From a590c38d8b1f4429535f49ff5cac9655a29483a7 Mon Sep 17 00:00:00 2001
From: eason <85663565+mango766@users.noreply.github.com>
Date: Tue, 17 Mar 2026 13:27:47 +0800
Subject: [PATCH] [client] Fix IPv6 address formatting in DNS address
 construction (#5603)

Replace fmt.Sprintf("%s:%d", ip, port) with net.JoinHostPort() to
properly handle IPv6 addresses that need bracket wrapping (e.g.,
[2606:4700:4700::1111]:53 instead of 2606:4700:4700::1111:53).

Without this fix, configuring IPv6 nameservers causes "too many colons
in address" errors because Go's net.Dial cannot parse the malformed
address string.

Fixes #5601
Related to #4074

Co-authored-by: easonysliu <easonysliu@tencent.com>
---
 client/internal/dns/service_listener.go                | 5 +++--
 client/internal/routemanager/client/client.go          | 4 +++-
 client/internal/routemanager/dnsinterceptor/handler.go | 4 +++-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/client/internal/dns/service_listener.go b/client/internal/dns/service_listener.go
index 806559444..f7ddfd40f 100644
--- a/client/internal/dns/service_listener.go
+++ b/client/internal/dns/service_listener.go
@@ -6,6 +6,7 @@ import (
 	"net"
 	"net/netip"
 	"runtime"
+	"strconv"
 	"sync"
 	"time"
 
@@ -69,7 +70,7 @@ func (s *serviceViaListener) Listen() error {
 		return fmt.Errorf("eval listen address: %w", err)
 	}
 	s.listenIP = s.listenIP.Unmap()
-	s.server.Addr = fmt.Sprintf("%s:%d", s.listenIP, s.listenPort)
+	s.server.Addr = net.JoinHostPort(s.listenIP.String(), strconv.Itoa(int(s.listenPort)))
 	log.Debugf("starting dns on %s", s.server.Addr)
 	go func() {
 		s.setListenerStatus(true)
@@ -186,7 +187,7 @@ func (s *serviceViaListener) testFreePort(port int) (netip.Addr, bool) {
 }
 
 func (s *serviceViaListener) tryToBind(ip netip.Addr, port int) bool {
-	addrString := fmt.Sprintf("%s:%d", ip, port)
+	addrString := net.JoinHostPort(ip.String(), strconv.Itoa(port))
 	udpAddr := net.UDPAddrFromAddrPort(netip.MustParseAddrPort(addrString))
 	probeListener, err := net.ListenUDP("udp", udpAddr)
 	if err != nil {
diff --git a/client/internal/routemanager/client/client.go b/client/internal/routemanager/client/client.go
index bad616271..e6ef8b876 100644
--- a/client/internal/routemanager/client/client.go
+++ b/client/internal/routemanager/client/client.go
@@ -3,7 +3,9 @@ package client
 import (
 	"context"
 	"fmt"
+	"net"
 	"reflect"
+	"strconv"
 	"time"
 
 	log "github.com/sirupsen/logrus"
@@ -564,7 +566,7 @@ func HandlerFromRoute(params common.HandlerParams) RouteHandler {
 		return dnsinterceptor.New(params)
 	case handlerTypeDynamic:
 		dns := nbdns.NewServiceViaMemory(params.WgInterface)
-		dnsAddr := fmt.Sprintf("%s:%d", dns.RuntimeIP(), dns.RuntimePort())
+		dnsAddr := net.JoinHostPort(dns.RuntimeIP().String(), strconv.Itoa(dns.RuntimePort()))
 		return dynamic.NewRoute(params, dnsAddr)
 	default:
 		return static.NewRoute(params)
diff --git a/client/internal/routemanager/dnsinterceptor/handler.go b/client/internal/routemanager/dnsinterceptor/handler.go
index 4bf0d5476..64f2a8789 100644
--- a/client/internal/routemanager/dnsinterceptor/handler.go
+++ b/client/internal/routemanager/dnsinterceptor/handler.go
@@ -4,8 +4,10 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net"
 	"net/netip"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -249,7 +251,7 @@ func (d *DnsInterceptor) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
 		r.MsgHdr.AuthenticatedData = true
 	}
 
-	upstream := fmt.Sprintf("%s:%d", upstreamIP.String(), uint16(d.forwarderPort.Load()))
+	upstream := net.JoinHostPort(upstreamIP.String(), strconv.FormatUint(uint64(d.forwarderPort.Load()), 10))
 	ctx, cancel := context.WithTimeout(context.Background(), dnsTimeout)
 	defer cancel()