package main
import (
"fmt"
"strconv"
"flag"
"strings"
"net"
"os"
)
/**
  掃描地址
*/
var ipAddrs chan string = make(chan string)
//掃描結果
var result chan string = make(chan string)
//線程數
var thread chan int = make(chan int)
var nowThread int;
//關閉程序
var clo chan bool = make(chan bool)
//保存結果
func writeResult(){
  fileName := "result.txt"
  fout,err := os.Create(fileName)
  if err != nil{
    //文件創建失敗
    fmt.Println(fileName + " create error")
  }
  defer fout.Close()
  s,ok := <- result
  for ;ok;{
    fout.WriteString(s + "\r\n")
    s,ok = <- result
  }
  //通知進程退出
  clo <- true; 
}
//根據線程參數啟動掃描線程
func runScan(){
  t,ok := <- thread
  nowThread = t;
  if ok{
    for i := 0;i < nowThread;i++{
    go scan(strconv.Itoa(i))
    }
  }
  //等待線程終止
  for;<-thread == 0;{
    nowThread--
    if nowThread == 0{
      //全部線程已終止,關閉結果寫入,退出程序
      close(result)
      break
    }
  }
}
/**
  掃描線程
*/
func scan(threadId string){
  s,ok := <-ipAddrs
  for;ok;{
    fmt.Println("[thread-" + threadId + "] scan:" + s)
    _,err := net.Dial("tcp",s)
    if err == nil{
      //端口開放
      result <- s     
    }
    s,ok = <-ipAddrs
  }
  fmt.Println("[thread-" + threadId + "] end")
  thread <- 0;
}
//獲取下一個IP
func nextIp(ip string) string{
  ips := strings.Split(ip,".")
  var i int;
  for i = len(ips) - 1;i >= 0;i--{
    n,_ := strconv.Atoi(ips[i])
    if n >= 255{
      //進位
      ips[i] = "1"  
    }else{
      //+1
      n++
      ips[i] = strconv.Itoa(n)
      break
    }
  }
  if i == -1{
    //全部IP段都進行了進位,說明此IP本身已超出范圍
    return "";
  }
  ip = ""
  leng := len(ips)
  for i := 0;i < leng;i++{
    if i == leng -1{
      ip += ips[i]
    }else{
      ip += ips[i] + "."
    }
  }
  return ip
}
//生成IP地址列表
func processIp(startIp,endIp string) []string{
  var ips = make([]string,0)
  for ;startIp != endIp;startIp = nextIp(startIp){
    if startIp != ""{
      ips = append(ips,startIp)
    }
  }
  ips = append(ips,startIp)
  return ips
}
//處理參數
func processFlag(arg []string){
  //開始IP,結束IP
  var startIp,endIp string
  //端口
  var ports []int = make([]int,0)
  index := 0
  startIp = arg[index]
  si := net.ParseIP(startIp)
  if si == nil{
    //開始IP不合法
    fmt.Println("'startIp' Setting error")
    return
  }
  index++
  endIp = arg[index]
  ei := net.ParseIP(endIp)
  if(ei == nil){
    //未指定結束IP,即只掃描一個IP
    endIp = startIp
  }else{
   index++
  }
  tmpPort := arg[index]
  if strings.Index(tmpPort,"-") != -1{
    //連續端口
    tmpPorts := strings.Split(tmpPort,"-")
    var startPort,endPort int
    var err error
    startPort,err = strconv.Atoi(tmpPorts[0])
    if err != nil || startPort < 1 || startPort > 65535{
      //開始端口不合法
      return
    }
    if len(tmpPorts) >= 2{
      //指定結束端口
      endPort,err = strconv.Atoi(tmpPorts[1])
      if err != nil || endPort < 1 || endPort > 65535 || endPort < startPort{
        //結束端口不合法
        fmt.Println("'endPort' Setting error")
        return
      }
    }else{
      //未指定結束端口
      endPort = 65535
    }
    for i := 0;startPort + i <= endPort;i++{
      ports = append(ports,startPort + i)
    }
  }else{
    //一個或多個端口
    ps := strings.Split(tmpPort,",")
    for i := 0;i < len(ps);i++{
      p,err := strconv.Atoi(ps[i])
      if err != nil{
        //端口不合法
        fmt.Println("'port' Setting error")
        return
      }
      ports = append(ports,p)
    }
  }
  index++
  t,err := strconv.Atoi(arg[index])
  if(err != nil){
    //線程不合法
    fmt.Println("'thread' Setting error")
    return
  }
  //最大線程2048
  if t < 1{
    t = 1;
  }else if t > 2048{
    t = 2048;
  }
  //傳送啟動線程數
  thread <- t
  //生成掃描地址列表
  ips := processIp(startIp,endIp)
  il := len(ips)
  for i := 0; i < il;i++{
    pl := len(ports)
    for j := 0;j < pl;j++{
      ipAddrs <- ips[i] + ":" + strconv.Itoa(ports[j]) 
    }
  }
  close(ipAddrs)
}
func main(){
  flag.Parse()
  if flag.NArg() != 3 && flag.NArg() != 4{
    //參數不合法
    fmt.Println("Parameter error")
    return
  }
  //獲取參數
  args := make([]string,0,4)
  for i := 0;i < flag.NArg();i++{
    args = append(args,flag.Arg(i))
  }
  //啟動掃描線程
  go runScan()
  //啟動結果寫入線程
  go writeResult()
  //參數處理
  processFlag(args)
  //等待退出指令
  <- clo;
  fmt.Println("Exit")
}