Question

When Tasks returned by (asynchronous) ASP.NET Web API controller methods throw exceptions, I would like to translate known exceptions to HttpResponseException. Is there some way to intercept these exceptions, and throw HttpResponseException instead?

The following code snippet should demonstrate the type of asynchronous API controller method I’m talking about.

class ObjectApiController : ApiController
{
    public Task<Object> GetObjectByIdAsync(string id)
    [...]
}

Let me know if I need to provide more information about what I’m trying to do.

EDIT:
Specifically I’d like to know if there’s some kind of hook with which I can intercept exceptions from Tasks returned by ApiController methods, and translate said exceptions to HttpResponseException.

Answer 1

I use an ExceptionFilter to do this:

/// <summary>
/// Formats uncaught exception in a common way, including preserving requested Content-Type
/// </summary>
public class FormatExceptionsFilterAttribute : ExceptionFilterAttribute
{

    public override void OnException(HttpActionExecutedContext actionExecutedContext)
    {
        Exception exception = actionExecutedContext.Exception;

        if (exception != null)
        {            
            HttpRequestMessage request = actionExecutedContext.Request;

            // we shouldn't be getting unhandled exceptions
            string msg = "Uncaught exception while processing request {0}: {1}";
            AspLog.Error(msg.Fmt(request.GetCorrelationId().ToString("N"), exception), this); 

            // common errror format, without sending stack dump to the client
            HttpError error = new HttpError(exception.Message);
            HttpResponseMessage newResponse = request.CreateErrorResponse(
                HttpStatusCode.InternalServerError,
                error);
            actionExecutedContext.Response = newResponse; 

        }
    }

}

It is registered like this:

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {
        config.Filters.Add(new ApiControllers.FormatExceptionsFilterAttribute());

        // other stuff
    }
}