Source code for django.middleware.cache

"""
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 = [
        '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.

* 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 DEFAULT_CACHE_ALIAS, caches
from django.utils.cache import (
    get_cache_key,
    get_max_age,
    has_vary_header,
    learn_cache_key,
    patch_response_headers,
)
from django.utils.deprecation import MiddlewareMixin


[docs] class UpdateCacheMiddleware(MiddlewareMixin): """ 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 so that it'll get called last during the response phase. """ def __init__(self, get_response): super().__init__(get_response) self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS self.page_timeout = None self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS @property def cache(self): return caches[self.cache_alias] def _should_update_cache(self, request, response): return hasattr(request, "_cache_update_cache") and request._cache_update_cache def process_response(self, request, response): """Set 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 response.streaming or response.status_code not in (200, 304): return response # Don't cache responses that set a user-specific (and maybe security # sensitive) cookie in response to a cookie-less request. if ( not request.COOKIES and response.cookies and has_vary_header(response, "Cookie") ): return response # Don't cache a response with 'Cache-Control: private' if "private" in response.get("Cache-Control", ()): return response # Page timeout takes precedence over the "max-age" and the default # cache timeout. timeout = self.page_timeout if timeout is None: # The timeout from the "max-age" section of the "Cache-Control" # header takes precedence over the default cache timeout. timeout = get_max_age(response) if timeout is None: timeout = self.cache_timeout elif timeout == 0: # max-age was set to 0, don't cache. return response patch_response_headers(response, timeout) if timeout and response.status_code == 200: 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
[docs] class FetchFromCacheMiddleware(MiddlewareMixin): """ 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 so that it'll get called last during the request phase. """ def __init__(self, get_response): super().__init__(get_response) self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS @property def cache(self): return caches[self.cache_alias] def process_request(self, request): """ Check whether the page is already cached and return the cached version if available. """ if request.method not 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) # 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) 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, get_response, cache_timeout=None, page_timeout=None, **kwargs): super().__init__(get_response) # 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. try: key_prefix = kwargs["key_prefix"] if key_prefix is None: key_prefix = "" self.key_prefix = key_prefix except KeyError: pass try: cache_alias = kwargs["cache_alias"] if cache_alias is None: cache_alias = DEFAULT_CACHE_ALIAS self.cache_alias = cache_alias except KeyError: pass if cache_timeout is not None: self.cache_timeout = cache_timeout self.page_timeout = page_timeout