Disallow NaN value for speed key.

The VideoBlock `handle_ajax` is allowing NaN values for speed key
and causing videos to not load. Also added a data migration to fix
the data for learners.

PROD-1148

common/lib/xmodule/xmodule/video_module/video_handlers.py

@@ -8,6 +8,7 @@ StudioViewHandlers are handlers for video descriptor instance.
 
 import json
 import logging
+import math
 
 import six
 from django.core.files.base import ContentFile
@@ -89,6 +90,11 @@ class VideoStudentViewHandlers(object):
                     if key == 'bumper_last_view_date':
                         value = now()
 
+                    if key == 'speed' and math.isnan(value):
+                        message = u"Invalid speed value {}, must be a float.".format(value)
+                        log.warning(message)
+                        return json.dumps({'success': False, 'error': message})
+
                     setattr(self, key, value)
 
                     if key == 'speed':

lms/djangoapps/courseware/migrations/0014_fix_nan_value_for_global_speed.py

@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.29 on 2020-03-11 10:07
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+def fix_nan_value_for_global_speed(apps, schema_editor):
+    XModuleStudentPrefsField = apps.get_model('courseware', 'XModuleStudentPrefsField')
+    XModuleStudentPrefsField.objects.filter(
+        field_name='global_speed', value='NaN'
+    ).update(
+        value=1.0
+    )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('courseware', '0013_auto_20191001_1858'),
+    ]
+
+    operations = [
+        migrations.RunPython(fix_nan_value_for_global_speed, reverse_code=migrations.RunPython.noop)
+    ]

lms/djangoapps/courseware/tests/test_video_handlers.py

@@ -165,6 +165,24 @@ class TestVideo(BaseTestVideoXBlock):
         status_codes = {response.status_code for response in responses.values()}
         self.assertEqual(status_codes.pop(), 404)
 
+    def test_handle_ajax_for_speed_with_nan(self):
+        self.item_descriptor.handle_ajax('save_user_state', {'speed': json.dumps(1.0)})
+        self.assertEqual(self.item_descriptor.speed, 1.0)
+        self.assertEqual(self.item_descriptor.global_speed, 1.0)
+
+        # try to set NaN value for speed.
+        response = self.item_descriptor.handle_ajax(
+            'save_user_state', {'speed': json.dumps(float('NaN'))}
+        )
+
+        self.assertFalse(json.loads(response)['success'])
+        expected_error = u"Invalid speed value nan, must be a float."
+        self.assertEqual(json.loads(response)['error'], expected_error)
+
+        # verify that the speed and global speed are still 1.0
+        self.assertEqual(self.item_descriptor.speed, 1.0)
+        self.assertEqual(self.item_descriptor.global_speed, 1.0)
+
     def test_handle_ajax(self):
 
         data = [