Merge pull request #202 from TheJokr/vary-star-no-cache

Removed unnecessary caching of Vary: * responses

Author: ionrock

cachecontrol/controller.py

@@ -293,6 +293,15 @@ def cache_response(self, request, response, body=None, status_codes=None):
         if no_store:
             return
 
+        # https://tools.ietf.org/html/rfc7234#section-4.1:
+        # A Vary header field-value of "*" always fails to match.
+        # Storing such a response leads to a deserialization warning
+        # during cache lookup and is not allowed to ever be served,
+        # so storing it can be avoided.
+        if "*" in response_headers.get("vary", ""):
+            logger.debug('Response header has "Vary: *"')
+            return
+
         # If we've been given an etag, then keep the response
         if self.cache_etags and "etag" in response_headers:
             logger.debug("Caching due to etag")

cachecontrol/serialize.py

@@ -107,6 +107,8 @@ def prepare_response(self, request, cached):
         """
         # Special case the '*' Vary value as it means we cannot actually
         # determine if the cached response is suitable for this request.
+        # This case is also handled in the controller code when creating
+        # a cache entry, but is left here for backwards compatibility.
         if "*" in cached.get("vary", {}):
             return
 

tests/test_cache_control.py

@@ -112,6 +112,14 @@ def test_cache_response_no_store_with_etag(self, cc):
 
         assert not cc.cache.set.called
 
+    def test_no_cache_with_vary_star(self, cc):
+        # Vary: * indicates that the response can never be served
+        # from the cache, so storing it can be avoided.
+        resp = self.resp({"vary": "*"})
+        cc.cache_response(self.req(), resp)
+
+        assert not cc.cache.set.called
+
     def test_update_cached_response_with_valid_headers(self):
         cached_resp = Mock(headers={"ETag": "jfd9094r808", "Content-Length": 100})