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:
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);
}
这是下载方法,它创建了我想在HttpContext.Response.Body上返回的json:
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);
}
}
}
现在,我收到此异常:“ ASP.NET Core 3.0中不允许进行同步操作”如何在不使用AllowSynchronousIO = true的情况下更改此代码以使其工作?
[AllowSynchronousIO
选项默认情况下是从[.Net core 3.0.0-preview3
,Kestrel
,HttpSys
,IIS in-process
)中的TestServer
禁用的,因为这些API是线程饥饿和应用程序挂起的源。
对于临时迁移,每个请求都可以覆盖该选项:
var allowSynchronousIoOption = HttpContext.Features.Get<IHttpBodyControlFeature>();
if (allowSynchronousIoOption != null)
{
allowSynchronousIoOption.AllowSynchronousIO = true;
}
您可以找到更多信息并关注ASP.NET Core问题跟踪器:AllowSynchronousIO disabled in all servers
通过退出using子句之前调用FlushAsync和DisposeAsync,您可以停止在编写器处置期间发生的同步操作。 BufferedStream似乎有同步写入问题,如何在StreamWriter中控制缓冲区大小。
using (var streamWriter = new StreamWriter(context.Response.Body, Encoding.UTF8, 1024))
using (var jsonWriter = new JsonTextWriter(streamWriter))
{
jsonWriter.Formatting = Formatting.None;
await jsonWriter.WriteStartObjectAsync();
await jsonWriter.WritePropertyNameAsync("test");
await jsonWriter.WriteValueAsync("value " + new string('a', 1024 * 65));
await jsonWriter.WriteEndObjectAsync();
await jsonWriter.FlushAsync();
await streamWriter.FlushAsync();
await streamWriter.DisposeAsync();
}
通过这种方式,您可以在没有AllowSynchronousIO = true
的情况下进行少量更改就可以工作代码>