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venv/Lib/site-packages/django/middleware/cache.py

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+"""
+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
+
+
+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
+        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):
+        """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
+
+
+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
+        self.cache = 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
+            self.cache = caches[self.cache_alias]
+        except KeyError:
+            pass
+
+        if cache_timeout is not None:
+            self.cache_timeout = cache_timeout
+        self.page_timeout = page_timeout