From ebb47bb38f9acd3a60eb96baf69ff12f567794b3 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 12 Mar 2013 20:35:36 -0700
Subject: [PATCH 01/16] Basic implementation of etags

Settings and options aren't sorted at all, but the functionality exists
in the rest verb methods.
---
 rest_framework/mixins.py | 14 +++++++++++++-
 rest_framework/views.py  |  9 +++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/rest_framework/mixins.py b/rest_framework/mixins.py
index 8e4012049..f2812b7bc 100644
--- a/rest_framework/mixins.py
+++ b/rest_framework/mixins.py
@@ -100,8 +100,12 @@ class RetrieveModelMixin(object):
         queryset = self.get_queryset()
         filtered_queryset = self.filter_queryset(queryset)
         self.object = self.get_object(filtered_queryset)
+        if self.use_etags:
+            if self.get_etag(self.object) == request.META.get('HTTP_IF_NONE_MATCH'):
+                return Response(status=304)
+            headers = {'ETag': self.get_etag(self.object)}
         serializer = self.get_serializer(self.object)
-        return Response(serializer.data)
+        return Response(serializer.data, headers=headers)
 
 
 class UpdateModelMixin(object):
@@ -110,6 +114,10 @@ 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:
@@ -121,6 +129,8 @@ 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)
             created = False
             success_status_code = status.HTTP_200_OK
 
@@ -164,5 +174,7 @@ 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)
         obj.delete()
         return Response(status=status.HTTP_204_NO_CONTENT)
diff --git a/rest_framework/views.py b/rest_framework/views.py
index 81cbdcbb2..9e2a0208a 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -398,6 +398,13 @@ class APIView(View):
             else:
                 handler = self.http_method_not_allowed
 
+            if self.use_etags and request.method.lower() in ('put', 'delete'):
+                etag_header = request.META.get('HTTP_IF_MATCH')
+                if etag_header is None:
+                    return Response({'error': 'IF_MATCH header is required'}, status=400)
+                else:
+                    self.etag_header = etag_header
+
             response = handler(request, *args, **kwargs)
 
         except Exception as exc:
@@ -413,3 +420,5 @@ class APIView(View):
         a less useful default implementation.
         """
         return Response(self.metadata(request), status=status.HTTP_200_OK)
+    def get_etag(self, obj):
+        return getattr(obj, self.etag_var)

From 53ca0c02b0c399f4cf17a6e0f8a8504e4dde4e91 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Wed, 20 Mar 2013 23:10:24 -0700
Subject: [PATCH 02/16] Add PreconditionFailed exception

---
 rest_framework/exceptions.py | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/rest_framework/exceptions.py b/rest_framework/exceptions.py
index 0c96ecdd5..9ceb64fe1 100644
--- a/rest_framework/exceptions.py
+++ b/rest_framework/exceptions.py
@@ -88,6 +88,14 @@ class Throttled(APIException):
             self.detail = detail or self.default_detail
 
 
+class PreconditionFailed(APIException):
+    status_code = status.HTTP_412_PRECONDITION_FAILED
+    default_detail = 'Object has been updated since you retrieved it.'
+
+    def __init__(self, detail=None):
+        self.detail = detail or self.default_detail
+
+
 class ConfigurationError(Exception):
     """
     Indicates an internal server error.

From bceca2364a9fc5e5c11a62e769c28335a322d309 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Wed, 20 Mar 2013 23:14:27 -0700
Subject: [PATCH 03/16] Switch to a view level setting for using etags

* Check for existance of `use_etags` as a precondition.
* Set etag_header irregardless of the HTTP_IF_MATCH header state.
---
 rest_framework/views.py | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/rest_framework/views.py b/rest_framework/views.py
index 9e2a0208a..98c7dcc64 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -398,12 +398,10 @@ class APIView(View):
             else:
                 handler = self.http_method_not_allowed
 
-            if self.use_etags and request.method.lower() in ('put', 'delete'):
-                etag_header = request.META.get('HTTP_IF_MATCH')
-                if etag_header is None:
-                    return Response({'error': 'IF_MATCH header is required'}, status=400)
-                else:
-                    self.etag_header = etag_header
+            if getattr(self, 'use_etags', False) and request.method.lower() in ('put', 'delete'):
+                self.etag_header = request.META.get('HTTP_IF_MATCH')
+                if self.etag_header is None:
+                    return Response({'detail': 'IF_MATCH header is required'}, status=400, exception=True)
 
             response = handler(request, *args, **kwargs)
 

