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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_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)
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
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