Why is ASP.NET Core's app.UseExceptionHandler() not working?

Question

I have in my startup.cs file:

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

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);
    }
}

Why is this not working?

What will happen then? I mean is the app crashes or do the exception appears in the log? or xyz? — Peter Csala
– Peter Csala, Commented Feb 26, 2021 at 14:34
In debug modus i see on the manual "throw exception" serilog logging "an exception of type xx occured in xxx.dll but was not handled in user code", it then jumps to the lines line of my testmethod of my test controller and returns a 500. — edelwater
– edelwater, Commented Feb 26, 2021 at 14:40
Where did you put the UseExceptionHandler calls before or after the UseRouting and UseEndpoints? — Peter Csala
– Peter Csala, Commented Feb 26, 2021 at 14:48
Please try to register them before. These could be the very first method calls in the Configure. — Peter Csala
– Peter Csala, Commented Feb 26, 2021 at 14:59

Peter Csala · Accepted Answer · 2023-11-13 14:46:26Z

19

It might seem strange but ordering does matter.

UseExceptionHandler and UseRouting are both registering middlewares under the hood.

The firstly registered will be the outer most middleware. So, if one of the inners throws an exception the outer can catch and handle 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.

edited Nov 13, 2023 at 14:46

answered Feb 26, 2021 at 15:25

Peter Csala

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5 Comments

Matthew MacFarland Over a year ago

I was really hoping this simple solution would have fixed my case. My called to UseExceptionHandler is called first, but the unhandled exception still does not call the error handling controller. There must be other causes for this issue.

Peter Csala Over a year ago

Hi @MatthewMacFarland, could you please share further details in order to be able to help you? (If needed please create a new question and paste here the link)

Matthew MacFarland Over a year ago

Hi @PeterCsala, Certainly. I will put my details together and post them soon.

Matthew MacFarland Over a year ago

Hi @PeterCsala, I discovered my problem while getting ready to post details here. I was running in development mode and the call to app.UseExceptionHandler() was only active for when IsDevelopmentMode = false. Silly mistake. Everything works perfectly now.

Peter Csala Over a year ago

Hi @MatthewMacFarland it happens to everyone, no worries. I'm glad that you could solve it on your own.

Peter Csala · Accepted Answer · 2022-12-16 07:20:28Z

3

It didn't help for me so, I changed this

app.UseExceptionHandler("Home/Error");

to this

app.UseExceptionHandler("/Error");

and aldo added an attribute route on the action

[Route("/Error")]
public IActionResult Error()

edited Dec 16, 2022 at 7:20

Peter Csala

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answered Nov 20, 2022 at 10:19

miri W.

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Comments

Mo D Genesis · Accepted Answer · 2023-04-28 21:41:54Z

0

For me it was the route name was not the same as the usEexceptionHandler:

I had

[Route("/errors")]
public IActionResult Error()

and in my program.cs:

app.UseExceptionHandler("/error");

both names must be the same for it to work

answered Apr 28, 2023 at 21:41

Mo D Genesis

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Comments

Gilbert · Accepted Answer · 2024-03-10 10:26:39Z

0

In my case, I set the exception handler to be called before UseEndpoints. If it comes after UseEndpoints the handler never gets called.

var app = builder.Build();
app.UseCors();
app.UseRouting();
app.UseAuthorization();

// should be called before UseEndpoints else the exception handler wont be called
app.UseExceptionHandler(); 
app.UseEndpoints(endpoints => endpoints.MapControllers());
app.MapControllers();
app.Run();

answered Mar 10, 2024 at 10:26

Gilbert

3,42232 silver badges40 bronze badges

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