Handle images with no data

There isn't really much we can do with these images, which glance tells
us are possible [1]. Simply raise an exception.

[1] https://docs.openstack.org/python-glanceclient/latest/reference/api/glanceclient.v2.images.html

Change-Id: I5f81393a5bb41e6a674369afb899d8a41bb2c3b4
Closes-Bug: #1736759
(cherry picked from commit c10a614e92)

nova/image/glance.py

@@ -294,6 +294,12 @@ class GlanceImageServiceV2(object):
         except Exception:
             _reraise_translated_image_exception(image_id)
 
+        if image_chunks.wrapped is None:
+            # None is a valid return value, but there's nothing we can do with
+            # a image with no associated data
+            raise exception.ImageUnacceptable(image_id=image_id,
+                reason='Image has no associated data')
+
         # Retrieve properties for verification of Glance image signature
         verifier = None
         if CONF.glance.verify_glance_signatures:

nova/tests/unit/image/test_glance.py

@@ -637,6 +637,19 @@ class TestDownloadNoDirectUri(test.NoDBTestCase):
         self.assertRaises(FakeDiskException, service.download, ctx,
                           mock.sentinel.image_id, data=Exceptionator())
 
+    @mock.patch.object(six.moves.builtins, 'open')
+    @mock.patch('nova.image.glance.GlanceImageServiceV2.show')
+    def test_download_no_returned_image_data_v2(
+            self, show_mock, open_mock):
+        """Verify images with no data are handled correctly."""
+        client = mock.MagicMock()
+        client.call.return_value = fake_glance_response(None)
+        ctx = mock.sentinel.ctx
+        service = glance.GlanceImageServiceV2(client)
+
+        with testtools.ExpectedException(exception.ImageUnacceptable):
+            service.download(ctx, mock.sentinel.image_id)
+
     @mock.patch('nova.image.glance.GlanceImageServiceV2._get_transfer_module')
     @mock.patch('nova.image.glance.GlanceImageServiceV2.show')
     def test_download_direct_file_uri_v2(self, show_mock, get_tran_mock):