@staticmethod
def is_within_content_length_limit(payload, api_config):
    """
        Check that the message content is within the configured length limit.
        """
    length_limit = api_config.get('content_length_limit')
    if length_limit is not None and payload['content'] is not None:
        content_length = len(payload['content'])
        if content_length > length_limit:
            return 'Payload content too long: %s > %s' % (content_length,
                length_limit)
    return None
