Go语言ICMP协议：向主机发送消息

下面我们实现这样一个例子：使用 ICMP 协议向在线的主机发送一个问候，并等待主机返回，具体代码如下所示。

package main
import (
    "net"
    "os"
    "bytes"
    "fmt"
)
func main() {
    if len(os.Args) != 2 {
        fmt.Println("Usage: ", os.Args[0], "host")
        os.Exit(1)
    }
    service := os.Args[1]
    conn, err := net.Dial("ip4:icmp", service)
    checkError(err)
    var msg [512]byte
    msg[0] = 8 // echo
    msg[1] = 0 // code 0
    msg[2] = 0 // checksum
    msg[3] = 0 // checksum
    msg[4] = 0 // identifier[0]
    msg[5] = 13 //identifier[1]
    msg[6] = 0 // sequence[0]
    msg[7] = 37 // sequence[1]
    len := 8
    check := checkSum(msg[0:len])
    msg[2] = byte(check >> 8)
    msg[3] = byte(check & 255)
    _, err = conn.Write(msg[0:len])
    checkError(err)
    _, err = conn.Read(msg[0:])
    checkError(err)
    fmt.Println("Got response")
    if msg[5] == 13 {
        fmt.Println("Identifier matches")
    }
    if msg[7] == 37 {
        fmt.Println("Sequence matches")
    }
    os.Exit(0)
}
func checkSum(msg []byte) uint16 {
    sum := 0
    // 先假设为偶数
    for n := 1; n <len(msg)-1; n += 2 {
        sum += int(msg[n])*256 + int(msg[n+1])
    }
    sum = (sum >> 16) + (sum & 0xffff)
    sum += (sum >> 16)
    var answer uint16 = uint16(^sum)
    return answer
}
func checkError(err error) {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Fatal error: %s", err.Error())
        os.Exit(1)
    }
}
func readFully(conn net.Conn) ([]byte, error) {
    defer conn.Close()
    result := bytes.NewBuffer(nil)
    var buf [512]byte
    for {
        n, err := conn.Read(buf[0:])
        result.Write(buf[0:n])
        if err != nil {
            if err == io.EOF {
                break
            }
            return nil, err
        }
    }
    return result.Bytes(), nil
}

执行结果如下：

$ go build icmptest.go
$ ./icmptest www.baidu.com
Got response
Identifier matches
Sequence matches