Fixed #33700 -- Skipped extra resolution for successful requests not ending with /.

By moving a should_redirect_with_slash call out of an if block, commit
9390da7fb6 negated the performance fix
of commit 434d309ef6 (#24720).
Meanwhile, the logging issue #26293 that it targeted was subsequently
fixed more fully by commit 40b69607c7
(#26504), so it is no longer needed.  This effectively reverts it.

This speeds up successful requests not ending with / when APPEND_SLASH
is enabled (the default, and still useful in projects with a mix of
URLs with and without trailing /).  The amount of speedup varies from
about 5% in a typical project to nearly 50% on a benchmark with many
routes.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

django/middleware/common.py

@@ -46,19 +46,18 @@ class CommonMiddleware(MiddlewareMixin):
 
         # Check for a redirect based on settings.PREPEND_WWW
         host = request.get_host()
-        must_prepend = settings.PREPEND_WWW and host and not host.startswith("www.")
-        redirect_url = ("%s://www.%s" % (request.scheme, host)) if must_prepend else ""
 
-        # Check if a slash should be appended
+        if settings.PREPEND_WWW and host and not host.startswith("www."):
+            # Check if we also need to append a slash so we can do it all
+            # with a single redirect. (This check may be somewhat expensive,
+            # so we only do it if we already know we're sending a redirect,
+            # or in process_response if we get a 404.)
             if self.should_redirect_with_slash(request):
                 path = self.get_full_path_with_slash(request)
             else:
                 path = request.get_full_path()
 
-        # Return a redirect if necessary
-        if redirect_url or path != request.get_full_path():
-            redirect_url += path
-            return self.response_redirect_class(redirect_url)
+            return self.response_redirect_class(f"{request.scheme}://www.{host}{path}")
 
     def should_redirect_with_slash(self, request):
         """

tests/middleware/tests.py

@@ -80,7 +80,11 @@ class CommonMiddlewareTest(SimpleTestCase):
         """
         request = self.rf.get("/slash")
         r = CommonMiddleware(get_response_empty).process_request(request)
+        self.assertIsNone(r)
+        response = HttpResponseNotFound()
+        r = CommonMiddleware(get_response_empty).process_response(request, response)
         self.assertEqual(r.status_code, 301)
+        self.assertEqual(r.url, "/slash/")
 
     @override_settings(APPEND_SLASH=True)
     def test_append_slash_redirect_querystring(self):
@@ -164,6 +168,9 @@ class CommonMiddlewareTest(SimpleTestCase):
         # Use 4 slashes because of RequestFactory behavior.
         request = self.rf.get("////evil.com/security")
         r = CommonMiddleware(get_response_404).process_request(request)
+        self.assertIsNone(r)
+        response = HttpResponseNotFound()
+        r = CommonMiddleware(get_response_404).process_response(request, response)
         self.assertEqual(r.status_code, 301)
         self.assertEqual(r.url, "/%2Fevil.com/security/")
         r = CommonMiddleware(get_response_404)(request)
@@ -354,6 +361,9 @@ class CommonMiddlewareTest(SimpleTestCase):
         request = self.rf.get("/slash")
         request.META["QUERY_STRING"] = "drink=café"
         r = CommonMiddleware(get_response_empty).process_request(request)
+        self.assertIsNone(r)
+        response = HttpResponseNotFound()
+        r = CommonMiddleware(get_response_empty).process_response(request, response)
         self.assertEqual(r.status_code, 301)
 
     def test_response_redirect_class(self):