Asp.Net 5/Core app.UseExceptionHandler() not working

Question

I have in startup

(UPDATE: the solution was to move UseRouting under the /api/error routes)

app.UseRouting();

if (env.IsDevelopment()) {               
    app.UseExceptionHandler("/api/error/error-local-development"); 
    SwaggerConfig.Configure(app);              
}
else {             
    app.UseExceptionHandler("/api/error/error");
}

 app.UseCors();
 app.UseHttpsRedirection();
 app.UseDefaultFiles();
 app.UseSpaStaticFiles(); 
 app.UseAuthentication();
 app.UseAuthorization();
 app.UseRequestLocalization(options);
  app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
                endpoints.MapHub<ResultHub>("/hubs/resultHub");
            });


            app.UseSpa(spa =>
            {
                spa.Options.SourcePath = "wwwroot";
            });

But when throw new Exception() in a controller action, the Error controller Methods are never called.

[Route("api/error")]
[ApiController]
[ApiExplorerSettings(IgnoreApi = true)]
public class ErrorController : OwnBaseController
{
    public ErrorController(IApplicationUserService applicationUserService, ILogger<ErrorController> logger, IDiagnosticContext diagnosticContext) : base(applicationUserService, logger, diagnosticContext)
    {
    }

    [Route("error")]
    public IActionResult Error()
    {
        return Problem(); 
    }

    [Route("error-local-development")]
    public IActionResult ErrorLocalDevelopment([FromServices] IWebHostEnvironment webHostEnvironment)
    {
       var context = HttpContext.Features.Get<IExceptionHandlerFeature>();
       return Problem(
            detail: context.Error.StackTrace,
            title: context.Error.Message);
    }
}

Answer 1

It might seem strange but ordering matters.

UseExceptionHandler and UseRouting are both registering middlewares under the hood.

The firstly registered will be the outer most middleware. So if the inner throws exception the outer can catch it and can handle (and/or log) it.

Source

MSDN has some warnings about this, for example:

• Handle Errors in ASP.NET Core's UseStatusCodePagesWithReExecute section

If an endpoint within the app is specified, create an MVC view or Razor page for the endpoint. Ensure UseStatusCodePagesWithReExecute is placed before UseRouting so the request can be rerouted to the status page.

• ASP.NET Core Middleware's Middleware order section

UseExceptionHandler is the first middleware component added to the pipeline. Therefore, the Exception Handler Middleware catches any exceptions that occur in later calls.