Fix issue with subscription list in Redis

In the Redis storage driver, we don't manage the marker of subscription
list properly, returning the same item as the marker when we are at the
list limit. This manages it properly by fixing how we handle the rank
calculated.

Change-Id: Ifedd970c467a8e9e2f59123240f3844d884984c9

zaqar/storage/redis/subscriptions.py

@@ -60,7 +60,7 @@ class SubscriptionController(base.Subscription):
                                                       project,
                                                       SUBSCRIPTION_IDS_SUFFIX)
         rank = client.zrank(subset_key, marker)
-        start = rank + 1 if rank else 0
+        start = rank + 1 if rank is not None else 0
 
         cursor = (q for q in client.zrange(subset_key, start,
                                            start + limit - 1))

zaqar/tests/unit/storage/base.py

@@ -1053,6 +1053,31 @@ class SubscriptionControllerTest(ControllerBaseTest):
                                 subscriptions)))
         self.assertEqual(5, len(subscriptions))
 
+    def test_small_list(self):
+        subscriber = 'http://fake'
+        s_id = self.subscription_controller.create(
+            self.source,
+            subscriber,
+            self.ttl,
+            self.options,
+            project=self.project)
+        self.addCleanup(self.subscription_controller.delete, self.source,
+                        s_id, self.project)
+
+        interaction = self.subscription_controller.list(self.source,
+                                                        project=self.project)
+        subscriptions = list(next(interaction))
+        marker = next(interaction)
+
+        self.assertEqual(1, len(subscriptions))
+
+        interaction = (self.subscription_controller.list(self.source,
+                                                         project=self.project,
+                       marker=marker))
+        subscriptions = list(next(interaction))
+
+        self.assertEqual([], subscriptions)
+
     @ddt.data(True, False)
     def test_get_raises_if_subscription_does_not_exist(self, precreate_queue):
         self._precreate_queue(precreate_queue)