*
   * @param defaultPort a port number, from [0..65535]
   * @return a HostAndPort instance, guaranteed to have a defined port.
   */
  public HostAndPort withDefaultPort(int defaultPort) {
    checkArgument(isValidPort(defaultPort));
    if (hasPort()) {
      return this;
    }
    return new HostAndPort(host, defaultPort, hasBracketlessColons);
  }

  /**