catering/mdns/mdns.go

package mdns

import (
	"fmt"
	"net"
	"os"
	"strconv"
	"strings"
)

const (
	SERVER_RECV_LEN = 20
)

func Mdns(servicename string,SERVER_PORT int) {

//	flag.StringVar(&servicename, "service", "getip", "ServiceName")
//	flag.IntVar(&SERVER_PORT, "port", 5354, "Port")
//	flag.Parse()

	sameIP := net.UDPAddr{
		IP:   net.IPv4(0, 0, 0, 0),
		Port: 0,
	}
	sameint := 0
	maxsameint := 0
	netInterfaces, err := net.Interfaces()
	if err != nil {
		fmt.Println("net.Interfaces failed, err:", err.Error())
		os.Exit(1)
	}

	address := ":" + strconv.Itoa(SERVER_PORT)
	addr, err := net.ResolveUDPAddr("udp", address)
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}

	conn, err := net.ListenUDP("udp", addr)
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}

	defer conn.Close()

	for {
		// Here must use make and give the lenth of buffer
		data := make([]byte, SERVER_RECV_LEN)
		_, rAddr, err := conn.ReadFromUDP(data)
		if err != nil {
		//	fmt.Println(err)
			continue
		}
		strData := string(data)
		maxsameint = 0
		if strings.Contains(strData, servicename) {
			for i := 0; i < len(netInterfaces); i++ {
				if (netInterfaces[i].Flags & net.FlagUp) != 0 {
					addrs, _ := netInterfaces[i].Addrs()
					for _, address := range addrs {
						sameint = 0
						if ipnet, ok := address.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
							if ipnet.IP.To4() != nil {
								if ipnet.IP[12] == rAddr.IP[12] {
									sameint++
									if ipnet.IP[13] == rAddr.IP[13] {
										sameint++
										if ipnet.IP[14] == rAddr.IP[14] {
											sameint++
											if ipnet.IP[15] == rAddr.IP[15] {
												sameint++
											}
										}
									}
								}
								if sameint>maxsameint{
									maxsameint=sameint
									sameIP.IP = ipnet.IP
								}

							}
						}
					}
				}
			}
			if maxsameint>0{
				_, err = conn.WriteToUDP([]byte("ip:" + sameIP.IP.String()), rAddr)
				if err != nil {
				//	fmt.Println(err)
					continue
				}
			}
		}
	}
}