How to replace Blazor default “soft 404” with an actual 404 status code response


The default Blazor approach to 404 is to create a soft 404 in App.razor, but I would like to adhere to search engine best practices to actually return the 404 status code while displaying a 404 page on Azure.

I tried to remove the element in App.razor to see if I could force a 404, however, that did not compile.

Any suggestions?


I was able to return 404 http status codes when using server side prerendering in the Blazor WebAssembly App (ASP.Net Core Hosted) Template

When I pointed the browser to http://localhost/fetchdata it returned a page. I wanted this to return a 404 status code as an example. This was possible using dependency injection and a stub class.

In BlazorApp1.Client I added a IResponse.cs file:

namespace BlazorApp1.Client { public interface IResponse { void SetNotFound(); } }

In BlazorApp1.Client I added a ResponseStub.cs file:

namespace BlazorApp1.Client { public class ResponseStub : IResponse { public void SetNotFound() { // Do nothing if we are browser side } } }

In FetchData.razor in BlazorApp1.Client I added:

@inject BlazorApp1.Client.IResponse Response

and in the code section:

protected override void OnInitialized() { Response.SetNotFound(); }

In Program.cs in BlazorApp1.Client I added:

builder.Services.AddScoped<IResponse, ResponseStub>();

Then in BlazorApp1.Server, in Startup.cs I added under ConfigureServices:

services.AddHttpContextAccessor(); services.AddScoped<IResponse, Response>();

and under Configure I replaced:




Then create the Server implementation of IResponse in Response.cs:

using BlazorApp1.Client; using Microsoft.AspNetCore.Http; using System.Net; namespace BlazorApp1.Server { public class Response : IResponse { private readonly IHttpContextAccessor _httpContextAccessor; public Response(IHttpContextAccessor accessor) { _httpContextAccessor = accessor; } public void SetNotFound() { _httpContextAccessor.HttpContext.Response.StatusCode = (int)HttpStatusCode.NotFound; } } }

And finally I create a _Host.cshtml file in BlazorApp1.Server/Pages:

@page "/fallback" @namespace BlazorPrerendering.Server.Pages @using BlazorApp1.Client @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers @{ Layout = "_Layout"; } <app> <component type="typeof(App)" render-mode="ServerPrerendered" /> </app> <div id="blazor-error-ui"> An unhandled error has occurred. <a href="" class="reload">Reload</a> <a class="dismiss">


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