feat: add cache ttl extension point

Adds the setting `CMS_CACHE_LIMIT_TTL_CLASS` that should have a
`limit_page_cache_ttl` method that would be called to limit the cache
ttl of a page using business logic.
Closes #7296

cms/cache/page.py

@@ -1,6 +1,7 @@
 
 import hashlib
 from datetime import timedelta
+from importlib import import_module
 
 from django.conf import settings
 from django.utils.cache import (
@@ -45,30 +46,37 @@ def set_page_cache(response):
 
     placeholders = toolbar.content_renderer.get_rendered_placeholders()
     # Checks if there's a plugin using the legacy "cache = False"
-    placeholder_ttl_list = []
+    ttl_list = []
     vary_cache_on_set = set()
     for ph in placeholders:
         # get_cache_expiration() always returns:
         #     EXPIRE_NOW <= int <= MAX_EXPIRATION_IN_SECONDS
         ttl = ph.get_cache_expiration(request, timestamp)
         vary_cache_on = ph.get_vary_cache_on(request)
 
-        placeholder_ttl_list.append(ttl)
+        ttl_list.append(ttl)
         if ttl and vary_cache_on:
             # We're only interested in vary headers if they come from
             # a cache-able placeholder.
             vary_cache_on_set |= set(vary_cache_on)
 
-    if EXPIRE_NOW not in placeholder_ttl_list:
-        if placeholder_ttl_list:
-            min_placeholder_ttl = min(x for x in placeholder_ttl_list)
-        else:
-            # Should only happen when there are no placeholders at all
-            min_placeholder_ttl = MAX_EXPIRATION_TTL
-        ttl = min(
-            get_cms_setting('CACHE_DURATIONS')['content'],
-            min_placeholder_ttl
-        )
+    if EXPIRE_NOW not in ttl_list:
+        ttl_list.append(get_cms_setting('CACHE_DURATIONS')['content'])
+        ttl_list.append(MAX_EXPIRATION_TTL)
+
+        if hasattr(settings, 'CMS_LIMIT_TTL_CACHE_FUNCTION'):
+            extension_point = settings.CMS_LIMIT_TTL_CACHE_FUNCTION
+
+            module, func_name = extension_point.rsplit('.', 1)
+            module = import_module(module)
+            limit_ttl_cache_function = getattr(module, func_name)
+            limit_ttl = limit_ttl_cache_function(response)
+
+            # if the extension point returns an integer as ttl
+            if isinstance(limit_ttl, int):
+                ttl_list.append(limit_ttl)
+
+        ttl = min(ttl_list)
 
         if ttl > 0:
             # Adds expiration, etc. to headers

cms/tests/test_cache.py

@@ -860,3 +860,44 @@ def test_set_get_placeholder_cache_with_long_prefix(self):
             # Prove it still works as expected
             cached_en_crazy_content = get_placeholder_cache(self.placeholder, 'en', 1, en_crazy_request)
             self.assertEqual(en_crazy_content, cached_en_crazy_content)
+
+    def test_cache_limit_ttl(self):
+        """"
+        Test the `CMS_LIMIT_TTL_CACHE_FUNCTION` setting that allows to change the default 40 seconds
+        default ttl cache value with a business logic function.
+        """
+        page1 = create_page('test page 1', 'nav_playground.html', 'en',
+                            published=True)
+        page1_url = page1.get_absolute_url()
+
+        limit_page_cache_ttl_function = ".".join([PlaceholderCacheTestCase.__module__, limit_page_cache_ttl_test_5.__name__])
+        with self.settings(CMS_LIMIT_TTL_CACHE_FUNCTION=limit_page_cache_ttl_function):
+            page1.publish('en')
+            request = self.get_request(page1_url)
+            request.current_page = Page.objects.get(pk=page1.pk)
+            response = self.client.get(page1_url)
+            self.assertTrue('max-age=5' in response['Cache-Control'], response['Cache-Control'])  # noqa
+
+    def test_cache_limit_ttl_greater_than_default_cache_ttl(self):
+        """
+        Test the `CMS_LIMIT_TTL_CACHE_FUNCTION` setting with a class that returns a value much
+        greater thant the default value of 40 seconds.
+        """
+        page1 = create_page('test page 1', 'nav_playground.html', 'en',
+                            published=True)
+        page1_url = page1.get_absolute_url()
+
+        limit_page_cache_ttl_function = ".".join([PlaceholderCacheTestCase.__module__, limit_page_cache_ttl_test_500.__name__])
+        with self.settings(CMS_LIMIT_TTL_CACHE_FUNCTION=limit_page_cache_ttl_function):
+            page1.publish('en')
+            request = self.get_request(page1_url)
+            request.current_page = Page.objects.get(pk=page1.pk)
+            response = self.client.get(page1_url)
+            self.assertTrue('max-age=40' in response['Cache-Control'], response['Cache-Control'])  # noqa
+
+
+def limit_page_cache_ttl_test_5(response):
+    return 5
+
+def limit_page_cache_ttl_test_500(response):
+    return 40

docs/how_to/caching.rst

@@ -54,6 +54,7 @@ Have a look at the following settings to enable/disable various caching behaviou
 - :setting:`CMS_PAGE_CACHE`
 - :setting:`CMS_PLACEHOLDER_CACHE`
 - :setting:`CMS_PLUGIN_CACHE`
+- :setting:`CMS_LIMIT_TTL_CACHE_FUNCTION`
 
 
 

docs/reference/configuration.rst

@@ -1006,6 +1006,18 @@ Default value of the ``cache`` attribute of plugins. Should plugins be cached by
     If you disable the plugin cache be sure to restart the server and clear the cache afterwards.
 
 
+..  setting:: CMS_LIMIT_TTL_CACHE_FUNCTION
+
+CMS_LIMIT_TTL_CACHE_FUNCTION
+============================
+
+default
+    ``None``
+
+If defined, specifies the function to be called that allows to limit the page cache ttl value 
+using a business logic. The function receives one argument, the `response`, and returns an `int`
+the max business value of the page cache ttl.
+
 ..  setting:: CMS_MAX_PAGE_PUBLISH_REVERSIONS