Use the LTI1.1 assignment ID after a failure to fetch a roster

We have seen some issues in production where the assignment roster fetch
fails with a cryptic error from Canvas.

We have not been able to reproduce this situation locally.

As we have two IDs for the same assignment lets try the LTI1.1 one.

We have tested the other following scenarios:

- LTI1.3 assignment. Use the LTI1.3 id works.

- Upgrade from LTI1.1 LTI1.3 assignment. Using the LTI1.1 ID fails while
  the 1.3 one works.

lms/services/roster.py

@@ -15,6 +15,7 @@
 )
 from lms.models.h_user import get_h_userid, get_h_username
 from lms.models.lti_user import display_name
+from lms.services.exceptions import ExternalRequestError
 from lms.services.lti_names_roles import LTINamesRolesService
 from lms.services.lti_role_service import LTIRoleService
 from lms.services.upsert import bulk_upsert
@@ -111,11 +112,33 @@ def fetch_assignment_roster(self, assignment: Assignment) -> None:
         ), "Trying fetch roster for course without service URL."
         lti_registration = self._get_lti_registration(lms_course)
 
-        roster = self._lti_names_roles_service.get_context_memberships(
-            lti_registration,
-            lms_course.lti_context_memberships_url,
-            resource_link_id=assignment.lti_v13_resource_link_id,
-        )
+        try:
+            roster = self._lti_names_roles_service.get_context_memberships(
+                lti_registration,
+                lms_course.lti_context_memberships_url,
+                resource_link_id=assignment.lti_v13_resource_link_id,
+            )
+        except ExternalRequestError as err:
+            if (
+                err.response_body
+                and (
+                    # Error message from Canvas
+                    "Requested ResourceLink bound to unexpected external tool"
+                    in err.response_body
+                )
+                # In cases for which we have different assignment IDs
+                and assignment.resource_link_id != assignment.lti_v13_resource_link_id
+            ):
+                # The LMS (Canvas) doesn't seem to be able to link our tool to this assignment
+                # Try the same call but with the LTI1.1 assignment identifier.
+                LOG.info("Try to fetch roster with the LTI1.1 identifier")
+                roster = self._lti_names_roles_service.get_context_memberships(
+                    lti_registration,
+                    lms_course.lti_context_memberships_url,
+                    resource_link_id=assignment.resource_link_id,
+                )
+            else:
+                raise
 
         # Insert any users we might be missing in the DB
         lms_users_by_lti_user_id = {

lms/tasks/roster.py

@@ -145,7 +145,7 @@ def fetch_course_roster(*, lms_course_id) -> None:
 def fetch_assignment_roster(*, assignment_id) -> None:
     """Fetch the roster for one course."""
     with app.request_context() as request:
-        roster_service = request.find_service(RosterService)
+        roster_service: RosterService = request.find_service(RosterService)
         with request.tm:
             assignment = request.db.get(Assignment, assignment_id)
             roster_service.fetch_assignment_roster(assignment)

tests/unit/lms/services/roster_test.py

@@ -1,10 +1,11 @@
-from unittest.mock import sentinel
+from unittest.mock import Mock, call, sentinel
 
 import pytest
 from h_matchers import Any
 from sqlalchemy import select
 
 from lms.models import AssignmentRoster, CourseRoster
+from lms.services.exceptions import ExternalRequestError
 from lms.services.roster import RosterService, factory
 from tests import factories
 
@@ -126,6 +127,56 @@ def test_fetch_assignment_roster(
         assert roster[3].lms_user.lti_user_id == "USER_ID_INACTIVE"
         assert not roster[3].active
 
+    def test_fetch_assignment_roster_retries_with_lti_v11_id(
+        self,
+        svc,
+        lti_names_roles_service,
+        lti_v13_application_instance,
+        assignment,
+        names_and_roles_roster_response,
+        lti_role_service,
+    ):
+        lti_role_service.get_roles.return_value = [
+            factories.LTIRole(value="ROLE1"),
+            factories.LTIRole(value="ROLE2"),
+        ]
+
+        lti_names_roles_service.get_context_memberships.side_effect = [
+            ExternalRequestError(
+                response=Mock(
+                    text="Requested ResourceLink bound to unexpected external tool"
+                )
+            ),
+            names_and_roles_roster_response,
+        ]
+
+        svc.fetch_assignment_roster(assignment)
+
+        lti_names_roles_service.get_context_memberships.assert_has_calls(
+            [
+                call(
+                    lti_v13_application_instance.lti_registration,
+                    "SERVICE_URL",
+                    assignment.lti_v13_resource_link_id,
+                ),
+                call(
+                    lti_v13_application_instance.lti_registration,
+                    "SERVICE_URL",
+                    assignment.resource_link_id,
+                ),
+            ]
+        )
+
+    def test_fetch_assignment_roster_raises_external_request_error(
+        self, svc, lti_names_roles_service, assignment
+    ):
+        lti_names_roles_service.get_context_memberships.side_effect = (
+            ExternalRequestError()
+        )
+
+        with pytest.raises(ExternalRequestError):
+            svc.fetch_assignment_roster(assignment)
+
     @pytest.fixture
     def lms_course(self, lti_v13_application_instance):
         lms_course = factories.LMSCourse(lti_context_memberships_url="SERVICE_URL")