"""
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=None):
self.cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
self.cache = caches[self.cache_alias]
self.get_response = get_response
def _should_update_cache(self, request, response):
return hasattr(request, '_cache_update_cache') and request._cache_update_cache
def process_response(self, request, response):
"""Sets 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
# 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 is 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 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=None):
self.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
self.cache = caches[self.cache_alias]
self.get_response = get_response
def process_request(self, request):
"""
Checks whether the page is already cached and returns 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=None, cache_timeout=None, **kwargs):
self.get_response = 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 = ''
except KeyError:
key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
self.key_prefix = key_prefix
try:
cache_alias = kwargs['cache_alias']
if cache_alias is None:
cache_alias = DEFAULT_CACHE_ALIAS
except KeyError:
cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
self.cache_alias = cache_alias
if cache_timeout is None:
cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
self.cache_timeout = cache_timeout
self.cache = caches[self.cache_alias]
Jun 14, 2020