Helper to format a LogRecord in in Stackdriver fluentd format.

        :rtype: str
        :returns: JSON str to be written to the log file.

def format_stackdriver_json(record, message):
    """Helper to format a LogRecord in in Stackdriver fluentd format.

        :rtype: str
        :returns: JSON str to be written to the log file.
    """
    subsecond, second = math.modf(record.created)

    payload = {
        "message": message,
        "timestamp": {"seconds": int(second), "nanos": int(subsecond * 1e9)},
        "thread": record.thread,
        "severity": record.levelname,
    }

    return json.dumps(payload)