# Django 2.2.9.dev20191202104323 文档

# django.middleware.gzip 源代码

    import re

    from django.utils.cache import patch_vary_headers
    from django.utils.deprecation import MiddlewareMixin
    from django.utils.text import compress_sequence, compress_string

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

    class GZipMiddleware(MiddlewareMixin):
        """
        Compress content if the browser allows gzip compression.
        Set the Vary header accordingly, so that caches will base their storage
        on the Accept-Encoding header.
        """
        def process_response(self, request, response):
            # It's not worth attempting to compress really short responses.
            if not response.streaming and len(response.content) < 200:
                return response

            # Avoid gzipping if we've already got a content-encoding.
            if response.has_header('Content-Encoding'):
                return response

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

            ae = request.META.get('HTTP_ACCEPT_ENCODING', '')
            if not re_accepts_gzip.search(ae):
                return response

            if response.streaming:
                # Delete the `Content-Length` header for streaming content, because
                # we won't know the compressed size until we stream it.
                response.streaming_content = compress_sequence(response.streaming_content)
                del response['Content-Length']
            else:
                # Return the compressed content only if it's actually shorter.
                compressed_content = compress_string(response.content)
                if len(compressed_content) >= len(response.content):
                    return response
                response.content = compressed_content
                response['Content-Length'] = str(len(response.content))

            # If there is a strong ETag, make it weak to fulfill the requirements
            # of RFC 7232 section-2.1 while also allowing conditional request
            # matches on ETags.
            etag = response.get('ETag')
            if etag and etag.startswith('"'):
                response['ETag'] = 'W/' + etag
            response['Content-Encoding'] = 'gzip'

            return response