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 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.