使用ASP.NET Web API,我的ExecutionContext不会在异步操作中流动

我很难理解ExecutionContext背后的机制。

根据我在网上读到的内容,上下文敏感的项目,如安全性(线程主体)、区域性等,应该在执行工作单元的范围内跨异步线程流动。

不过,我遇到了非常令人困惑和潜在危险的bug。我注意到我的线程的CurrentPrincipal在异步执行中丢失了。

下面是ASP.NET Web API场景的示例:

首先,让我们设置一个简单的Web API配置,其中包含两个用于测试的委托处理程序。

除了第一个“DummyHandler”设置线程的主体以及要在上下文中共享的一段数据(请求的关联ID)之外,他们所做的只是写出调试信息并将请求/响应传递出去。

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.MessageHandlers.Add(new DummyHandler());
        config.MessageHandlers.Add(new AnotherDummyHandler());

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}

public class DummyHandler : DelegatingHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        CallContext.LogicalSetData("rcid", request.GetCorrelationId());
        Thread.CurrentPrincipal = new ClaimsPrincipal(new ClaimsPrincipal(new ClaimsIdentity(new[]{ new Claim("http://schemas.xmlsoap.org/ws/2005/05/identity/claims/name", "dgdev") }, "myauthisthebest")));

        Debug.WriteLine("Dummy Handler Thread: {0}", Thread.CurrentThread.ManagedThreadId);
        Debug.WriteLine("User: {0}", (Object)Thread.CurrentPrincipal.Identity.Name);
        Debug.WriteLine("RCID: {0}", CallContext.LogicalGetData("rcid"));

        return base.SendAsync(request, cancellationToken)
                   .ContinueWith(task =>
                       {
                           Debug.WriteLine("Dummy Handler Thread: {0}", Thread.CurrentThread.ManagedThreadId);
                           Debug.WriteLine("User: {0}", (Object)Thread.CurrentPrincipal.Identity.Name);
                           Debug.WriteLine("RCID: {0}", CallContext.LogicalGetData("rcid"));

                           return task.Result;
                       });
    }
}

public class AnotherDummyHandler : MessageProcessingHandler
{
    protected override HttpRequestMessage ProcessRequest(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        Debug.WriteLine("  Another Dummy Handler Thread: {0}", Thread.CurrentThread.ManagedThreadId);
        Debug.WriteLine("  User: {0}", (Object)Thread.CurrentPrincipal.Identity.Name);
        Debug.WriteLine("  RCID: {0}", CallContext.LogicalGetData("rcid"));

        return request;
    }

    protected override HttpResponseMessage ProcessResponse(HttpResponseMessage response, CancellationToken cancellationToken)
    {
        Debug.WriteLine("  Another Dummy Handler Thread: {0}", Thread.CurrentThread.ManagedThreadId);
        Debug.WriteLine("  User: {0}", (Object)Thread.CurrentPrincipal.Identity.Name);
        Debug.WriteLine("  RCID: {0}", CallContext.LogicalGetData("rcid"));

        return response;
    }
}

很简单。接下来,让我们添加一个ApiController来处理HTTPPOST,就好像您在上传文件一样。

public class UploadController : ApiController
{
    public async Task<HttpResponseMessage> PostFile()
    {
        Debug.WriteLine("    Thread: {0}", Thread.CurrentThread.ManagedThreadId);
        Debug.WriteLine("    User: {0}", (Object)Thread.CurrentPrincipal.Identity.Name);
        Debug.WriteLine("    RCID: {0}", CallContext.LogicalGetData("rcid"));

        if (!Request.Content.IsMimeMultipartContent())
        {
            throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
        }

        try
        {
            await Request.Content.ReadAsMultipartAsync(
                new MultipartFormDataStreamProvider(
                    HttpRuntime.AppDomainAppPath + @"upload\temp"));

            Debug.WriteLine("    Thread: {0}", Thread.CurrentThread.ManagedThreadId);
            Debug.WriteLine("    User: {0}", (Object)Thread.CurrentPrincipal.Identity.Name);
            Debug.WriteLine("    RCID: {0}", CallContext.LogicalGetData("rcid"));

            return new HttpResponseMessage(HttpStatusCode.Created);
        }
        catch (Exception e)
        {
            return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, e);
        }
    }
}

在使用Fiddler运行测试时,这是我收到的输出:

Dummy Handler Thread: 63
User: dgdev
RCID: 6d542847-4ceb-4511-85e5-d1b5bf3be476

  Another Dummy Handler Thread: 63
  User: dgdev
  RCID: 6d542847-4ceb-4511-85e5-d1b5bf3be476

    Thread: 63
    User: dgdev
    RCID: 6d542847-4ceb-4511-85e5-d1b5bf3be476

    Thread: 77
    User:                                     <<<  PRINCIPAL IS LOST AFTER ASYNC
    RCID: 6d542847-4ceb-4511-85e5-d1b5bf3be476

  Another Dummy Handler Thread: 63
  User:                                       <<<  PRINCIPAL IS STILL LOST
  RCID: 6d542847-4ceb-4511-85e5-d1b5bf3be476

Dummy Handler Thread: 65
User: dgdev                                   <<<  PRINCIPAL IS BACK?!?
RCID: 6d542847-4ceb-4511-85e5-d1b5bf3be476

更令人困惑的是,当我将以下内容附加到异步行时:

await Request.Content.ReadAsMultipartAsync(
    new MultipartFormDataStreamProvider(..same as before..))
.ConfigureAwait(false); <<<<<<

我现在收到这个输出:

Dummy Handler Thread: 40
User: dgdev
RCID: 8d944500-cb52-4362-8537-dab405fa12a2

  Another Dummy Handler Thread: 40
  User: dgdev
  RCID: 8d944500-cb52-4362-8537-dab405fa12a2

    Thread: 40
    User: dgdev
    RCID: 8d944500-cb52-4362-8537-dab405fa12a2

    Thread: 65
    User: dgdev                               <<<  PRINCIPAL IS HERE!
    RCID: 8d944500-cb52-4362-8537-dab405fa12a2

  Another Dummy Handler Thread: 65
  User:                                       <<<  PRINCIPAL IS LOST
  RCID: 8d944500-cb52-4362-8537-dab405fa12a2

Dummy Handler Thread: 40
User: dgdev
RCID: 8d944500-cb52-4362-8537-dab405fa12a2

这里的重点是这个。async my后面的代码实际上调用了我的业务逻辑,或者只是要求正确设置安全上下文。存在潜在的完整性问题。

有人能帮助我们了解一下正在发生的事情吗?

提前谢谢。