Question

这节，您将学习怎样使用 syscall 库获取原始 ICMP 网络数据，和 syscall.SetsockoptInt() 去设置 socket 选项。牢记发送原始 ICMP 数据是非常困难的，因为您不得不自己构造原始网络包。这个程序的名称是 syscallNet.go，并显示在四个部分中。

syscallNet.go 的第一部分如下：

package main

import(
    "fmt"
    "os"
    "syscall"
)

syscallNet.go 的第二部分包含代码如下：

func main() {
    fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_RAW, syscall.IPPROTO_ICMP)
    if err != nil {
        fmt.Println("Error in syscall.Socket:", err)
        return
    }
    f := os.NewFile(uintptr(fd), "captureICMP")
    if f == nil {
        fmt.Println("Error is os.NewFile:", err)
        return
    }

syscall.AF_INET 参数告诉 syscall.Socket() 您想使用 IPv4。 syscall.SOCK_RAW 参数使生成的 socket 成为原始 socket。这最后一个参数，syscall.IPPROTO_ICMP，告诉 syscall.Socket() 您只对 ICMP 通信感兴趣。

syscallNet.go 的第三部分如下：

    err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_RCVBUF, 256)
    if err != nil {
        fmt.Println("Error in syscall.Socket:", err)
        return
    }

调用 syscall.SetsockoptInt() 设置 socket 的接收 buffer 大小为 256。syscall.SOL_SOCKET 参数是为了说明您想要在 socket 层级上工作。

syscallNet.go 的其余 Go 代码如下：

    for {
        buf := make([]byte, 1024)
        numRead, err := f.Read(buf)
        if err != nil {
            fmt.Println(err)
        }
        fmt.Printf("% X\n", buf[:numRead])
    }
}

由于 for 循环，syscallNet.go 将一直抓取 ICMP 网络包直到您手动终止它。

在 macOS High Sierra 机器上执行 syscallNet.go 将产生如下输出：

$ sudo go run syscallNet.go
45 00 40 00 BC B6 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 3F 36 71 45 00 00 5A CB 6A 90 00 0B 9F 1A 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 40 00 62 FB 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 31 EF 71 45 00 01 5A CB 6A 91 00 0B AC 5F 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 40 00 9A 5F 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 31 EF 71 45 00 01 5A CB 6A 91 00 0B AC 5F 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 40 00 6E 0D 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 31 EF 71 45 00 01 5A CB 6A 91 00 0B AC 5F 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 40 00 3A 07 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 31 EF 71 45 00 01 5A CB 6A 91 00 0B AC 5F 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 24 00 45 55 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 31 EF 71 45 00 01 5A CB 6A 91 00 0B AC 5F 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 24 00 E8 1E 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 31 EF 71 45 00 01 5A CB 6A 91 00 0B AC 5F 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 24 00 2A 4B 00 00 40 01 00 00 7F 00 00 01 7F 00 00 01 00 00 31 EF 71 45 00 01 5A CB 6A 91 00 0B AC 5F 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37

在 Debian Linux 机器上运行 syscallNet.go 将产生如下输出：

# go run syscallNet.go
45 00 00 54 7F E9 40 00 40 01 BC BD 7F 00 00 01 7F 00 00 01 08 00 6F 07 53 E3 00 01 FA 6A CB 5A 00 00 00 00 AA 7B 06 00 00 00 00 00 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 00 54 7F EA 00 00 40 01 FC BC 7F 00 00 01 7F 00 00 01 00 00 77 07 53 E3 00 01 FA 6A CB 5A 00 00 00 00 AA 7B 06 00 00 00 00 00 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 C0 00 44 68 54 00 00 34 01 8B 8E 86 77 DC 57 6D 4A C1 FD 03 0A 8F 27 00 00 00 00 45 00 00 28 40 4F 40 00 34 06 74 6A 6D 4A C1 FD 86 77 DC 57 B0 B8 DD 96 00 00 00 00 52 F1 AB DA 50 14 00 00 90 9E 00 00
45 00 00 54 80 4E 40 00 40 01 BC 58 7F 00 00 01 7F 00 00 01 08 00 7E 01 53 E3 00 02 FB 6A CB 5A 00 00 00 00 9A 80 06 00 00 00 00 00 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 00 54 80 4F 00 00 40 01 FC 57 7F 00 00 01 7F 00 00 01 00 00 86 01 53 E3 00 02 FB 6A CB 5A 00 00 00 00 9A 80 06 00 00 00 00 00 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37
45 00 00 54 80 9B 40 00 40 01 BC 0B 7F 00 00 01 7F 00 00 01 08 00 93 EC 53 E3 00 03 FC 6A CB 5A 00 00 00 00 9A 80 06 00 00 00 00 00 10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37