In .net 5, When timeout happens, HttpClient throws TaskCaneledException. But the innerException is IOException instead of TimeoutException

[arisewanggithub]

Based on .net 5 document, when timeout happens, HttpClient should throw TaskCanceledException. And the InnerException should be a TimeoutException. But I'm receiving IOException as the InnerException instead. Any reason why this can happen?

[scalablecory]

Based on .net 5 document, when timeout happens, HttpClient should throw TaskCanceledException. And the InnerException should be a TimeoutException. But I'm receiving IOException as the InnerException instead. Any reason why this can happen?

Can you give us a full stack trace and the message of the exceptions?

An IOException indicates the Stream or Socket threw an exception. It may not have been timeout related.

[arisewanggithub]

Here is the stack trace:
at System.Net.Http.HttpConnection.d__56.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Net.Http.HttpConnectionPool.d__72.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Net.Http.RedirectHandler.d__4.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Net.Http.DiagnosticsHandler.d__5.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
at Client.HttpMessageHandlers.RequestTimeoutHandler.d__5.MoveNext()

The RequestTimeoutHandler is an delegating handler we wrote to detect request timeout.
The exception message is: The operation was canceled.

Here is the stack trace info for the InnerException:
at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError error, CancellationToken cancellationToken)
at System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.GetResult(Int16 token)
at System.Net.Http.HttpConnection.d__97.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Net.Http.HttpConnection.RawConnectionStream.d__6.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Net.Security.SslStream.d__181`1.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Net.Http.HttpConnection.d__94.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Net.Http.HttpConnection.d__91.MoveNext()
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Net.Http.HttpConnection.d__56.MoveNext()

Here is the error message for the InnerException:
Unable to read data from the transport connection: The I/O operation has been aborted because of either a thread exit or an application request..

This exception is thrown every time timeout happens. I can use fiddler to set send mock response and set response delay. Every time it throws this exception.

[arisewanggithub]

OK, got the issue figured out. So this is a .net 5 restriction. The conversion to TimeoutException is at HttpClient level: https://github.com/dotnet/runtime/blob/main/src/libraries/System.Net.Http/src/System/Net/Http/HttpClient.cs#L586-L591
So capturing this inside a delegating handler can't detect the TimeoutException.