udp/tcp port open check

check_udp_tcp_port_open.go

package main

import (
	"fmt"
	"net"
	"strings"
	"time"

	"github.com/ziutek/telnet"
)

func check_udp(ip1, ip2, ip3, ip4 byte, port int) bool {
	conn, err := net.DialUDP("udp", nil, &net.UDPAddr{net.IPv4(ip1, ip2, ip3, ip4), port, ""})
	if err != nil {
		fmt.Println(err)
		return false
	}
	defer conn.Close()

	conn.Write([]byte(""))

	buffer := make([]byte, 1024)
	conn.SetReadDeadline(time.Now().Add(3 * time.Second))
	_, _, err = conn.ReadFrom(buffer)
	if err != nil {
		fmt.Println("readfrom", err)
		return !strings.Contains(err.Error(), "recvfrom: connection refused")
	}
	return true
}
func check_tcp(addr string) bool {
	_, err := telnet.DialTimeout("tcp", addr, 5*time.Second)
	if err != nil {
		fmt.Println(err)
		return false
	}
	return true
}

func main() {
	fmt.Println(check_udp(192, 168, 1, 99, 123)) // true
	fmt.Println(check_udp(192, 168, 1, 99, 234)) // false
	fmt.Println(check_tcp("192.168.1.99:1234"))  // false
	fmt.Println(check_tcp("192.168.1.99:8081"))  // true
}