[Blazor] SSR Error page gets overwritten by NotFound WASM component on InteractiveWebAssembly handoff

[yugabe]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Using the default template with InteractiveWebAssembly in .NET 10 (or earlier), the Error page is defined on the Server project, and the Routes are defined in the Client project. When navigating to /error, the Error page is rendered statically on the server, then when the client app starts, overwrites the Error page with the NotFound page content on the client.

Expected Behavior

The default project should demonstrate how to mix server-rendered and client-rendered content properly in the same app. Currently, the default project itself demonstrates mixing the render modes incorrectly.

While putting @attribute [ExcludeFromInteractiveRouting] can be considered a workaround, it is undesirable: the layout of the application itself might still be using WebAssembly for even simple interactivity, like collapsing menus. ExcludeFromInteractiveRouting bypasses starting the WebAssembly runtime altogether.

Possible solutions:

• Mark server-rendered content to persist on the client after client interactive routing kicks in. Possibly a marker attribute on the element, a directive, or an @attribute similar to ExcludeFromInteractiveRoutingAttribute.
• Allow ExcludeFromInteractiveRoutingAttribute to actually initialize the WebAssembly app, but leave the components marked with this attribute as-is in the DOM. Consider renaming the attribute if so. This might be easy to do using similar mechanics as seen in PersistentState
• Allow customizing the Router. For example, allow a behavior that lets the router "keep" the content as-is when a navigation event occurs, by overriding/passing OnNavigatingAsync or similar, or by inheriting from the built-in Router.
• Allow supplying a custom Router altogether. This would also allow multiple additional scenarios if community-built routers were to show up: handling localization in the URL, multiple hierarchic routers, etc.
• Allow rendering content on the server and let the client WebAssembly app "consume" the rendered static HTML as interactive. This might be a stretch, but for some simple cases, it can work.
• Modify/implement a new RenderMode that allows server-client handoff.

Steps To Reproduce

dotnet new blazor --name BlazorSSRCSR --all-interactive --interactivity WebAssembly
cd BlazorSSRCSR
dotnet run

Navigate to the created app's /error endpoint. The endpoint will show the server side error, then after a short time, the client side router overwrites the content with the client side NotFound page content.

Exceptions (if any)

No response

.NET Version

10.0.100-rc.1.25451.107

Anything else?

This is NOT the same as similar (possibly slightly related) issues:

• Ability to run multiple Blazor server / Web assembly apps in the same document (micro-frontends) #38128
• Avoid completely replacing the DOM when Blazor components are re-rendered after prerendering #42561

Note that there's also the implication that if this is done, "mixing" render modes across a hierarchy might become possible. That would also require the user be able to set RenderMode to Static explicitly, which is currently not possible because it's not even defined in RenderMode: it's condered Static rendering when the RenderMode evaluates to null.

[MihuBot]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• New Blazor Web Application, navigate to the server project's component auto display "Not Found". #58480

[yugabe]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• New Blazor Web Application, navigate to the server project's component auto display "Not Found". #58480

Thanks, yes, it is related, but certainly not a duplicate. The issue I raised is in the template by default.

[yugabe]

I see this was added to the Backlog unfortunately. Any possible workarounds known at the moment, @javiercn? As it stands, it might be more prudent for me to just switch to WebAssembly and skip all the SSR stuff if them coexisting in the same app is so problematic.

[wendellestradairely]

I am experiencing the same issue. Same issue happens if I have a referenced class library. When navigating to pages in that library, they are being displayed but NotFound overrides them after a few seconds.