# Django 4.2.11 documentation

# Source code for django.middleware.gzip

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

    re_accepts_gzip = _lazy_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.
        """

        max_random_bytes = 100

        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:
                if response.is_async:
                    # pull to lexical scope to capture fixed reference in case
                    # streaming_content is set again later.
                    orignal_iterator = response.streaming_content

                    async def gzip_wrapper():
                        async for chunk in orignal_iterator:
                            yield compress_string(
                                chunk,
                                max_random_bytes=self.max_random_bytes,
                            )

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

            # If there is a strong ETag, make it weak to fulfill the requirements
            # of RFC 9110 Section 8.8.1 while also allowing conditional request
            # matches on ETags.
            etag = response.get("ETag")
            if etag and etag.startswith('"'):
                response.headers["ETag"] = "W/" + etag
            response.headers["Content-Encoding"] = "gzip"

            return response