code: func (c *Client) SetLocalAddr(ip string, port int) error {
  	laddr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", ip, port))
  	if err != nil {
  		return err
  	}
  	c.laddr = laddr
  	return nil
  }
docs: // SetLocalAddr sets the local address.