Additional logic to handle more course_image URL edge cases

This changes logic to allow more missed use cases of course_image to
work properly.  The cases are:

. XML courses with the course_image attribute set
. Mongo courses that are imported without a contentstore
. Mongo courses that have course_image set but don't have a content store

It also exports default images_static_course.jpg to
images/static_course.jpg to handle a use case where a course author
uploaded an image to the default location in studio without using the
studio interface for adding course images, they then export the course, and then
import it without a contentstore

common/lib/xmodule/xmodule/modulestore/tests/test_mongo.py

@@ -1,11 +1,14 @@
 from pprint import pprint
 # pylint: disable=E0611
 from nose.tools import assert_equals, assert_raises, \
-    assert_not_equals, assert_false
+    assert_not_equals, assert_false, assert_true
 from itertools import ifilter
 # pylint: enable=E0611
+from path import path
 import pymongo
 import logging
+import shutil
+from tempfile import mkdtemp
 from uuid import uuid4
 
 from xblock.fields import Scope
@@ -16,6 +19,7 @@ from xmodule.tests import DATA_DIR
 from xmodule.modulestore import Location, MONGO_MODULESTORE_TYPE
 from xmodule.modulestore.mongo import MongoModuleStore, MongoKeyValueStore
 from xmodule.modulestore.draft import DraftModuleStore
+from xmodule.modulestore.xml_exporter import export_to_xml
 from xmodule.modulestore.xml_importer import import_from_xml, perform_xlint
 from xmodule.contentstore.mongo import MongoContentStore
 
@@ -310,6 +314,50 @@ class TestMongoModuleStore(object):
         assert_equals(len(course_locations), 1)
         assert_in(Location('i4x', 'edX', 'simple', 'course', '2012_Fall'), course_locations)
 
+    def test_export_course_image(self):
+        """
+        Test to make sure that we have a course image in the contentstore,
+        then export it to ensure it gets copied to both file locations.
+        """
+        location = Location('c4x', 'edX', 'simple', 'asset', 'images_course_image.jpg')
+        course_location = Location('i4x', 'edX', 'simple', 'course', '2012_Fall')
+
+        # This will raise if the course image is missing
+        self.content_store.find(location)
+
+        root_dir = path(mkdtemp())
+        export_to_xml(self.store, self.content_store, course_location, root_dir, 'test_export')
+        assert_true(path(root_dir / 'test_export/static/images/course_image.jpg').isfile())
+        assert_true(path(root_dir / 'test_export/static/images_course_image.jpg').isfile())
+        shutil.rmtree(root_dir)
+
+    def test_export_course_image_nondefault(self):
+        """
+        Make sure that if a non-default image path is specified that we
+        don't export it to the static default location
+        """
+        course = self.get_course_by_id('edX/toy/2012_Fall')
+        assert_true(course.course_image, 'just_a_test.jpg')
+
+        root_dir = path(mkdtemp())
+        export_to_xml(self.store, self.content_store, course.location, root_dir, 'test_export')
+        assert_true(path(root_dir / 'test_export/static/just_a_test.jpg').isfile())
+        assert_false(path(root_dir / 'test_export/static/images/course_image.jpg').isfile())
+        shutil.rmtree(root_dir)
+
+    def test_course_without_image(self):
+        """
+        Make sure we elegantly passover our code when there isn't a static
+        image
+        """
+        course = self.get_course_by_id('edX/simple_with_draft/2012_Fall')
+        root_dir = path(mkdtemp())
+        export_to_xml(self.store, self.content_store, course.location, root_dir, 'test_export')
+        assert_false(path(root_dir / 'test_export/static/images/course_image.jpg').isfile())
+        assert_false(path(root_dir / 'test_export/static/images_course_image.jpg').isfile())
+        shutil.rmtree(root_dir)
+
+
 
 class TestMongoKeyValueStore(object):
     """

common/lib/xmodule/xmodule/modulestore/xml_exporter.py

@@ -5,6 +5,8 @@ Methods for exporting course data to XML
 import logging
 import lxml.etree
 from xblock.fields import Scope
+from xmodule.contentstore.content import StaticContent
+from xmodule.exceptions import NotFoundError
 from xmodule.modulestore import Location
 from xmodule.modulestore.inheritance import own_metadata
 from fs.osfs import OSFS
@@ -79,6 +81,26 @@ def export_to_xml(modulestore, contentstore, course_location, root_dir, course_d
             root_dir + '/' + course_dir + '/policies/assets.json',
         )
 
+        # If we are using the default course image, export it to the
+        # legacy location to support backwards compatibility.
+        if course.course_image == course.fields['course_image'].default:
+            try:
+                course_image = contentstore.find(
+                    StaticContent.compute_location(
+                        course.location.org,
+                        course.location.course,
+                        course.course_image
+                    ),
+                )
+            except NotFoundError:
+                pass
+            else:
+                output_dir = root_dir + '/' + course_dir + '/static/images/'
+                if not os.path.isdir(output_dir):
+                    os.makedirs(output_dir)
+                with OSFS(output_dir).open('course_image.jpg', 'wb') as course_image_file:
+                    course_image_file.write(course_image.data)
+
     # export the static tabs
     export_extra_content(export_fs, modulestore, course_id, course_location, 'static_tab', 'tabs', '.html')
 

common/test/data/toy/course/2012_Fall.xml

@@ -1,4 +1,4 @@
-<course>
+<course course_image="just_a_test.jpg">
     <textbook title="Textbook" book_url="https://s3.amazonaws.com/edx-textbooks/guttag_computation_v3/"/>
   <chapter url_name="Overview">
     <videosequence url_name="Toy_Videos">