From 607cd5468f53f7904421d11a8fc3ae6d3490069b Mon Sep 17 00:00:00 2001
From: Mzack9999 <mzack9999@protonmail.com>
Date: Fri, 27 Jan 2023 13:09:00 +0100
Subject: [PATCH] adding reverse ptr

---
 ip/iputil.go      | 20 ++++++++++++++++++++
 ip/iputil_test.go |  8 ++++++++
 2 files changed, 28 insertions(+)

diff --git a/ip/iputil.go b/ip/iputil.go
index 3e09814..ed7b147 100644
--- a/ip/iputil.go
+++ b/ip/iputil.go
@@ -315,3 +315,23 @@ func GetBindableAddress(port int, ips ...string) (string, error) {
 
 	return "", errs
 }
+
+// ToFQDN performs a reverse PTR using default system resolvers
+func ToFQDN(target string) ([]string, error) {
+	if !IsIP(target) {
+		return []string{target}, fmt.Errorf("%s is not an IP", target)
+	}
+	names, err := net.LookupAddr(target)
+	if err != nil {
+		return nil, err
+	}
+	if len(names) == 0 {
+		return names, fmt.Errorf("no names found for ip: %s", target)
+	}
+
+	for i, name := range names {
+		names[i] = stringsutil.TrimSuffixAny(name, ".")
+	}
+
+	return names, nil
+}
diff --git a/ip/iputil_test.go b/ip/iputil_test.go
index ff3ba22..cc93493 100644
--- a/ip/iputil_test.go
+++ b/ip/iputil_test.go
@@ -108,3 +108,11 @@ func TestWhatsMyIP(t *testing.T) {
 	_, err := WhatsMyIP()
 	require.Nil(t, err, "couldn't retrieve ip")
 }
+
+func TestToFQDN(t *testing.T) {
+	// we can't compare the ip with local interfaces as it might be the external gateway one
+	// so we just verify we can contact the api endpoint
+	fqdns, err := ToFQDN("1.1.1.1")
+	require.Nil(t, err, "couldn't retrieve ip")
+	require.NotNil(t, fqdns)
+}