package main

import (
	"flag"
	"fmt"
	"log"
	"net"
)

func main() {
	var addr, dest string
	flag.StringVar(&addr, "addr", ":9999", "listen address")
	flag.StringVar(&dest, "dest", "", "destination")

	flag.Parse()

	if dest == "" {
		fmt.Println("Error: missing -dest")
		fmt.Println("run with -h to see options.")

		return
	}

	log.Printf("Listening to %s - Relaying to %s", addr, dest)
	raddr, err := net.ResolveUDPAddr("udp", dest)
	if err != nil {
		panic(err)
	}
	udpConn, err := net.DialUDP("udp", nil, raddr)
	if err != nil {
		panic(err)
	}
	defer udpConn.Close()

	laddr, err := net.ResolveUDPAddr("udp", addr)
	if err != nil {
		panic(err)
	}

	l, err := net.ListenUDP("udp", laddr)
	if err != nil {
		panic(err)
	}
	defer l.Close()

	buf := make([]byte, 1024)
	for {
		n, raddr, err := l.ReadFrom(buf)
		log.Printf("received packet %d\n", n)

		if err != nil {
			panic(err)
		}

		if _, err := udpConn.Write(buf[0:n]); err != nil {
			log.Printf("error relaying data: %s\n", err)
		}

		log.Printf("%d bytes relayed from %s to destination.\n", n, raddr.String())
	}
}