From cfd083d7595bf92b02e4d9cce3ab1a1614abddd6 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Wed, 20 Mar 2013 23:17:30 -0700
Subject: [PATCH 04/16] Tidy up etag precondition checks

---
 rest_framework/mixins.py | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/rest_framework/mixins.py b/rest_framework/mixins.py
index f2812b7bc..1290dffc5 100644
--- a/rest_framework/mixins.py
+++ b/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)

From a337dc3b5f3816987515ccb3ce31a6801aa46520 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Wed, 20 Mar 2013 23:55:13 -0700
Subject: [PATCH 05/16] Add IfMatchMissing exception

Needed to make testing easier.
---
 rest_framework/exceptions.py | 8 ++++++++
 rest_framework/views.py      | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/rest_framework/exceptions.py b/rest_framework/exceptions.py
index 9ceb64fe1..229c8df82 100644
--- a/rest_framework/exceptions.py
+++ b/rest_framework/exceptions.py
@@ -96,6 +96,14 @@ class PreconditionFailed(APIException):
         self.detail = detail or self.default_detail
 
 
+class IfMatchMissing(APIException):
+    default_detail = 'IF_MATCH header is required'
+    status_code = 400
+
+    def __init__(self, detail=None):
+        self.detail = detail or self.default_detail
+
+
 class ConfigurationError(Exception):
     """
     Indicates an internal server error.
diff --git a/rest_framework/views.py b/rest_framework/views.py
index 98c7dcc64..36f5a92fa 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -401,7 +401,7 @@ class APIView(View):
             if getattr(self, 'use_etags', False) and request.method.lower() in ('put', 'delete'):
                 self.etag_header = request.META.get('HTTP_IF_MATCH')
                 if self.etag_header is None:
-                    return Response({'detail': 'IF_MATCH header is required'}, status=400, exception=True)
+                    raise exceptions.IfMatchMissing
 
             response = handler(request, *args, **kwargs)
 

From 61f6fe2b8158c955000277915d2af2acffae0646 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Thu, 21 Mar 2013 00:03:41 -0700
Subject: [PATCH 06/16] Check `use_etags` before trying to set ETag header

---
 rest_framework/mixins.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/rest_framework/mixins.py b/rest_framework/mixins.py
index 1290dffc5..ada821754 100644
--- a/rest_framework/mixins.py
+++ b/rest_framework/mixins.py
@@ -101,10 +101,11 @@ class RetrieveModelMixin(object):
         queryset = self.get_queryset()
         filtered_queryset = self.filter_queryset(queryset)
         self.object = self.get_object(filtered_queryset)
-        if self.use_etags:
+        headers = {}
+        if getattr(self, 'use_etags', False):
             if self.get_etag(self.object) == request.META.get('HTTP_IF_NONE_MATCH'):
                 return Response(status=304)
-            headers = {'ETag': self.get_etag(self.object)}
+            headers.update({'ETag': self.get_etag(self.object)})
         serializer = self.get_serializer(self.object)
         return Response(serializer.data, headers=headers)
 

From 00778e3d2425bb6b84fcab6bc36676feafcfb01c Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Thu, 21 Mar 2013 00:23:31 -0700
Subject: [PATCH 07/16] Use built-in status code variables

---
 rest_framework/exceptions.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rest_framework/exceptions.py b/rest_framework/exceptions.py
index 229c8df82..89dc88fe3 100644
--- a/rest_framework/exceptions.py
+++ b/rest_framework/exceptions.py
@@ -98,7 +98,7 @@ class PreconditionFailed(APIException):
 
 class IfMatchMissing(APIException):
     default_detail = 'IF_MATCH header is required'
-    status_code = 400
+    status_code = status.HTTP_400_BAD_REQUEST
 
     def __init__(self, detail=None):
         self.detail = detail or self.default_detail

