Given the WSGI environ and the response,
    log this event in Common Log Format.

def common_log(environ, response, response_time=None):
    """
    Given the WSGI environ and the response,
    log this event in Common Log Format.

    """

    logger = logging.getLogger()

    if response_time:
        formatter = ApacheFormatter(with_response_time=True)
        try:
            log_entry = formatter(response.status_code, environ,
                                  len(response.content), rt_us=response_time)
        except TypeError:
            # Upstream introduced a very annoying breaking change on the rt_ms/rt_us kwarg.
            log_entry = formatter(response.status_code, environ,
                                  len(response.content), rt_ms=response_time)
    else:
        formatter = ApacheFormatter(with_response_time=False)
        log_entry = formatter(response.status_code, environ,
                              len(response.content))

    logger.info(log_entry)

    return log_entry