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from django.utils.http import http_date, parse_http_date_safe
class ConditionalGetMiddleware(object):
"""
Handles conditional GET operations. If the response has an ETag or
Last-Modified header, and the request has If-None-Match or
If-Modified-Since, the response is replaced by an HttpNotModified.
Also sets the Date and Content-Length response-headers.
"""
def process_response(self, request, response):
response['Date'] = http_date()
if not response.streaming and not response.has_header('Content-Length'):
response['Content-Length'] = str(len(response.content))
# If-None-Match must be ignored if original result would be anything
# other than a 2XX or 304 status. 304 status would result in no change.
# http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26
if 200 <= response.status_code < 300 and response.has_header('ETag'):
if_none_match = request.META.get('HTTP_IF_NONE_MATCH')
if if_none_match == response['ETag']:
# Setting the status is enough here. The response handling path
# automatically removes content for this status code (in
# http.conditional_content_removal()).
response.status_code = 304
# If-Modified-Since must be ignored if the original result was not a 200.
# http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.25
if response.status_code == 200 and response.has_header('Last-Modified'):
if_modified_since = request.META.get('HTTP_IF_MODIFIED_SINCE')
if if_modified_since is not None:
if_modified_since = parse_http_date_safe(if_modified_since)
if if_modified_since is not None:
last_modified = parse_http_date_safe(response['Last-Modified'])
if last_modified is not None and last_modified <= if_modified_since:
# Setting the status code is enough here (same reasons as
# above).
response.status_code = 304
return response
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