From 4f43804d42d521753ce0dee55941dd1e7f22f755 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Mon, 1 Apr 2013 16:15:05 +0100
Subject: [PATCH 08/16] Move cache lookup code to a pluggable backend

ETagCacheLookup is the first example implementation.
---
 rest_framework/cache_lookups.py | 42 +++++++++++++++++++++++++++++++
 rest_framework/mixins.py        | 15 ++++-------
 rest_framework/settings.py      |  2 ++
 rest_framework/views.py         | 44 ++++++++++++++++++++++++++++-----
 4 files changed, 87 insertions(+), 16 deletions(-)
 create mode 100644 rest_framework/cache_lookups.py

diff --git a/rest_framework/cache_lookups.py b/rest_framework/cache_lookups.py
new file mode 100644
index 000000000..4d51c426e
--- /dev/null
+++ b/rest_framework/cache_lookups.py
@@ -0,0 +1,42 @@
+"""
+Provides a set of pluggable cache policies.
+"""
+from django.core.cache import cache
+
+
+class BaseCacheLookup(object):
+    def get_header(self, obj):
+        return {}
+
+    def resource_unchanged(self, request):
+        """
+        Return `False` if resource has changed, `True` otherwise.
+        """
+        return False
+
+
+class ETagCacheLookup(BaseCacheLookup):
+    """
+    """
+    etag_variable = 'etag'
+
+    @staticmethod
+    def get_cache_key(cls, pk):
+        class_name = cls.__class__.__name__
+        return 'etag-{}-{}'.format(class_name, pk)
+
+    def get_etag(self, obj):
+        return getattr(obj, self.etag_variable)
+
+    def get_header(self, obj):
+        key = self.get_cache_key(obj, 'pk')
+        etag = self.get_etag(obj)
+        cache.set(key, etag)
+        return {'ETag': etag}
+
+    def resource_unchanged(self, request, key):
+        etag = cache.get(key)
+        header = request.META.get('HTTP_IF_NONE_MATCH')
+        if etag is not None and etag == header:
+            return True
+        return False
diff --git a/rest_framework/mixins.py b/rest_framework/mixins.py
index ada821754..a0fc51e35 100644
--- a/rest_framework/mixins.py
+++ b/rest_framework/mixins.py
@@ -8,7 +8,6 @@ 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
 
@@ -101,11 +100,9 @@ class RetrieveModelMixin(object):
         queryset = self.get_queryset()
         filtered_queryset = self.filter_queryset(queryset)
         self.object = self.get_object(filtered_queryset)
-        headers = {}
-        if getattr(self, 'use_etags', False):
-            if self.get_etag(self.object) == request.META.get('HTTP_IF_NONE_MATCH'):
-                return Response(status=304)
-            headers.update({'ETag': self.get_etag(self.object)})
+
+        headers = self.get_cache_lookup_headers(self.object)
+
         serializer = self.get_serializer(self.object)
         return Response(serializer.data, headers=headers)
 
@@ -127,8 +124,7 @@ class UpdateModelMixin(object):
             created = True
             success_status_code = status.HTTP_201_CREATED
         else:
-            if getattr(self, 'use_etags', False) and self.object.etag != self.etag_header:
-                raise PreconditionFailed
+            self.cache_precondition_check(self.object, request)
             created = False
             success_status_code = status.HTTP_200_OK
 
@@ -172,7 +168,6 @@ class DestroyModelMixin(object):
     """
     def destroy(self, request, *args, **kwargs):
         obj = self.get_object()
-        if self.get_etag(obj) != self.etag_header:
-            raise PreconditionFailed
+        self.cache_precondition_check(obj, request)
         obj.delete()
         return Response(status=status.HTTP_204_NO_CONTENT)
diff --git a/rest_framework/settings.py b/rest_framework/settings.py
index eede0c5a0..be687b86a 100644
--- a/rest_framework/settings.py
+++ b/rest_framework/settings.py
@@ -47,6 +47,8 @@ DEFAULTS = {
     ),
     'DEFAULT_THROTTLE_CLASSES': (
     ),
+    'DEFAULT_CACHE_LOOKUP_CLASSES': (
+    ),
 
