code: func NewSimpleSender(addr string) (Sender, error) {
  	c, err := net.ListenPacket("udp", ":0")
  	if err != nil {
  		return nil, err
  	}
  
  	ra, err := net.ResolveUDPAddr("udp", addr)
  	if err != nil {
  		c.Close()
  		return nil, err
  	}
  
  	sender := &SimpleSender{
  		c:  c,
  		ra: ra,
  	}
  
  	return sender, nil
  }
docs: // NewSimpleSender returns a new SimpleSender for sending to the supplied
  // addresss.
  //
  // addr is a string of the format "hostname:port", and must be parsable by
  // net.ResolveUDPAddr.