Add timezone to timestamp

Before this commit, when a JsonFormatter is created with the timestamp=
True parameter, it used utcnow(). Which is not time when the log record
was created, but when the field was added. Also, utcnow is not timezone
aware, so the serialized datetime is missing the timezone designator at
the end.  This commit uses the time at which the log record was created
and sets the timezone to UTC, which results in an additional "+000" end

Author: lalten

src/pythonjsonlogger/jsonlogger.py

@@ -5,7 +5,7 @@
 import logging
 import json
 import re
-from datetime import date, datetime, time
+from datetime import date, datetime, time, timezone
 import traceback
 import importlib
 
@@ -154,7 +154,7 @@ def add_fields(self, log_record, record, message_dict):
 
         if self.timestamp:
             key = self.timestamp if type(self.timestamp) == str else 'timestamp'
-            log_record[key] = datetime.utcnow()
+            log_record[key] = datetime.fromtimestamp(record.created, tz=timezone.utc)
 
     def process_log_record(self, log_record):
         """

tests/tests.py

@@ -1,18 +1,19 @@
 # -*- coding: utf-8 -*-
 import unittest
+import unittest.mock
 import logging
 import json
 import sys
 import traceback
 import random
 
 try:
-    import xmlrunner
+    import xmlrunner  # noqa
 except ImportError:
     pass
 
 try:
-    from StringIO import StringIO
+    from StringIO import StringIO  # noqa
 except ImportError:
     # Python 3 Support
     from io import StringIO
@@ -131,6 +132,17 @@ def testJsonDefaultEncoder(self):
         self.assertEqual(logJson.get("otherdatetimeagain"),
                          "1900-01-01T00:00:00")
 
+    @unittest.mock.patch('time.time', return_value=1500000000.0)
+    def testJsonDefaultEncoderWithTimestamp(self, time_mock):
+        fr = jsonlogger.JsonFormatter(timestamp=True)
+        self.logHandler.setFormatter(fr)
+
+        self.logger.info("Hello")
+
+        self.assertTrue(time_mock.called)
+        logJson = json.loads(self.buffer.getvalue())
+        self.assertEqual(logJson.get("timestamp"), "2017-07-14T02:40:00+00:00")
+
     def testJsonCustomDefault(self):
         def custom(o):
             return "very custom"