Multicast replies in unicast

multicast.go

package main

import "log"
import "net"
import "os"

var gaddr *net.UDPAddr = &net.UDPAddr{IP: net.IPv4(224, 0, 0, 254), Port: 12345}
func listener(c chan int) {
  	logger := log.New(os.Stdout, "[L]", log.Ltime | log.Lshortfile)
	conn, err := net.ListenMulticastUDP("udp", nil, gaddr)
	if err != nil {
		logger.Fatalf("failed to listen: %s\n", err)
		return
	}
	c <- 1
	defer conn.Close()
	logger.Printf("laddr = %s", conn.LocalAddr().String())

	buf := make([]byte, 512)
	_, dest, err := conn.ReadFromUDP(buf)
	if err != nil {
		logger.Fatalf("failed to read: %s\n", err)
		return
	}
	logger.Printf("read from %s: %s\n", dest.String(), string(buf))

	msg := "world"
	_, err = conn.WriteToUDP([]byte(msg), dest)
	if err != nil {
		logger.Fatalf("failed to write: %s\n", err)
	}

	logger.Printf("end of listener\n")
	c <- 1
}

func sender(c chan int) {
	logger := log.New(os.Stdout, "[S]", log.Ltime | log.Lshortfile)
	<-c

	laddr := &net.UDPAddr{IP: net.IPv4(0, 0, 0, 0), Port: 3333}
	conn, err := net.DialUDP("udp", laddr, gaddr)
	if err != nil {
		logger.Fatalf("failed to dial: %s\n", err)
		return
	}
	defer conn.Close()
	logger.Printf("laddr = %s", conn.LocalAddr().String())

	msg := "hello"
	n, err := conn.Write([]byte(msg))
	if err != nil {
		logger.Fatalf("client failed to write: %s\n", err)
		return
	}
	logger.Printf("%d bytes written\n", n)

	buf := make([]byte, 512)
	_, remote, err := conn.ReadFrom(buf)
	if err != nil {
		logger.Fatalf("client failed to read: %s\n", err)
		return
	}
	logger.Printf("client read from %s: %s\n", remote, string(buf))

	<-c
}

func main() {
	c := make(chan int, 1)
	go listener(c)

	sender(c)
}