Tidy up etag precondition checks

rest_framework/mixins.py

@@ -8,6 +8,7 @@ from __future__ import unicode_literals
 
 from django.http import Http404
 from rest_framework import status
+from rest_framework.exceptions import PreconditionFailed
 from rest_framework.response import Response
 from rest_framework.request import clone_request
 
@@ -114,10 +115,6 @@ class UpdateModelMixin(object):
     Should be mixed in with `SingleObjectAPIView`.
     """
     def update(self, request, *args, **kwargs):
-        header_etag = request.META.get('HTTP_IF_MATCH')
-        if header_etag is None:
-            return Response({'error': 'IF_MATCH header is required'}, status=400)
-
         partial = kwargs.pop('partial', False)
         self.object = None
         try:
@@ -129,8 +126,8 @@ class UpdateModelMixin(object):
             created = True
             success_status_code = status.HTTP_201_CREATED
         else:
-            if self.object.etag != header_etag:
-                return Response({'error': 'object has been updated since you last saw it'}, status=412)
+            if getattr(self, 'use_etags', False) and self.object.etag != self.etag_header:
+                raise PreconditionFailed
             created = False
             success_status_code = status.HTTP_200_OK
 
@@ -174,7 +171,7 @@ class DestroyModelMixin(object):
     """
     def destroy(self, request, *args, **kwargs):
         obj = self.get_object()
-        if self.get_etag(obj) != self.header_etag:
-            return Response({'error': 'object has been updated since you last saw it'}, status=412)
+        if self.get_etag(obj) != self.etag_header:
+            raise PreconditionFailed
         obj.delete()
         return Response(status=status.HTTP_204_NO_CONTENT)