Add questionnaire reset functionality

Fixes #494

Author: reppuli92

exercise/async_views.py

@@ -9,6 +9,7 @@
 from notification.models import Notification
 from lti_tool.utils import send_lti_points
 
+from .cache.exercise import ExerciseCache
 from .forms import SubmissionCallbackForm
 from .models import SubmissionTagging
 
@@ -94,6 +95,15 @@ def _post_async_submission(request, exercise, submission, errors=None): # pylint
         # the LTI Platform.
         if submission.meta_data == "":
             submission.meta_data = {}
+        exercise_version = form.cleaned_data["exercise_version"]
+        if exercise_version:
+            language = submission.lang or exercise.course_instance.default_language
+            cached_version = ExerciseCache.cached_exercise_version(exercise, language)
+            if cached_version and cached_version != exercise_version:
+                ExerciseCache.invalidate(exercise, modifiers=[language])
+            if not isinstance(submission.meta_data, dict):
+                submission.meta_data = {}
+            submission.meta_data["exercise_version"] = exercise_version
         if (form.cleaned_data["lti_launch_id"]
                 and submission.meta_data.get("lti-launch-id") is None):
             submission.meta_data["lti-launch-id"] = form.cleaned_data["lti_launch_id"]

exercise/cache/exercise.py

@@ -3,6 +3,7 @@
 from typing import Any, Dict, List, Optional, TYPE_CHECKING
 
 from django.conf import settings
+from django.core.cache import cache
 from django.http.request import HttpRequest
 
 from lib.cache import CachedAbstract
@@ -29,6 +30,7 @@ def compress(data):
 class ExerciseCache(CachedAbstract):
     """ Exercise HTML content """
     KEY_PREFIX = "exercisepage"
+    VERSION_MAX_AGE = 15 * 60
 
     def __init__( # pylint: disable=too-many-arguments
             self,
@@ -44,14 +46,24 @@ def __init__( # pylint: disable=too-many-arguments
         super().__init__(exercise, modifiers=[language])
 
     def _needs_generation(self, data: Dict[str, Any]) -> bool:
+        if data and 'exercise_version' not in data:
+            # Cache entries created before exercise version stamping was added must be refreshed
+            # so update detection can work.
+            return True
         expires = data['expires'] if data else None
         return not expires or time.time() > expires
     # pylint: disable-next=arguments-differ
     def _generate_data(self, exercise: 'BaseExercise', data: Optional[Dict[str, Any]] = None) -> Dict[str, Any]:
         try:
             page = exercise.load_page(
                 *self.load_args,
-                last_modified=data['last_modified'] if data else None
+                # A versionless cache entry must receive a full response. Reusing
+                # its timestamp could produce a 304 that can not add the version.
+                last_modified=(
+                    data['last_modified']
+                    if data and 'exercise_version' in data
+                    else None
+                )
             )
 
             content = compress(page.content.encode('utf-8'))
@@ -60,6 +72,7 @@ def _generate_data(self, exercise: 'BaseExercise', data: Optional[Dict[str, Any]
                 'head': page.head,
                 'content': content,
                 'last_modified': page.last_modified,
+                'exercise_version': page.exercise_version,
                 'expires': page.expires if page.is_loaded else 0,
             }
         except RemotePageNotModified as e:
@@ -74,6 +87,29 @@ def content(self) -> str:
         content = decompress(self.data['content']).decode('utf-8')
         return content
 
+    def exercise_version(self) -> str:
+        return self.data.get('exercise_version') or ''
+
+    @classmethod
+    def cached_exercise_version(
+            cls,
+            exercise: 'BaseExercise',
+            language: str,
+            max_age: Optional[int] = None,
+            ) -> str:
+        """Return a recently cached version without regenerating exercise HTML."""
+        raw = cache.get(cls._key(exercise, modifiers=[language]))
+        if not isinstance(raw, tuple) or len(raw) != 2:
+            return ''
+        updated, data = raw
+        if updated is None or not isinstance(data, dict):
+            return ''
+        if max_age is not None:
+            expires = data.get('expires') or 0
+            if time.time() - updated > max_age or (expires and time.time() > expires):
+                return ''
+        return data.get('exercise_version') or ''
+
 
 def invalidate_instance(instance: 'CourseInstance') -> None:
     for module in instance.course_modules.all():

exercise/exercise_models.py

@@ -405,6 +405,7 @@ def load(
         cache = ExerciseCache(self, language, request, students, url_name, ordinal)
         page.head = cache.head()
         page.content = cache.content()
+        page.exercise_version = cache.exercise_version()
         page.is_loaded = True
         return page
 

exercise/forms.py

@@ -21,6 +21,7 @@ class SubmissionCallbackForm(forms.Form):
     notify = forms.CharField(required=False)
     regrade_when_notification_seen = forms.BooleanField(required=False)
     grading_payload = forms.CharField(required=False)
+    exercise_version = forms.CharField(required=False)
     lti_launch_id = forms.CharField(required=False)
     lti_session_id = forms.CharField(required=False)
     error = forms.BooleanField(required=False)

exercise/protocol/aplus.py

@@ -7,6 +7,7 @@
 
 from lib.email_messages import email_course_error
 from lib.remote_page import RemotePage, RemotePageException
+from ..cache.exercise import ExerciseCache
 from .exercise_page import ExercisePage
 
 from lti_tool.utils import send_lti_points
@@ -64,6 +65,14 @@ def load_feedback_page(request, url, exercise, submission, no_penalties=False):
 
     if page.is_loaded:
         submission.feedback = page.clean_content
+        if page.exercise_version:
+            language = submission.lang or exercise.course_instance.default_language
+            cached_version = ExerciseCache.cached_exercise_version(exercise, language)
+            if cached_version and cached_version != page.exercise_version:
+                ExerciseCache.invalidate(exercise, modifiers=[language])
+            if not isinstance(submission.meta_data, dict):
+                submission.meta_data = {}
+            submission.meta_data['exercise_version'] = page.exercise_version
         if page.is_accepted:
             submission.set_waiting()
             if page.is_graded:
@@ -181,4 +190,5 @@ def parse_page_content(
     id_attrs_to_remove = ('exercise', 'chapter', 'aplus')
     page.content, page.clean_content = remote_page.element_or_body(element_selectors, id_attrs_to_remove)
     page.last_modified = remote_page.last_modified()
+    page.exercise_version = remote_page.meta("aplus-exercise-version") or ""
     page.expires = remote_page.expires()

exercise/protocol/exercise_page.py

@@ -23,6 +23,7 @@ def __init__(self, exercise):
         self.content = ""
         self.clean_content = ""
         self.last_modified = ""
+        self.exercise_version = ""  # Content hash supplied by MOOC-Grader
         self.expires = 0
         self.meta = {
             "title": exercise.name,

exercise/submission_models.py

@@ -252,6 +252,7 @@ def create_from_post(self, exercise, submitters, request):
             meta_data_dict = json.loads(request.POST.get('__aplus__', '{}'))
         except json.JSONDecodeError as exc:
             raise ValueError("The content of the field __aplus__ is not valid json") from exc
+        meta_data_dict.pop('exercise_version', None)
         if 'lang' not in meta_data_dict:
             meta_data_dict['lang'] = get_language()