async_basic_tcp_port_scanner.go

package main

import (
	"fmt"
	"net"
	"sync"
	"time"
)

type TargetHost struct {
	ip string
}

func checkPortOpen(ip string, port int, timeout time.Duration) bool {
	conn, _ := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", ip, port), timeout)

	if conn == nil {
		return false
	}

	conn.Close()

	return true
}

func (t *TargetHost) AsyncFindOpenPorts(start, stop int) <-chan int {
	ports := make(chan int)
	seconds := 1
	timeout := (time.Duration(seconds) * time.Second)
	wg := sync.WaitGroup{}
	for port := start; port <= stop; port++ {
		wg.Add(1)
		go func(port int) {
			defer wg.Done()
			if checkPortOpen(t.ip, port, timeout) {
				ports <- port
			}
		}(port)
	}
	go func() {
		defer close(ports)
		wg.Wait()
	}()
	return ports
}

func main() {
	t := TargetHost{"127.0.0.1"}
	for p := range t.AsyncFindOpenPorts(500, 2500) {
		fmt.Println(p)
	}
}