Handle unicode when dealing with duplicate flavors during online migrations

In python 2.7 you can't cast unicode to str and you'll get a
UnicodeEncodeError if you try. Since our exception messages are
translated, they can contain unicode and if we hit a duplicate flavor
exception while performing online flavor migrations it will break the
migration and block any further migrations until resolved - which would
require manual intervention.

This patch fixes the bug so that we use six.text_type instead of str
for logging the duplicate exception and adds a test to exhibit the bug
and prove it's fixed.

On a side note, it's curious that we don't delete the duplicate flavor
from the main database during the online data migration, but it's also
strange that you'd have duplicates in the API database because the
Flavor.create() checks to see if all flavors have been migrated from
the main DB to the API DB and if not you can't create new flavors in
the API DB - so the only way to get the duplicates is either by inserting
them into the API DB manually or perhaps some other kind of race issue.
Anyway, that's not dealt with here.

Change-Id: I3bdb1a8ca72c3e72ddc3bc5102cff8df18148617
Partial-Bug: #1653261

nova/objects/flavor.py

@@ -15,6 +15,7 @@
 from oslo_db import exception as db_exc
 from oslo_db.sqlalchemy import utils as sqlalchemyutils
 from oslo_log import log as logging
+import six
 from sqlalchemy import or_
 from sqlalchemy.orm import joinedload
 from sqlalchemy.sql.expression import asc
@@ -723,7 +724,7 @@ def migrate_flavors(ctxt, count, hard_delete=False):
             LOG.warning(_LW('Flavor id %(id)i disappeared during migration'),
                         {'id': flavor_id})
         except (exception.FlavorExists, exception.FlavorIdExists) as e:
-            LOG.error(str(e))
+            LOG.error(six.text_type(e))
 
     return count_all, count_hit
 

nova/tests/functional/db/test_flavor.py

@@ -10,6 +10,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import mock
+
 from nova import context
 from nova import db
 from nova.db.sqlalchemy import api as db_api
@@ -291,3 +293,29 @@ class FlavorMigrationTestCase(test.NoDBTestCase):
             self.context, 0)
         self.assertEqual(0, match)
         self.assertEqual(0, done)
+
+    @mock.patch('nova.objects.flavor.LOG.error')
+    def test_migrate_flavors_duplicate_unicode(self, mock_log_error):
+        """Tests that we handle a duplicate flavor when migrating and that
+        we handle when the exception message is in unicode.
+        """
+        # First create a flavor that will be migrated from main to API DB.
+        main_flavor = _create_main_flavor(self.context)
+        # Now create that same flavor in the API DB.
+        del main_flavor['id']
+        api_flavor = ForcedFlavor(self.context, **main_flavor)
+        api_flavor.create()
+        # Now let's run the online data migration which will fail to create
+        # a duplicate flavor in the API database and will raise FlavorIdExists
+        # or FlavorExists which we want to modify to have a unicode message.
+        with mock.patch.object(exception.FlavorIdExists, 'msg_fmt',
+                               u'\xF0\x9F\x92\xA9'):
+            with mock.patch.object(exception.FlavorExists, 'msg_fmt',
+                                   u'\xF0\x9F\x92\xA9'):
+                match, done = flavor_obj.migrate_flavors(self.context, 50)
+                # we found one
+                self.assertEqual(1, match)
+                # but we didn't migrate it
+                self.assertEqual(0, done)
+                # and we logged an error for the duplicate flavor
+                mock_log_error.assert_called()