HttpClient 似乎忽略了 Timeout 属性

Question

MultiPartContent我试图通过返回响应来从服务器加载大量数据。但是，在该HttpGet方法期间，我设置的超时值将被忽略。我正在尝试设置更长的超时，因为在这种情况下等待是可以的。

我尝试过 10 分钟到 2 小时之间的各种超时值。实际上，用户第一次使用我们的应用程序时只需等待约 5 分钟，其他时候等待的时间会更少。我还尝试存储 HttpClient 的引用，以确保 api.HttpClient 不会每次都重新创建 HttpClient 对象。

var handler = new HttpClientHandler();
var progress = new ProgressMessageHandler(handler);
var api = APIHelpers.GetSession(progress);

progress.HttpReceiveProgress += (e, args) => ProgressChanged.Invoke(e, new SyncEventArgs(GlobalEnums.SyncStage.Downloading, args.ProgressPercentage * 0.01f));

api.HttpClient.Timeout = new TimeSpan(0, 10, 0);

var downloadUri = BuildURI();
var response = await api.HttpClient.GetAsync(downloadUri, HttpCompletionOption.ResponseHeadersRead);

我希望应用程序在抛出超时异常之前等待 10 分钟，但异常是在 100 秒后抛出的（我相信这是默认值？）。设置后检查该HttpClient.Timeout值确实表明它设置正确。

该APIHelpers.GetSession()方法返回一个带有创建的授权标头的 API 对象。该HttpClient对象可通过继承的类访问。这是由 Swashbuckle 和 Swagger 创建的。我api.HttpClient.Timeout = x之前已经成功使用过这种方式，所以我认为这不是问题。它似乎特别针对这种情况。

抛出的异常：

{System.Net.Http.HttpRequestException: An error occurred while sending the request ---> System.Net.WebException: The operation has timed out.
  at System.Net.HttpWebRequest.RunWithTimeoutWorker[T] (System.Threading.Tasks.Task`1[TResult] workerTask, System.Int32 timeout, System.Action abort, System.Func`1[TResult] aborted, System.Threading.CancellationTokenSource cts) [0x000f8] in <a1ab7fc4639d4d84af41d68234158b1c>:0 
  at System.Net.HttpWebRequest.EndGetResponse (System.IAsyncResult asyncResult) [0x00019] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System/System.Net/HttpWebRequest.cs:1200 
  at System.Threading.Tasks.TaskFactory`1[TResult].FromAsyncCoreLogic (System.IAsyncResult iar, System.Func`2[T,TResult] endFunction, System.Action`1[T] endAction, System.Threading.Tasks.Task`1[TResult] promise, System.Boolean requiresSynchronization) [0x0000f] in <939d99b14d934342858948926287beba>:0 
--- End of stack trace from previous location where exception was thrown ---

  at System.Net.Http.MonoWebRequestHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x003d1] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System.Net.Http/MonoWebRequestHandler.cs:499 
   --- End of inner exception stack trace ---
  at System.Net.Http.MonoWebRequestHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x0046a] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System.Net.Http/MonoWebRequestHandler.cs:503 
  at Microsoft.Rest.RetryDelegatingHandler+<>c__DisplayClass11_0.<SendAsync>b__1 () [0x000ad] in <6a6c837cafbb4f1faffaba1ff30ca4e3>:0 
  at Microsoft.Rest.RetryDelegatingHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x00150] in <6a6c837cafbb4f1faffaba1ff30ca4e3>:0 
  at System.Net.Http.Handlers.ProgressMessageHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x00087] in <19af20e76ce04547b3fc150a0f8f2d47>:0 
  at System.Net.Http.HttpClient.SendAsyncWorker (System.Net.Http.HttpRequestMessage request, System.Net.Http.HttpCompletionOption completionOption, System.Threading.CancellationToken cancellationToken) [0x0009e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System.Net.Http/System.Net.Http/HttpClient.cs:281 
  at ...

编辑：我只是添加一些我尝试过的其他东西来尝试解决这个问题。

1. 我尝试使用 Xamarin.Forms 中的 DependencyService 来获取每个平台的本机HttpClientHandlers和HttpClient对象，在其中我可以设置每个平台的超时，而不是依赖于Xamarin.Forms为我翻译它。这得到了完全相同的结果。

{System.Net.Http.HttpRequestException: An error occurred while sending the request ---> System.Net.WebException: The operation has timed out.
  at System.Net.HttpWebRequest.RunWithTimeoutWorker[T] (System.Threading.Tasks.Task`1[TResult] workerTask, System.Int32 timeout, System.Action abort, System.Func`1[TResult] aborted, System.Threading.CancellationTokenSource cts) [0x000f8] in <a1ab7fc4639d4d84af41d68234158b1c>:0 
  at System.Net.HttpWebRequest.EndGetResponse (System.IAsyncResult asyncResult) [0x00019] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System/System.Net/HttpWebRequest.cs:1200 
  at System.Threading.Tasks.TaskFactory`1[TResult].FromAsyncCoreLogic (System.IAsyncResult iar, System.Func`2[T,TResult] endFunction, System.Action`1[T] endAction, System.Threading.Tasks.Task`1[TResult] promise, System.Boolean requiresSynchronization) [0x0000f] in <939d99b14d934342858948926287beba>:0 
--- End of stack trace from previous location where exception was thrown ---

  at System.Net.Http.MonoWebRequestHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x003d1] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System.Net.Http/MonoWebRequestHandler.cs:499 
   --- End of inner exception stack trace ---
  at System.Net.Http.MonoWebRequestHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x0046a] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System.Net.Http/MonoWebRequestHandler.cs:503 
  at Microsoft.Rest.RetryDelegatingHandler+<>c__DisplayClass11_0.<SendAsync>b__1 () [0x000ad] in <6a6c837cafbb4f1faffaba1ff30ca4e3>:0 
  at Microsoft.Rest.RetryDelegatingHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x00150] in <6a6c837cafbb4f1faffaba1ff30ca4e3>:0 
  at System.Net.Http.Handlers.ProgressMessageHandler.SendAsync (System.Net.Http.HttpRequestMessage request, System.Threading.CancellationToken cancellationToken) [0x00087] in <19af20e76ce04547b3fc150a0f8f2d47>:0 
  at System.Net.Http.HttpClient.SendAsyncWorker (System.Net.Http.HttpRequestMessage request, System.Net.Http.HttpCompletionOption completionOption, System.Threading.CancellationToken cancellationToken) [0x0009e] in /Library/Frameworks/Xamarin.iOS.framework/Versions/12.14.0.114/src/Xamarin.iOS/mcs/class/System.Net.Http/System.Net.Http/HttpClient.cs:281 
  at ...

2. 我尝试HttpClient为这个 API 调用创建一个新对象，但也没有成功。（这在我的代码中替换Apihelpers.GetSession()）

Answer 1

Xamarin.iOS 和 Xamarin.Android 中存在一个已知问题，即大于 100 秒的 HttpClient.Timeout 值将被忽略。这是因为底层本机 http 客户端的超时设置为 100 秒，因此当 HttpClient.Timeout 值 > 100 秒时，该超时会在 .NET HttpClient 超时之前超时。所有最新的稳定版本都应该修复此问题，因此请确保您已更新。如果您使用的是 Visual Studio 2017，则不会获得修复，您需要获取 VS 2019 才能修复。