Fix divison-by-zero when adding requirement to dynamic challenge (#782)

* Fixing a bug where prerequisites could not be set for dynamic challenges due to a division by zero error where defaults were being set unnecessarily. 
* Creating unit test for adding requirement to dynamic challenges

CTFd/plugins/dynamic_challenges/__init__.py

@@ -87,10 +87,11 @@ class DynamicValueChallenge(BaseChallenge):
         :return:
         """
         data = request.form or request.get_json()
-        data['initial'] = float(data.get('initial', 0))
-        data['minimum'] = float(data.get('minimum', 0))
-        data['decay'] = float(data.get('decay', 0))
+
         for attr, value in data.items():
+            # We need to set these to floats so that the next operations don't operate on strings
+            if attr in ('initial', 'minimum', 'decay'):
+                value = float(value)
             setattr(challenge, attr, value)
 
         Model = get_model()
@@ -228,9 +229,9 @@ class DynamicValueChallenge(BaseChallenge):
 class DynamicChallenge(Challenges):
     __mapper_args__ = {'polymorphic_identity': 'dynamic'}
     id = db.Column(None, db.ForeignKey('challenges.id'), primary_key=True)
-    initial = db.Column(db.Integer)
-    minimum = db.Column(db.Integer)
-    decay = db.Column(db.Integer)
+    initial = db.Column(db.Integer, default=0)
+    minimum = db.Column(db.Integer, default=0)
+    decay = db.Column(db.Integer, default=0)
 
     def __init__(self, *args, **kwargs):
         super(DynamicChallenge, self).__init__(**kwargs)

tests/challenges/test_dynamic.py

@@ -85,6 +85,63 @@ def test_can_update_dynamic_challenge():
     destroy_ctfd(app)
 
 
+def test_can_add_requirement_dynamic_challenge():
+    """Test that requirements can be added to dynamic challenges"""
+    app = create_ctfd(enable_plugins=True)
+    with app.app_context():
+        challenge_data = {
+            "name": "name",
+            "category": "category",
+            "description": "description",
+            "value": 100,
+            "decay": 20,
+            "minimum": 1,
+            "state": "hidden",
+            "type": "dynamic"
+        }
+        req = FakeRequest(form=challenge_data)
+        challenge = DynamicValueChallenge.create(req)
+
+        assert challenge.value == 100
+        assert challenge.initial == 100
+        assert challenge.decay == 20
+        assert challenge.minimum == 1
+
+        challenge_data = {
+            "name": "second_name",
+            "category": "category",
+            "description": "new_description",
+            "value": "200",
+            "initial": "200",
+            "decay": "40",
+            "minimum": "5",
+            "max_attempts": "0",
+            "state": "visible"
+        }
+
+        req = FakeRequest(form=challenge_data)
+        challenge = DynamicValueChallenge.create(req)
+
+        assert challenge.name == 'second_name'
+        assert challenge.description == "new_description"
+        assert challenge.value == 200
+        assert challenge.initial == 200
+        assert challenge.decay == 40
+        assert challenge.minimum == 5
+        assert challenge.state == "visible"
+
+        challenge_data = {
+            "requirements": [1]
+        }
+
+        req = FakeRequest(form=challenge_data)
+        challenge = DynamicValueChallenge.update(challenge, req)
+
+        assert challenge.requirements == [1]
+
+    destroy_ctfd(app)
+
+
 def test_can_delete_dynamic_challenge():
     app = create_ctfd(enable_plugins=True)
     with app.app_context():