all: use controld dialer for probing network

cmd/ctrld/net.go

@@ -8,11 +8,12 @@ import (
 	"time"
 
 	"tailscale.com/logtail/backoff"
+
+	"github.com/Control-D-Inc/ctrld/internal/controld"
 )
 
 const (
 	controldIPv6Test = "ipv6.controld.io"
-	controldIPv4Test = "ipv4.controld.io"
 )
 
 var (
@@ -28,14 +29,14 @@ func probeStack() {
 	}
 	b := backoff.NewBackoff("probeStack", logf, time.Minute)
 	for {
-		if _, err := net.Dial("tcp", net.JoinHostPort(controldIPv4Test, "80")); err == nil {
+		if _, err := controld.Dialer.Dial("udp", net.JoinHostPort(bootstrapDNS, "53")); err == nil {
 			hasNetworkUp = true
 			break
 		} else {
 			b.BackOff(context.Background(), err)
 		}
 	}
-	if _, err := net.Dial("tcp6", net.JoinHostPort(controldIPv6Test, "80")); err == nil {
+	if _, err := controld.Dialer.Dial("tcp6", net.JoinHostPort(controldIPv6Test, "80")); err == nil {
 		ipv6Enabled = true
 	}
 	if ln, err := net.Listen("tcp6", "[::1]:53"); err == nil {

internal/controld/config.go

@@ -17,7 +17,7 @@ const (
 
 const bootstrapDNS = "76.76.2.0:53"
 
-var dialer = &net.Dialer{
+var Dialer = &net.Dialer{
 	Resolver: &net.Resolver{
 		PreferGo: true,
 		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
@@ -70,7 +70,7 @@ func FetchResolverConfig(uid string) (*ResolverConfig, error) {
 	req.Header.Add("Content-Type", "application/json")
 	transport := http.DefaultTransport.(*http.Transport).Clone()
 	transport.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
-		return dialer.DialContext(ctx, network, addr)
+		return Dialer.DialContext(ctx, network, addr)
 	}
 	client := http.Client{
 		Timeout:   10 * time.Second,