+
−"""
+
−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 parameter-less 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 a response
+
−  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 cache
+
−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)
+
−
+
−    def process_response(self, request, response):
+
−        """Sets the cache, if needed."""
+
−        if not hasattr(request, '_cache_update_cache') or not request._cache_update_cache:
+
−            # We don't need to update the cache, just return.
+
−            return response
+
−        if request.method != 'GET':
+
−            # This is a stronger requirement than above. It is needed
+
−            # because of interactions between this middleware and the
+
−            # HTTPMiddleware, which throws the body of a HEAD-request
+
−            # away before this middleware gets a chance to cache it.
+
−            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.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)
+
−
+
−    def process_request(self, request):
+
−        """
+
−        Checks whether the page is already cached and returns the cached
+
−        version if available.
+
−        """
+
−        if self.cache_anonymous_only:
+
−            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 not request.method in ('GET', 'HEAD') or request.GET:
+
−            request._cache_update_cache = False
+
−            return None # Don't bother checking the cache.
+
−
+
−        if self.cache_anonymous_only and request.user.is_authenticated():
+
−            request._cache_update_cache = False
+
−            return None # Don't cache requests from authenticated users.
+
−
+
−        cache_key = get_cache_key(request, self.key_prefix)
+
−        if cache_key is None:
+
−            request._cache_update_cache = True
+
−            return None # No cache information available, need to rebuild.
+
−
+
−        response = cache.get(cache_key, None)
+
−        if response is None:
+
−            request._cache_update_cache = True
+
−            return None # No cache information available, need to rebuild.
+
−
+
−        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, key_prefix=None, cache_anonymous_only=None):
+
−        self.cache_timeout = cache_timeout
+
−        if cache_timeout is None:
+
−            self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
+
−        self.key_prefix = key_prefix
+
−        if key_prefix is None:
+
−            self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
+
−        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