internal/controld: check if ipv4 is available before connect to API

Updates #53

cmd/ctrld/cli.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/Control-D-Inc/ctrld"
 	"github.com/Control-D-Inc/ctrld/internal/controld"
+	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 )
 
 var (
@@ -105,7 +106,7 @@ func initCLI() {
 				log.Fatalf("failed to unmarshal config: %v", err)
 			}
 			// Wait for network up.
-			if !netUp() {
+			if !ctrldnet.Up() {
 				log.Fatal("network is not up yet")
 			}
 			processLogAndCacheFlags()

cmd/ctrld/dns_proxy.go

@@ -15,6 +15,7 @@ import (
 
 	"github.com/Control-D-Inc/ctrld"
 	"github.com/Control-D-Inc/ctrld/internal/dnscache"
+	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 )
 
 const staleTTL = 60 * time.Second
@@ -55,7 +56,7 @@ func (p *prog) serveUDP(listenerNum string) error {
 
 	// On Windows, there's no easy way for disabling/removing IPv6 DNS resolver, so we check whether we can
 	// listen on ::1, then spawn a listener for receiving DNS requests.
-	if runtime.GOOS == "windows" && supportsIPv6ListenLocal() {
+	if runtime.GOOS == "windows" && ctrldnet.SupportsIPv6() {
 		go func() {
 			s := &dns.Server{
 				Addr:    net.JoinHostPort("::1", strconv.Itoa(listenerConfig.Port)),

cmd/ctrld/net.go

@@ -1,65 +0,0 @@
-package main
-
-import (
-	"context"
-	"net"
-	"sync"
-	"time"
-
-	"tailscale.com/logtail/backoff"
-
-	"github.com/Control-D-Inc/ctrld/internal/controld"
-)
-
-const (
-	controldIPv6Test = "ipv6.controld.io"
-)
-
-var (
-	stackOnce          sync.Once
-	ipv6Enabled        bool
-	canListenIPv6Local bool
-	hasNetworkUp       bool
-)
-
-func probeStack() {
-	b := backoff.NewBackoff("probeStack", func(format string, args ...any) {}, time.Minute)
-	for {
-		if _, err := controld.Dialer.Dial("udp", net.JoinHostPort(bootstrapDNS, "53")); err == nil {
-			hasNetworkUp = true
-			break
-		} else {
-			b.BackOff(context.Background(), err)
-		}
-	}
-	if _, err := controld.Dialer.Dial("tcp6", net.JoinHostPort(controldIPv6Test, "80")); err == nil {
-		ipv6Enabled = true
-	}
-	if ln, err := net.Listen("tcp6", "[::1]:53"); err == nil {
-		ln.Close()
-		canListenIPv6Local = true
-	}
-}
-
-func netUp() bool {
-	stackOnce.Do(probeStack)
-	return hasNetworkUp
-}
-
-func supportsIPv6() bool {
-	stackOnce.Do(probeStack)
-	return ipv6Enabled
-}
-
-func supportsIPv6ListenLocal() bool {
-	stackOnce.Do(probeStack)
-	return canListenIPv6Local
-}
-
-// isIPv6 checks if the provided IP is v6.
-//
-//lint:ignore U1000 use in os_windows.go
-func isIPv6(ip string) bool {
-	parsedIP := net.ParseIP(ip)
-	return parsedIP != nil && parsedIP.To4() == nil && parsedIP.To16() != nil
-}

cmd/ctrld/os_linux.go

@@ -19,6 +19,7 @@ import (
 	"tailscale.com/util/dnsname"
 
 	"github.com/Control-D-Inc/ctrld/internal/dns"
+	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 	"github.com/Control-D-Inc/ctrld/internal/resolvconffile"
 )
 
@@ -111,7 +112,7 @@ func resetDNS(iface *net.Interface) error {
 	}
 
 	// TODO(cuonglm): handle DHCPv6 properly.
-	if supportsIPv6() {
+	if ctrldnet.SupportsIPv6() {
 		c := client6.NewClient()
 		conversation, err := c.Exchange(iface.Name)
 		if err != nil {

cmd/ctrld/os_windows.go

@@ -10,6 +10,8 @@ import (
 	"strconv"
 
 	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
+
+	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 )
 
 // TODO(cuonglm): implement.
@@ -39,7 +41,7 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 
 // TODO(cuonglm): should we use system API?
 func resetDNS(iface *net.Interface) error {
-	if supportsIPv6ListenLocal() {
+	if ctrldnet.SupportsIPv6ListenLocal() {
 		if output, err := netsh("interface", "ipv6", "set", "dnsserver", strconv.Itoa(iface.Index), "dhcp"); err != nil {
 			mainLog.Warn().Err(err).Msgf("failed to reset ipv6 DNS: %s", string(output))
 		}
@@ -54,7 +56,7 @@ func resetDNS(iface *net.Interface) error {
 
 func setPrimaryDNS(iface *net.Interface, dns string) error {
 	ipVer := "ipv4"
-	if isIPv6(dns) {
+	if ctrldnet.IsIPv6(dns) {
 		ipVer = "ipv6"
 	}
 	idx := strconv.Itoa(iface.Index)
@@ -73,7 +75,7 @@ func setPrimaryDNS(iface *net.Interface, dns string) error {
 
 func addSecondaryDNS(iface *net.Interface, dns string) error {
 	ipVer := "ipv4"
-	if isIPv6(dns) {
+	if ctrldnet.IsIPv6(dns) {
 		ipVer = "ipv6"
 	}
 	output, err := netsh("interface", ipVer, "add", "dns", strconv.Itoa(iface.Index), dns, "index=2")

cmd/ctrld/prog.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/Control-D-Inc/ctrld"
 	"github.com/Control-D-Inc/ctrld/internal/dnscache"
+	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 )
 
 var errWindowsAddrInUse = syscall.Errno(0x2740)
@@ -64,7 +65,7 @@ func (p *prog) run() {
 			// resolve it manually and set the bootstrap ip
 			c := new(dns.Client)
 			for _, dnsType := range []uint16{dns.TypeAAAA, dns.TypeA} {
-				if !supportsIPv6() && dnsType == dns.TypeAAAA {
+				if !ctrldnet.SupportsIPv6() && dnsType == dns.TypeAAAA {
 					continue
 				}
 				m := new(dns.Msg)