缓冲的流-ASP.NET Core 3.0中不允许进行同步操作 [英] Buffered Stream - Synchronous operations are disallowed in ASP.NET Core 3.0

问题描述

我有一个针对AspNetCore 2.2的REST API，该API的端点允许下载一些大的json文件.迁移到AspNetCore 3.1后，此代码停止工作:

 试试{HttpContext.Response.StatusCode =(int)HttpStatusCode.OK;HttpContext.Response.Headers.Add("Content-Type"，"application/json");使用(var bufferedOutput = new BufferedStream(HttpContext.Response.Body，bufferSize:4 * 1024 * 1024)){等待_downloadService.Download(_applicationId，bufferedOutput);}}抓住(前例外){_logger.LogError(ex，ex.Message);} 

这是下载方法，它创建了我要在HttpContext.Response.Body上返回的json:

 公共异步任务下载(字符串applicationId，流输出，CancellationToken cancelToken =默认(CancellationToken)){使用(var textWriter = new StreamWriter(output，Constants.Utf8)){使用(var jsonWriter = new JsonTextWriter(textWriter)){jsonWriter.Formatting = Formatting.None;等待jsonWriter.WriteStartArrayAsync(cancellationToken);//写入json ...等待jsonWriter.WritePropertyNameAsync("Status"，cancelledToken);等待jsonWriter.WriteValueAsync(someStatus，cancelledToken);等待jsonWriter.WriteEndArrayAsync(cancellationToken);}}} 

现在，我收到此异常:"ASP.NET Core 3.0中不允许进行同步操作"我如何在不使用AllowSynchronousIO = true的情况下更改此代码以使其工作?

解决方案

AllowSynchronousIO 选项默认情况下在( Kestrel ， HttpSys ， IIS进程内， TestServer )，因为这些API是线程饥饿和应用程序挂起的源./p>

对于每次临时迁移的请求，都可以覆盖该选项:

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

您可以找到更多信息，并遵循ASP.NET Core问题跟踪器:在所有情况下均禁用AllowSynchronousIO服务器

I had an REST API targeting AspNetCore 2.2 with an endpoint that allows download of some big json files. After migrating to AspNetCore 3.1 this code stopped working:

    try
    {
        HttpContext.Response.StatusCode = (int)HttpStatusCode.OK;
        HttpContext.Response.Headers.Add("Content-Type", "application/json");

        using (var bufferedOutput = new BufferedStream(HttpContext.Response.Body, bufferSize: 4 * 1024 * 1024))
        {
            await _downloadService.Download(_applicationId, bufferedOutput);
        }
    }
    catch (Exception ex)
    {
        _logger.LogError(ex, ex.Message);                
    }

This is the download method, that created the json that I want to return on the HttpContext.Response.Body:

    public async Task Download(string applicationId, Stream output, CancellationToken cancellationToken = default(CancellationToken))
    {       
        using (var textWriter = new StreamWriter(output, Constants.Utf8))
        {
            using (var jsonWriter = new JsonTextWriter(textWriter))
            {
                jsonWriter.Formatting = Formatting.None;
                await jsonWriter.WriteStartArrayAsync(cancellationToken);

                //write json...
                await jsonWriter.WritePropertyNameAsync("Status", cancellationToken);
                await jsonWriter.WriteValueAsync(someStatus, cancellationToken); 

                await jsonWriter.WriteEndArrayAsync(cancellationToken);
            }
        }
    }

Now I get this exception: "Synchronous operations are disallowed in ASP.NET Core 3.0" How can I change this code to work without using AllowSynchronousIO = true;

解决方案

AllowSynchronousIO option is disabled by default from .Net core 3.0.0-preview3 in (Kestrel, HttpSys, IIS in-process, TestServer) because these APIs are source of thread starvation and application hangs.

The option can be overridden on a per request for a temporary migration :

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

You can find more info and follow the ASP.NET Core Issue Tracker : AllowSynchronousIO disabled in all servers

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