Add pagination class for the Messaging Stats viewset

onadata/apps/api/viewsets/v2/messaging_stats_viewset.py

@@ -15,6 +15,7 @@
     TargetTypeFilterBackend,
 )
 from onadata.apps.messaging.permissions import TargetObjectPermissions
+from onadata.libs.pagination import StandardPageNumberPagination
 
 
 class MessagingStatsViewSet(mixins.ListModelMixin, viewsets.GenericViewSet):
@@ -51,13 +52,15 @@ class MessagingStatsViewSet(mixins.ListModelMixin, viewsets.GenericViewSet):
     queryset = Action.objects.filter(verb__in=MESSAGE_VERBS)
     permission_classes = [IsAuthenticated, TargetObjectPermissions]
     filter_backends = [TargetTypeFilterBackend, TargetIDFilterBackend]
+    pagination_class = StandardPageNumberPagination
 
     def _stream_annotated_queryset(self, queryset):
         yield "["
         group = None
         prev_group = None
         out = {}
-        for item in queryset.iterator():
+        iterator = iter(queryset) if isinstance(queryset, list) else queryset.iterator()
+        for item in iterator:
             if group is None:
                 group = item.get("group")
             elif group != item.get("group"):
@@ -94,7 +97,14 @@ def list(self, request, *args, **kwargs):
         queryset = self._generate_annotated_queryset(
             request, self.filter_queryset(self.get_queryset())
         )
-        response = StreamingHttpResponse(  # pylint: disable=http-response-with-content-type-json
-            self._stream_annotated_queryset(queryset), content_type="application/json"
+        page = self.paginate_queryset(queryset)
+        headers = {}
+        if page:
+            stream = self._stream_annotated_queryset(page)
+            headers = self.paginator.generate_link_header(request, page)
+        else:
+            stream = self._stream_annotated_queryset(queryset)
+        response = StreamingHttpResponse(
+            stream, content_type="application/json", headers=headers
         )
         return response