JSONFormatter convert unserializable with repr()3.30.2

The JSONFormatter formatter now converts unserializable objects with
repr() to prevent JSON serialization errors on logging.

The fix requires oslo.serialization 2.20.2 or newer to get the new
fallback parameter of jsonutils.to_primitive().

Backport/cherry-pick note: 2.21.1 replaced with 2.20.2.

Closes-Bug: #1593641
Change-Id: Ibda7d145af95903b2bf8d87113804350330a93b4
(cherry picked from commit 22bd3d532125f1a7126b66d10f37de893d48df9a)

3 files changed, 48 insertions, 1 deletions

diff --git a/oslo_log/formatters.py b/oslo_log/formatters.py
index bc1ae0d..7af3688 100644
--- a/oslo_log/formatters.py
+++ b/oslo_log/formatters.py
@@ -12,6 +12,7 @@
 
 import datetime
 import debtcollector
+import functools
 import itertools
 import logging
 import logging.config
@@ -32,6 +33,15 @@ if six.PY3:
     from functools import reduce
 
 
+try:
+    # Test if to_primitive() has the fallback parameter added
+    # in oslo.serialization 2.20.2
+    jsonutils.to_primitive(1, fallback=repr)
+    _HAVE_JSONUTILS_FALLBACK = True
+except TypeError:
+    _HAVE_JSONUTILS_FALLBACK = False
+
+
 def _dictify_context(context):
     if getattr(context, 'get_logging_values', None):
         return context.get_logging_values()
@@ -222,7 +232,16 @@ class JSONFormatter(logging.Formatter):
         if record.exc_info:
             message['traceback'] = self.formatException(record.exc_info)
 
-        return jsonutils.dumps(message)
+        if _HAVE_JSONUTILS_FALLBACK:
+            # Bug #1593641: If an object cannot be serialized to JSON, convert
+            # it using repr() to prevent serialization errors. Using repr() is
+            # not ideal, but serialization errors are unexpected on logs,
+            # especially when the code using logs is not aware that the
+            # JSONFormatter will be used.
+            convert = functools.partial(jsonutils.to_primitive, fallback=repr)
+            return jsonutils.dumps(message, default=convert)
+        else:
+            return jsonutils.dumps(message)
 
 
 class FluentFormatter(logging.Formatter):
diff --git a/oslo_log/tests/unit/test_log.py b/oslo_log/tests/unit/test_log.py
index 1482de7..544f097 100644
--- a/oslo_log/tests/unit/test_log.py
+++ b/oslo_log/tests/unit/test_log.py
@@ -522,6 +522,28 @@ class JSONFormatterTestCase(LogTestBase):
         self.assertIn('error_summary', data)
         self.assertEqual('', data['error_summary'])
 
+    def test_fallback(self):
+        if not formatters._HAVE_JSONUTILS_FALLBACK:
+            self.skipTest("need the fallback parameter of "
+                          "jsonutils.to_primitive() added in "
+                          "oslo_serialization 2.20.2")
+
+        class MyObject(object):
+            def __str__(self):
+                return 'str'
+
+            def __repr__(self):
+                return 'repr'
+
+        obj = MyObject()
+        self.log.debug('obj=%s', obj)
+
+        data = jsonutils.loads(self.stream.getvalue())
+        self.assertEqual('obj=str', data['message'])
+        # Bug #1593641: If an object of record.args cannot be serialized,
+        # convert it using repr() to prevent serialization error on logging.
+        self.assertEqual(['repr'], data['args'])
+
 
 def get_fake_datetime(retval):
     class FakeDateTime(datetime.datetime):
diff --git a/releasenotes/notes/jsonformatter-repr-fd616eb6fa6caeb3.yaml b/releasenotes/notes/jsonformatter-repr-fd616eb6fa6caeb3.yaml
new file mode 100644
index 0000000..c809750
--- /dev/null
+++ b/releasenotes/notes/jsonformatter-repr-fd616eb6fa6caeb3.yaml
@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The JSONFormatter formatter now converts unserializable objects with
+    repr() to prevent JSON serialization errors on logging. The fix requires
+    oslo.serialization 2.20.2 or newer. (Bug #1593641)