Fixed #27346 -- Stopped setting the Content-Length header in ConditionalGetMiddleware.

AUTHORS

@@ -9,6 +9,7 @@ answer newbie questions, and generally made Django that much better:
     Aaron Swartz <http://www.aaronsw.com/>
     Aaron T. Myers <atmyers@gmail.com>
     Adam Johnson <https://github.com/adamchainz>
+    Adam Malinowski <http://adammalinowski.co.uk>
     Adam Vandenberg
     Adrian Holovaty <adrian@holovaty.com>
     Adrien Lemaire <lemaire.adrien@gmail.com>

django/middleware/http.py

@@ -11,13 +11,8 @@ class ConditionalGetMiddleware(MiddlewareMixin):
     Last-Modified header, and the request has If-None-Match or
     If-Modified-Since, the response is replaced by an HttpNotModified. An ETag
     header is added if needed.
-
-    Also sets the Content-Length response-header.
     """
     def process_response(self, request, response):
-        if not response.streaming and not response.has_header('Content-Length'):
-            response['Content-Length'] = str(len(response.content))
-
         # It's too late to prevent an unsafe request with a 412 response, and
         # for a HEAD request, the response body is always empty so computing
         # an accurate ETag isn't possible.

docs/ref/middleware.txt

@@ -181,12 +181,10 @@ header, the middleware adds one if needed. If the response has a ``ETag`` or
 ``If-Modified-Since``, the response is replaced by an
 :class:`~django.http.HttpResponseNotModified`.
 
-Also sets ``Content-Length`` response-header.
-
 .. versionchanged:: 1.11
 
-    In older versions, the middleware set the ``Date`` header and didn't set
+    In older versions, the middleware set the ``Content-Length`` and ``Date``
-    the ``ETag`` header.
+    headers and didn't set the ``ETag`` header.
 
 Locale middleware
 -----------------

docs/releases/1.11.txt

@@ -579,8 +579,10 @@ Miscellaneous
 * In the admin templates, ``<p class="help">`` is replaced with a ``<div>`` tag
   to allow including lists inside help text.
 
-* ``ConditionalGetMiddleware`` no longer sets the ``Date`` header as Web
+* :class:`~django.middleware.http.ConditionalGetMiddleware` no longer sets the
-  servers set that header.
+  ``Date`` header as Web servers set that header. It also no longer sets the
+  ``Content-Length`` header as this is now done by
+  :class:`~django.middleware.common.CommonMiddleware`.
 
 * :meth:`~django.apps.AppConfig.get_model` and
   :meth:`~django.apps.AppConfig.get_models` now raise

tests/middleware/tests.py

@@ -478,30 +478,6 @@ class ConditionalGetMiddlewareTest(SimpleTestCase):
         self.req = RequestFactory().get('/')
         self.resp = self.client.get(self.req.path_info)
 
-    # Tests for the Content-Length header
-
-    def test_content_length_header_added(self):
-        content_length = len(self.resp.content)
-        # Already set by CommonMiddleware, remove it to check that
-        # ConditionalGetMiddleware readds it.
-        del self.resp['Content-Length']
-        self.assertNotIn('Content-Length', self.resp)
-        self.resp = ConditionalGetMiddleware().process_response(self.req, self.resp)
-        self.assertIn('Content-Length', self.resp)
-        self.assertEqual(int(self.resp['Content-Length']), content_length)
-
-    def test_content_length_header_not_added(self):
-        resp = StreamingHttpResponse('content')
-        self.assertNotIn('Content-Length', resp)
-        resp = ConditionalGetMiddleware().process_response(self.req, resp)
-        self.assertNotIn('Content-Length', resp)
-
-    def test_content_length_header_not_changed(self):
-        bad_content_length = len(self.resp.content) + 10
-        self.resp['Content-Length'] = bad_content_length
-        self.resp = ConditionalGetMiddleware().process_response(self.req, self.resp)
-        self.assertEqual(int(self.resp['Content-Length']), bad_content_length)
-
     # Tests for the ETag header
 
     def test_middleware_calculates_etag(self):