如果引发异常，.Net Web API有时会完全不返回任何响应

Question

First of all a bit of background.
I am using .Net Framework 4.6.1, Microsoft.AspNet.WebApi 5.2.4 in Visual Studio 2017 Community.

My ApiController's implement endpoints which throw intended Exceptions for example if certain requirements are not met. I added global ExceptionFilterAttribute and ExceptionHandler to handle those Exceptions and to return a proper response. The Exceptions are of a type which are inherited of System.Exception.
This is only working occasionally as intended. Every second or third or sometimes fifth (no real pattern) request the api server returns no response at all eg for example Postman says: "Could not get any response".
To test this I used the same endpoint with the same input.

Here are a few things I did to get a better idea of the problem:
I added exception logging to Global.asax (to catch First Chance Exceptions)
I subscribed to Global.asax Application_Error Event
I looked at the IIS logs

None of those got my closer to the issue. The exception was caught and logged in Global.asax like expected but no additional error or exception which could give me more info to my problem.

Here is my code:
I simplified the ApiController's function and removed the business logic.

[Route("test")]
[HttpGet]
public IHttpActionResult GetTest()
{
    throw new ObjectAlreadyExistsException("test");
    return ResponseFactory.CreateOkResponse(null);
}

public class ExceptionFilter : ExceptionFilterAttribute
{
    public override void OnException(HttpActionExecutedContext context)
    {
        if (context.Exception is ObjectAlreadyExistsException)
        {
            context.Response = ResponseFactory.CreateErrorResponseMessage(context.Exception.Message, new Error("OBJECT_ALREADY_EXISTS_ERROR", context.Exception.Message));
        }
        else if (context.Exception is ObjectNotFoundException)
        {
            context.Response = ResponseFactory.CreateErrorResponseMessage(context.Exception.Message, new Error("OBJECT_NOT_FOUND_ERROR", context.Exception.Message));
        }

        base.OnException(context);
    }
}

public class GlobalExceptionHandler : ExceptionHandler
{
    private static readonly ILogger Log = new LoggerConfiguration()
            .WriteTo.File(new CompactJsonFormatter(), Path.Combine(@Properties.Settings.Default.LOG_DIRECTORY, @"error.json"), rollOnFileSizeLimit: true, retainedFileCountLimit: 5, shared: true)
            .Enrich.WithWebApiControllerName()
            .Enrich.WithWebApiActionName()
            .Enrich.WithWebApiRouteTemplate()
            .Enrich.WithWebApiRouteData()
            .Enrich.With(new AuthTokenEnricher())
            .CreateLogger();

    public override void Handle(ExceptionHandlerContext context)
    {
        if (context != null && context.Exception != null)
        {
            Log.Error("Unexpected Internal Server Error {Exception}", context.Exception);
        }

        context.Result = ResponseFactory.CreateErrorResponse(HttpStatusCode.InternalServerError, "Unexpected Internal Server Error", new Error("INTERNAL_SERVER_ERROR", "This request failed because of an unexpected server error."));
    }
}

public static class WebApiConfig
{
    public static void Register(HttpConfiguration config)
    {

        //Exception filters
        config.Filters.Add(new ExceptionFilter());
        config.Services.Replace(typeof(IExceptionHandler), new GlobalExceptionHandler());

        // Web API routes
        config.MapHttpAttributeRoutes();
    }
}

public class ObjectAlreadyExistsException : Exception
{
    public ObjectAlreadyExistsException(string message) : base(message)
    {
    }

    public ObjectAlreadyExistsException(string message, Exception inner) : base(message, inner)
    {
    }
}

For now I put a workaround in place which looks like this:

[Route("test")]
[HttpGet]
public IHttpActionResult GetTest()
{
    try
    {
        throw new ObjectAlreadyExistsException("test");
    }
    catch (Exception ex)
    {
        return CustomExceptionHandler.Handle(ex);
    }
}

public class CustomExceptionHandler
{
    private static readonly ILogger Log = new LoggerConfiguration()
            .WriteTo.File(new CompactJsonFormatter(), Path.Combine(@Properties.Settings.Default.LOG_DIRECTORY, @"error.json"), rollOnFileSizeLimit: true, retainedFileCountLimit: 5, shared: true)
            .Enrich.WithWebApiControllerName()
            .Enrich.WithWebApiActionName()
            .Enrich.WithWebApiRouteTemplate()
            .Enrich.WithWebApiRouteData()
            .Enrich.With(new AuthTokenEnricher())
            .CreateLogger();

    public static IHttpActionResult Handle(Exception ex)
    {
        IHttpActionResult result = null;

        if (ex != null)
        {
            if (ex is ObjectAlreadyExistsException)
            {
                result = ResponseFactory.CreateErrorResponse(ex.Message, new Error("OBJECT_ALREADY_EXISTS_ERROR", ex.Message));
            }
            else if (ex is ObjectNotFoundException)
            {
                result = ResponseFactory.CreateErrorResponse(ex.Message, new Error("OBJECT_NOT_FOUND_ERROR", ex.Message));
            }
        }

        if (result == null)
        {
            if (ex != null)
            {
                Log.Error("Unexpected Internal Server Error {Exception}", ex);
            }

            result = ResponseFactory.CreateErrorResponse(HttpStatusCode.InternalServerError, "Unexpected Internal Server Error", new Error("INTERNAL_SERVER_ERROR", "This request failed because of an unexpected server error."));
        }

        return result;
    }
}

I would appreciate any ideas how to debug this or any suggestions to fix it.

Answer 1

Can you try inheriting from IHttpActionResult and use it as returning the exception from your GlobalExceptionHandler

 private class ErrorMessageResult : IHttpActionResult
    {
        private readonly HttpResponseMessage _httpResponseMessage;
        private HttpRequestMessage _request;

        public ErrorMessageResult(HttpRequestMessage request, HttpResponseMessage httpResponseMessage)
        {
            _request = request;
            _httpResponseMessage = httpResponseMessage;
        }

        public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
        {
            return Task.FromResult(_httpResponseMessage);
        }
    }

and call it like,

public override void Handle(ExceptionHandlerContext context)
{
    var result = new HttpResponseMessage(HttpStatusCode.InternalServerError)
    {
        Content = new StringContent("Internal Server Error Occurred"),
        ReasonPhrase = "Exception"
    };

    context.Result = new ErrorMessageResult(context.Request, result);
}

From GlobalExceptionHandler : ExceptionHandler