Fixed #14560 -- Enable HEAD requests to be cached properly. Thanks, codemonkey!

Introducing ability to cache HEAD requests and GET requests separately by
adding the method to the cache key while preserving the functionality that HEAD
requests can use cached reponses generated by a GET request.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14391 bcc190cf-cafb-0310-a4f2-bffc1f526a37

4 files changed, 86 insertions, 22 deletions

diff --git a/django/middleware/cache.py b/django/middleware/cache.py
index 3f602fe652..a3076acd22 100644
--- a/django/middleware/cache.py
+++ b/django/middleware/cache.py
@@ -34,8 +34,8 @@ More details about how the caching works:
   and effective way of avoiding the caching of the Django admin (and any other
   user-specific content).
 
-* This middleware expects that a HEAD request is answered with a response
-  exactly like the corresponding GET request.
+* 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.
@@ -71,12 +71,6 @@ class UpdateCacheMiddleware(object):
         if not hasattr(request, '_cache_update_cache') or not request._cache_update_cache:
             # We don't need to update the cache, just return.
             return response
-        if request.method != 'GET':
-            # This is a stronger requirement than above. It is needed
-            # because of interactions between this middleware and the
-            # HTTPMiddleware, which throws the body of a HEAD-request
-            # away before this middleware gets a chance to cache it.
-            return response
         if not response.status_code == 200:
             return response
         # Try to get the timeout from the "max-age" section of the "Cache-
@@ -123,16 +117,25 @@ class FetchFromCacheMiddleware(object):
             request._cache_update_cache = False
             return None # Don't cache requests from authenticated users.
 
-        cache_key = get_cache_key(request, self.key_prefix)
+        # try and get the cached GET response
+        cache_key = get_cache_key(request, self.key_prefix, 'GET')
+
         if cache_key is None:
             request._cache_update_cache = True
             return None # No cache information available, need to rebuild.
 
         response = cache.get(cache_key, None)
+
+        # 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')
+            response = cache.get(cache_key, None)
+
         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
 
diff --git a/django/utils/cache.py b/django/utils/cache.py
index 6cfd893668..b1b35b5a05 100644
--- a/django/utils/cache.py
+++ b/django/utils/cache.py
@@ -143,7 +143,7 @@ def _i18n_cache_key_suffix(request, cache_key):
         cache_key += '.%s' % getattr(request, 'LANGUAGE_CODE', get_language())
     return cache_key
 
-def _generate_cache_key(request, headerlist, key_prefix):
+def _generate_cache_key(request, method, headerlist, key_prefix):
     """Returns a cache key from the headers given in the header list."""
     ctx = md5_constructor()
     for header in headerlist:
@@ -151,8 +151,8 @@ def _generate_cache_key(request, headerlist, key_prefix):
         if value is not None:
             ctx.update(value)
     path = md5_constructor(iri_to_uri(request.path))
-    cache_key = 'views.decorators.cache.cache_page.%s.%s.%s' % (
-        key_prefix, path.hexdigest(), ctx.hexdigest())
+    cache_key = 'views.decorators.cache.cache_page.%s.%s.%s.%s' % (
+        key_prefix, request.method, path.hexdigest(), ctx.hexdigest())
     return _i18n_cache_key_suffix(request, cache_key)
 
 def _generate_cache_header_key(key_prefix, request):
@@ -162,7 +162,7 @@ def _generate_cache_header_key(key_prefix, request):
         key_prefix, path.hexdigest())
     return _i18n_cache_key_suffix(request, cache_key)
 
-def get_cache_key(request, key_prefix=None):
+def get_cache_key(request, key_prefix=None, method='GET'):
     """
     Returns a cache key based on the request path. It can be used in the
     request phase because it pulls the list of headers to take into account
@@ -177,7 +177,7 @@ def get_cache_key(request, key_prefix=None):
     cache_key = _generate_cache_header_key(key_prefix, request)
     headerlist = cache.get(cache_key, None)
     if headerlist is not None:
-        return _generate_cache_key(request, headerlist, key_prefix)
+        return _generate_cache_key(request, method, headerlist, key_prefix)
     else:
         return None
 
@@ -203,12 +203,12 @@ def learn_cache_key(request, response, cache_timeout=None, key_prefix=None):
         headerlist = ['HTTP_'+header.upper().replace('-', '_')
                       for header in cc_delim_re.split(response['Vary'])]
         cache.set(cache_key, headerlist, cache_timeout)
-        return _generate_cache_key(request, headerlist, key_prefix)
+        return _generate_cache_key(request, request.method, headerlist, key_prefix)
     else:
         # if there is no Vary header, we still need a cache key
         # for the request.path
         cache.set(cache_key, [], cache_timeout)
-        return _generate_cache_key(request, [], key_prefix)
+        return _generate_cache_key(request, request.method, [], key_prefix)
 
 
 def _to_tuple(s):
diff --git a/docs/topics/cache.txt b/docs/topics/cache.txt
index 5797199411..f2b7a594d3 100644
--- a/docs/topics/cache.txt
+++ b/docs/topics/cache.txt
@@ -328,7 +328,9 @@ parameters. Optionally, if the ``CACHE_MIDDLEWARE_ANONYMOUS_ONLY`` setting is
 will be cached. This is a simple and effective way of disabling caching for any
 user-specific pages (include Django's admin interface). Note that if you use
 ``CACHE_MIDDLEWARE_ANONYMOUS_ONLY``, you should make sure you've activated
-``AuthenticationMiddleware``.
+``AuthenticationMiddleware``. The cache middleware expects that a HEAD request
+is answered with the same response headers exactly like the corresponding GET
+request, in that case it could return cached GET response for HEAD request.
 
