Decode exception parameters to expand exception message properly

If a multibyte string without unicode prefix 'u' is passed to
NeutronException in python 2, string subsitution will fail.
In python 2, multibyte string without 'u' prefix is encoded into bytes.
As a result a string substitution in NeutronException.__init__ will fail.

Change-Id: I1aa08b69fe119087a7a49fda768a24f85f0e7c76
Closes-Bug: #1235228

neutronclient/common/exceptions.py

@@ -13,6 +13,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from oslo_utils import encodeutils
 import six
 
 from neutronclient._i18n import _
@@ -31,6 +32,14 @@ Exceptions are classified into three categories:
 """
 
 
+# NOTE: This method is defined here to avoid
+# an import loop between common.utils and this module.
+def _safe_decode_dict(kwargs):
+    for k, v in kwargs.items():
+        kwargs[k] = encodeutils.safe_decode(v)
+    return kwargs
+
+
 @six.python_2_unicode_compatible
 class NeutronException(Exception):
     """Base Neutron Exception.
@@ -45,7 +54,7 @@ class NeutronException(Exception):
         if message:
             self.message = message
         try:
-            self._error_string = self.message % kwargs
+            self._error_string = self.message % _safe_decode_dict(kwargs)
         except Exception:
             # at least get the core message out if something happened
             self._error_string = self.message

neutronclient/tests/unit/test_exceptions.py

@@ -13,6 +13,8 @@
 #    under the License.
 
 import fixtures
+from oslo_utils import encodeutils
+import six
 import testtools
 
 from neutronclient.common import exceptions
@@ -34,3 +36,13 @@ class TestExceptions(testtools.TestCase):
             print(e)
         self.assertEqual('Exception with %s' % multibyte_unicode_string,
                          fixture.getDetails().get('stdout').as_text())
+
+    def test_exception_message_with_encoded_unicode(self):
+        class TestException(exceptions.NeutronException):
+            message = _('Exception with %(reason)s')
+
+        multibyte_string = u'\uff21\uff22\uff23'
+        multibyte_binary = encodeutils.safe_encode(multibyte_string)
+        e = TestException(reason=multibyte_binary)
+        self.assertEqual('Exception with %s' % multibyte_string,
+                         six.text_type(e))