Displaying a 404 Not Found Page for ASP.NET Core MVC

Question

I am using the middle-ware below to set up error pages for HTTP status codes 400 to 599. So visiting /error/400 shows a 400 Bad Request error page.

application.UseStatusCodePagesWithReExecute("/error/{0}");  [Route("[controller]")] public class ErrorController : Controller {     [HttpGet("{statusCode}")]     public IActionResult Error(int statusCode)     {         this.Response.StatusCode = statusCode;         return this.View(statusCode);     } } 

However, visiting /this-page-does-not-exist results in a generic IIS 404 Not Found error page.

Is there a way to handle requests that do not match any routes? How can I handle this type of request before IIS takes over? Ideally I would like to forward the request to /error/404 so that my error controller can handle it.

In ASP.NET 4.6 MVC 5, we had to use the httpErrors section in the Web.config file to do this.

<?xml version="1.0" encoding="utf-8"?> <configuration>   <system.webServer>     <httpErrors errorMode="Custom" existingResponse="Replace">       <remove statusCode="404" />       <error statusCode="404" responseMode="ExecuteURL" path="/error/404/" />     </httpErrors>   </system.webServer> </configuration> 

Answer 1

One of the best tutorials I found is this: https://joonasw.net/view/custom-error-pages

The summary is here:

1. First add a controller like ErrorController then add this action to it:

[Route("404")] public IActionResult PageNotFound() {     string originalPath = "unknown";     if (HttpContext.Items.ContainsKey("originalPath"))     {         originalPath = HttpContext.Items["originalPath"] as string;     }     return View(); } 

Note: You can add the action to another existing controller like HomeController.

2. Now add the PageNotFound.cshtml view. Something like this:

@{     ViewBag.Title = "404"; }  <h1>404 - Page not found</h1>  <p>Oops, better check that URL.</p> 

3. And the important part is here. Add this code to Startup class, inside Configure method:

app.Use(async (ctx, next) => {     await next();      if(ctx.Response.StatusCode == 404 && !ctx.Response.HasStarted)     {         //Re-execute the request so the user gets the error page         string originalPath = ctx.Request.Path.Value;         ctx.Items["originalPath"] = originalPath;         ctx.Request.Path = "/error/404";         await next();     } }); 

Note that it must be added before routing configs like app.UseEndpoints....

Answer 2

Based on this SO item, IIS gets the 404 (and therefore handles it) before it reaches UseStatusCodePagesWithReExecute.

Have you tried this: https://github.com/aspnet/Diagnostics/issues/144? It suggests terminating the request that received a 404 so it does not go to IIS to handle. And here's the code to add to your Startup to do so:

app.Run(context => {    context.Response.StatusCode = 404;    return Task.FromResult(0); }); 

This appears to be an IIS-only issue.