     'DEFAULT_CONTENT_NEGOTIATION_CLASS':
         'rest_framework.negotiation.DefaultContentNegotiation',
diff --git a/rest_framework/views.py b/rest_framework/views.py
index 36f5a92fa..8e38d7e6a 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -60,6 +60,7 @@ class APIView(View):
     throttle_classes = api_settings.DEFAULT_THROTTLE_CLASSES
     permission_classes = api_settings.DEFAULT_PERMISSION_CLASSES
     content_negotiation_class = api_settings.DEFAULT_CONTENT_NEGOTIATION_CLASS
+    cache_lookup_classes = api_settings.DEFAULT_CACHE_LOOKUP_CLASSES
 
     @classmethod
     def as_view(cls, **initkwargs):
@@ -241,6 +242,12 @@ class APIView(View):
             self._negotiator = self.content_negotiation_class()
         return self._negotiator
 
+    def get_cache_lookups(self):
+        """
+        Instantiates and returns the list of cache lookups that this view requires.
+        """
+        return [cache_lookup() for cache_lookup in self.cache_lookup_classes]
+
     # API policy implementation methods
 
     def perform_content_negotiation(self, request, force=False):
@@ -294,6 +301,33 @@ class APIView(View):
             if not throttle.allow_request(request, self):
                 self.throttled(request, throttle.wait())
 
+    def check_preemptive_cache(self, request):
+        for cache_lookup in self.get_cache_lookups():
+            cache_key = cache_lookup.get_cache_key(self.model, self.kwargs['pk'])
+            if cache_lookup.resource_unchanged(request, cache_key):
+                return Response(status=304)
+
+    def get_cache_lookup_headers(self, obj):
+        headers = {}
+        for cache_lookup in self.get_cache_lookups():
+            headers.update(cache_lookup.get_header(obj))
+        return headers
+
+    def check_update_validity(self, request):
+        """
+        """
+        # TODO add setting to cover
+        #  * raise IfMatchMissing when it's missing (if it's there, carry on)
+        #  * continue regardless
+        if request.META.get('HTTP_IF_MATCH') is None:
+            raise exceptions.IfMatchMissing
+
+    def cache_precondition_check(self, obj, request):
+        header = request.META.get('HTTP_IF_MATCH')
+        for cache_lookup in self.get_cache_lookups():
+            if cache_lookup.get_etag(obj) != header:
+                raise exceptions.PreconditionFailed
+
     # Dispatch methods
 
     def initialize_request(self, request, *args, **kargs):
@@ -318,6 +352,7 @@ class APIView(View):
         self.perform_authentication(request)
         self.check_permissions(request)
         self.check_throttles(request)
+        self.check_preemptive_cache(request)
 
         # Perform content negotiation and store the accepted info on the request
         neg = self.perform_content_negotiation(request)
@@ -398,10 +433,9 @@ class APIView(View):
             else:
                 handler = self.http_method_not_allowed
 
-            if getattr(self, 'use_etags', False) and request.method.lower() in ('put', 'delete'):
-                self.etag_header = request.META.get('HTTP_IF_MATCH')
-                if self.etag_header is None:
-                    raise exceptions.IfMatchMissing
+            if request.method.lower() in ('put', 'delete'):
+                # FIXME this method name isn't obvious
+                self.check_update_validity(request)
 
             response = handler(request, *args, **kwargs)
 
@@ -418,5 +452,3 @@ class APIView(View):
         a less useful default implementation.
         """
         return Response(self.metadata(request), status=status.HTTP_200_OK)
-    def get_etag(self, obj):
-        return getattr(obj, self.etag_var)

From 65b16071c480ffd5761ce9e0c1656428c339940e Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 10:43:44 +0100
Subject: [PATCH 09/16] Get cache keys from a model or instance

---
 rest_framework/cache_lookups.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/rest_framework/cache_lookups.py b/rest_framework/cache_lookups.py
index 4d51c426e..628e3c748 100644
--- a/rest_framework/cache_lookups.py
+++ b/rest_framework/cache_lookups.py
@@ -22,7 +22,10 @@ class ETagCacheLookup(BaseCacheLookup):
 
