182 lines
7.1 KiB
Python
182 lines
7.1 KiB
Python
"""
|
|
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 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,
|
|
)
|
|
|
|
|
|
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_alias = settings.CACHE_MIDDLEWARE_ALIAS
|
|
self.cache = 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):
|
|
"""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 != 200:
|
|
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:
|
|
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
|
|
|
|
|
|
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.key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
|
|
self.cache_alias = settings.CACHE_MIDDLEWARE_ALIAS
|
|
self.cache = caches[self.cache_alias]
|
|
|
|
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, cache_timeout=None, **kwargs):
|
|
# 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]
|