ping.go

package main

import (
	"fmt"
	"net"
	"os"
	"time"

	"golang.org/x/net/icmp"
	"golang.org/x/net/ipv4"
)

func main() {
	if len(os.Args) != 2 {
		fmt.Fprintf(os.Stderr, "usage: %v ip address\n", os.Args[0])
		os.Exit(1)
	}
	addr := os.Args[1]
	rtt, err := ping(addr)
	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	fmt.Println(addr, rtt)
}

func ping(addr string) (time.Duration, error) {
	dst := net.ParseIP(addr)
	if dst == nil {
		return 0, fmt.Errorf("%q is not a valid ip address", addr)
	}
	c, err := icmp.ListenPacket("udp4", "0.0.0.0")
	if err != nil {
		return 0, err
	}
	c.SetDeadline(time.Now().Add(3 * time.Second))
	defer c.Close()

	msg := icmp.Message{
		Type: ipv4.ICMPTypeEcho,
		Body: &icmp.Echo{
			ID: os.Getpid() & 0xffff, Seq: 1,
			Data: []byte("ping"),
		},
	}
	b, err := msg.Marshal(nil)
	if err != nil {
		return 0, err
	}
	buf := make([]byte, 1500)
	start := time.Now()
	if _, err := c.WriteTo(b, &net.UDPAddr{IP: dst}); err != nil {
		return 0, err
	}
	n, _, err := c.ReadFrom(buf)
	if err != nil {
		return 0, err
	}
	rtt := time.Since(start)
	rm, err := icmp.ParseMessage(1, buf[:n])
	if err != nil {
		return 0, err
	}
	if rm.Type != ipv4.ICMPTypeEchoReply {
		return 0, fmt.Errorf("got %+v; want echo reply\n", rm)
	}
	return rtt, nil
}