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from django.utils.cache import (
cc_delim_re, get_conditional_response, set_response_etag,
)
from django.utils.deprecation import MiddlewareMixin
from django.utils.http import parse_http_date_safe
class ConditionalGetMiddleware(MiddlewareMixin):
"""
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. An ETag
header is added if needed.
"""
def process_response(self, request, response):
# It's too late to prevent an unsafe request with a 412 response, and
# for a HEAD request, the response body is always empty so computing
# an accurate ETag isn't possible.
if request.method != 'GET':
return response
if self.needs_etag(response) and not response.has_header('ETag'):
set_response_etag(response)
etag = response.get('ETag')
last_modified = response.get('Last-Modified')
if last_modified:
last_modified = parse_http_date_safe(last_modified)
if etag or last_modified:
return get_conditional_response(
request,
etag=etag,
last_modified=last_modified,
response=response,
)
return response
def needs_etag(self, response):
"""
Return True if an ETag header should be added to response.
"""
cache_control_headers = cc_delim_re.split(response.get('Cache-Control', ''))
return all(header.lower() != 'no-store' for header in cache_control_headers)