Golang 写一个端口扫描器

前话

最近痴迷于Golang这个新兴语言，由于它是强类型编译型语言，能够直接编译成三大平台的二进制执行文件，能够直接运行无需其余依赖环境。并且Golang独特的goroutine使得多线程任务执行如new一个对象般简单。

带着为学习理解Golang的好奇心情，我试着写了个端口扫描器。

github项目连接以下， 更多的实用工具我会慢慢添加。
https://github.com/pwcong/go-tools

源码

package main

import (
    "flag"
    "fmt"
    "net"
    "os"
    "regexp"
    "strconv"
    "strings"
    "sync"
)

var port int
var portRange string

var parallelCounts int

func init() {

    flag.IntVar(&port, "p", 80, "port")
    flag.StringVar(&portRange, "r", "", "range ports. format is <from>~<to>. eg. 100~200")
    flag.IntVar(&parallelCounts, "n", 1, "parallel counts")

    // 修改提示信息
    flag.Usage = func() {
        fmt.Fprintf(os.Stderr, "\nUsage: %s [Options] <IP>\n\nOptions:\n\n", os.Args[0])
        flag.PrintDefaults()
    }

    flag.Parse()

}

func printOpeningPort(port int) {

    fmt.Println("port " + strconv.Itoa(port) + " is opening")

}

func checkPort(ip net.IP, port int, wg *sync.WaitGroup, parallelChan *chan int) {

    defer wg.Done()

    tcpAddr := net.TCPAddr{
        IP:   ip,
        Port: port,
    }

    conn, err := net.DialTCP("tcp", nil, &tcpAddr)

    if err == nil {
        printOpeningPort(port)
        conn.Close()

    }

    <-*parallelChan

}

func main() {

    args := flag.Args()

    if len(args) != 1 {
        flag.Usage()
    } else {

        ip := net.ParseIP(flag.Arg(0))

        // 用于协程任务控制
        wg := sync.WaitGroup{}

        if portRange != "" {

            matched, _ := regexp.Match(`^\d+~\d+$`, []byte(portRange))

            if !matched {

                flag.Usage()

            } else {

                portSecs := strings.Split(portRange, "~")

                startPort, err1 := strconv.Atoi(portSecs[0])
                endPort, err2 := strconv.Atoi(portSecs[1])

                if err1 != nil || err2 != nil || startPort < 1 || endPort < 2 || endPort <= startPort || parallelCounts < 1 {
                    flag.Usage()
                } else {

                    wg.Add(endPort - startPort + 1)

                    // 用于控制协程数
                    parallelChan := make(chan int, parallelCounts)

                    for i := startPort; i <= endPort; i++ {

                        parallelChan <- 1

                        go checkPort(ip, i, &wg, &parallelChan)

                    }

                    wg.Wait()

                }

            }

        } else {

            wg.Add(1)

            parallelChan := make(chan int)

            go func() {
                parallelChan <- 1
            }()

            go checkPort(ip, port, &wg, &parallelChan)

            wg.Wait()

        }

    }

}

运行结果

1. 执行 go build ./main.go， 生成二进制文件

2. 运行二进制文件，结果以下：
   ```
   $ port-scanner.exe

   Usage: E:\Program Files\GoPath\bin\port-scanner.exe [Options]

   Options:

   -n int
   parallel counts (default 1)
   -p int
   port (default 80)
   -r string
   range ports. format is ~ . eg. 100~200

   $ port-scanner.exe -p 80 127.0.0.1
   port 80 is opening

   $ port-scanner.exe -r 1~100 -n 50 127.0.0.1
   port 80 is opening
   ```