Fixed #30765 -- Made cache_page decorator take precedence over max-age Cache-Control directive.

django/middleware/cache.py

@@ -63,6 +63,7 @@ class UpdateCacheMiddleware(MiddlewareMixin):
     """
     def __init__(self, get_response=None):
         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]
@@ -89,15 +90,18 @@ class UpdateCacheMiddleware(MiddlewareMixin):
         if 'private' in response.get('Cache-Control', ()):
             return response
 
-        # Try to get the timeout from the "max-age" section of the "Cache-
+        # Page timeout takes precedence over the "max-age" and the default
-        # Control" header before reverting to using the default cache_timeout
+        # cache timeout.
-        # length.
+        timeout = self.page_timeout
-        timeout = get_max_age(response)
         if timeout is None:
-            timeout = self.cache_timeout
+            # The timeout from the "max-age" section of the "Cache-Control"
-        elif timeout == 0:
+            # header takes precedence over the default cache timeout.
-            # max-age was set to 0, don't bother caching.
+            timeout = get_max_age(response)
-            return 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)
@@ -160,7 +164,7 @@ class CacheMiddleware(UpdateCacheMiddleware, FetchFromCacheMiddleware):
     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):
+    def __init__(self, get_response=None, cache_timeout=None, page_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
@@ -186,4 +190,5 @@ class CacheMiddleware(UpdateCacheMiddleware, FetchFromCacheMiddleware):
         if cache_timeout is None:
             cache_timeout = settings.CACHE_MIDDLEWARE_SECONDS
         self.cache_timeout = cache_timeout
+        self.page_timeout = page_timeout
         self.cache = caches[self.cache_alias]

django/views/decorators/cache.py

@@ -20,7 +20,7 @@ def cache_page(timeout, *, cache=None, key_prefix=None):
     into account on caching -- just like the middleware does.
     """
     return decorator_from_middleware_with_args(CacheMiddleware)(
-        cache_timeout=timeout, cache_alias=cache, key_prefix=key_prefix
+        page_timeout=timeout, cache_alias=cache, key_prefix=key_prefix,
     )
 
 

docs/releases/3.1.txt

@@ -430,6 +430,10 @@ Miscellaneous
   used with :setting:`DEFAULT_EXCEPTION_REPORTER_FILTER` needs to inherit from
   :class:`django.views.debug.SafeExceptionReporterFilter`.
 
+* The cache timeout set by :func:`~django.views.decorators.cache.cache_page`
+  decorator now takes precedence over the ``max-age`` directive from the
+  ``Cache-Control`` header.
+
 .. _deprecated-features-3.1:
 
 Features deprecated in 3.1

docs/topics/cache.txt

@@ -570,6 +570,9 @@ minutes. (Note that we've written it as ``60 * 15`` for the purpose of
 readability. ``60 * 15`` will be evaluated to ``900`` -- that is, 15 minutes
 multiplied by 60 seconds per minute.)
 
+The cache timeout set by ``cache_page`` takes precedence over the ``max-age``
+directive from the ``Cache-Control`` header.
+
 The per-view cache, like the per-site cache, is keyed off of the URL. If
 multiple URLs point at the same view, each URL will be cached separately.
 Continuing the ``my_view`` example, if your URLconf looks like this::
@@ -605,6 +608,11 @@ The ``key_prefix`` and ``cache`` arguments may be specified together. The
 ``key_prefix`` argument and the :setting:`KEY_PREFIX <CACHES-KEY_PREFIX>`
 specified under :setting:`CACHES` will be concatenated.
 
+.. versionchanged:: 3.1
+
+    In older versions, the ``max-age`` directive from the ``Cache-Control``
+    header had precedence over the cache timeout set by ``cache_page``.
+
 Specifying per-view cache in the URLconf
 ----------------------------------------
 

tests/cache/tests.py

@@ -2188,6 +2188,29 @@ class CacheMiddlewareTest(SimpleTestCase):
         response = other_with_prefix_view(request, '16')
         self.assertEqual(response.content, b'Hello World 16')
 
+    def test_cache_page_timeout(self):
+        # Page timeout takes precedence over the "max-age" section of the
+        # "Cache-Control".
+        tests = [
+            (1, 3),  # max_age < page_timeout.
+            (3, 1),  # max_age > page_timeout.
+        ]
+        for max_age, page_timeout in tests:
+            with self.subTest(max_age=max_age, page_timeout=page_timeout):
+                view = cache_page(timeout=page_timeout)(
+                    cache_control(max_age=max_age)(hello_world_view)
+                )
+                request = self.factory.get('/view/')
+                response = view(request, '1')
+                self.assertEqual(response.content, b'Hello World 1')
+                time.sleep(1)
+                response = view(request, '2')
+                self.assertEqual(
+                    response.content,
+                    b'Hello World 1' if page_timeout > max_age else b'Hello World 2',
+                )
+            cache.clear()
+
     def test_cached_control_private_not_cached(self):
         """Responses with 'Cache-Control: private' are not cached."""
         view_with_private_cache = cache_page(3)(cache_control(private=True)(hello_world_view))