     @staticmethod
     def get_cache_key(cls, pk):
-        class_name = cls.__class__.__name__
+        try:
+            class_name = cls.__name__  # class
+        except AttributeError:
+            class_name = cls.__class__.__name__  # instance
         return 'etag-{}-{}'.format(class_name, pk)
 
     def get_etag(self, obj):

From cede7d86a3db9cf45c29c2f5a8a4d1f8e22e7bbd Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 10:45:47 +0100
Subject: [PATCH 10/16] Refactor precondition check into the cache lookup
 backends

---
 rest_framework/cache_lookups.py | 5 +++++
 rest_framework/views.py         | 4 +---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/rest_framework/cache_lookups.py b/rest_framework/cache_lookups.py
index 628e3c748..2d9271b0c 100644
--- a/rest_framework/cache_lookups.py
+++ b/rest_framework/cache_lookups.py
@@ -2,6 +2,7 @@
 Provides a set of pluggable cache policies.
 """
 from django.core.cache import cache
+from rest_framework.exceptions import PreconditionFailed
 
 
 class BaseCacheLookup(object):
@@ -37,6 +38,10 @@ class ETagCacheLookup(BaseCacheLookup):
         cache.set(key, etag)
         return {'ETag': etag}
 
+    def precondition_check(self, obj, request):
+        if self.get_etag(obj) != request.META.get('HTTP_IF_NONE_MATCH'):
+            raise PreconditionFailed
+
     def resource_unchanged(self, request, key):
         etag = cache.get(key)
         header = request.META.get('HTTP_IF_NONE_MATCH')
diff --git a/rest_framework/views.py b/rest_framework/views.py
index 8e38d7e6a..0c780be74 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -323,10 +323,8 @@ class APIView(View):
             raise exceptions.IfMatchMissing
 
     def cache_precondition_check(self, obj, request):
-        header = request.META.get('HTTP_IF_MATCH')
         for cache_lookup in self.get_cache_lookups():
-            if cache_lookup.get_etag(obj) != header:
-                raise exceptions.PreconditionFailed
+            cache_lookup.precondition_check(obj, request)
 
     # Dispatch methods
 

From 5e5de9c499b95fdfd32ec20853bb4732c4c71d31 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 10:46:48 +0100
Subject: [PATCH 11/16] Only preemptively check the cache on GET requests

---
 rest_framework/mixins.py | 4 ++++
 rest_framework/views.py  | 1 -
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/rest_framework/mixins.py b/rest_framework/mixins.py
index a0fc51e35..e5de46abb 100644
--- a/rest_framework/mixins.py
+++ b/rest_framework/mixins.py
@@ -97,6 +97,10 @@ class RetrieveModelMixin(object):
     Should be mixed in with `SingleObjectAPIView`.
     """
     def retrieve(self, request, *args, **kwargs):
+        cached_object = self.check_preemptive_cache(request)
+        if cached_object:
+            return cached_object
+
         queryset = self.get_queryset()
         filtered_queryset = self.filter_queryset(queryset)
         self.object = self.get_object(filtered_queryset)
diff --git a/rest_framework/views.py b/rest_framework/views.py
index 0c780be74..4caec27c0 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -350,7 +350,6 @@ class APIView(View):
         self.perform_authentication(request)
         self.check_permissions(request)
         self.check_throttles(request)
-        self.check_preemptive_cache(request)
 
         # Perform content negotiation and store the accepted info on the request
         neg = self.perform_content_negotiation(request)

From 70199d9755223a95c7d68adf8f943309f2ee7e58 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 10:50:49 +0100
Subject: [PATCH 12/16] Tidy up header usage

Explicity define request and response headers.
---
 rest_framework/cache_lookups.py | 10 +++++++---
 rest_framework/mixins.py        |  2 +-
 rest_framework/views.py         |  4 ++--
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/rest_framework/cache_lookups.py b/rest_framework/cache_lookups.py
index 2d9271b0c..2973d5029 100644
--- a/rest_framework/cache_lookups.py
+++ b/rest_framework/cache_lookups.py
@@ -20,6 +20,7 @@ class ETagCacheLookup(BaseCacheLookup):
     """
     """
     etag_variable = 'etag'
+    request_header = 'HTTP_IF_NONE_MATCH'
 
