While following the Flask file upload tutorial here, you might get a "This webpage is not available" message due to the connection being interrupted (ERR_CONNECTION_RESET). This is due to a problem with how modern browsers interact with the Werkzeug WGSI.
To fix this we need to make a small adjustment to Werkzeug's behaviour. Add the below snippet to your application, where app is the flask application:
Thanks to Armin Ronacher's snippet found here: http://flask.pocoo.org/snippets/47/