Fix json to_primitive when using IO OBjects

Currently, using Cinder's backup service with RBD the
backup-create operation gets stuck when logging
('use_json=True' must be set in the config file).

The oslo.log JSONFormatter gets stuck when passing an
RBDVolumeIOWrapper from os-brick. This happens via os-brick's
utils.trace() method which passes a connector containing
{'path': RBDVolumeIOWrapper}.
The oslo.log JSONFormatter format() method calls
oslo_serialization's jsonutils.to_primitive and passes in
this RBDVolumeIOWrapper object.
 
Therefore the to_primitive method eventually calls
RBDVolumeIOWrapper.read(). In order to fix this the current
path avoids mapping io.IOBase objects and fallback the wrapper
RBD volume object.

Co-authored-by: Eric Harney <eharney@redhat.com>
Closes-Bug: #1908607
Change-Id: I3c416e855cb5f0dc32d14b2749ba92aba8964574
(cherry picked from commit 02037330d8)

oslo_serialization/jsonutils.py

@@ -33,6 +33,7 @@ import codecs
 import datetime
 import functools
 import inspect
+import io
 import itertools
 import json
 import uuid
@@ -161,7 +162,7 @@ def to_primitive(value, convert_instances=False, convert_datetime=True,
         # Python 3 does not have iteritems
         elif hasattr(value, 'items'):
             return recursive(dict(value.items()), level=level + 1)
-        elif hasattr(value, '__iter__'):
+        elif hasattr(value, '__iter__') and not isinstance(value, io.IOBase):
             return list(map(recursive, value))
         elif convert_instances and hasattr(value, '__dict__'):
             # Likely an instance of something. Watch for cycles.

oslo_serialization/tests/test_jsonutils.py

@@ -401,6 +401,16 @@ class ToPrimitiveTestCase(test_base.BaseTestCase):
         ret = jsonutils.to_primitive(obj, fallback=lambda _: 'fallback')
         self.assertEqual('fallback', ret)
 
+    def test_fallback_typeerror_IO_object(self):
+        # IO Objects are not callable, cause a TypeError in to_primitive()
+        obj = io.IOBase
+
+        ret = jsonutils.to_primitive(obj)
+        self.assertEqual(str(obj), ret)
+
+        ret = jsonutils.to_primitive(obj, fallback=lambda _: 'fallback')
+        self.assertEqual('fallback', ret)
+
     def test_exception(self):
         self.assertIn(jsonutils.to_primitive(ValueError("an exception")),
                       ["ValueError('an exception',)",

releasenotes/notes/bug-1908607-fix-json-to_primitive-IO-OBjects-04faff4a1b5cf48f.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    `Bug #1908607 <https://bugs.launchpad.net/cinder/+bug/1908607>`_: Fix
+    json to_primitive when using IO OBjects.