Go multicast example

gistfile1.go

package main

import (
	"encoding/hex"
	"log"
	"net"
	"time"
)

const (
	srvAddr         = "224.0.0.1:9999"
	maxDatagramSize = 8192
)

func main() {
	go ping(srvAddr)
	serveMulticastUDP(srvAddr, msgHandler)
}

func ping(a string) {
	addr, err := net.ResolveUDPAddr("udp", a)
	if err != nil {
		log.Fatal(err)
	}
	c, err := net.DialUDP("udp", nil, addr)
	for {
		c.Write([]byte("hello, world\n"))
		time.Sleep(1 * time.Second)
	}
}

func msgHandler(src *net.UDPAddr, n int, b []byte) {
	log.Println(n, "bytes read from", src)
	log.Println(hex.Dump(b[:n]))
}

func serveMulticastUDP(a string, h func(*net.UDPAddr, int, []byte)) {
	addr, err := net.ResolveUDPAddr("udp", a)
	if err != nil {
		log.Fatal(err)
	}
	l, err := net.ListenMulticastUDP("udp", nil, addr)
	l.SetReadBuffer(maxDatagramSize)
	for {
		b := make([]byte, maxDatagramSize)
		n, src, err := l.ReadFromUDP(b)
		if err != nil {
			log.Fatal("ReadFromUDP failed:", err)
		}
		h(src, n, b)
	}
}

@freignat91 it worked for me. Try to run one instance with go run gistfile1.go. Leave it running and comment the line with go ping(srvAddr) before launching it again in a different terminal.

Just first launch is multicasting UDP packets but you should be receiving them in both terminals.

@freignat91 Is multicast enabled on your router?

Note that the switch may need mcast enabled (igmp snooping) and then the router (if it goes from switch to router to switch) will also have to understand what to do about mcast packets.

Unsurprisingly, it does not work on MacOS X but that is because they don't load balance on SO_REUSEPORT.