create a Custom Exception Handler Middleware generating response based on client request - exception

Question

How to create a Custom Exception Handler Middleware. This middleware should generate a custom response based on the Calling Client. If the client is requesting via AJAX then the response should be a JSON Response describing the Error otherwise Redirect the client to Error page.
Controller code
public IActionResult Index()
{
return View();
}
public IActionResult Privacy()
{
return View();
}
[ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
public IActionResult Error()
{
return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
}
middleware code
public class ErrorHandlerMiddleware
{
private readonly RequestDelegate _next;
public ErrorHandlerMiddleware(RequestDelegate next)
{
_next = next;
}
public async Task Invoke(HttpContext context)
{
try
{
await _next(context);
}
catch (Exception error)
{
var response = context.Response;
var customError = new CustomError();
switch (error)
{
case AppException e:
// custom application error
customError.StatusCode = (int)HttpStatusCode.BadRequest;
break;
case KeyNotFoundException e:
// not found error
customError.StatusCode = (int)HttpStatusCode.NotFound;
break;
default:
// unhandled error
customError.StatusCode = (int)HttpStatusCode.InternalServerError;
break;
}
customError.ErrorMessage = error?.Message;
if (context.Request.ContentType == "application/json;")
{
var result = JsonSerializer.Serialize(customError);
await response.WriteAsync(result);
}
else
{
context.Response.Redirect("/Errors/CustomError");
}
}
}
Custom Error class code
public class CustomError
{
public int StatusCode { get; set; }
public string ErrorMessage { get; set; }
}
Error View model
public class ErrorViewModel
{
public string RequestId { get; set; }
public bool ShowRequestId => !string.IsNullOrEmpty(RequestId);
}

Answer 1

you could add the code in your startup class:
app.UseStatusCodePagesWithReExecute("/errors/{0}");
add a controller(In my case I tested with HttpContext.Request.Headers["Content-Type"] ,it should be context.Request.ContentType == "application/json;" for MVC project ):
public class ErrorsController : Controller
{
[Route("errors/{statusCode}")]
public IActionResult CustomError(int statusCode)
{
if (HttpContext.Request.Headers["Content-Type"] == "application/json")
{
var cuserr = new CustomError() { ErrorMessage = "err", StatusCode = statusCode };
return new JsonResult(cuserr);
}
else
{
if (statusCode == 404)
{
return View("~/Views/Errors/404.cshtml");
}
return View("~/Views/Errors/500.cshtml");
}
}
}
and the views:
The result:
for more details,you could read the offcial document:
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/error-handling?view=aspnetcore-6.0