Truncate encoded instance message to 255

In nova/compute/utils.py function exception_to_dict truncates unicode
message to 255. However, in non-English locales, instance message may
be longer than 255 after encoding the unicode message to byte message.
Need to truncate the encoded byte message to 255, in order to ensure
db insert operation succeed.

Change-Id: I70cd2d6e4590ea95510c1ea3d51287f0dea14956
Closes-Bug: 1389102

nova/compute/utils.py

@@ -19,6 +19,7 @@ import string
 import traceback
 
 from oslo.config import cfg
+from oslo.utils import encodeutils
 
 from nova import block_device
 from nova.compute import flavors
@@ -64,7 +65,7 @@ def exception_to_dict(fault):
     # NOTE(dripton) The message field in the database is limited to 255 chars.
     # MySQL silently truncates overly long messages, but PostgreSQL throws an
     # error if we don't truncate it.
-    u_message = unicode(message)[:255]
+    u_message = encodeutils.safe_decode(encodeutils.safe_encode(message)[:255])
 
     fault_dict = dict(exception=fault)
     fault_dict["message"] = u_message

nova/tests/unit/compute/test_compute_utils.py

@@ -22,6 +22,7 @@ import string
 import mock
 from oslo.config import cfg
 from oslo.serialization import jsonutils
+from oslo.utils import encodeutils
 from oslo.utils import importutils
 import six
 import testtools
@@ -825,3 +826,13 @@ class ComputeUtilsGetRebootTypes(test.TestCase):
     def test_get_reboot_not_running_hard(self):
         reboot_type = compute_utils.get_reboot_type('foo', 'bar')
         self.assertEqual(reboot_type, 'HARD')
+
+
+class ComputeUtilsTestCase(test.NoDBTestCase):
+    def test_exception_to_dict_with_long_message(self):
+        # Generate Russian byte message whose length is 300
+        msg = encodeutils.safe_decode(' \xd0\xb2' * 100)
+        exc = exception.NovaException(message=msg)
+        fault_dict = compute_utils.exception_to_dict(exc)
+        byte_message = encodeutils.safe_encode(fault_dict["message"])
+        self.assertEqual(255, len(byte_message))