fix: improve iSH compatibility and DNS reliability

Configure global DNS resolver to use Yandex DNS by default.
Apply wrapISHListener to the manual captcha server to fix the missing syscall in iSH.

client/main.go

@@ -1783,7 +1783,31 @@ func oneTurnConnectionLoop(ctx context.Context, turnParams *turnParams, peer *ne
 	}
 }
 
+func setupGlobalResolver() {
+	dialer := &net.Dialer{
+		Timeout:   5 * time.Second,
+		KeepAlive: 30 * time.Second,
+	}
+	dnsServers := []string{"77.88.8.8:53", "77.88.8.1:53", "8.8.8.8:53", "8.8.4.4:53", "1.1.1.1:53", "1.0.0.1:53"}
+
+	net.DefaultResolver = &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
+			var lastErr error
+			for _, dns := range dnsServers {
+				conn, err := dialer.DialContext(ctx, "udp", dns)
+				if err == nil {
+					return conn, nil
+				}
+				lastErr = err
+			}
+			return nil, lastErr
+		},
+	}
+}
+
 func main() {
+	setupGlobalResolver()
 	ctx, cancel := context.WithCancel(context.Background())
 	globalAppCancel = cancel
 	defer cancel()

client/manual_captcha.go

@@ -361,11 +361,16 @@ func startCaptchaServer(srv *http.Server, logPrefix string) error {
 			continue
 		}
 		listening = true
+		wrappedListener, err := wrapISHListener(listener)
+		if err != nil {
+			log.Printf("%s: failed to wrap listener for iSH: %v", logPrefix, err)
+			wrappedListener = listener
+		}
 		go func(listener net.Listener) {
 			if err := srv.Serve(listener); err != nil && !errors.Is(err, http.ErrServerClosed) {
 				log.Printf("%s: %s", logPrefix, err)
 			}
-		}(listener)
+		}(wrappedListener)
 	}
 
 	if listening {
@@ -385,7 +390,8 @@ func runCaptchaServerAndWait(handler http.Handler, captchaURL string, keyCh <-ch
 
 	fmt.Println("\n==============================================")
 	fmt.Println("ACTION REQUIRED: MANUAL CAPTCHA SOLVING NEEDED")
-	fmt.Println("Open this URL in your browser: " + localCaptchaOrigin())
+	fmt.Println("If your browser didn't open automatically,")
+	fmt.Println("manually open this URL: " + captchaURL)
 	fmt.Println("==============================================")
 	fmt.Println()