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Source code for django.middleware.cache

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::


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.


import warnings

from django.conf import settings
from django.core.cache import caches, DEFAULT_CACHE_ALIAS
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 RemovedInDjango18Warning

[docs]class UpdateCacheMiddleware(object): """ 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_CLASSES so that it'll get called last during the response phase. """ def __init__(self): self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX self.cache_anonymous_only = getattr(settings, 'CACHE_MIDDLEWARE_ANONYMOUS_ONLY', False) self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS self.cache = caches[self.cache_alias] def _session_accessed(self, request): try: return request.session.accessed except AttributeError: return False def _should_update_cache(self, request, response): if not hasattr(request, '_cache_update_cache') or not request._cache_update_cache: return False # If the session has not been accessed otherwise, we don't want to # cause it to be accessed here. If it hasn't been accessed, then the # user's logged-in status has not affected the response anyway. if self.cache_anonymous_only and self._session_accessed(request): assert hasattr(request, 'user'), "The Django cache middleware with CACHE_MIDDLEWARE_ANONYMOUS_ONLY=True requires authentication middleware to be installed. Edit your MIDDLEWARE_CLASSES setting to insert 'django.contrib.auth.middleware.AuthenticationMiddleware' before the CacheMiddleware." if request.user.is_authenticated(): # Don't cache user-variable requests from authenticated users. return False return True def process_response(self, request, response): """Sets 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 != 200: 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 # Try to get the timeout from the "max-age" section of the "Cache- # Control" header before reverting to using the default cache_timeout # length. timeout = get_max_age(response) if timeout is None: timeout = self.cache_timeout elif timeout == 0: # max-age was set to 0, don't bother caching. return response patch_response_headers(response, timeout) if timeout: 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
[docs]class FetchFromCacheMiddleware(object): """ 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_CLASSES so that it'll get called last during the request phase. """ def __init__(self): self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS self.cache = caches[self.cache_alias] def process_request(self, request): """ Checks whether the page is already cached and returns 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, None) # 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, None) 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, cache_timeout=None, cache_anonymous_only=None, **kwargs): # 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 = '' except KeyError: key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX self.key_prefix = key_prefix try: cache_alias = kwargs['cache_alias'] if cache_alias is None: cache_alias = DEFAULT_CACHE_ALIAS except KeyError: cache_alias = settings.CACHE_MIDDLEWARE_ALIAS self.cache_alias = cache_alias if cache_timeout is None: cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS self.cache_timeout = cache_timeout if cache_anonymous_only is None: cache_anonymous_only = getattr(settings, 'CACHE_MIDDLEWARE_ANONYMOUS_ONLY', False) self.cache_anonymous_only = cache_anonymous_only if self.cache_anonymous_only: msg = "CACHE_MIDDLEWARE_ANONYMOUS_ONLY has been deprecated and will be removed in Django 1.8." warnings.warn(msg, RemovedInDjango18Warning, stacklevel=1) self.cache = caches[self.cache_alias]
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