chore: Better reverse DNS resolving

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"github.com/go-git/go-git/v5"
@@ -94,6 +95,71 @@ func updateRunner() {
 	}
 }
 
+func resolver(addr string) net.Resolver {
+	var (
+		dnsResolverProto     = "udp" // Protocol to use for the DNS resolver
+		dnsResolverTimeoutMs = 5000  // Timeout (ms) for the DNS resolver (optional)
+	)
+
+	return net.Resolver{
+		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+			d := net.Dialer{
+				Timeout: time.Duration(dnsResolverTimeoutMs) * time.Millisecond,
+			}
+			return d.DialContext(ctx, dnsResolverProto, addr)
+		},
+	}
+}
+
+func reverseDNS(ip net.IP) ([]string, error) {
+	results := make([]string, 0)
+
+	// resolve using system resolver
+	names, err := net.LookupAddr(ip.String())
+	if err == nil {
+		results = append(results, names...)
+	}
+
+	// resolve using 1.1.1.1
+	cloudflare := resolver("1.1.1.1")
+	names, err = cloudflare.LookupAddr(context.Background(), ip.String())
+	if err == nil {
+		results = append(results, names...)
+	} else {
+		log.Tracef("Failed to resolve reverse DNS using Cloduflare for %s: %s", ip.String(), err.Error())
+	}
+
+	// resolve using 8.8.8.8
+	google := resolver("8.8.8.8")
+	names, err = google.LookupAddr(context.Background(), ip.String())
+	if err == nil {
+		results = append(results, names...)
+	} else {
+		log.Tracef("Failed to resolve reverse DNS using Google for %s: %s", ip.String(), err.Error())
+	}
+
+	// resolve using 77.88.8.8
+	yandex := resolver("77.88.8.8")
+	names, err = yandex.LookupAddr(context.Background(), ip.String())
+	if err == nil {
+		results = append(results, names...)
+	} else {
+		log.Tracef("Failed to resolve reverse DNS using Yandex for %s: %s", ip.String(), err.Error())
+	}
+
+	// remove duplicates
+	unique := make(map[string]struct{})
+	for _, v := range results {
+		unique[v] = struct{}{}
+	}
+
+	results = make([]string, 0, len(unique))
+	for k := range unique {
+		results = append(results, k)
+	}
+	return results, nil
+}
+
 func update(repository *git.Repository, branch string, auth transport.AuthMethod, fileName string) {
 	type structuredBlacklist []string
 
@@ -269,11 +335,13 @@ func update(repository *git.Repository, branch string, auth transport.AuthMethod
 		logMessages.WriteString(fmt.Sprintf("server='%s' addr='%s'", v.Server, v.IP.String()))
 
 		commitMessage.WriteString(v.IP.String())
-		reverseDNSNames, err := net.LookupAddr(v.IP.String())
+		reverseDNSNames, err := reverseDNS(v.IP)
 		if err == nil {
-			line := fmt.Sprintf(" hostname='%s'", reverseDNSNames[0])
-			commitMessage.WriteString(line)
-			logMessages.WriteString(line)
+			for _, name := range reverseDNSNames {
+				line := fmt.Sprintf(" hostname='%s'", name)
+				commitMessage.WriteString(line)
+				logMessages.WriteString(line)
+			}
 		} else {
 			log.Warnf("Failed to lookup reverse DNS for %s: %s", v.IP.String(), err.Error())
 		}