dns-lookup.go

func dnsTCPLookup(resolverIP string, domain string) (string, error) {
	tcpResolver := net.Resolver{
		PreferGo: true,
		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
			dialer := net.Dialer{}
			return dialer.DialContext(ctx, "tcp", fmt.Sprintf("%s:53", resolverIP))
		},
	}
	log.Printf("[dns] lookup -> %s", domain)
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	txts, err := tcpResolver.LookupTXT(ctx, domain)
	if err != nil || len(txts) == 0 {
		log.Printf("[!] failure -> %s", domain)
		return "", err
	}
	return strings.Join(txts, ""), nil
}