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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):
"""
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):
# 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