asp.net core 3.1 中Synchronous operations are disallowed. Call FlushAsync or set AllowSynchronousIO to true instead

　　　　　在進行　Asp.NetCore.MVC  文件上傳時，後臺無法正常讀取文件流保存，出現：Synchronous operations are disallowed. Call WriteAsync or set AllowSynchronousIO to true instead.

 　　查找資料，發現需要添加允許條件，才可以； 感謝：https://www.cnblogs.com/lonelyxmas/p/12060869.html

　　有三種解決方式：第一種：在處理文件的Action 中添加：　　

var syncIOFeature = HttpContext.Features.Get<IHttpBodyControlFeature>();
if (syncIOFeature != null)
{
    syncIOFeature.AllowSynchronousIO = true;
}

　　第二種：或者在Startup.cs 中註冊

 public void ConfigureServices(IServiceCollection services)
        {
            // If using Kestrel:
            services.Configure<KestrelServerOptions>(options =>
            {
                options.AllowSynchronousIO = true;
            });

            // If using IIS:
            services.Configure<IISServerOptions>(options =>
            {
                options.AllowSynchronousIO = true;
            });
}

　　第三種:(不太理解。。。)

            Request.EnableBuffering();
            using (var reader = new StreamReader(Request.Body, encoding: Encoding.UTF8))
            {
                var body = reader.ReadToEndAsync();
                // Do some processing with body…
                // Reset the request body stream position so the next middleware can read it
                Request.Body.Position = 0;
            }