package main
import (
 "net"
 "fmt"
 "os"
 "runtime"
 "time"
 "strconv"
)

 

func loop(startport, endport int, inport chan int) {
  for i := startport; i <= endport; i++{
   inport <- i
  }
}

func scanner(inport, outport, out chan int, ip net.IP, endport int){
 for{
  in := <- inport
  //fmt.Println(in)
  tcpaddr := &net.TCPAddr{ip,in}
  conn, err := net.DialTCP("tcp", nil, tcpaddr)
  if err != nil {
   outport <- 0
  }else{
   outport <- in 
  }
  conn.Close()
  if in == endport{
   out <- in
  }
 }
}

func main() {
 starttime := time.Now().Unix()
 runtime.GOMAXPROCS(4)
 inport := make(chan int)
 outport := make(chan int)
 out := make(chan int)
 collect := []int{}
 if len(os.Args) != 4 {
  fmt.Println("Usage: scanner.exe IP startport endport")
  fmt.Println("Endport must be larger than startport")
  os.Exit(0)
 }
 ip := net.ParseIP(os.Args[1])
 if(os.Args[3] < os.Args[2]) {
  fmt.Println("Usage: scanner IP startport endport")
  fmt.Println("Endport must be larger than startport")
  os.Exit(0)
 }
 startport, _:= strconv.Atoi(os.Args[2])
 endport, _ := strconv.Atoi(os.Args[3])
 go loop(startport, endport, inport)
 for{
  select {
   case <-out:
    fmt.Println(collect)
    endtime := time.Now().Unix()
    fmt.Println("The scan process has spent ",endtime-starttime,"second")
    os.Exit(0)
   default:
    go scanner(inport, outport, out, ip, endport)
    port := <- outport
    
    if port != 0{
     collect = append(collect, port)
    }
  }  
 }
}