code: func encodeRemoteAddr(remoteAddr net.Addr) []byte {
  	if udpAddr, ok := remoteAddr.(*net.UDPAddr); ok {
  		return append([]byte{cookiePrefixIP}, udpAddr.IP...)
  	}
  	return append([]byte{cookiePrefixString}, []byte(remoteAddr.String())...)
  }
docs: // encodeRemoteAddr encodes a remote address such that it can be saved in the Cookie