From 37de5441c188265f55cc0e412ef18671df9c5609 Mon Sep 17 00:00:00 2001
From: Cuong Manh Le <cuong@windscribe.com>
Date: Tue, 31 Jan 2023 21:36:24 +0700
Subject: [PATCH] cmd/ctrld: silent DHCPv6 error

It's hard to imagine a system with IPv6 but not IPv4, so silent the
DHCPv6 error if any.
---
 cmd/ctrld/cli.go      |  6 +++---
 cmd/ctrld/os_linux.go | 42 +++++++++++++++++-------------------------
 2 files changed, 20 insertions(+), 28 deletions(-)

diff --git a/cmd/ctrld/cli.go b/cmd/ctrld/cli.go
index 5c897a4..9fff2f8 100644
--- a/cmd/ctrld/cli.go
+++ b/cmd/ctrld/cli.go
@@ -221,8 +221,8 @@ func initCLI() {
 				{s.Start, true},
 			}
 			if doTasks(tasks) {
-				mainLog.Info().Msg("Service started")
 				prog.setDNS()
+				mainLog.Info().Msg("Service started")
 			}
 		},
 	}
@@ -252,8 +252,8 @@ func initCLI() {
 			}
 			initLogging()
 			if doTasks([]task{{s.Stop, true}}) {
-				mainLog.Info().Msg("Service stopped")
 				prog.resetDNS()
+				mainLog.Info().Msg("Service stopped")
 			}
 		},
 	}
@@ -321,8 +321,8 @@ func initCLI() {
 			}
 			initLogging()
 			if doTasks(tasks) {
-				mainLog.Info().Msg("Service uninstalled")
 				prog.resetDNS()
+				mainLog.Info().Msg("Service uninstalled")
 				return
 			}
 		},
diff --git a/cmd/ctrld/os_linux.go b/cmd/ctrld/os_linux.go
index 4439bd9..53d52b9 100644
--- a/cmd/ctrld/os_linux.go
+++ b/cmd/ctrld/os_linux.go
@@ -14,7 +14,7 @@ import (
 
 	"github.com/insomniacslk/dhcp/dhcpv4/nclient4"
 	"github.com/insomniacslk/dhcp/dhcpv6"
-	"github.com/insomniacslk/dhcp/dhcpv6/nclient6"
+	"github.com/insomniacslk/dhcp/dhcpv6/client6"
 	"tailscale.com/net/dns"
 	"tailscale.com/util/dnsname"
 
@@ -84,37 +84,29 @@ func resetDNS(iface *net.Interface) error {
 		ns = append(ns, nameserver.String())
 	}
 
+	// TODO(cuonglm): handle DHCPv6 properly.
 	if supportsIPv6() {
-		c, err := nclient6.New(iface.Name)
+		c := client6.NewClient()
+		conversation, err := c.Exchange(iface.Name)
 		if err != nil {
-			mainLog.Warn().Err(err).Msg("could not create DHCPv6 client")
+			mainLog.Debug().Err(err).Msg("could not exchange DHCPv6")
 			return nil
 		}
-		defer c.Close()
-		ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
-		defer cancel()
-
-		solicit, err := dhcpv6.NewSolicit(iface.HardwareAddr)
-		if err != nil {
-			return fmt.Errorf("dhcpv6.NewSolicit: %w", err)
-		}
-		advertise, err := dhcpv6.NewAdvertiseFromSolicit(solicit)
-		if err != nil {
-			return fmt.Errorf("dhcpv6.NewAdvertiseFromSolicit: %w", err)
-		}
-		msg, err := c.Request(ctx, advertise)
-		if err != nil {
-			return fmt.Errorf("nclient6.Request: %w", err)
-		}
-		nameservers := msg.Options.DNS()
-		for _, nameserver := range nameservers {
-			if nameserver.Equal(net.IPv6zero) {
-				continue
+		for _, packet := range conversation {
+			if packet.Type() == dhcpv6.MessageTypeReply {
+				msg, err := packet.GetInnerMessage()
+				if err != nil {
+					mainLog.Debug().Err(err).Msg("could not get inner DHCPv6 message")
+					return nil
+				}
+				nameservers := msg.Options.DNS()
+				for _, nameserver := range nameservers {
+					ns = append(ns, nameserver.String())
+				}
 			}
-			ns = append(ns, nameserver.String())
 		}
-
 	}
+
 	return ignoringEINTR(func() error {
 		return setDNS(iface, ns)
 	})