Blazor WebAssembly上传大型文件时会在上传过程中卡住，这个问题通常是由于WebSockets的默认配置引起的。要解决这个问题，需要在Client端ConfigureWebHostDefaults ()辅助方法中对WebSockets进行一些设置，以允许文件上传。

以下是一个实例：

public class Program
{
    public static async Task Main(string[] args)
    {
        var builder = WebAssemblyHostBuilder.CreateDefault(args);
        builder.RootComponents.Add("app");

        builder.Services.AddTransient(sp => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) });

        builder.Services.AddApiAuthorization();

        builder.Services.AddSingleton();

        builder.Services.AddScoped();

        builder.Services.AddScoped();

        builder.Services.AddBlazoredLocalStorage();

        builder.Services.AddBlazoredToast();

        builder.Services.AddBlazoredModal();

        builder.Services.AddBlazorContextMenu();

        builder.Services.AddHttpContextAccessor();

        builder.Services.AddHttpClient("ServerAPI", client => client.BaseAddress = new Uri(builder.HostEnvironment.BaseAddress));

        builder.Services.AddScoped(sp => sp.GetService().CreateClient("ServerAPI"));

        builder.Services.Configure(options =>
        {
            options.AllowSynchronousIO = true;
        });

        builder.Services.Configure(options =>
        {
            options.KeepAliveInterval = TimeSpan.FromSeconds(120);
            options.ReceiveBufferSize = 4 * 1024;
        });

        await builder.Build().RunAsync();
    }
}

在此示例中，WebSocketOptions中的ReceiveBufferSize属性设置为4 KB，以确保大文件可以顺利上传。此外，KeepAliveInterval属性允许WebSocket保持打开状态的时间增加到120秒，降低了WebSocket在上传期间关闭的可能性。