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- """
- Cache middleware. If enabled, each Django-powered page will be cached based on
- URL. The canonical way to enable cache middleware is to set
- ``UpdateCacheMiddleware`` as your first piece of middleware, and
- ``FetchFromCacheMiddleware`` as the last::
-
- MIDDLEWARE = [
- 'django.middleware.cache.UpdateCacheMiddleware',
- ...
- 'django.middleware.cache.FetchFromCacheMiddleware'
- ]
-
- This is counter-intuitive, but correct: ``UpdateCacheMiddleware`` needs to run
- last during the response phase, which processes middleware bottom-up;
- ``FetchFromCacheMiddleware`` needs to run last during the request phase, which
- processes middleware top-down.
-
- The single-class ``CacheMiddleware`` can be used for some simple sites.
- However, if any other piece of middleware needs to affect the cache key, you'll
- need to use the two-part ``UpdateCacheMiddleware`` and
- ``FetchFromCacheMiddleware``. This'll most often happen when you're using
- Django's ``LocaleMiddleware``.
-
- More details about how the caching works:
-
- * Only GET or HEAD-requests with status code 200 are cached.
-
- * The number of seconds each page is stored for is set by the "max-age" section
- of the response's "Cache-Control" header, falling back to the
- CACHE_MIDDLEWARE_SECONDS setting if the section was not found.
-
- * This middleware expects that a HEAD request is answered with the same response
- headers exactly like the corresponding GET request.
-
- * When a hit occurs, a shallow copy of the original response object is returned
- from process_request.
-
- * Pages will be cached based on the contents of the request headers listed in
- the response's "Vary" header.
-
- * This middleware also sets ETag, Last-Modified, Expires and Cache-Control
- headers on the response object.
-
- """
-
- from django.conf import settings
- from django.core.cache import DEFAULT_CACHE_ALIAS, caches
- from django.utils.cache import (
- get_cache_key,
- get_max_age,
- has_vary_header,
- learn_cache_key,
- patch_response_headers,
- )
- from django.utils.deprecation import MiddlewareMixin
-
-
- class UpdateCacheMiddleware(MiddlewareMixin):
- """
- Response-phase cache middleware that updates the cache if the response is
- cacheable.
-
- Must be used as part of the two-part update/fetch cache middleware.
- UpdateCacheMiddleware must be the first piece of middleware in MIDDLEWARE
- so that it'll get called last during the response phase.
- """
-
- def __init__(self, get_response):
- super().__init__(get_response)
- self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
- self.page_timeout = None
- self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
- self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
-
- @property
- def cache(self):
- return caches[self.cache_alias]
-
- def _should_update_cache(self, request, response):
- return hasattr(request, "_cache_update_cache") and request._cache_update_cache
-
- def process_response(self, request, response):
- """Set the cache, if needed."""
- if not self._should_update_cache(request, response):
- # We don't need to update the cache, just return.
- return response
-
- if response.streaming or response.status_code not in (200, 304):
- return response
-
- # Don't cache responses that set a user-specific (and maybe security
- # sensitive) cookie in response to a cookie-less request.
- if (
- not request.COOKIES
- and response.cookies
- and has_vary_header(response, "Cookie")
- ):
- return response
-
- # Don't cache a response with 'Cache-Control: private'
- if "private" in response.get("Cache-Control", ()):
- return response
-
- # Page timeout takes precedence over the "max-age" and the default
- # cache timeout.
- timeout = self.page_timeout
- if timeout is None:
- # The timeout from the "max-age" section of the "Cache-Control"
- # header takes precedence over the default cache timeout.
- timeout = get_max_age(response)
- if timeout is None:
- timeout = self.cache_timeout
- elif timeout == 0:
- # max-age was set to 0, don't cache.
- return response
- patch_response_headers(response, timeout)
- if timeout and response.status_code == 200:
- cache_key = learn_cache_key(
- request, response, timeout, self.key_prefix, cache=self.cache
- )
- if hasattr(response, "render") and callable(response.render):
- response.add_post_render_callback(
- lambda r: self.cache.set(cache_key, r, timeout)
- )
- else:
- self.cache.set(cache_key, response, timeout)
- return response
-
-
- class FetchFromCacheMiddleware(MiddlewareMixin):
- """
- Request-phase cache middleware that fetches a page from the cache.
-
- Must be used as part of the two-part update/fetch cache middleware.
- FetchFromCacheMiddleware must be the last piece of middleware in MIDDLEWARE
- so that it'll get called last during the request phase.
- """
-
- def __init__(self, get_response):
- super().__init__(get_response)
- self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
- self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
-
- @property
- def cache(self):
- return caches[self.cache_alias]
-
- def process_request(self, request):
- """
- Check whether the page is already cached and return the cached
- version if available.
- """
- if request.method not in ("GET", "HEAD"):
- request._cache_update_cache = False
- return None # Don't bother checking the cache.
-
- # try and get the cached GET response
- cache_key = get_cache_key(request, self.key_prefix, "GET", cache=self.cache)
- if cache_key is None:
- request._cache_update_cache = True
- return None # No cache information available, need to rebuild.
- response = self.cache.get(cache_key)
- # if it wasn't found and we are looking for a HEAD, try looking just for that
- if response is None and request.method == "HEAD":
- cache_key = get_cache_key(
- request, self.key_prefix, "HEAD", cache=self.cache
- )
- response = self.cache.get(cache_key)
-
- if response is None:
- request._cache_update_cache = True
- return None # No cache information available, need to rebuild.
-
- # hit, return cached response
- request._cache_update_cache = False
- return response
-
-
- class CacheMiddleware(UpdateCacheMiddleware, FetchFromCacheMiddleware):
- """
- Cache middleware that provides basic behavior for many simple sites.
-
- Also used as the hook point for the cache decorator, which is generated
- using the decorator-from-middleware utility.
- """
-
- def __init__(self, get_response, cache_timeout=None, page_timeout=None, **kwargs):
- super().__init__(get_response)
- # We need to differentiate between "provided, but using default value",
- # and "not provided". If the value is provided using a default, then
- # we fall back to system defaults. If it is not provided at all,
- # we need to use middleware defaults.
-
- try:
- key_prefix = kwargs["key_prefix"]
- if key_prefix is None:
- key_prefix = ""
- self.key_prefix = key_prefix
- except KeyError:
- pass
- try:
- cache_alias = kwargs["cache_alias"]
- if cache_alias is None:
- cache_alias = DEFAULT_CACHE_ALIAS
- self.cache_alias = cache_alias
- except KeyError:
- pass
-
- if cache_timeout is not None:
- self.cache_timeout = cache_timeout
- self.page_timeout = page_timeout
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