initial commit

utils/dns_utils.go

@@ -0,0 +1,55 @@
+package utils
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+type WrongAnswerError struct {
+	Message string
+}
+
+func (e *WrongAnswerError) Error() string {
+	return fmt.Sprintf("Wrong Answer: %s", e.Message)
+}
+
+func SendQuery(addr string, dn string) (string, error) {
+	var (
+		domain  string
+		rdns_ip string
+	)
+	if dn == "timestamp" {
+		timestamp := strconv.FormatInt(time.Now().UnixNano(), 10)
+		domain = strings.Join([]string{timestamp, "-scan.echodns.xyz."}, "")
+	} else {
+		domain = strings.Join([]string{dn, ".echodns.xyz."}, "")
+	}
+	//fmt.Println(domain)
+	m := new(dns.Msg)
+	m.SetQuestion(domain, dns.TypeA)
+	m.RecursionDesired = true
+
+	res, err := dns.Exchange(m, addr)
+	if err == nil {
+		if len(res.Answer) == 1 {
+			if a, ok := res.Answer[0].(*dns.A); ok {
+				rdns_ip = a.A.String()
+			} else {
+				rdns_ip = ""
+				err = &WrongAnswerError{
+					Message: "Wrong Record Type",
+				}
+			}
+		} else {
+			rdns_ip = ""
+			err = &WrongAnswerError{
+				Message: "Wrong Answer Section",
+			}
+		}
+	}
+	return rdns_ip, err
+}