Why (-(StatusPagesWithReexecute)*) Might Not Work with UseExceptionHandler

Custom Error Handling in Kentico 13 with ErrorController and UseExceptionHandler

Introduction

In web applications, handling errors gracefully and displaying user-friendly error pages is crucial for a seamless user experience. In Kentico 13, a modern CMS built on .NET Core, you can configure custom error pages using an ErrorController to capture and handle errors such as 404 (Not Found), 500 (Internal Server Error), and other HTTP error codes.

However, while Kentico 13 offers flexibility in error handling, certain challenges might arise when integrating custom error pages with certain .NET Core middleware configurations, such as UseExceptionHandler or StatusPagesWithReexecute. If you've encountered an issue where StatusPagesWithReexecute does not work as expected with UseExceptionHandler, you're not alone.

This article explores how to properly configure custom error pages in Kentico 13, the role of UseExceptionHandler, and troubleshooting tips related to the StatusPagesWithReexecute setting.

Understanding Custom Error Pages in Kentico 13

In Kentico 13, error handling is an important part of the site configuration. You can configure custom error pages in several ways, but one of the most common and flexible methods is through the use of an ErrorController. The ErrorController can be used to return custom views for specific HTTP error codes.

Here's a simple walkthrough of the steps involved in setting up an ErrorController in a Kentico 13 website.

1. Set Up the ErrorController

To create an ErrorController in Kentico 13, you need to create a controller class in your application that will handle error responses.

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using Microsoft.AspNetCore.Mvc; namespace YourProject.Controllers { public class ErrorController : Controller { // Handle 404 errors public IActionResult NotFound() { return View("Error404"); // Custom 404 view } // Handle 500 errors public IActionResult InternalServerError() { return View("Error500"); // Custom 500 view } // Handle general exceptions public IActionResult Index() { return View("ErrorGeneral"); // Custom error view } } }

In this example, you create an ErrorController that has different action methods for different types of errors. You can customize these methods to handle errors such as 404, 500, or any other HTTP error.

2. Create Custom Error Views

Next, create corresponding views for each error type under the Views/Error directory.

For example, create an Error404.cshtml view for handling 404 errors:

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@{ ViewData["Title"] = "Page Not Found"; } 404 - Page Not Found

Sorry, the page you are looking for cannot be found.

Similarly, create views for Error500.cshtml and ErrorGeneral.cshtml as needed.

3. Configure the Error Handling Middleware

To ensure that your custom error pages are served properly, you need to configure the error handling middleware in your Startup.cs file (or Program.cs if you're using the newer ASP.NET Core startup pattern).

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public class Startup { public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); } else { // Global error handler app.UseExceptionHandler("/Error"); // Custom error page middleware app.UseStatusCodePagesWithReexecute("/Error/{0}"); // Fallback routing for unhandled errors app.UseStatusCodePagesWithReexecute("/Error/{0}"); } // Additional middleware... } }

In this configuration, the UseExceptionHandler middleware is used to handle unhandled exceptions and redirect users to the ErrorController. The UseStatusCodePagesWithReexecute middleware handles different HTTP status codes like 404 and 500.

StatusPagesWithReexecute and UseExceptionHandler

While setting up custom error pages is typically straightforward, there may be certain cases where things don't work as expected. For instance, if you're using StatusPagesWithReexecute together with UseExceptionHandler, you may run into issues where the error page is not rendered properly.

What Is StatusPagesWithReexecute?

StatusPagesWithReexecute is a feature in ASP.NET Core that allows you to show custom error pages for specific HTTP status codes, and it attempts to re-execute the request pipeline. This is useful for situations where you want to display a custom error page without causing a full page reload.

For example, if a 404 error occurs, you can re-execute the request to the error handler (like /Error/404), rather than just rendering an error directly. This can allow for more flexible error handling and more advanced scenarios, such as adding dynamic content to the error pages.

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app.UseStatusCodePagesWithReexecute("/Error/{0}");

This tells the application to show a custom error page when an HTTP error code is returned (like a 404 or 500), by re-executing the request and passing the status code to the ErrorController.

What Is UseExceptionHandler?

UseExceptionHandler is middleware used for catching unhandled exceptions in an application. When an exception occurs, UseExceptionHandler redirects the user to a specified route (like /Error), where a custom error page or view is rendered.

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app.UseExceptionHandler("/Error");

This is typically used to catch server-side exceptions and render a custom error page, while allowing the application to continue running.

Why StatusPagesWithReexecute Might Not Work with UseExceptionHandler

In some cases, the combination of StatusPagesWithReexecute and UseExceptionHandler may cause conflicts or unexpected behavior. Here's why this might happen:

Error Handling Flow: UseExceptionHandler captures all unhandled exceptions and redirects to a specific route (like /Error). However, StatusPagesWithReexecute also attempts to execute the error-handling route again, which can result in a loop or misdirected behavior.

Middleware Order: The order in which the middleware is registered is crucial. If UseStatusCodePagesWithReexecute is placed after UseExceptionHandler, it might interfere with the error-handling flow or prevent the error pages from being displayed as intended.

Conflict with Custom Error Logic: If you have custom error logic in the ErrorController that relies on the status code, StatusPagesWithReexecute might re-execute the request before the error can be handled correctly, causing an incomplete or incorrect error page.

Solution to the Issue

To resolve issues with StatusPagesWithReexecute and UseExceptionHandler, it's recommended to carefully configure the middleware order and ensure that they don't conflict. Here's a suggested configuration:

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public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); } else { // Handle exceptions and redirect to error pages app.UseExceptionHandler("/Error"); // Handle status codes (e.g., 404, 500) app.UseStatusCodePagesWithReexecute("/Error/{0}"); } // Other middleware... }

In this configuration:

UseExceptionHandler("/Error") is placed first to catch unhandled exceptions and redirect to the ErrorController.

UseStatusCodePagesWithReexecute("/Error/{0}") is placed after UseExceptionHandler to handle specific HTTP status codes.

This ensures that the exception handler takes priority while also allowing you to handle status codes like 404 and 500 with custom pages.

FAQ

1. Why is my custom 404 error page not showing?

Possible causes: Make sure UseStatusCodePagesWithReexecute("/Error/{0}") is properly configured in your Startup.cs.

Ensure that the error page view (e.g., Error404.cshtml) exists in the correct directory and is properly referenced in the ErrorController.

2. Why do I get a redirect loop when an exception occurs?

Possible causes: Check the order of your middleware. If UseExceptionHandler and UseStatusCodePagesWithReexecute are incorrectly ordered, they might conflict. Ensure that UseExceptionHandler comes first, followed by UseStatusCodePagesWithReexecute.

3. Can I use UseStatusCodePagesWithReexecute for all HTTP errors?

Yes, UseStatusCodePagesWithReexecute allows you to handle specific HTTP status codes (like 404, 500) and re-execute the request pipeline to show custom error pages.

4. How do I log errors in my ErrorController?

You can inject a logging service (like ILogger) into your ErrorController and log errors in the methods for each error code.

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private readonly ILogger _logger; public ErrorController(ILogger logger) { _logger = logger; } public IActionResult NotFound() { _logger.LogError("Page not found"); return View("Error404"); }

Conclusion

In this guide, we've walked through how to configure custom error pages in Kentico 13, using an ErrorController to display error views based on HTTP status codes. We've also discussed the potential issues when using StatusPagesWithReexecute together with UseExceptionHandler, and provided solutions to ensure they work together without conflicts. By carefully configuring middleware and understanding how the request pipeline works, you can create a robust error handling strategy for your Kentico 13 website.