Fix module loading from modulestore (#117)

lti_consumer/models.py

@@ -11,6 +11,7 @@
 from lti_consumer.lti_1p1.consumer import LtiConsumer1p1
 # LTI 1.3
 from lti_consumer.lti_1p3.consumer import LtiAdvantageConsumer
+from lti_consumer.plugin import compat
 from lti_consumer.utils import get_lms_base, get_lti_ags_lineitems_url
 
 
@@ -77,11 +78,7 @@ def block(self):
         if block is None:
             if self.location is None:
                 raise ValueError("Block location not set, it's not possible to retrieve the block.")
-
-            # Import on runtime only
-            # pylint: disable=import-outside-toplevel,import-error
-            from xmodule.modulestore.django import modulestore
-            block = self._block = modulestore().get_item(self.location)
+            block = self._block = compat.load_block_as_anonymous_user(self.location)
         return block
 
     @block.setter

lti_consumer/plugin/compat.py

@@ -19,3 +19,33 @@ def run_xblock_handler_noauth(*args, **kwargs):
     # pylint: disable=import-error,import-outside-toplevel
     from lms.djangoapps.courseware.module_render import handle_xblock_callback_noauth
     return handle_xblock_callback_noauth(*args, **kwargs)
+
+
+def load_block_as_anonymous_user(location):
+    """
+    Load a block as anonymous user.
+
+    This uses a few internal courseware methods to retrieve the descriptor
+    and bind an AnonymousUser to it, in a similar fashion as a `noauth` XBlock
+    handler.
+    """
+    # pylint: disable=import-error,import-outside-toplevel
+    from django.contrib.auth.models import AnonymousUser
+    from xmodule.modulestore.django import modulestore
+    from lms.djangoapps.courseware.module_render import get_module_for_descriptor_internal
+
+    # Retrieve descriptor from modulestore
+    descriptor = modulestore().get_item(location)
+
+    # Load block, attaching it to AnonymousUser
+    get_module_for_descriptor_internal(
+        user=AnonymousUser(),
+        descriptor=descriptor,
+        student_data=None,
+        course_id=location.course_key,
+        track_function=None,
+        xqueue_callback_url_prefix="",
+        request_token="",
+    )
+
+    return descriptor

lti_consumer/tests/unit/test_models.py

@@ -108,6 +108,24 @@ def test_lti_consumer_ags_enabled(self):
             }
         )
 
+    @patch("lti_consumer.models.compat")
+    def test_block_property(self, compat_mock):
+        """
+        Check if a block is properly loaded when calling the `block` property.
+        """
+        compat_mock.load_block_as_anonymous_user.return_value = self.xblock
+
+        block = self.lti_1p3_config.block
+        self.assertEqual(block, self.xblock)
+
+    def test_block_property_missing_location(self):
+        """
+        Check the `block` property raises when failing to retrieve a block.
+        """
+        self.lti_1p3_config.location = None
+        with self.assertRaises(ValueError):
+            _ = self.lti_1p3_config.block
+
 
 class TestLtiAgsLineItemModel(TestCase):
     """