Add student_view_data to HTML XBlock (openedx#853)

* added student_view_data to HtmlBlock to allow html to be downloadable via the course blocks API
* added tests for html xblock student_view_data

common/lib/xmodule/xmodule/html_module.py

@@ -75,6 +75,17 @@ def student_view(self, _context):
         """
         return Fragment(self.get_html())
 
+    def student_view_data(self):
+        """
+        Returns a JSON representation of the student_view of this XBlock,
+        retrievable from the Course Block API.
+        Since this data is not user-specific, fields like `html` may contain
+        placeholders like %%USER_ID%%.
+        """
+        return {
+            'html': self.data
+        }
+
     def get_html(self):
         """ Returns html required for rendering XModule. """
 

common/lib/xmodule/xmodule/tests/test_html_module.py

@@ -1,5 +1,5 @@
 import unittest
-
+import ddt
 from mock import Mock
 
 from xblock.field_data import DictFieldData
@@ -24,6 +24,30 @@ def instantiate_descriptor(**field_data):
     )
 
 
+@ddt.ddt
+class HtmlModuleCourseApiTestCase(unittest.TestCase):
+    """
+    Ensure that student_view_data can handle likely input,
+    and doesn't modify the HTML in any way.
+    This means that it does NOT protect against XSS, escape HTML tags, etc.
+    """
+    @ddt.data(
+        '<h1>Some content</h1>',  # Valid HTML
+        '',
+        None,
+        '<h1>Some content</h',  # Invalid HTML
+        '<script>alert()</script>',  # Does not escape tags
+        '<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7">',  # Images allowed
+        'short string ' * 100,  # May contain long strings
+    )
+    def test_common_values(self, html):
+        descriptor = Mock()
+        field_data = DictFieldData({'data': html})
+        module_system = get_test_system()
+        module = HtmlModule(descriptor, module_system, field_data, Mock())
+        self.assertEqual(module.student_view_data(), {'html': html})
+
+
 class HtmlModuleSubstitutionTestCase(unittest.TestCase):
     descriptor = Mock()
 

lms/djangoapps/course_api/blocks/tests/test_views.py

@@ -22,7 +22,7 @@ class TestBlocksView(SharedModuleStoreTestCase):
     Test class for BlocksView
     """
     requested_fields = ['graded', 'format', 'student_view_multi_device', 'children', 'not_a_field', 'due']
-    BLOCK_TYPES_WITH_STUDENT_VIEW_DATA = ['video', 'discussion']
+    BLOCK_TYPES_WITH_STUDENT_VIEW_DATA = ['video', 'discussion', 'html']
 
     @classmethod
     def setUpClass(cls):

lms/djangoapps/course_api/blocks/transformers/tests/test_student_view.py

@@ -44,7 +44,7 @@ def test_transform(self):
 
         # verify html data
         html_block_key = self.course_key.make_usage_key('html', 'toyhtml')
-        self.assertIsNone(
+        self.assertIsNotNone(
             self.block_structure.get_transformer_block_field(
                 html_block_key, StudentViewTransformer, StudentViewTransformer.STUDENT_VIEW_DATA,
             )