feat(dns_resolver): add custom DNS server support for reverse lookups

- Use config.DNSServers for reverse DNS lookups
- Try each configured DNS server with fallback
- Add proper port handling (default :53)

Author: lordixir

modules/dns_resolver.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"ipmap/config"
 	"net"
+	"strings"
 	"time"
 )
 
@@ -18,6 +19,19 @@ func ReverseDNS(ip string) string {
 			d := net.Dialer{
 				Timeout: time.Second * 2,
 			}
+			// Use custom DNS servers if configured
+			if len(config.DNSServers) > 0 {
+				for _, dns := range config.DNSServers {
+					dnsAddr := strings.TrimSpace(dns)
+					if !strings.Contains(dnsAddr, ":") {
+						dnsAddr = dnsAddr + ":53"
+					}
+					conn, err := d.DialContext(ctx, network, dnsAddr)
+					if err == nil {
+						return conn, nil
+					}
+				}
+			}
 			return d.DialContext(ctx, network, address)
 		},
 	}