A small traceroute written in go

traceroute.go

package main

import (
	//"bufio"
	"fmt"
	"golang.org/x/net/icmp"
	"golang.org/x/net/internal/iana"
	"golang.org/x/net/ipv4"
	"log"
	"net"
	"os"
	"time"
)

const (
	DEFAULT_TTL     = 32
	DEFAULT_TIMEOUT = 3 * time.Second
)

func ParseReplies(routers chan string) {

	c, err := icmp.ListenPacket("ip4:icmp", "0.0.0.0")
	if err != nil {
		panic(err)
	}

	for {
		c.SetReadDeadline(time.Now().Add(DEFAULT_TIMEOUT))

		rb := make([]byte, 1500)
		readed, peer, _ := c.ReadFrom(rb)

		if readed <= 0 {
			routers <- "*"
			continue
		}

		message, err := icmp.ParseMessage(iana.ProtocolICMP, rb[:readed])
		if err != nil {
			routers <- "*"
			continue
		}

		switch message.Type {
		case ipv4.ICMPTypeTimeExceeded:
			routers <- peer.String()
		default:
			continue
		}
	}
}

func main() {
	var router string
	routers := make(chan string)

	addr, err := net.ResolveUDPAddr("udp4", fmt.Sprintf("%s:%d", os.Args[1], 33434))
	if err != nil {
		log.Fatal(err)
	}

	go ParseReplies(routers)

	for i := 1; i <= DEFAULT_TTL; i++ {
		conn, err := net.DialUDP("udp4", nil, addr)
		if err != nil {
			log.Fatal(err)
		}
		defer conn.Close()

		start := time.Now()
		pkt := ipv4.NewPacketConn(conn)
		defer pkt.Close()

		pkt.SetTTL(i)
		buffer := make([]byte, 1024)
		_, err = pkt.Write(buffer) // write bytes through connected socket

		if err != nil {
			continue
		}

		router = <-routers
		fmt.Printf("TTL: %d - Router: %s - Roundtrip: %f\n", i, router, time.Since(start).Seconds())
	}
}