main.go

package main

import (
	"fmt"
	"log"

	"github.com/panjf2000/gnet/v2"
)

func main() {
	echo := &echoServer{}
  	log.Fatal(gnet.Run(echo, 
	   "udp://239.0.0.1:9999", 
	   gnet.WithNumEventLoop(2), // running 2 loops.
	))
}

type echoServer struct {
	gnet.BuiltinEventEngine
}

func (es *echoServer) OnTraffic(c gnet.Conn) gnet.Action {
	data, err := c.Next(-1)
	if err != nil {
		log.Printf("faield to read: %v", err)
	} else {
		// this happens 2 times for every single packet i send to the above
		// multicast address.
		fmt.Println(string(data))
	}
	return gnet.None
}