HttpClient is eating useful exception information

[MihaZupan]

Consider a scenario like the .NET 6 connection pool issue w.r.t. ConnectTimeout, here's the exception you'd see if you used HttpClient:

System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at System.Net.Http.HttpClient.HandleFailure(Exception e, Boolean telemetryStarted, HttpResponseMessage response, CancellationTokenSource cts, CancellationToken cancellationToken, CancellationTokenSource pendingRequestsCts)
   at System.Net.Http.HttpClient.<SendAsync>g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)

and if you used HttpMessageInvoker instead:

System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at System.Threading.Tasks.TaskCompletionSourceWithCancellation`1.WaitWithCancellationAsync(CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.HttpConnectionWaiter`1.WaitForConnectionAsync(Boolean async, CancellationToken requestCancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken)
   at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)

and a similar example in .NET 5:

System.Threading.Tasks.TaskCanceledException: The operation was canceled.
   at System.Net.Http.ConnectHelper.ConnectAsync(Func`3 callback, DnsEndPoint endPoint, HttpRequestMessage requestMessage, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.ConnectAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.CreateHttp11ConnectionAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.GetHttpConnectionAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken)
   at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpClient.SendAsyncCore(HttpRequestMessage request, HttpCompletionOption completionOption, Boolean async, Boolean emitTelemetryStartStop, CancellationToken cancellationToken)

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Part of the reason is that in HttpClient.HadleFailure, we're only capturing the InnerException in some cases

runtime/src/libraries/System.Net.Http/src/System/Net/Http/HttpClient.cs

Line 602 in 7526a4c

e = toThrow = new TaskCanceledException(oce.Message, oce.InnerException, cancellationToken);

In the above example, oce.InnerException is null, and oce itself contains the useful stack trace.

And in this edge case we're throwing away the original exception entirely

runtime/src/libraries/System.Net.Http/src/System/Net/Http/HttpClient.cs

Line 623 in 7526a4c

e = toThrow = new OperationCanceledException(cancellationToken.IsCancellationRequested ? cancellationToken : cts.Token);

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Issue Details

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Consider a scenario like the .NET 6 connection pool issue w.r.t. ConnectTimeout, here's the exception you'd see if you used HttpClient:

System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at System.Net.Http.HttpClient.HandleFailure(Exception e, Boolean telemetryStarted, HttpResponseMessage response, CancellationTokenSource cts, CancellationToken cancellationToken, CancellationTokenSource pendingRequestsCts)
   at System.Net.Http.HttpClient.<SendAsync>g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)

and if you used HttpMessageInvoker instead:

System.Threading.Tasks.TaskCanceledException: A task was canceled.
   at System.Threading.Tasks.TaskCompletionSourceWithCancellation`1.WaitWithCancellationAsync(CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.HttpConnectionWaiter`1.WaitForConnectionAsync(Boolean async, CancellationToken requestCancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken)
   at System.Net.Http.RedirectHandler.SendAsync(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)

Part of the reason is that in HttpClient.HadleFailure, we're only capturing the InnerException in some cases

runtime/src/libraries/System.Net.Http/src/System/Net/Http/HttpClient.cs

Line 602 in 7526a4c

e = toThrow = new TaskCanceledException(oce.Message, oce.InnerException, cancellationToken);

In the above example, oce.InnerException is null, and oce itself contains the useful stack trace.

And in this edge case we're throwing away the original exception entirely

runtime/src/libraries/System.Net.Http/src/System/Net/Http/HttpClient.cs

Line 623 in 7526a4c

e = toThrow = new OperationCanceledException(cancellationToken.IsCancellationRequested ? cancellationToken : cts.Token);

Author:	MihaZupan
Assignees:	-
Labels:	bug, area-System.Net.Http
Milestone:	-