/django/middleware/cache.py
Python | 205 lines | 151 code | 12 blank | 42 comment | 21 complexity | 080e87991c5bb9630aa2a10055220a19 MD5 | raw file
Possible License(s): BSD-3-Clause
- """
- 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_CLASSES = [
- '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.
- * If CACHE_MIDDLEWARE_ANONYMOUS_ONLY is set to True, only anonymous requests
- (i.e., those not made by a logged-in user) will be cached. This is a simple
- and effective way of avoiding the caching of the Django admin (and any other
- user-specific content).
- * 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 get_cache, DEFAULT_CACHE_ALIAS
- from django.utils.cache import get_cache_key, learn_cache_key, patch_response_headers, get_max_age
- 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 = get_cache(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 not response.status_code == 200:
- 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 == 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
- 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.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 = get_cache(self.cache_alias)
- def process_request(self, request):
- """
- Checks whether the page is already cached and returns the cached
- version if available.
- """
- if not request.method 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.
- cache_kwargs = {}
- try:
- self.key_prefix = kwargs['key_prefix']
- if self.key_prefix is not None:
- cache_kwargs['KEY_PREFIX'] = self.key_prefix
- else:
- self.key_prefix = ''
- except KeyError:
- self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
- cache_kwargs['KEY_PREFIX'] = self.key_prefix
- try:
- self.cache_alias = kwargs['cache_alias']
- if self.cache_alias is None:
- self.cache_alias = DEFAULT_CACHE_ALIAS
- if cache_timeout is not None:
- cache_kwargs['TIMEOUT'] = cache_timeout
- except KeyError:
- self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
- if cache_timeout is None:
- cache_kwargs['TIMEOUT'] = settings.CACHE_MIDDLEWARE_SECONDS
- else:
- cache_kwargs['TIMEOUT'] = cache_timeout
- if cache_anonymous_only is None:
- self.cache_anonymous_only = getattr(settings, 'CACHE_MIDDLEWARE_ANONYMOUS_ONLY', False)
- else:
- self.cache_anonymous_only = cache_anonymous_only
- self.cache = get_cache(self.cache_alias, **cache_kwargs)
- self.cache_timeout = self.cache.default_timeout