recorder.go

package main

import (
	_ "code.google.com/p/gcfg"
	"code.google.com/p/go.net/ipv4"
	_ "encoding/json"
	"fmt"
	_ "io/ioutil"
	"net"
	_ "net/http"
	"os"
	"strconv"
	_ "time"
)

func main() {
	iface, err := net.InterfaceByName("eth0")
	if err != nil {
		fmt.Println("net.InterfaceByName failed")
		return
	}

	mcast := "232.50.100.1"
	port := "3001"

	b1, _ := strconv.Atoi(mcast[0:3])
	b2, _ := strconv.Atoi(mcast[4:6])
	b3, _ := strconv.Atoi(mcast[7:10])
	b4, _ := strconv.Atoi(mcast[11:])

	group := net.IPv4(byte(b1), byte(b2), byte(b3), byte(b4))

	localSock, err := net.ListenPacket("udp4", mcast+":"+port)
	if err != nil {
		fmt.Println("net.ListenPacket failed")
		return
	}

	defer localSock.Close()
	pktSock := ipv4.NewPacketConn(localSock)

	if err := pktSock.SetControlMessage(ipv4.FlagDst, true); err != nil {
		fmt.Println("pktSock.SetControlMessage failed")
		return
	}

	if err := pktSock.JoinGroup(iface, &net.UDPAddr{IP: group}); err != nil {
		fmt.Println("Failed to join mcast!")
		return
	}

	file, err := os.OpenFile("/home/mkozjak/file", os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0600)
	if err != nil {
		fmt.Println("error opening file for appending")
	}

	defer file.Close()

	pktSock.SetMulticastInterface(iface)

	for {
		pkt := make([]byte, 1500)
		n, cmsg, _, err := pktSock.ReadFrom(pkt)
		if err != nil {
			fmt.Println("pktSock.ReadFrom failed")
			return
		}

		// Check if created packet buffer is too large and slice it if needed
		if len(pkt) > n {
			newPkt := make([]byte, n)
			copy(newPkt, pkt)
			pkt = newPkt
		}

		// Slice off udp header
		pkt = pkt[12:]

		// Store file
		if cmsg.Dst.IsMulticast() {
			if cmsg.Dst.Equal(group) {
				_, err := file.Write(pkt)
				if err != nil {
					fmt.Println("error writing to file")
					return
				}
			} else {
				continue
			}
		}
	}
}