Add CustomScopedRateThrolle throttling class

This will throttle anonymous enketo users more fairly

onadata/libs/tests/test_throttle.py

@@ -3,13 +3,32 @@
 
 from rest_framework.test import APIRequestFactory
 
-from onadata.libs.throttle import RequestHeaderThrottle
+from onadata.libs.throttle import RequestHeaderThrottle, CustomScopedRateThrottle
+
+class CustomScopedRateThrottleTest(TestCase):
+    def setUp(self):
+        """
+        Reset the cache so that no throttles will be active
+        """
+        cache.clear()
+        self.factory = APIRequestFactory()
+        self.throttle = CustomScopedRateThrottle()
+
+    def test_anonymous_users_get_throttled_based_on_uri_path(self):
+        request = self.factory.get("/enketo/1234/submission")
+        self.throttle.scope = "submission"
+        cache_key = self.throttle.get_cache_key(request, None)
+        self.assertEqual(cache_key, "submission_/enketo/1234/submission")
+
+    def test_users_get_throttled_based_on_uri_path(self):
+        request = self.factory.get("/enketo/1234/submission")
+        request.user = self.user
+        self.throttle.scope = "submission"
+        cache_key = self.throttle.get_cache_key(request, None)
+        self.assertEqual(cache_key, f"submission_{self.user.id}")
 
 
 class ThrottlingTests(TestCase):
-    """
-    Test Renderer class.
-    """
 
     def setUp(self):
         """

onadata/libs/throttle.py

@@ -4,7 +4,20 @@
 
 from django.conf import settings
 
-from rest_framework.throttling import SimpleRateThrottle
+from rest_framework.throttling import SimpleRateThrottle, ScopedRateThrottle
+
+
+class CustomScopedRateThrottle(ScopedRateThrottle):
+    """
+    Custom throttling for fair throttling for anonymous users sharing IP
+    """
+
+    def get_cache_key(self, request, view):
+        if request.user and request.user.is_authenticated:
+            return super().get_cache_key(request, view)
+
+        return self.cache_format % \
+                { 'scope': self.scope,'ident': request.path }
 
 
 class RequestHeaderThrottle(SimpleRateThrottle):