a simple threaded port scanner in go

portscanner.go

package main

import (
	"errors"
	"fmt"
	"net"
	"os"
	"sort"
	"time"
)

type portinfo struct {
	number int
	isOpen bool
}

var tcpTimeout, _ = time.ParseDuration("200ms")

type ByPortNumber []portinfo

func (a ByPortNumber) Len() int      { return len(a) }
func (a ByPortNumber) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a ByPortNumber) Less(i, j int) bool {
	return a[i].number < a[j].number
}

func scanPort(channel chan portinfo, host string, port int) (err error) {
	target := fmt.Sprintf("%s:%d", host, port)
	tcpAddress, err := net.ResolveTCPAddr("tcp4", target)
	if err != nil {
		channel <- portinfo{port, false}
		return errors.New("Resolving of address failed.")
	}

	conn, err := net.DialTimeout("tcp", tcpAddress.String(), tcpTimeout)
	if err != nil {
		channel <- portinfo{port, false}
	} else {
		channel <- portinfo{port, true}
		conn.Close()
	}
	return nil
}

func main() {
	numports := 32768

	startTime := time.Now()
	if len(os.Args) != 2 {
		fmt.Println("usage: portscanner idealo.de")
		return
	}
	host := os.Args[1]
	channel := make(chan portinfo, numports)

	fmt.Printf("Scanning host '%s'\n", host)
	for port := 1; port < numports; port++ {
		go scanPort(channel, host, port)
	}

	var results []portinfo
	for port := 1; port < numports; port++ {
		s := <-channel
		results = append(results, s)
	}
	close(channel)
	sort.Sort(ByPortNumber(results))
	for idx := range results {
		if results[idx].isOpen == true {
			fmt.Printf("%10d: open\n", results[idx].number)
		}
	}
	fmt.Printf("Finished in %v\n", time.Now().Sub(startTime))
}