Added django.middleware.cache, which lets you cache an entire Django-powered…

Added django.middleware.cache, which lets you cache an entire Django-powered site by adding a line to your settings

git-svn-id: http://code.djangoproject.com/svn/django/trunk@178 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/middleware/cache.py

+from django.conf import settings
+from django.core.cache import cache
+from django.utils.httpwrappers import HttpResponseNotModified
+from django.utils.text import compress_string
+import datetime, md5
+
+class CacheMiddleware:
+    """
+    Cache middleware. If this is enabled, each Django-powered page will be
+    cached for CACHE_MIDDLEWARE_SECONDS seconds. Cache is based on URLs. Pages
+    with GET or POST parameters are not cached.
+
+    If the cache is shared across multiple sites using the same Django
+    installation, set the CACHE_MIDDLEWARE_KEY_PREFIX to the name of the site,
+    or some other string that is unique to this Django instance, to prevent key
+    collisions.
+
+    This middleware will also make the following optimizations:
+
+    * If the CACHE_MIDDLEWARE_GZIP setting is True, the content will be
+      gzipped.
+
+    * ETags will be added, using a simple MD5 hash of the page's content.
+    """
+    def process_request(self, request):
+        """
+        Checks whether the page is already cached. If it is, returns the cached
+        version. Also handles ETag stuff.
+        """
+        if request.GET or request.POST:
+            request._cache_middleware_set_cache = False
+            return None # Don't bother checking the cache.
+
+        accept_encoding = ''
+        if settings.CACHE_MIDDLEWARE_GZIP:
+            try:
+                accept_encoding = request.META['HTTP_ACCEPT_ENCODING']
+            except KeyError:
+                pass
+        accepts_gzip = 'gzip' in accept_encoding
+        request._cache_middleware_accepts_gzip = accepts_gzip
+
+        # This uses the same cache_key as views.decorators.cache.cache_page,
+        # so the cache can be shared.
+        cache_key = 'views.decorators.cache.cache_page.%s.%s.%s' % \
+            (settings.CACHE_MIDDLEWARE_KEY_PREFIX, request.path, accepts_gzip)
+        request._cache_middleware_key = cache_key
+
+        response = cache.get(cache_key, None)
+        if response is None:
+            request._cache_middleware_set_cache = True
+            return None
+        else:
+            request._cache_middleware_set_cache = False
+            # Logic is from http://simon.incutio.com/archive/2003/04/23/conditionalGet
+            try:
+                if_none_match = request.META['HTTP_IF_NONE_MATCH']
+            except KeyError:
+                if_none_match = None
+            try:
+                if_modified_since = request.META['HTTP_IF_MODIFIED_SINCE']
+            except KeyError:
+                if_modified_since = None
+            if if_none_match is None and if_modified_since is None:
+                pass
+            elif if_none_match is not None and response['ETag'] != if_none_match:
+                pass
+            elif if_modified_since is not None and response['Last-Modified'] != if_modified_since:
+                pass
+            else:
+                return HttpResponseNotModified()
+        return response
+
+    def process_response(self, request, response):
+        """
+        Sets the cache, if needed.
+        """
+        if request._cache_middleware_set_cache:
+            content = response.get_content_as_string('utf-8')
+            if request._cache_middleware_accepts_gzip:
+                content = compress_string(content)
+                response.content = content
+                response['Content-Encoding'] = 'gzip'
+            response['ETag'] = md5.new(content).hexdigest()
+            response['Content-Length'] = '%d' % len(content)
+            response['Last-Modified'] = datetime.datetime.utcnow().strftime('%a, %d %b %Y %H:%M:%S GMT')
+            cache.set(request._cache_middleware_key, response, settings.CACHE_MIDDLEWARE_SECONDS)
+        return response