Fixed #26447 -- Deprecated settings.USE_ETAGS in favor of ConditionalGetMiddleware.

django/conf/global_settings.py

@@ -23,6 +23,8 @@ DEBUG = False
 DEBUG_PROPAGATE_EXCEPTIONS = False
 
 # Whether to use the "ETag" header. This saves bandwidth but slows down performance.
+# Deprecated (RemovedInDjango21Warning) in favor of ConditionalGetMiddleware
+# which sets the ETag regardless of this setting.
 USE_ETAGS = False
 
 # People who get code error notifications.

django/middleware/common.py

@@ -1,4 +1,5 @@
 import re
+import warnings
 
 from django import http
 from django.conf import settings
@@ -8,7 +9,7 @@ from django.urls import is_valid_path
 from django.utils.cache import (
     cc_delim_re, get_conditional_response, set_response_etag,
 )
-from django.utils.deprecation import MiddlewareMixin
+from django.utils.deprecation import MiddlewareMixin, RemovedInDjango21Warning
 from django.utils.encoding import force_text
 from django.utils.six.moves.urllib.parse import urlparse
 
@@ -34,7 +35,8 @@ class CommonMiddleware(MiddlewareMixin):
 
         - ETags: If the USE_ETAGS setting is set, ETags will be calculated from
           the entire page content and Not Modified responses will be returned
-          appropriately.
+          appropriately. USE_ETAGS is deprecated in favor of
+          ConditionalGetMiddleware.
     """
 
     response_redirect_class = http.HttpResponsePermanentRedirect
@@ -115,6 +117,13 @@ class CommonMiddleware(MiddlewareMixin):
                 return self.response_redirect_class(self.get_full_path_with_slash(request))
 
         if settings.USE_ETAGS and self.needs_etag(response):
+            warnings.warn(
+                "The USE_ETAGS setting is deprecated in favor of "
+                "ConditionalGetMiddleware which sets the ETag regardless of "
+                "the setting. CommonMiddleware won't do ETag processing in "
+                "Django 2.1.",
+                RemovedInDjango21Warning
+            )
             if not response.has_header('ETag'):
                 set_response_etag(response)
 

django/middleware/http.py

@@ -1,4 +1,6 @@
-from django.utils.cache import get_conditional_response
+from django.utils.cache import (
+    cc_delim_re, get_conditional_response, set_response_etag,
+)
 from django.utils.deprecation import MiddlewareMixin
 from django.utils.http import http_date, parse_http_date_safe
 
@@ -7,7 +9,8 @@ class ConditionalGetMiddleware(MiddlewareMixin):
     """
     Handles conditional GET operations. If the response has an ETag or
     Last-Modified header, and the request has If-None-Match or
-    If-Modified-Since, the response is replaced by an HttpNotModified.
+    If-Modified-Since, the response is replaced by an HttpNotModified. An ETag
+    header is added if needed.
 
     Also sets the Date and Content-Length response-headers.
     """
@@ -16,6 +19,9 @@ class ConditionalGetMiddleware(MiddlewareMixin):
         if not response.streaming and not response.has_header('Content-Length'):
             response['Content-Length'] = str(len(response.content))
 
+        if self.needs_etag(response) and not response.has_header('ETag'):
+            set_response_etag(response)
+
         etag = response.get('ETag')
         last_modified = response.get('Last-Modified')
         if last_modified:
@@ -30,3 +36,10 @@ class ConditionalGetMiddleware(MiddlewareMixin):
             )
 
         return response
+
+    def needs_etag(self, response):
+        """
+        Return True if an ETag header should be added to response.
+        """
+        cache_control_headers = cc_delim_re.split(response.get('Cache-Control', ''))
+        return all(header.lower() != 'no-store' for header in cache_control_headers)

django/utils/cache.py

@@ -22,10 +22,12 @@ import hashlib
 import logging
 import re
 import time
+import warnings
 
 from django.conf import settings
 from django.core.cache import caches
 from django.http import HttpResponse, HttpResponseNotModified
+from django.utils.deprecation import RemovedInDjango21Warning
 from django.utils.encoding import force_bytes, force_text, iri_to_uri
 from django.utils.http import (
     http_date, parse_etags, parse_http_date_safe, quote_etag,
@@ -242,6 +244,13 @@ def patch_response_headers(response, cache_timeout=None):
     if cache_timeout < 0:
         cache_timeout = 0  # Can't have max-age negative
     if settings.USE_ETAGS and not response.has_header('ETag'):
+        warnings.warn(
+            "The USE_ETAGS setting is deprecated in favor of "
+            "ConditionalGetMiddleware which sets the ETag regardless of the "
+            "setting. patch_response_headers() won't do ETag processing in "
+            "Django 2.1.",
+            RemovedInDjango21Warning
+        )
         if hasattr(response, 'render') and callable(response.render):
             response.add_post_render_callback(set_response_etag)
         else: