get_requested_site: configurable backend to get the site for an API call

Description
-----------

Dashboard needs to be able to access Figures API with privileged access by sending site's UUID parameter.

This concept is Tahoe-specific and shouldn't make it into Figures (thanks John for advocating for that). Therefor this PR adds a plugin to customize the logic we use to `get_current_site()`

I've added a Figures plugin repo to do that:

 - appsembler/tahoe-figures-plugins#1

Using the backend
-----------------

 - Install a package which has the custom backend e.g. `pip install tahoe-figures-plugins`
 - In the `server-vars.yml` configure Figures like below:

   ```yaml
   FIGURES:
     REQUESTED_SITE_BACKEND: 'tahoe_figures_plugins.sites:get_current_site_or_by_uuid'
   ```

Backward compatibility
----------------------

 - By default this PR changes nothing for both community and Tahoe installations
 - The tests works as-is for all Figures views
 - The plugin only used when configured

Benchmark
---------

I tested the `import_from_path` function and the load takes 0.0069ms per call if the backend is already imported in the Python module system on a staging server.

Loading the backend for the first time (e.g. a new Python gunicorn worker) takes 0.5ms.

This seems like an acceptable delay to add on top of the each request.

figures/sites.py

@@ -12,6 +12,7 @@
 
 from __future__ import absolute_import
 from django.contrib.auth import get_user_model
+from django.contrib.sites import shortcuts as sites_shortcuts
 from django.contrib.sites.models import Site
 from django.conf import settings
 
@@ -304,6 +305,24 @@ def _get_all_sites():
     return Site.objects.all()
 
 
+def get_requested_site(request):
+    """
+    From a request return the corresponding site.
+
+    This functions makes use of the `REQUESTED_SITE_BACKEND` setting if configured, otherwise
+    it defaults to Django's get_current_site().
+
+    :return Site
+    """
+    backend_path = settings.ENV_TOKENS['FIGURES'].get('REQUESTED_SITE_BACKEND')
+    if backend_path:
+        requested_site_backend = import_from_path(backend_path)
+        requested_site = requested_site_backend(request)
+    else:
+        requested_site = sites_shortcuts.get_current_site(request)
+    return requested_site
+
+
 def get_sites():
     """
     Get a list of sites for Figures purposes in a configurable manner.

figures/views.py

@@ -7,7 +7,6 @@
 from django.conf import settings
 from django.contrib.auth import get_user_model
 from django.contrib.auth.decorators import login_required, user_passes_test
-import django.contrib.sites.shortcuts
 from django.contrib.sites.models import Site
 from django.http import HttpResponseRedirect
 from django.shortcuts import get_object_or_404, render
@@ -170,7 +169,7 @@ class CourseOverviewViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     lookup_value_regex = settings.COURSE_ID_PATTERN
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = figures.sites.get_courses_for_site(site)
         return queryset
 
@@ -194,7 +193,7 @@ def get_course_key(self, course_id_str):
     def retrieve(self, request, *args, **kwargs):
         course_key = self.get_course_key(
             kwargs.get('pk', ''))
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(self.request)
         if figures.helpers.is_multisite():
             if site != figures.sites.get_site_for_course(course_key):
                 # Raising NotFound instead of PermissionDenied
@@ -243,7 +242,7 @@ class UserIndexViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     filter_class = UserFilterSet
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = figures.sites.get_users_for_site(site)
         return queryset
 
@@ -256,7 +255,7 @@ class CourseEnrollmentViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     filter_class = CourseEnrollmentFilter
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = figures.sites.get_course_enrollments_for_site(site)
         return queryset
 
@@ -270,7 +269,7 @@ class CourseDailyMetricsViewSet(CommonAuthMixin, viewsets.ModelViewSet):
     filter_class = CourseDailyMetricsFilter
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = CourseDailyMetrics.objects.filter(site=site)
         return queryset
 
@@ -284,7 +283,7 @@ class SiteDailyMetricsViewSet(CommonAuthMixin, viewsets.ModelViewSet):
     filter_class = SiteDailyMetricsFilter
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = SiteDailyMetrics.objects.filter(site=site)
         return queryset
 
@@ -316,7 +315,7 @@ def get(self, request, format=None):  # pylint: disable=redefined-builtin
         '''
         Does not yet support multi-tenancy
         '''
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         date_for = request.query_params.get('date_for')
         data = self.metrics_method(site=site, date_for=date_for)
 
