Allow NUM_PROXIES=0 and include more docs

docs/api-guide/settings.md

@@ -359,5 +359,11 @@ The name of a parameter in the URL conf that may be used to provide a format suf
 
 Default: `'format'`
 
+#### NUM_PROXIES
+
+An integer of 0 or more, that may be used to specify the number of application proxies that the API runs behind.  This allows throttling to more accurately identify client IP addresses.  If set to `None` then less strict IP matching will be used by the throttle classes.
+
+Default: `None`
+
 [cite]: http://www.python.org/dev/peps/pep-0020/
 [strftime]: http://docs.python.org/2/library/time.html#time.strftime

docs/api-guide/throttling.md

@@ -35,16 +35,11 @@ The default throttling policy may be set globally, using the `DEFAULT_THROTTLE_C
         'DEFAULT_THROTTLE_RATES': {
             'anon': '100/day',
             'user': '1000/day'
-        },
-        'NUM_PROXIES': 2,
+        }
     }
 
 The rate descriptions used in `DEFAULT_THROTTLE_RATES` may include `second`, `minute`, `hour` or `day` as the throttle period.
 
-By default Django REST Framework will try to use the `HTTP_X_FORWARDED_FOR` header to uniquely identify client machines for throttling. If `HTTP_X_FORWARDED_FOR` is not present `REMOTE_ADDR` header value will be used.
-
-To help Django REST Framework identify unique clients the number of application proxies can be set using `NUM_PROXIES`. This setting will allow the throttle to correctly identify unique requests when there are multiple application side proxies in front of the server. `NUM_PROXIES` should be set to an integer. It is important to understand that if you configure `NUM_PROXIES > 0` all clients behind a unique [NAT'd](http://en.wikipedia.org/wiki/Network_address_translation) gateway will be treated as a single client.
-
 You can also set the throttling policy on a per-view or per-viewset basis,
 using the `APIView` class based views.
 
@@ -71,6 +66,16 @@ Or, if you're using the `@api_view` decorator with function based views.
         }
         return Response(content)
 
+## How clients are identified
+
+By default the `X-Forwarded-For` HTTP header is used to uniquely identify client machines for throttling.  If the `X-Forwarded-For` header is not present, then the value of the `Remote-Addr` header will be used.
+
+If you need to more strictly identify unique clients, you'll need to configure the number of application proxies that the API runs behind by setting the `NUM_PROXIES` setting. This setting should be an integer of 0 or more, and will allow the throttle to identify the client IP as being the last IP address in the `X-Forwarded-For` header, once any application proxy IP addresses have first been excluded.
+
+It is important to understand that if you configure the `NUM_PROXIES` setting, then all clients behind a unique [NAT'd](http://en.wikipedia.org/wiki/Network_address_translation) gateway will be treated as a single client.
+
+Further context on how the `X-Forwarded-For` header works, and identifier a remote client IP can be [found here][identifing-clients].
+
 ## Setting up the cache
 
 The throttle classes provided by REST framework use Django's cache backend.  You should make sure that you've set appropriate [cache settings][cache-setting].  The default value of `LocMemCache` backend should be okay for simple setups.  See Django's [cache documentation][cache-docs] for more details.
@@ -183,5 +188,6 @@ The following is an example of a rate throttle, that will randomly throttle 1 in
 
 [cite]: https://dev.twitter.com/docs/error-codes-responses
 [permissions]: permissions.md
+[identifing-clients]: http://oxpedia.org/wiki/index.php?title=AppSuite:Grizzly#Multiple_Proxies_in_front_of_the_cluster
 [cache-setting]: https://docs.djangoproject.com/en/dev/ref/settings/#caches
 [cache-docs]: https://docs.djangoproject.com/en/dev/topics/cache/#setting-up-the-cache

rest_framework/throttling.py

@@ -28,8 +28,12 @@ class BaseThrottle(object):
         remote_addr = request.META.get('REMOTE_ADDR')
         num_proxies = api_settings.NUM_PROXIES
 
-        if xff and num_proxies:
-            return xff.split(',')[-min(num_proxies, len(xff))].strip()
+        if num_proxies is not None:
+            if num_proxies == 0 or xff is None:
+                return remote_addr
+            addrs = xff.split(',')
+            client_addr = addrs[-min(num_proxies, len(xff))]
+            return client_addr.strip()
 
         return xff if xff else remote_addr