Returns the updated caching headers.

        Args:
            response (HttpResponse): The response from the remote service

        Returns:
            response:(HttpResponse.Headers): Http caching headers

def update_headers(self, response):
        """
        Returns the updated caching headers.

        Args:
            response (HttpResponse): The response from the remote service

        Returns:
            response:(HttpResponse.Headers): Http caching headers
        """
        if 'expires' in response.headers and 'cache-control' in response.headers:
            self.msg = self.server_cache_headers
            return response.headers
        else:
            self.msg = self.default_cache_vars
            date = parsedate(response.headers['date'])
            expires = datetime(*date[:6]) + timedelta(0, self.expire_after)
            response.headers.update({'expires': formatdate(calendar.timegm(expires.timetuple())),
                                'cache-control': 'public'})
            return response.headers