HttpClient throws TaskCanceledException on timeout

[awithy]

HttpClient is throwing a TaskCanceledException on timeout in some circumstances. This is happening for us when the server is under heavy load. We were able to work around by increasing the default timeout. The following MSDN forum thread captures the essence of the experienced issue: https://social.msdn.microsoft.com/Forums/en-US/d8d87789-0ac9-4294-84a0-91c9fa27e353/bug-in-httpclientgetasync-should-throw-webexception-not-taskcanceledexception?forum=netfxnetcom&prof=required

Thanks

[danmoseley]

@awithy what version of .NET Core are you using?

[awithy]

1.1

[stephentoub]

Whether the right design or not, by design OperationCanceledExceptions are thrown for timeouts (and TaskCanceledException is an OperationCanceledException).
cc: @davidsh

[awithy]

Our team found this unintuitive, but it does seem to be working as designed. Unfortunately, when we hit this, we wasted a bit of time trying to find a source of cancelation. Having to handle this scenario differently from task cancelation is pretty ugly (we created custom handler to manage this). This also seems to be an overuse of cancelation as a concept.

Thanks again for thee quick response.

[karelz]

Seems like by design + there were only 2 customers complains in last 6+ months.
Closing.

[jamescrowley]

@karelz adding a note as another customer impacted by this misleading exception :)

[karelz]

Thanks for info, please upvote also top post (issues can be sorted by it), thanks!

[thomaslevesque]

Whether the right design or not, by design OperationCanceledExceptions are thrown for timeouts

This is a bad design IMO. There's no way to tell if the request was actually canceled (i.e. the cancellation token passed to SendAsync was canceled) or if the timeout was elapsed. In the latter case, it would make sense to retry, whereas in the former case it wouldn't. There's a TimeoutException that would be perfect for this case, why not use it?

[csrowell]

Yeah, this also threw our team for a loop. There's an entire Stack Overflow thread dedicated to trying to deal with it: https://stackoverflow.com/questions/10547895/how-can-i-tell-when-httpclient-has-timed-out/32230327#32230327

[thomaslevesque]

I published a workaround a few days ago: https://www.thomaslevesque.com/2018/02/25/better-timeout-handling-with-httpclient/

[csrowell]

Awesome, thanks.

[karelz]

Reopening as the interest is now bigger - the StackOverflow thread has now 69 upvotes.

cc @dotnet/ncl

[Davilink]

Any news ? Still happen in dotnet core 2.0

[adydeshmukh]

Don't see a Timeout exception wrapped inside TaskCanceledException on PostAsync() call, it is returning under aggregate exception - .net version 4.5
System.AggregateException: One or more errors occurred. (A task was canceled.)
---> System.Threading.Tasks.TaskCanceledException: A task was canceled.
--- End of inner exception stack trace ---
at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
at System.Threading.Tasks.Task1.GetResultCore(Boolean waitCompletionNotification) at System.Threading.Tasks.Task1.get_Result()

[wfurt]

This discussion his not relevant to .NET Framework @adydeshmukh. That is completely different implementation.