Make Exception.format_message aware of Messages

Many API extensions are casting NovaExceptions
directly to unicode with format_message(),
which results in a loss of localization information
from the possibly wrapped Message objects.

This change lets Messages be returned from
NovaException.format_message() if possible, which
will then be translated and resolved to unicode
later when needed.

fixes bug 1229410

Change-Id: I818a35b1d7d910c4f058d870e69c5ff73e45c6bb

nova/exception.py

@@ -136,10 +136,9 @@ class NovaException(Exception):
         super(NovaException, self).__init__(message)
 
     def format_message(self):
-        if self.__class__.__name__.endswith('_Remote'):
-            return self.args[0]
-        else:
-            return unicode(self)
+        # NOTE(mrodden): use the first argument to the python Exception object
+        # which should be our full NovaException message, (see __init__)
+        return self.args[0]
 
 
 class EncryptionFailure(NovaException):

nova/tests/test_exception.py

@@ -20,6 +20,7 @@ import inspect
 
 from nova import context
 from nova import exception
+from nova.openstack.common import gettextutils
 from nova import test
 
 
@@ -141,6 +142,15 @@ class NovaExceptionTestCase(test.NoDBTestCase):
         exc = FakeNovaException_Remote(lame_arg='lame')
         self.assertEquals(exc.format_message(), "some message %(somearg)s")
 
+    def test_format_message_gettext_msg_returned(self):
+        class FakeNovaException(exception.NovaException):
+            msg_fmt = gettextutils.Message("Some message %(param)s", 'nova')
+
+        exc = FakeNovaException(param='blah')
+        msg = exc.format_message()
+        self.assertIsInstance(msg, gettextutils.Message)
+        self.assertEqual(msg, "Some message blah")
+
 
 class ExceptionTestCase(test.NoDBTestCase):
     @staticmethod