Fix datetime conversion issue on python < 3.6

tests/stores/test_azure_log_analytics.py

@@ -1,3 +1,4 @@
+from datetime import datetime
 from dateutil import parser
 from django.test import SimpleTestCase
 from zentral.core.stores.backends.azure_log_analytics import datetime_to_iso8601z_truncated_to_milliseconds
@@ -25,3 +26,9 @@ def test_microseconds_to_milliseconds(self):
             ("2019-01-12T11:11:11.000999+00:00", "2019-01-12T11:11:11.001Z"),
             ("2019-01-12T11:11:11.000234+00:00", "2019-01-12T11:11:11Z"),
         ))
+
+    def test_naive_datetime(self):
+        self.assertEqual(
+            datetime_to_iso8601z_truncated_to_milliseconds(datetime(2019, 1, 1, 0, 0, 0).replace(tzinfo=None)),
+            "2019-01-01T00:00:00Z"
+        )

zentral/core/stores/backends/azure_log_analytics.py

@@ -25,8 +25,12 @@ def datetime_to_iso8601z_truncated_to_milliseconds(dt):
         else:
             dt = dt.replace(microsecond=1000 * dt_millisecond)
 
-    # convert created at to UTC, remove the TZ info (naive datetime), convert to isoformat
-    dt_iso = dt.astimezone(pytz.utc).replace(tzinfo=None).isoformat()
+    # convert to UTC only if not naive (python<3.6)
+    if dt.utcoffset() is not None:
+        dt = dt.astimezone(pytz.utc)
+
+    # ensure naive, convert to isoformat
+    dt_iso = dt.replace(tzinfo=None).isoformat()
 
     # truncate the microseconds in isoformat if necessary
     if "." in dt_iso: