41 lines
1.6 KiB
Python
41 lines
1.6 KiB
Python
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from django.utils.cache import cc_delim_re, get_conditional_response, set_response_etag
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from django.utils.deprecation import MiddlewareMixin
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from django.utils.http import parse_http_date_safe
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class ConditionalGetMiddleware(MiddlewareMixin):
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"""
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Handle conditional GET operations. If the response has an ETag or
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Last-Modified header and the request has If-None-Match or If-Modified-Since,
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replace the response with HttpNotModified. Add an ETag header if needed.
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"""
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def process_response(self, request, response):
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# It's too late to prevent an unsafe request with a 412 response, and
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# for a HEAD request, the response body is always empty so computing
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# an accurate ETag isn't possible.
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if request.method != "GET":
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return response
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if self.needs_etag(response) and not response.has_header("ETag"):
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set_response_etag(response)
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etag = response.get("ETag")
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last_modified = response.get("Last-Modified")
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last_modified = last_modified and parse_http_date_safe(last_modified)
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if etag or last_modified:
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return get_conditional_response(
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request,
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etag=etag,
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last_modified=last_modified,
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response=response,
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)
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return response
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def needs_etag(self, response):
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"""Return True if an ETag header should be added to response."""
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cache_control_headers = cc_delim_re.split(response.get("Cache-Control", ""))
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return all(header.lower() != "no-store" for header in cache_control_headers)
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