Exception handling middleware doesn't handle exceptions - Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware is called (ASP.NET Core WebAPI)

Question

I created an exception handling middleware according to this example:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseExceptionHandler("/error");
    
    // ...
}

[AllowAnonymous]
[ApiExplorerSettings(IgnoreApi = true)]
[ApiController]
public class ErrorsController : ControllerBase
{
    [Route("error")]
    public IActionResult Error()
    {
        return Problem();
    }
}

Now let's say that I threw the following exception: throw new Exception("BAX");
My exception handling middleware catches this exception and works great. But the problem is that in console I see the following log:

|ERROR|Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware|An unhandled exception has occurred while executing the request.|System.Exception: BAX (stack trace goes here)

Note: I removed stack trace to make it a little bit shorter.

Maybe I should also say that I use NLog for logging. Here is the configuration of it:

<target xsi:
    type = "ColoredConsole" name = "colored_console"
    layout = "|${level:uppercase=true}|${logger}|${message}|${exception:format=tostring}">
</target >

Question

My exception was caught by Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware. It looks like my exception handling middleware didn't handle the exception. Am I right?

My question is why it works so and how can I fix it?

osman Rahimi · Accepted Answer · 2021-05-17 11:06:08Z

2

The duty of app.UseExceptionHandler("errors") is log errors then redirect users to a page in order to show them a proper message.

First of all, when you have app.UseExceptionHandler("errors") it means, ASP.NET Core redirects to a controller named errors and according to your code, it won't work because your Conroller name is Errors and in your code you defined error as its path.

if you don't want Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware to be called, then you have to write your own middleware and log errors there. here is an example of custom middleware to catch all exceptions.

   public class CustomMiddlewareMiddleware
{
    private readonly RequestDelegate _next;

    public CustomMiddlewareMiddleware(RequestDelegate next)
    {
        _next = next;
    }
    public async Task InvokeAsync(HttpContext httpContext)
    {
        try
        {
            await _next(httpContext);
           
        }
        catch (System.Exception)
        {

            /// log it here and then redirect to spesific path
       
            if (httpContext.Response.StatusCode == 404 && !httpContext.Response.HasStarted)
            {
                httpContext.Request.Path = "/error/404/";
                await _next(httpContext);
            }
        }
      
    }
}

answered May 17, 2021 at 11:06

osman Rahimi

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5 Comments

Boris Makhlin Over a year ago

Thanks for the answer! In my project I don't have app.UseExceptionHandler("errors") -I have app.UseExceptionHandler("error"), so because of this it works great. But why to create a middleware instead of exception filter?

osman Rahimi Over a year ago

in your question, you have this ` app.UseExceptionHandler("/error");` and your controller name is errors, these are not same

Boris Makhlin Over a year ago

ErrorsController doesn't have any route. Route /error is a route to the action method of this controller. As you can see, there is an action method called Error inside of this controller. This action method has the following attribute above: [Route("error")]

Boris Makhlin Over a year ago

But again, I want to know, why I should use a middleware instead of exception filter in this situation?

osman Rahimi Over a year ago

in your comment you said, how can we avoid calling Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware, I thought you might want to have your own middleware.

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