     @staticmethod
     def get_cache_key(cls, pk):
@@ -32,19 +33,22 @@ class ETagCacheLookup(BaseCacheLookup):
     def get_etag(self, obj):
         return getattr(obj, self.etag_variable)
 
-    def get_header(self, obj):
+    def get_request_header(self):
+        return self.request_header
+
+    def get_response_header(self, obj):
         key = self.get_cache_key(obj, 'pk')
         etag = self.get_etag(obj)
         cache.set(key, etag)
         return {'ETag': etag}
 
     def precondition_check(self, obj, request):
-        if self.get_etag(obj) != request.META.get('HTTP_IF_NONE_MATCH'):
+        if self.get_etag(obj) != request.META.get(self.get_request_header()):
             raise PreconditionFailed
 
     def resource_unchanged(self, request, key):
         etag = cache.get(key)
-        header = request.META.get('HTTP_IF_NONE_MATCH')
+        header = request.META.get(self.get_request_header())
         if etag is not None and etag == header:
             return True
         return False
diff --git a/rest_framework/mixins.py b/rest_framework/mixins.py
index e5de46abb..29d0f03dc 100644
--- a/rest_framework/mixins.py
+++ b/rest_framework/mixins.py
@@ -105,7 +105,7 @@ class RetrieveModelMixin(object):
         filtered_queryset = self.filter_queryset(queryset)
         self.object = self.get_object(filtered_queryset)
 
-        headers = self.get_cache_lookup_headers(self.object)
+        headers = self.get_cache_lookup_response_headers(self.object)
 
         serializer = self.get_serializer(self.object)
         return Response(serializer.data, headers=headers)
diff --git a/rest_framework/views.py b/rest_framework/views.py
index 4caec27c0..837d20912 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -307,10 +307,10 @@ class APIView(View):
             if cache_lookup.resource_unchanged(request, cache_key):
                 return Response(status=304)
 
-    def get_cache_lookup_headers(self, obj):
+    def get_cache_lookup_response_headers(self, obj):
         headers = {}
         for cache_lookup in self.get_cache_lookups():
-            headers.update(cache_lookup.get_header(obj))
+            headers.update(cache_lookup.get_response_header(obj))
         return headers
 
     def check_update_validity(self, request):

From 879302c815b22a9aa6fbe7b6263daf1c1e66d4ab Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 12:02:26 +0100
Subject: [PATCH 13/16] Add update header to ETagCacheLookup

Need to use the IF_MATCH header to check the validity of updating a
model in PUT and DELETE methods.
---
 rest_framework/cache_lookups.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/rest_framework/cache_lookups.py b/rest_framework/cache_lookups.py
index 2973d5029..eb314ca42 100644
--- a/rest_framework/cache_lookups.py
+++ b/rest_framework/cache_lookups.py
@@ -21,6 +21,7 @@ class ETagCacheLookup(BaseCacheLookup):
     """
     etag_variable = 'etag'
     request_header = 'HTTP_IF_NONE_MATCH'
+    update_header = 'HTTP_IF_MATCH'
 
     @staticmethod
     def get_cache_key(cls, pk):
@@ -36,6 +37,9 @@ class ETagCacheLookup(BaseCacheLookup):
     def get_request_header(self):
         return self.request_header
 
+    def get_update_header(self):
+        return self.update_header
+
     def get_response_header(self, obj):
         key = self.get_cache_key(obj, 'pk')
         etag = self.get_etag(obj)
@@ -43,7 +47,7 @@ class ETagCacheLookup(BaseCacheLookup):
         return {'ETag': etag}
 
     def precondition_check(self, obj, request):
-        if self.get_etag(obj) != request.META.get(self.get_request_header()):
+        if self.get_etag(obj) != request.META.get(self.get_update_header()):
             raise PreconditionFailed
 
     def resource_unchanged(self, request, key):

From 2139c109abd327d68bef4823128b4ca093fe6623 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 12:28:58 +0100
Subject: [PATCH 14/16] Dont' require IF_MATCH header

The HTTP RFC doesn't require the IF_MATCH header and it's language on
what to do when it's not included isn't absolute so removing this check.

