Create simpler way to show Not Found 404 UI with Blazor

[Alerinos]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

Currently, we support the lack of a page in blazor, unfortunately, if we want to place a 404 header for SEO and, for example, google bot, it creates a problem.
It's worth handling this exception.
There is currently a workaround that doesn't look very good to me.

App.razor

        <NotFound>
            <PageTitle>Not found</PageTitle>
            <LayoutView Layout="@typeof(Pages._404)">
                404
            </LayoutView>
        </NotFound>

404 layout:

@layout Shared.MainLayout
@inherits LayoutComponentBase
@using Microsoft.AspNetCore.Http

@Body

@code {
    [Inject] IHttpContextAccessor httpContextAccessor { get; set; } = null!;

    [Inject] PersistentComponentState _ApplicationState { get; set; } = null!;

    PersistingComponentStateSubscription persistingSubscription;

    bool model = true;

    protected override void OnInitialized()
    {
        persistingSubscription = _ApplicationState.RegisterOnPersisting(Task () => { _ApplicationState.PersistAsJson($"404", model); return Task.CompletedTask; });
        if (!_ApplicationState.TryTakeFromJson<bool>($"404", out var dto))
        {
            if (httpContextAccessor.HttpContext is not null)
                httpContextAccessor.HttpContext.Response.StatusCode = StatusCodes.Status404NotFound;
        }
    }
}

Also I read in the documentation that we shouldn't use httpcontext in blazor subpages.

Describe the solution you'd like

I think Not Found blazor server side should automatically handle and ship. I've searched the internet and the documentation and found nothing useful.

Additional context

No response

Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
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[Alerinos]

@danroth27 I noticed that the new template (VS 17.8.0 Preview 2.0) lacks custom 404 error support.

[danroth27]

@danroth27 I noticed that the new template (VS 17.8.0 Preview 2.0) lacks custom 404 error support.

Yes, this something we still expect to address in an upcoming .NET 8 update: #50550

[danroth27]

@mkArtakMSFT Looks like we still have a functionality gap here that we need to discuss. #50550 didn't actually address this scenario. There was some related discussion in #48983 about having a way to trigger a 404 response, but that work wasn't done in #49801 either.

[SteveSandersonMS]

Could you clarify more about what doesn't work here? I just tried adding this to a page:

    [CascadingParameter] public HttpContext HttpContext { get; set; }

    protected override async Task OnInitializedAsync()
    {
        HttpContext.Response.StatusCode = 404;
    }

... and it worked immediately. It's also not necessary to add anything in <Router> because with SSR you already get a native ASP.NET Core 404 page if there's no matching .razor endpoint.

[Alerinos]

@SteveSandersonMS
Before there was Blazor Web there was only Blazor Server Side, then the circuit worked the same way you would use it:

@attribute [RenderModeServer].

In this case, there were problems alone.

[SteveSandersonMS]

You certainly can't set a 404 status code, or any HTTP response headers, while in the middle of interactive rendering. At that time there is no HTTP response to set properties on, so it's not applicable as a concept.

But just to clarify, are you confirming this now works for you as you'd expect for SSR pages? Or are you saying that there is still a missing feature (and if so, what)?

[Alerinos]

@SteveSandersonMS Here you have a case where a 404 should be returned, what if the page will be rendered in RenderModeServer?

https://github.com/danroth27/BlazorScaffolding/blob/9a6cc450c4dbb144523a1081d9f987ecf668a87a/Components/Pages/Movies/Edit.razor#L67

[SteveSandersonMS]

what if the page will be rendered in RenderModeServer?

During prerendering you can set a status code on the HttpContext.

However, once the component has actually become interactive, there is no HTTP response so it would be meaningless to even talk about status codes. When fully interactive, all that matters is what UI you display, so you would just need to show in the UI that the item doesn't exist (which you also need to do in the SSR/prerendering cases, since normal users don't see or care about HTTP status codes either).