c# - Cancelling an HttpClient Request - Why is TaskCanceledException.CancellationToken.IsCancellationRequested false? -

given following code:

var cts = new cancellationtokensource();  try  {     // "hot" task     var task = new httpclient().getasync("http://www.google.com", cts.token);      // request cancellation     cts.cancel();      await task;      // pass:     assert.fail("expected taskcanceledexception thrown"); } catch (taskcanceledexception ex)  {     // pass:     assert.istrue(cts.token.iscancellationrequested,         "expected cancellation requested on original token");      // fail:     assert.istrue(ex.cancellationtoken.iscancellationrequested,         "expected cancellation requested on token attached exception"); } 

i expect ex.cancellationtoken.iscancellationrequested true inside catch block, not. misunderstanding something?

that's case because httpclient internally (in sendasync) using taskcompletionsource represent async operation. returns taskcompletionsource.task , that's task await on.

it calls base.sendasync , registers continuation on returned task cancels/completes/faults taskcompletionsource's task accordingly.

in case of cancellation uses taskcompletionsource.trysetcanceled associates canceled task new cancellationtoken (default(cancellationtoken)).

you can see looking @ taskcanceledexception. on top of ex.cancellationtoken.iscancellationrequested being false ex.cancellationtoken.canbecanceled false, meaning cancellationtoken can never canceled wasn't created using cancellationtokensource.

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imo should using taskcompletionsource.trysetcanceled(cancellationtoken) instead. way taskcompletionsource associated cancellationtoken passed in consumer , not default cancellationtoken. think it's bug (though minor one) , submitted issue on connect it.