ping.go

package main

//Stolen/addapted from https://github.com/atomaths/gtug8/blob/master/ping/ping.go

import (
	"bytes"
	"flag"
	"fmt"
	"log"
	"net"
	"os"
	"time"
)

const (
	ICMP_ECHO_REQUEST = 8
	ICMP_ECHO_REPLY   = 0
)

// returns a suitable 'ping request' packet, with id & seq and a
// payload length of pktlen
func makePingRequest(id, seq, pktlen int, filler []byte) []byte {
	p := make([]byte, pktlen)
	copy(p[8:], bytes.Repeat(filler, (pktlen-8)/len(filler)+1))

	p[0] = ICMP_ECHO_REQUEST // type
	p[1] = 0                 // code
	p[2] = 0                 // cksum
	p[3] = 0                 // cksum
	p[4] = uint8(id >> 8)    // id
	p[5] = uint8(id & 0xff)  // id
	p[6] = uint8(seq >> 8)   // sequence
	p[7] = uint8(seq & 0xff) // sequence

	// calculate icmp checksum
	cklen := len(p)
	s := uint32(0)
	for i := 0; i < (cklen - 1); i += 2 {
		s += uint32(p[i+1])<<8 | uint32(p[i])
	}
	if cklen&1 == 1 {
		s += uint32(p[cklen-1])
	}
	s = (s >> 16) + (s & 0xffff)
	s = s + (s >> 16)

	// place checksum back in header; using ^= avoids the
	// assumption the checksum bytes are zero
	p[2] ^= uint8(^s & 0xff)
	p[3] ^= uint8(^s >> 8)

	return p
}

func parsePingReply(p []byte) (id, seq int) {
	id = int(p[4])<<8 | int(p[5])
	seq = int(p[6])<<8 | int(p[7])
	return
}

func elapsedTime(start int64) float32 {
	t := float32(time.Now().UnixNano()-start) / 1000000.0
	return t
}

func main() {
	flag.Parse()
	dst := flag.Arg(0)
	//dst := "121.254.177.105"

	raddr, err := net.ResolveIPAddr("ip4", dst) // *IPAddr
	if err != nil {
		log.Fatalf(`net.ResolveIPAddr("ip4", %v") = %v, %v`, dst, raddr, err)
	}

	ipconn, err := net.DialIP("ip4:icmp", nil, raddr) // *IPConn (Conn 인터페이스 구현)
	if err != nil {
		log.Fatalf(`net.DialIP("ip4:icmp", %v) = %v`, ipconn, err)
	}

	sendid := os.Getpid() & 0xffff
	sendseq := 1
	pingpktlen := 64

	for {
		sendpkt := makePingRequest(sendid, sendseq, pingpktlen, []byte("Go Ping"))

		//fmt.Printf("%v, %v\n", sendpkt[0:8], string(sendpkt[8:]))

		start := time.Now().UnixNano()

		n, err := ipconn.WriteToIP(sendpkt, raddr)
		if err != nil || n != pingpktlen {
			log.Fatalf(`net.WriteToIP(..., %v) = %v, %v`, raddr, n, err)
		}

		//ipconn.SetTimeout(5e8) // 0.5 second

		resp := make([]byte, 1024)
		for {
			n, from, err := ipconn.ReadFrom(resp)
			fmt.Printf("%d bytes from %s: icmp_req=%d time=%.2f ms\n", n, dst, sendseq, elapsedTime(start))

			// log.Printf("%x", resp)

			if err != nil {
				log.Fatalf(`ReadFrom(...) = %v, %v, %v`, n, from, err)
			}
			if resp[0] != ICMP_ECHO_REPLY {
				continue
			}
			rcvid, rcvseq := parsePingReply(resp)
			if rcvid != sendid || rcvseq != sendseq {
				log.Fatalf(`Ping reply saw id,seq=0x%x,0x%x (expected 0x%x, 0x%x)`, rcvid, rcvseq, sendid, sendseq)
			}
			break
		}

		sendseq++
		time.Sleep(1e9) // 1 second. like -i (interval) option
	}
}