fix: quiz is broken if user is not logged in (hedyorg#1192)

If the user is not logged in, the username is `''`.

First of all, DynamoDB rejects this value with an error.

Second of all, if we would record all anonymous users under the same
key, the data partition would become too big.

Instead, we'll record the responses under a username like
`'anonymous:e91f5ac2a6c946e893683c5c02781117'`.

app.py

@@ -603,9 +603,12 @@ def submit_answer(level_source, question_nr, attempt):
 
     is_correct = quiz.is_correct_answer(question, chosen_letter)
 
-    # Store the answer in the database
+    # Store the answer in the database. If we don't have a username,
+    # use the session ID as a username.
+    username = current_user()['username'] or f'anonymous:{session_id()}'
+
     DATABASE.record_quiz_answer(session['quiz-attempt-id'],
-            username=current_user()['username'],
+            username=username,
             level=level_source,
             is_correct=is_correct,
             question_number=question_nr,

utils.py

@@ -39,11 +39,20 @@ def wrapper(*args, **kwargs):
   return wrapper
 
 
-
 def timems():
+    """Return the UNIX timestamp in milliseconds.
+
+    You only need to use this function if you are doing performance-sensitive
+    timing. Otherwise, `times` (which returns second-resolution) is probably
+    a better choice.
+    """
     return int(round(time.time() * 1000))
 
 def times():
+    """Return the UNIX timestamp in seconds.
+
+    If you need to store a date/time in the database, prefer this function.
+    """
     return int(round(time.time()))
 
 

website/database.py

@@ -1,4 +1,4 @@
-from utils import timems
+from utils import timems, times
 from . import dynamo
 
 storage = dynamo.AwsDynamoStorage.from_env() or dynamo.MemoryStorage('dev_database.json')
@@ -43,7 +43,7 @@ def record_quiz_answer(self, attempt_id, username, level, question_number, answe
         updates = {
             "attemptId": attempt_id,
             "level": level,
-            "date": timems(),
+            "date": times(),
             "q" + str(question_number): dynamo.DynamoAddToList(answer),
         }
 

website/dynamo.py

@@ -86,6 +86,8 @@ def create(self, data):
         """Put a single complete record into the database."""
         if self.partition_key not in data:
             raise ValueError(f"Expecting '{self.partition_key}' field in create() call, got: {data}")
+        if self.sort_key and self.sort_key not in data:
+            raise ValueError(f"Expecting '{self.sort_key}' field in create() call, got: {data}")
 
         querylog.log_counter(f'db_create:{self.table_name}')
         self.storage.put(self.table_name, self._extract_key(data), data)
@@ -99,8 +101,7 @@ def update(self, key, updates):
         updates that aren't representable as plain values.
         """
         querylog.log_counter(f'db_update:{self.table_name}')
-        if key.keys() != self._key_names():
-            raise RuntimeError(f'update: key fields incorrect: {key} != {self._key_names()}')
+        self._validate_key(key)
 
         return self.storage.update(self.table_name, key, updates)
 
@@ -111,8 +112,7 @@ def delete(self, key):
         Returns the delete item.
         """
         querylog.log_counter('db_del:' + self.table_name)
-        if key.keys() != self._key_names():
-            raise RuntimeError(f'update: key fields incorrect: {key} != {self._key_names()}')
+        self._validate_key(key)
 
         return self.storage.delete(self.table_name, key)
 
@@ -138,7 +138,7 @@ def del_many (self, key):
     def scan(self):
         """Reads the entire table into memory."""
         querylog.log_counter('db_scan:' + self.table_name)
-        return self.storage.scan (self.table_name)
+        return self.storage.scan(self.table_name)
 
 
     @querylog.timed_as('db_describe')
@@ -147,6 +147,9 @@ def item_count(self):
         return self.storage.item_count(self.table_name)
 
     def _determine_lookup(self, key_data, many):
+        if any(not v for v in key_data.values()):
+            raise ValueError(f'Key data cannot have empty values: {key_data}')
+
         keys = set(key_data.keys())
         expected_keys = self._key_names()
 
@@ -186,6 +189,12 @@ def _extract_key(self, data):
     def _key_names(self):
         return set(x for x in [self.partition_key, self.sort_key] if x is not None)
 
+    def _validate_key(self, key):
+        if key.keys() != self._key_names():
+            raise RuntimeError(f'key fields incorrect: {key} != {self._key_names()}')
+        if any(not v for v in key.values()):
+            raise RuntimeError(f'key fields cannot be empty: {key}')
+
 DDB_SERIALIZER = TypeSerializer()
 DDB_DESERIALIZER = TypeDeserializer()