'Respond to the WSGI request.
.. warning::
This will translate any relative Location header value to an
absolute URL using the WSGI environment\'s HOST_URL as a
prefix, as RFC 2616 specifies.
However, it is quite common to use relative redirects,
especially when it is difficult to know the exact HOST_URL
the browser would have used when behind several CNAMEs, CDN
services, etc. All modern browsers support relative
redirects.
To skip over RFC enforcement of the Location header value,
you may set ``env[\'swift.leave_relative_location\'] = True``
in the WSGI environment.'

def __call__(self, env, start_response):

    if (not self.request):
        self.request = Request(env)
    self.environ = env
    if (not self.response_iter):
        self.response_iter = self._response_iter(self.app_iter, self._body)
    if (('location' in self.headers) and (not env.get('swift.leave_relative_location'))):
        self.location = self.absolute_location()
    start_response(self.status, self.headers.items())
    return self.response_iter
