From 9e7578fb294628bca41a37884e4b1297c2371058 Mon Sep 17 00:00:00 2001
From: Cuong Manh Le <cuong@windscribe.com>
Date: Fri, 23 Dec 2022 01:49:01 +0700
Subject: [PATCH] cmd/ctrld: use better approach for checking IPv6 available

Some operating systems may throw a confirmation dialog when attempting
to listen on any interface other than loopback. A better approach is
checking for any interface which is up and can be routed IP traffic.
---
 cmd/ctrld/net.go | 6 ++++--
 go.mod           | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/cmd/ctrld/net.go b/cmd/ctrld/net.go
index 76265d8..ce98405 100644
--- a/cmd/ctrld/net.go
+++ b/cmd/ctrld/net.go
@@ -3,6 +3,8 @@ package main
 import (
 	"net"
 	"sync"
+
+	"golang.org/x/net/nettest"
 )
 
 var (
@@ -11,8 +13,8 @@ var (
 )
 
 func probeStack() {
-	if ln, err := net.Listen("tcp6", "[::]:0"); err == nil {
-		ln.Close()
+	// TODO(cuonglm): use nettest.SupportsIPv6 once https://github.com/golang/go/issues/57386 fixed.
+	if _, err := nettest.RoutedInterface("ip6", net.FlagUp); err == nil {
 		ipv6Enabled = true
 	}
 }
diff --git a/go.mod b/go.mod
index 668925e..f6d12e4 100644
--- a/go.mod
+++ b/go.mod
@@ -13,6 +13,7 @@ require (
 	github.com/spf13/cobra v1.4.0
 	github.com/spf13/viper v1.9.0
 	github.com/stretchr/testify v1.8.0
+	golang.org/x/net v0.1.0
 	golang.org/x/sys v0.1.0
 	tailscale.com v1.34.1
 )
@@ -45,7 +46,6 @@ require (
 	golang.org/x/crypto v0.0.0-20220829220503-c86fa9a7ed90 // indirect
 	golang.org/x/exp v0.0.0-20220827204233-334a2380cb91 // indirect
 	golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 // indirect
-	golang.org/x/net v0.1.0 // indirect
 	golang.org/x/text v0.4.0 // indirect
 	golang.org/x/tools v0.1.12 // indirect
 	gopkg.in/ini.v1 v1.66.2 // indirect