Web API 2 - Global Exception Handler not working with TaskCancellation

Question

Code to demonstrate the problem:

Assume Test Thing is an real implementation, such as DB invocation.
The documentation for Web API states that unhanded exceptions will be caught in a global handler allowing you to process them.
If I replace MyErrorHandler with an ExceptionFilter this does indeed work, except the code base I'm working with uses handlers because the error logic is a cross cutting concern and will be the same regardless of where the error came from.
If the type of exception thrown is not a TaskCancelledException this invokes the handler as expected.
I've tried the latest version of Web API too (5.2.3).
The only work around is to add a try/catch block around everywhere that can throw this type of exception, needless to say this is painful and something I wish to avoid hence the use of the handler.

I hate to call this a bug given this is not my code, but after hours of attempts it's starting to feel that way.

using System;
using System.Net;
using System.Threading;
using System.Threading.Tasks;
using System.Web.Http;
using System.Web.Http.ExceptionHandling;

namespace WebApplication3.Controllers
{
    public class TestController : ApiController
    {
        public async Task<string> Get()
        {
            var cancellationTokenSource = new CancellationTokenSource(TimeSpan.FromSeconds(1));
            return await new TestThing().ExecuteAsync(cancellationTokenSource.Token);
        }
    }

    public class MyErrorHandler : ExceptionHandler
    {
        public override Task HandleAsync(ExceptionHandlerContext context, CancellationToken cancellationToken)
        {
            throw new HttpResponseException(HttpStatusCode.InternalServerError);
        }
    }


    public class TestThing
    {
        public async Task<string> ExecuteAsync(CancellationToken cancellationToken)
        {
            // Remove this to see the problem, I don't want to add these
            // try/catch statements all over the codebase.
            try
            {
                await Task.Delay(TimeSpan.FromMinutes(1), cancellationToken);
            }
            catch (Exception ex)
            {
                throw new Exception("Failure...");
            }

            return await Task.FromResult("Testing...");
        }
    }
}

Does this help? [WebApi v2 ExceptionHandler not called](http://stackoverflow.com/questions/22169889/webapi-v2-exceptionhandler-not-called) — Absolom, Sep 14 '15 at 16:36

score 2 · Accepted Answer · answered Sep 16 '15 at 11:08

Given the lack of suggestions or answers I went with a custom message handler.

    public class AsyncFixHandler : DelegatingHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            try
            {
                return await base.SendAsync(request, cancellationToken);
            }
            catch (TaskCanceledException)
            {
                // TODO: Log the issue here
                return new HttpResponseMessage(HttpStatusCode.InternalServerError);
            }
        }
    }

This isn't ideal, but the try/catch is in one place. I'm using this successfully as the solution until something better comes along.

Thanks for this workaround. For others who, like me, want their global exception handler and logger to be engaged, simply throw a new replacement exception instead of returning an HttpResponseMessage — BCA, Jul 02 '16 at 15:18

score 1 · Answer 2 · edited May 23 '17 at 12:09

1

It seems like it's and old bug, and there are some people reporting issues still. I suggest you to create an issue in ASP.NET Github repo and use your workaround or another one for the moment.

edited May 23 '17 at 12:09

Community

1
1

answered Sep 16 '15 at 13:49

Hernan Guzman

1,235
8
14

1

Thanks for the link to the bug report, I never found that in my many attempts to solve/research this. I can confirm this is still a problem in 5.2.3 though :( – Finglas Sep 17 '15 at 06:39

Web API 2 - Global Exception Handler not working with TaskCancellation

2 Answers2