TCP端口扫描器

TCP端口扫描器

一、TCP扫描器

• TCP的握手有三个过程。
  • 客户端发送一个 syn 的包，表示建立回话的开始
  • 如果服务端应答 syn-ack 包，意味着这个端口是打开的，否则会返回 rst 包。最后，
  • 客户端需要另外发送一个 ack 包。从这时起，连接就已经建立。
• 构建简易的TCP扫描器

package mainimport ("flag""fmt""net""sync""time"
)func main() {hostname := flag.String("hostname", "www.baidu", "hostname to test")startPort := flag.Int("start-port", 80, "the port on which the scanning starts")endPort := flag.Int("end-port", 100, "the port from which the scanning ends")timeout := flag.Duration("timeout", time.Millisecond*200, "timeout")flag.Parse()ports := make([]int, 0)//同步机制wg := &sync.WaitGroup{}for port := *startPort; port <= *endPort; port++ {wg.Add(1)go func(p int) {opened := isOpen(*hostname, p, *timeout)if opened {ports = append(ports, p)}wg.Done()}(port)}wg.Wait()fmt.Printf("opened ports: %vn", ports)/**opened ports: [80]*/
}/**
检测端口是否可连接
*/
func isOpen(host string, port int, timeout time.Duration) bool {time.Sleep(time.Millisecond * 1)conn, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", host, port), timeout)if err == nil {_ = conn.Close()return true}return false
}