When serializing an exception return its 'repr'

When serializing an exception return its 'repr'. A 'repr' is a
printable representation of an object.

For example the exception: ValueError("an exception") will be returned
as the string: "ValueError('an exception',)"

Change-Id: Iac9f4624bcc4ff65e27c9ca20c6cbbe9481cf334

oslo_serialization/jsonutils.py

@@ -132,6 +132,10 @@ def to_primitive(value, convert_instances=False, convert_datetime=True,
                                  ipaddress.IPv6Address)):
         return six.text_type(value)
 
+    # For exceptions, return the 'repr' of the exception object
+    if isinstance(value, Exception):
+        return repr(value)
+
     # value of itertools.count doesn't get caught by nasty_type_tests
     # and results in infinite loop when list(value) is called.
     if type(value) == itertools.count:

oslo_serialization/tests/test_jsonutils.py

@@ -115,6 +115,10 @@ class JSONUtilsTestMixin(object):
                 self.assertIsInstance(key, six.text_type)
                 self.assertIsInstance(val, six.text_type)
 
+    def test_dumps_exception_value(self):
+        self.assertEqual('{"a": "ValueError(\'hello\',)"}',
+                         jsonutils.dumps({"a": ValueError("hello")}))
+
 
 class JSONUtilsTestJson(JSONUtilsTestMixin, test_base.BaseTestCase):
     json_impl = json
@@ -401,3 +405,7 @@ class ToPrimitiveTestCase(test_base.BaseTestCase):
 
         ret = jsonutils.to_primitive(obj, fallback=lambda _: 'fallback')
         self.assertEqual('fallback', ret)
+
+    def test_exception(self):
+        self.assertEqual("ValueError('an exception',)",
+                         jsonutils.to_primitive(ValueError("an exception")))