Handle unicode when dealing with duplicate aggregate errors during migration

The AggregateNameExists message can be translated and have unicode in it
so we can't cast it to a str in python 2.7 else we'll get a
UnicodeEncodeError. That would break the online data migration for
aggregates along with any other online data migrations that run after
that one which impacts upgrades.

This uses six.text_type rather than str for logging the error and adds
a test to recreate the bug and show that it's fixed.

Change-Id: I040db22ecbb9fabe5bbda8a3d9600cc9f76cb170
Closes-Bug: #1653261

nova/objects/aggregate.py

@@ -16,6 +16,7 @@ from oslo_db import exception as db_exc
 from oslo_log import log as logging
 from oslo_utils import excutils
 from oslo_utils import uuidutils
+import six
 from sqlalchemy.orm import contains_eager
 from sqlalchemy.orm import joinedload
 from sqlalchemy.sql import func
@@ -593,7 +594,7 @@ def migrate_aggregates(ctxt, count):
                 _LW('Aggregate id %(id)i disappeared during migration'),
                 {'id': aggregate_id})
         except (exception.AggregateNameExists) as e:
-            LOG.error(str(e))
+            LOG.error(six.text_type(e))
 
     return count_all, count_hit
 

nova/tests/functional/db/test_aggregate.py

@@ -635,3 +635,26 @@ class AggregateMigrationTestCase(test.TestCase):
             self.context, 0)
         self.assertEqual(0, match)
         self.assertEqual(0, done)
+
+    @mock.patch('nova.objects.aggregate.LOG.error')
+    def test_migrate_aggregates_duplicate_unicode(self, mock_log_error):
+        """Tests that we handle a duplicate aggregate when migrating and that
+        we handle when the exception message is in unicode.
+        """
+        # First create an aggregate that will be migrated from main to API DB.
+        create_aggregate(self.context, 1, in_api=False)
+        # Now create that same aggregate in the API DB.
+        create_aggregate(self.context, 1, in_api=True)
+        # Now let's run the online data migration which will fail to create
+        # a duplicate aggregate in the API database and will raise
+        # AggregateNameExists which we want to modify to have a unicode
+        # message.
+        with mock.patch.object(exception.AggregateNameExists, 'msg_fmt',
+                               u'\xF0\x9F\x92\xA9'):
+            match, done = aggregate_obj.migrate_aggregates(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 aggregate
+            mock_log_error.assert_called()