package main

import (
	"bytes"
	"encoding/binary"
	"flag"
	"fmt"
	"net"
	"os"
	"time"
)

var (
	timeout   int64
	size      int
	count     int
	host      string
	icmp_type uint8 = 8
	icmp_code uint8 = 0
)

type Icmp struct {
	Type     uint8  //类型  固定8
	Code     uint8  //代码  固定0
	CheckSum uint16 //校验和
	Id       uint16 //唯一标识
	Sequnce  uint16 //序列号

}

func main() {
	getCommandArgs()

	for count > 0 {
		t1 := time.Now()
		conn, e := net.DialTimeout("ip:icmp", host, time.Duration(timeout)*time.Millisecond)
		if e != nil {
			panic(e)
		}
		defer conn.Close()

		icmp := Icmp{
			Type:     icmp_type,
			Code:     icmp_code,
			CheckSum: 0,
			Id:       1,
			Sequnce:  1,
		}

		//var buf bytes.Buffer
		var buf bytes.Buffer
		//将icmp写入buf
		binary.Write(&buf, binary.BigEndian, icmp) //大端写入：先写低位（左边是高位  右边是低位）

		//定义需要发送的数据
		data := make([]byte, size)
		buf.Write(data)
		data = buf.Bytes()

		//将整个数据包进行签名
		sum := checkSum(data)
		data[2] = byte(sum >> 8) //checksum的高位值
		data[3] = byte(sum)      //checksum的低位值
		conn.SetDeadline(time.Now().Add(time.Duration(timeout) * time.Millisecond))
		conn.Write(data)

		response := make([]byte, 1000)
		n, _ := conn.Read(response)

		byteCount := n - 28 //字节数
		ttl := response[8]
		remoteIp := conn.RemoteAddr()

		fmt.Printf("Reply from %s: bytes=%d time=%dms TTL=%d\n", remoteIp, byteCount, time.Since(t1).Milliseconds(), ttl)

		time.Sleep(time.Duration(1000) * time.Millisecond)
		count--
	}

}

//计算签名
func checkSum(data []byte) uint16 {
	//计算相邻的两个数相加
	index := 0
	var sum uint32
	lenght := len(data)
	for lenght > 1 {
		sum += uint32(data[index])<<8 + uint32(data[index+1])
		lenght -= 2
		index += 2
	}

	if lenght != 0 {
		sum += uint32(data[index])
	}

	//获取sum的高16位
	high16 := sum >> 16
	for high16 != 0 {
		sum += high16 + uint32(uint16(sum))
		high16 = sum >> 16
	}
	return uint16(^sum)
}

//获取命令行参数
func getCommandArgs() {
	flag.Int64Var(&timeout, "w", 1000, "超时时长")
	flag.IntVar(&size, "l", 32, "发送数据大小")
	flag.IntVar(&count, "n", 4, "发送请求的次数")
	flag.Parse()

	args := os.Args
	if len(args) == 0 {
		panic("参数错误")
	}
	host = args[len(args)-1]
}