212 lines
7.8 KiB
Python
212 lines
7.8 KiB
Python
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"""
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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 = [
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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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* 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 DEFAULT_CACHE_ALIAS, caches
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from django.utils.cache import (
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get_cache_key,
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get_max_age,
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has_vary_header,
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learn_cache_key,
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patch_response_headers,
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)
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from django.utils.deprecation import MiddlewareMixin
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class UpdateCacheMiddleware(MiddlewareMixin):
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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 MIDDLEWARE
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so that it'll get called last during the response phase.
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"""
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def __init__(self, get_response):
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super().__init__(get_response)
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self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
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self.page_timeout = None
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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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@property
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def cache(self):
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return caches[self.cache_alias]
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def _should_update_cache(self, request, response):
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return hasattr(request, "_cache_update_cache") and request._cache_update_cache
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def process_response(self, request, response):
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"""Set 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 response.streaming or response.status_code not in (200, 304):
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return response
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# Don't cache responses that set a user-specific (and maybe security
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# sensitive) cookie in response to a cookie-less request.
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if (
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not request.COOKIES
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and response.cookies
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and has_vary_header(response, "Cookie")
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):
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return response
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# Don't cache a response with 'Cache-Control: private'
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if "private" in response.get("Cache-Control", ()):
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return response
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# Page timeout takes precedence over the "max-age" and the default
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# cache timeout.
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timeout = self.page_timeout
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if timeout is None:
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# The timeout from the "max-age" section of the "Cache-Control"
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# header takes precedence over the default cache timeout.
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timeout = get_max_age(response)
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if timeout is 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 cache.
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return response
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patch_response_headers(response, timeout)
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if timeout and response.status_code == 200:
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cache_key = learn_cache_key(
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request, response, timeout, self.key_prefix, cache=self.cache
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)
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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(MiddlewareMixin):
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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 MIDDLEWARE
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so that it'll get called last during the request phase.
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"""
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def __init__(self, get_response):
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super().__init__(get_response)
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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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@property
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def cache(self):
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return caches[self.cache_alias]
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def process_request(self, request):
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"""
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Check whether the page is already cached and return the cached
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version if available.
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"""
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if request.method not 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)
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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(
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request, self.key_prefix, "HEAD", cache=self.cache
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)
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response = self.cache.get(cache_key)
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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, get_response, cache_timeout=None, page_timeout=None, **kwargs):
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super().__init__(get_response)
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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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try:
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key_prefix = kwargs["key_prefix"]
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if key_prefix is None:
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key_prefix = ""
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self.key_prefix = key_prefix
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except KeyError:
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pass
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try:
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cache_alias = kwargs["cache_alias"]
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if cache_alias is None:
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cache_alias = DEFAULT_CACHE_ALIAS
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self.cache_alias = cache_alias
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except KeyError:
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pass
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if cache_timeout is not None:
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self.cache_timeout = cache_timeout
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self.page_timeout = page_timeout
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