The implementing codebase can easily add this by overriding
precondition_check in ETagCacheLookup if necessary.
---
 rest_framework/exceptions.py |  8 --------
 rest_framework/views.py      | 13 -------------
 2 files changed, 21 deletions(-)

diff --git a/rest_framework/exceptions.py b/rest_framework/exceptions.py
index 89dc88fe3..9ceb64fe1 100644
--- a/rest_framework/exceptions.py
+++ b/rest_framework/exceptions.py
@@ -96,14 +96,6 @@ class PreconditionFailed(APIException):
         self.detail = detail or self.default_detail
 
 
-class IfMatchMissing(APIException):
-    default_detail = 'IF_MATCH header is required'
-    status_code = status.HTTP_400_BAD_REQUEST
-
-    def __init__(self, detail=None):
-        self.detail = detail or self.default_detail
-
-
 class ConfigurationError(Exception):
     """
     Indicates an internal server error.
diff --git a/rest_framework/views.py b/rest_framework/views.py
index 837d20912..59b15e998 100644
--- a/rest_framework/views.py
+++ b/rest_framework/views.py
@@ -313,15 +313,6 @@ class APIView(View):
             headers.update(cache_lookup.get_response_header(obj))
         return headers
 
-    def check_update_validity(self, request):
-        """
-        """
-        # TODO add setting to cover
-        #  * raise IfMatchMissing when it's missing (if it's there, carry on)
-        #  * continue regardless
-        if request.META.get('HTTP_IF_MATCH') is None:
-            raise exceptions.IfMatchMissing
-
     def cache_precondition_check(self, obj, request):
         for cache_lookup in self.get_cache_lookups():
             cache_lookup.precondition_check(obj, request)
@@ -430,10 +421,6 @@ class APIView(View):
             else:
                 handler = self.http_method_not_allowed
 
-            if request.method.lower() in ('put', 'delete'):
-                # FIXME this method name isn't obvious
-                self.check_update_validity(request)
-
             response = handler(request, *args, **kwargs)
 
         except Exception as exc:

From e5d66d3ef89b354d37e5efe68281fd4d35f61969 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 14:21:19 +0100
Subject: [PATCH 15/16] Add public facing methods to BaseCacheLookup

There seems little point in using BaseCacheLookup by default so it can
act as an example to implementing classes.
---
 rest_framework/cache_lookups.py | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/rest_framework/cache_lookups.py b/rest_framework/cache_lookups.py
index eb314ca42..8ee96e197 100644
--- a/rest_framework/cache_lookups.py
+++ b/rest_framework/cache_lookups.py
@@ -2,18 +2,25 @@
 Provides a set of pluggable cache policies.
 """
 from django.core.cache import cache
+from django.core.exceptions import ImproperlyConfigured
 from rest_framework.exceptions import PreconditionFailed
 
 
 class BaseCacheLookup(object):
-    def get_header(self, obj):
-        return {}
+    def get_request_header(self):
+        raise ImproperlyConfigured('Subclass must implement `get_request_header`.')
+
+    def get_update_header(self):
+        raise ImproperlyConfigured('Subclass must implement `get_update_header`.')
+
+    def get_response_header(self, obj):
+        raise ImproperlyConfigured('Subclass must impelement `get_response_header`.')
+
+    def precondition_check(self, obj, request):
+        raise ImproperlyConfigured('Subclass must implement `precondition_check`.')
 
     def resource_unchanged(self, request):
-        """
-        Return `False` if resource has changed, `True` otherwise.
-        """
-        return False
+        raise ImproperlyConfigured('Subclass must implement `resource_unchanged`.')
 
 
 class ETagCacheLookup(BaseCacheLookup):

From 077c4a69acbec6aef0e1597a58a38aee87c93e04 Mon Sep 17 00:00:00 2001
From: George Hickman <george@ghickman.co.uk>
Date: Tue, 2 Apr 2013 14:30:11 +0100
Subject: [PATCH 16/16] Follow naming convention more closely

---
 rest_framework/{cache_lookups.py => caches.py} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename rest_framework/{cache_lookups.py => caches.py} (100%)

diff --git a/rest_framework/cache_lookups.py b/rest_framework/caches.py
similarity index 100%
rename from rest_framework/cache_lookups.py
rename to rest_framework/caches.py