 Additionally, the cache middleware automatically sets a few headers in each
 ``HttpResponse``:
diff --git a/tests/regressiontests/cache/tests.py b/tests/regressiontests/cache/tests.py
index a91b842ebd..9818b03661 100644
--- a/tests/regressiontests/cache/tests.py
+++ b/tests/regressiontests/cache/tests.py
@@ -507,12 +507,13 @@ class CacheUtils(unittest.TestCase):
         settings.CACHE_MIDDLEWARE_SECONDS = self.old_middleware_seconds
         settings.USE_I18N = self.orig_use_i18n
 
-    def _get_request(self, path):
+    def _get_request(self, path, method='GET'):
         request = HttpRequest()
         request.META = {
             'SERVER_NAME': 'testserver',
             'SERVER_PORT': 80,
         }
+        request.method = method
         request.path = request.path_info = "/cache/%s" % path
         return request
 
@@ -544,18 +545,76 @@ class CacheUtils(unittest.TestCase):
         self.assertEqual(get_cache_key(request), None)
         # Set headers to an empty list.
         learn_cache_key(request, response)
-        self.assertEqual(get_cache_key(request), 'views.decorators.cache.cache_page.settingsprefix.a8c87a3d8c44853d7f79474f7ffe4ad5.d41d8cd98f00b204e9800998ecf8427e')
+        self.assertEqual(get_cache_key(request), 'views.decorators.cache.cache_page.settingsprefix.GET.a8c87a3d8c44853d7f79474f7ffe4ad5.d41d8cd98f00b204e9800998ecf8427e')
         # Verify that a specified key_prefix is taken in to account.
         learn_cache_key(request, response, key_prefix=key_prefix)
-        self.assertEqual(get_cache_key(request, key_prefix=key_prefix), 'views.decorators.cache.cache_page.localprefix.a8c87a3d8c44853d7f79474f7ffe4ad5.d41d8cd98f00b204e9800998ecf8427e')
+        self.assertEqual(get_cache_key(request, key_prefix=key_prefix), 'views.decorators.cache.cache_page.localprefix.GET.a8c87a3d8c44853d7f79474f7ffe4ad5.d41d8cd98f00b204e9800998ecf8427e')
 
     def test_learn_cache_key(self):
-        request = self._get_request(self.path)
+        request = self._get_request(self.path, 'HEAD')
         response = HttpResponse()
         response['Vary'] = 'Pony'
         # Make sure that the Vary header is added to the key hash
         learn_cache_key(request, response)
-        self.assertEqual(get_cache_key(request), 'views.decorators.cache.cache_page.settingsprefix.a8c87a3d8c44853d7f79474f7ffe4ad5.d41d8cd98f00b204e9800998ecf8427e')
+        self.assertEqual(get_cache_key(request), 'views.decorators.cache.cache_page.settingsprefix.HEAD.a8c87a3d8c44853d7f79474f7ffe4ad5.d41d8cd98f00b204e9800998ecf8427e')
+
+class CacheHEADTest(unittest.TestCase):
+
+    def setUp(self):
+        self.orig_cache_middleware_seconds = settings.CACHE_MIDDLEWARE_SECONDS
+        self.orig_cache_middleware_key_prefix = settings.CACHE_MIDDLEWARE_KEY_PREFIX
+        self.orig_cache_backend = settings.CACHE_BACKEND
+        settings.CACHE_MIDDLEWARE_SECONDS = 60
+        settings.CACHE_MIDDLEWARE_KEY_PREFIX = 'test'
+        settings.CACHE_BACKEND = 'locmem:///'
+        self.path = '/cache/test/'
+
+    def tearDown(self):
+        settings.CACHE_MIDDLEWARE_SECONDS = self.orig_cache_middleware_seconds
+        settings.CACHE_MIDDLEWARE_KEY_PREFIX = self.orig_cache_middleware_key_prefix
+        settings.CACHE_BACKEND = self.orig_cache_backend
+
+    def _get_request(self, method):
+        request = HttpRequest()
+        request.META = {
+            'SERVER_NAME': 'testserver',
+            'SERVER_PORT': 80,
+        }
+        request.method = method
+        request.path = request.path_info = self.path
+        return request
+
+    def _get_request_cache(self, method):
+        request = self._get_request(method)
+        request._cache_update_cache = True
+        return request
+
+    def _set_cache(self, request, msg):
+        response = HttpResponse()
+        response.content = msg
+        return UpdateCacheMiddleware().process_response(request, response)
+
+    def test_head_caches_correctly(self):
+        test_content = 'test content'
+
+        request = self._get_request_cache('HEAD')
+        self._set_cache(request, test_content)
+
+        request = self._get_request('HEAD')
+        get_cache_data = FetchFromCacheMiddleware().process_request(request)
+        self.assertNotEqual(get_cache_data, None)
+        self.assertEqual(test_content, get_cache_data.content)
+
+    def test_head_with_cached_get(self):
+        test_content = 'test content'
+
+        request = self._get_request_cache('GET')
+        self._set_cache(request, test_content)
+
+        request = self._get_request('HEAD')
+        get_cache_data = FetchFromCacheMiddleware().process_request(request)
+        self.assertNotEqual(get_cache_data, None)
+        self.assertEqual(test_content, get_cache_data.content)
 
 class CacheI18nTest(unittest.TestCase):