WebApi 2: Custom HttpResponseMessage after handling OperationCanceledException in Message Handler is not returned to client - asp.net-web-api2

Question

I am currently investigating in WebApi 2 Message Handler and how to implement a server side timeout using cancellation tokens. If a cancellation occurs a OperationCanceledException is thrown and handled in my Message Handler. In this case I return a HttpResponseMessage with a adequate HttpStatusCode (HttpStatusCode.RequestTimeout).
I expected that my consuming client (using postman) retrieves this HttpStatusCode, but instead "Could not get any response" is displayed, thus my client aborts without any additional information. Could someone explain to me whats the deal with this behavior? What am I missing?
See following example code:
public class RequestTimeoutHandler : DelegatingHandler
{
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
TimeSpan timeout = TimeSpan.FromSeconds(10.0);
using (CancellationTokenSource timeoutCancellationTokenSource = new CancellationTokenSource(timeout))
using (CancellationTokenSource linkedCancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutCancellationTokenSource.Token))
{
try
{
return await base.SendAsync(request, linkedCancellationTokenSource.Token);
}
catch (OperationCanceledException e)
{
return new HttpResponseMessage(HttpStatusCode.RequestTimeout);
}
}
return null;
}
}
My Test Controller Method looks as follows:
[Route("testTimeoutAsyncHandleException"), HttpPost]
public IHttpActionResult TestTimeoutAsynchandle(string hugo, CancellationToken ct)
{
for (int i = 0; i < 500; i++)
{
Thread.Sleep(1000); //sleep 1 sec until exception is thown
if (ct.IsCancellationRequested)
{
ct.ThrowIfCancellationRequested();
}
}
return Ok("yes");
}

Answer 1

turns out, using postman was not my best idea. I created a console application using a httpclient and requested my test method. the httpstatus 408 is returned as expected.