205 lines
8.8 KiB
Python
205 lines
8.8 KiB
Python
"""
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Cache middleware. If enabled, each Django-powered page will be cached based on
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URL. The canonical way to enable cache middleware is to set
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``UpdateCacheMiddleware`` as your first piece of middleware, and
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``FetchFromCacheMiddleware`` as the last::
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MIDDLEWARE_CLASSES = [
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'django.middleware.cache.UpdateCacheMiddleware',
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...
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'django.middleware.cache.FetchFromCacheMiddleware'
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]
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This is counter-intuitive, but correct: ``UpdateCacheMiddleware`` needs to run
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last during the response phase, which processes middleware bottom-up;
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``FetchFromCacheMiddleware`` needs to run last during the request phase, which
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processes middleware top-down.
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The single-class ``CacheMiddleware`` can be used for some simple sites.
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However, if any other piece of middleware needs to affect the cache key, you'll
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need to use the two-part ``UpdateCacheMiddleware`` and
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``FetchFromCacheMiddleware``. This'll most often happen when you're using
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Django's ``LocaleMiddleware``.
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More details about how the caching works:
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* Only GET or HEAD-requests with status code 200 are cached.
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* The number of seconds each page is stored for is set by the "max-age" section
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of the response's "Cache-Control" header, falling back to the
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CACHE_MIDDLEWARE_SECONDS setting if the section was not found.
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* If CACHE_MIDDLEWARE_ANONYMOUS_ONLY is set to True, only anonymous requests
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(i.e., those not made by a logged-in user) will be cached. This is a simple
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and effective way of avoiding the caching of the Django admin (and any other
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user-specific content).
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* This middleware expects that a HEAD request is answered with the same response
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headers exactly like the corresponding GET request.
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* When a hit occurs, a shallow copy of the original response object is returned
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from process_request.
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* Pages will be cached based on the contents of the request headers listed in
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the response's "Vary" header.
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* This middleware also sets ETag, Last-Modified, Expires and Cache-Control
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headers on the response object.
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"""
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from django.conf import settings
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from django.core.cache import get_cache, DEFAULT_CACHE_ALIAS
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from django.utils.cache import get_cache_key, learn_cache_key, patch_response_headers, get_max_age
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class UpdateCacheMiddleware(object):
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"""
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Response-phase cache middleware that updates the cache if the response is
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cacheable.
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Must be used as part of the two-part update/fetch cache middleware.
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UpdateCacheMiddleware must be the first piece of middleware in
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MIDDLEWARE_CLASSES so that it'll get called last during the response phase.
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"""
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def __init__(self):
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self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
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self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
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self.cache_anonymous_only = getattr(settings, 'CACHE_MIDDLEWARE_ANONYMOUS_ONLY', False)
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self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
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self.cache = get_cache(self.cache_alias)
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def _session_accessed(self, request):
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try:
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return request.session.accessed
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except AttributeError:
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return False
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def _should_update_cache(self, request, response):
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if not hasattr(request, '_cache_update_cache') or not request._cache_update_cache:
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return False
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# If the session has not been accessed otherwise, we don't want to
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# cause it to be accessed here. If it hasn't been accessed, then the
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# user's logged-in status has not affected the response anyway.
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if self.cache_anonymous_only and self._session_accessed(request):
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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."
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if request.user.is_authenticated():
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# Don't cache user-variable requests from authenticated users.
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return False
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return True
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def process_response(self, request, response):
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"""Sets the cache, if needed."""
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if not self._should_update_cache(request, response):
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# We don't need to update the cache, just return.
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return response
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if not response.status_code == 200:
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return response
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# Try to get the timeout from the "max-age" section of the "Cache-
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# Control" header before reverting to using the default cache_timeout
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# length.
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timeout = get_max_age(response)
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if timeout == None:
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timeout = self.cache_timeout
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elif timeout == 0:
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# max-age was set to 0, don't bother caching.
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return response
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patch_response_headers(response, timeout)
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if timeout:
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cache_key = learn_cache_key(request, response, timeout, self.key_prefix, cache=self.cache)
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if hasattr(response, 'render') and callable(response.render):
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response.add_post_render_callback(
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lambda r: self.cache.set(cache_key, r, timeout)
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)
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else:
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self.cache.set(cache_key, response, timeout)
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return response
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class FetchFromCacheMiddleware(object):
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"""
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Request-phase cache middleware that fetches a page from the cache.
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Must be used as part of the two-part update/fetch cache middleware.
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FetchFromCacheMiddleware must be the last piece of middleware in
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MIDDLEWARE_CLASSES so that it'll get called last during the request phase.
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"""
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def __init__(self):
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self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
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self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
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self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
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self.cache = get_cache(self.cache_alias)
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def process_request(self, request):
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"""
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Checks whether the page is already cached and returns the cached
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version if available.
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"""
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if not request.method in ('GET', 'HEAD'):
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request._cache_update_cache = False
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return None # Don't bother checking the cache.
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# try and get the cached GET response
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cache_key = get_cache_key(request, self.key_prefix, 'GET', cache=self.cache)
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if cache_key is None:
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request._cache_update_cache = True
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return None # No cache information available, need to rebuild.
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response = self.cache.get(cache_key, None)
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# if it wasn't found and we are looking for a HEAD, try looking just for that
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if response is None and request.method == 'HEAD':
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cache_key = get_cache_key(request, self.key_prefix, 'HEAD', cache=self.cache)
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response = self.cache.get(cache_key, None)
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if response is None:
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request._cache_update_cache = True
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return None # No cache information available, need to rebuild.
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# hit, return cached response
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request._cache_update_cache = False
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return response
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class CacheMiddleware(UpdateCacheMiddleware, FetchFromCacheMiddleware):
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"""
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Cache middleware that provides basic behavior for many simple sites.
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Also used as the hook point for the cache decorator, which is generated
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using the decorator-from-middleware utility.
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"""
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def __init__(self, cache_timeout=None, cache_anonymous_only=None, **kwargs):
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# We need to differentiate between "provided, but using default value",
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# and "not provided". If the value is provided using a default, then
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# we fall back to system defaults. If it is not provided at all,
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# we need to use middleware defaults.
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cache_kwargs = {}
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try:
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self.key_prefix = kwargs['key_prefix']
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if self.key_prefix is not None:
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cache_kwargs['KEY_PREFIX'] = self.key_prefix
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else:
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self.key_prefix = ''
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except KeyError:
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self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
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cache_kwargs['KEY_PREFIX'] = self.key_prefix
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try:
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self.cache_alias = kwargs['cache_alias']
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if self.cache_alias is None:
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self.cache_alias = DEFAULT_CACHE_ALIAS
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if cache_timeout is not None:
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cache_kwargs['TIMEOUT'] = cache_timeout
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except KeyError:
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self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
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if cache_timeout is None:
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cache_kwargs['TIMEOUT'] = settings.CACHE_MIDDLEWARE_SECONDS
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else:
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cache_kwargs['TIMEOUT'] = cache_timeout
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if cache_anonymous_only is None:
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self.cache_anonymous_only = getattr(settings, 'CACHE_MIDDLEWARE_ANONYMOUS_ONLY', False)
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else:
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self.cache_anonymous_only = cache_anonymous_only
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self.cache = get_cache(self.cache_alias, **cache_kwargs)
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self.cache_timeout = self.cache.default_timeout
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