import re

from django.utils.text import compress_string

from django.utils.cache import patch_vary_headers

re_accepts_gzip = re.compile(r'\bgzip\b')

class GZipMiddleware(object):

    """

    This middleware compresses content if the browser allows gzip compression.

    It sets the Vary header accordingly, so that caches will base their storage

    on the Accept-Encoding header.

    """

    def process_response(self, request, response):

        patch_vary_headers(response, ('Accept-Encoding',))

        # Avoid gzipping if we've already got a content-encoding or if the

        # content-type is Javascript (silly IE...)

        is_js = "javascript" in response.headers.get('Content-Type', '').lower()

        if response.has_header('Content-Encoding') or is_js:

            return response

        ae = request.META.get('HTTP_ACCEPT_ENCODING', '')

        if not re_accepts_gzip.search(ae):

            return response

        response.content = compress_string(response.content)

        response['Content-Encoding'] = 'gzip'

        response['Content-Length'] = str(len(response.content))

        return response