser with Express 4.x: http://andrewkelley.me/post/do-not-use-bodyparser-with-express-js.html
use
app.use(express.json());
app.use(express.urlencoded());
instead. The problem with your code is that you will return before the callback will be called so the result will not be send to the user.
Change your code to:
return res.end(util.inspect({fields: fields, files: files}));
and remove the return at the end.