@@ -348,7 +347,7 @@ class GeneralUserDataViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     ordering_fields = ['username', 'email', 'profile__name', 'is_active', 'date_joined']
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = figures.sites.get_users_for_site(site)
         return queryset
 
@@ -361,13 +360,13 @@ class LearnerDetailsViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     filter_class = UserFilterSet
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = figures.sites.get_users_for_site(site)
         return queryset
 
     def get_serializer_context(self):
         context = super(LearnerDetailsViewSet, self).get_serializer_context()
-        context['site'] = django.contrib.sites.shortcuts.get_current_site(self.request)
+        context['site'] = figures.sites.get_requested_site(self.request)
         return context
 
 
@@ -426,7 +425,7 @@ def get_queryset(self):
         * If no valid course keys are found, then an empty list is returned from
           this view
         """
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         course_keys = figures.sites.get_course_keys_for_site(site)
         try:
             param_course_keys = self.query_param_course_keys()
@@ -441,7 +440,7 @@ def get_queryset(self):
 
     def get_serializer_context(self):
         context = super(LearnerMetricsViewSetV1, self).get_serializer_context()
-        context['site'] = django.contrib.sites.shortcuts.get_current_site(self.request)
+        context['site'] = figures.sites.get_requested_site(self.request)
         context['course_keys'] = self.query_param_course_keys()
         return context
 
@@ -493,13 +492,13 @@ def get_queryset(self):
         * If no valid course keys are found, then an empty list is returned from
           this view
         """
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         course_ids = self.query_param_course_ids()
         return site_users_enrollment_data(site=site, course_ids=course_ids)
 
     def get_serializer_context(self):
         context = super(LearnerMetricsViewSetV2, self).get_serializer_context()
-        context['site'] = django.contrib.sites.shortcuts.get_current_site(self.request)
+        context['site'] = figures.sites.get_requested_site(self.request)
         context['course_ids'] = self.query_param_course_ids()
         return context
 
@@ -521,7 +520,7 @@ class EnrollmentMetricsViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     filter_class = EnrollmentMetricsFilter
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = LearnerCourseGradeMetrics.objects.filter(site=site)
         return queryset
 
@@ -534,7 +533,7 @@ def completed_ids(self, request):
         The default router does not support hyphen in the custom action, so
         we need to use the underscore until we implement a custom router
         """
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         qs = self.model.objects.completed_ids_for_site(site=site)
         page = self.paginate_queryset(qs)
         if page is not None:
@@ -552,7 +551,7 @@ def completed(self, request):
         Return matching LearnerCourseGradeMetric rows that have completed
         enrollments
         """
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         qs = self.model.objects.completed_for_site(site=site)
         page = self.paginate_queryset(qs)
         if page is not None:
@@ -582,7 +581,7 @@ def site_course_helper(self, pk):
         except InvalidKeyError:
             raise NotFound()
 
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         if figures.helpers.is_multisite():
             if site != figures.sites.get_site_for_course(course_id):
                 raise NotFound()
@@ -609,7 +608,7 @@ def list(self, request):
         TODO: NEXT Add query params to get data from previous months
         TODO: Add paginagation
         """
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         course_keys = figures.sites.get_course_keys_for_site(site)
         date_for = datetime.utcnow().date()
         month_for = '{}/{}'.format(date_for.month, date_for.year)
@@ -711,13 +710,13 @@ def list(self, request):
         Returns site metrics data for current month
         """
 
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         data = metrics.get_current_month_site_metrics(site)
         return Response(data)
 
     @list_route()
     def registered_users(self, request):
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         date_for = datetime.utcnow().date()
         months_back = 6
 
@@ -735,7 +734,7 @@ def new_users(self, request):
         """
         TODO: Rename the metrics module function to "new_users" to match this
         """
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         date_for = datetime.utcnow().date()
         months_back = 6
 
@@ -750,7 +749,7 @@ def new_users(self, request):
 
     @list_route()
     def course_completions(self, request):
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         date_for = datetime.utcnow().date()
         months_back = 6
 
@@ -765,7 +764,7 @@ def course_completions(self, request):
 
     @list_route()
     def course_enrollments(self, request):
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         date_for = datetime.utcnow().date()
         months_back = 6
 
@@ -780,7 +779,7 @@ def course_enrollments(self, request):
 
     @list_route()
     def site_courses(self, request):
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         date_for = datetime.utcnow().date()
         months_back = 6
 
@@ -795,7 +794,7 @@ def site_courses(self, request):
 
     @list_route()
     def active_users(self, request):
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         months_back = 6
         active_users = metrics.get_site_mau_history_metrics(site=site,
                                                             months_back=months_back)
@@ -816,7 +815,7 @@ def get_queryset(self):
     def retrieve(self, request, **kwargs):
         course_id_str = kwargs.get('pk', '')
         course_key = CourseKey.from_string(course_id_str.replace(' ', '+'))
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
 
         if figures.helpers.is_multisite():
             if site != figures.sites.get_site_for_course(course_key):
@@ -827,7 +826,7 @@ def retrieve(self, request, **kwargs):
         return Response(serializer.data)
 
     def list(self, request):
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         course_overviews = figures.sites.get_courses_for_site(site)
         data = []
         for co in course_overviews:
@@ -858,7 +857,7 @@ def list(self, request):
         We use list instead of retrieve because retrieve requires a resource
         identifier, like a PK
         """
-        site = django.contrib.sites.shortcuts.get_current_site(request)
+        site = figures.sites.get_requested_site(request)
         data = retrieve_live_site_mau_data(site)
         serializer = self.serializer_class(data)
         return Response(serializer.data)
@@ -872,7 +871,7 @@ class CourseMauMetricsViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     lookup_value_regex = settings.COURSE_ID_PATTERN
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = CourseMauMetrics.objects.filter(site=site)
         return queryset
 
@@ -885,7 +884,7 @@ class SiteMauMetricsViewSet(CommonAuthMixin, viewsets.ReadOnlyModelViewSet):
     filter_class = SiteMauMetricsFilter
 
     def get_queryset(self):
-        site = django.contrib.sites.shortcuts.get_current_site(self.request)
+        site = figures.sites.get_requested_site(self.request)
         queryset = SiteMauMetrics.objects.filter(site=site)
         return queryset
 

tests/test_sites.py

@@ -437,6 +437,54 @@ def test_student_modules_for_course_enrollment(monkeypatch):
     assert set(sm) == set(ce_sm)
 
 
+@pytest.mark.django_db
+def test_get_requested_site_default_behaviour(settings):
+    """
+    Test `get_requested_site` returns Django's get_current_site() by default.
+    """
+    example_site = Site.objects.get()  # gets the example site
+    settings.SITE_ID = example_site.id
+
+    current_site = figures.sites.get_requested_site(request=mock.Mock())
+    assert current_site == example_site, 'Use Django\'s get_current_site().'
+
+
+@pytest.mark.django_db
+def test_get_requested_site_custom_backend(settings):
+    """
+    Test `get_requested_site` can use custom backends.
+    """
+    orange_site = SiteFactory.create(name='orange site')
+
+    settings.ENV_TOKENS = {
+        'FIGURES': {
+            'REQUESTED_SITE_BACKEND': 'organizations:get_orange_site'
+        }
+    }
+    with mock.patch('organizations.get_orange_site', create=True, return_value=orange_site):
+        requested_site = figures.sites.get_requested_site(request=mock.Mock())
+    assert requested_site == orange_site, 'Should use custom backend.'
+
+
+@pytest.mark.django_db
+def test_get_requested_site_broken_backend(settings):
+    """
+    Test `get_requested_site` don't hide errors from custom backends.
+
+    Figures should keep a simple backend implementation without attempting to fix errors in site configuration or
+    faulty backends.
+    """
+    settings.ENV_TOKENS = {
+        'FIGURES': {
+            'REQUESTED_SITE_BACKEND': 'organizations:broken_backend'
+        }
+    }
+    with mock.patch('organizations.broken_backend', create=True, side_effect=RuntimeError):
+        with pytest.raises(RuntimeError):
+            # Should fail if the REQUESTED_SITE_BACKEND fails
+            figures.sites.get_requested_site(request=mock.Mock())
+
+
 @pytest.mark.skipif(not organizations_support_sites(), reason='needed only in multisite mode')
 @pytest.mark.django_db
 def test_get_sites_default_behaviour():