code: func (c *cmd) listenParts() (string, int, error) {
  	host, portRaw, err := net.SplitHostPort(c.listen)
  	if err != nil {
  		return "", 0, err
  	}
  
  	port, err := strconv.ParseInt(portRaw, 0, 0)
  	if err != nil {
  		return "", 0, err
  	}
  
  	return host, int(port), nil
  }
docs: // listenParts returns the host and port parts of the -listen flag. The
  // -listen flag must be non-empty prior to calling this.