Blazor Server does not work after upgrade to .NET 8.0

[Suchiman]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I have an ASP.NET Core 7 app that mostly uses traditional MVC with razor views that utilizes blazor server on some subpaths.
After upgrading to .NET 8.0, by upgrading the TargetFramework and PackageReferences, not doing any code changes, the blazor pages stopped working correctly.

They pre-render correctly but are not interactive. I include them by having <component type="typeof(App)" render-mode="ServerPrerendered" /> in a cshtml file at the subpath where blazor starts being used, e.g. https://app.tld/Admin hits an MVC controller that returns a View that includes said markup. If i change it from ServerPrerendered to Server, all i get is a white page.

I can see that a websocket connection for blazor is established but there's no error message in the browser console nor on the ASP.NET Core console window.
All the Browser console says is

[2023-11-15T18:41:50.278Z] Information: Normalizing '/_blazor' to 'https://localhost:44311/_blazor'. blazor.server.js:1
[2023-11-15T18:41:50.327Z] Information: WebSocket connected to wss://localhost:44311/_blazor.

If necessary, i can try to create a minimal project but if anyone knows off the top of their head what i'm doing wrong, that would be great.

Expected Behavior

Blazor Server should just continue to work in .NET 8 as it did in .NET 7 per the upgrade guide https://learn.microsoft.com/en-us/aspnet/core/migration/70-80?view=aspnetcore-7.0&tabs=visual-studio#update-a-blazor-server-app

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

8.0.100

Anything else?

No response

[augustevn]

Hi, I see you're using a lot of the old notations still (before .NET 8). <component type="typeof(App)" render-mode="ServerPrerendered" /> should look more like <Routes @render-mode="InteractiveServer" />

Also, blazor.server.js should look more like blazor.web.js. I suggest you start a new .NET 8 InteractiveServer project and look how it's done there, then copy over what's applicable.

Also, clean and rebuilding after major upgrades can do wonders for your project's interactivity.

[Suchiman]

@augustevn those are the steps to upgrade from a Blazor Server app to a Blazor Web App as outlined here, which i'm trying to avoid for now since i need the Blazor Code to be able to slot into MVC Views and Blazor Web Apps appear to be all or nothing. That same link however points out that

which is the route i would like to go for now.

[christallire]

They forgot Identity migration.

[javiercn]

@Suchiman I've you've just updated the libraries and TargetFramework, that should work. There are a few things to try:

• Use an in-private window.
• Turn server logging on to Debug.
• Turn webassembly logging on to Debug.

See if there are more logs. You should also be able to put a breakpoint on your component to see if it's rendering anything at all. You shouldn't change the script on the page (in case you did) It should still be "_framework/blazor.server.js"

[Suchiman]

Been sinking a few hours into investigating this closer. Took a look at the logs and saw it connecting and creating a circuit and then nothing for a while until the circuit got disposed because token expired 2 minutes later. Wanted to compare with .NET 7 so i've switched branches and then it suprisingly was broken there too.

Closing VS, cleaning everything the git clean -xfd way, etc. did not help. After a while i've figured that the webapp, that was definitively running from a bin\Debug\net7.0 folder, was delivering the net8.0 version of the blazor.server.js. I've checked everything, browser caching disabled via devtools network tab and the asp.net core console output confirmed that blazor.server.js has been sent with 200 OK (not 304 not modified).

So i've manually retrieved the net7.0 version of blazor.server.js and put that in my wwwroot and used that instead of the _framework one. That fixed net7.0. Then i switched back to net8.0 and used the net7.0 blazor.server.js there as well. That made the non pre rendered version of blazor server also render again, although trying to click on buttons error'd with No interop methods are registered for renderer 0 but that's to be expected i guess.

Digging around in the net8.0 version of blazor.server.js, it seems that the code that uses const blazorCommentRegularExpression = new RegExp(/^\s*Blazor:[^{]*(?<descriptor>.*)$/); to match the comments that the components generate never gets hit because it seems like it enumerates the head only, not the body. But that's all i could figure so far and now it's 3:30am so i'll have another look tomorrow

[augustevn]

@Suchiman I see what you mean & I'm sorry you're having so much trouble.
I just upgraded a 66+ projects solution with 6 Blazor WASM hosted projects from .NET 6 to .NET 8 without doing the conversion. Everything still renders and works as intended. Well done Microsoft!

I didn't expect that to go as smoothly since it didn't go smoothly between RC1, RC2 and RTM but that was understandably not the focus and was meant to break.

[Suchiman]

Waking up with a fresh head, i had an epiphany. I've moved this piece of code

<script src="/_framework/blazor.server.js" autostart="false"></script>
<script>
    Blazor.start({
        configureSignalR: function (builder) {
            builder.withUrl("/_blazor", {
                skipNegotiation: true,
                transport: 1
            });
        }
    });
</script>

from just before </head> to just before the </body> and now it works again.

[javiercn]

@Suchiman yes, that would do it.

That's why we put it at the end of the file. You could have also done deferred=true on the script for the same effect, but essentially what's happening is that the script was loading too early.

[jonrmorgan99]

@Suchiman yes, that would do it.

That's why we put it at the end of the file. You could have also done deferred=true on the script for the same effect, but essentially what's happening is that the script was loading too early.

@javiercn I'm having similar startup problems with an app I migrated from Net7 Blazor server to Net8. I've been using

<script src="/_framework/blazor.web.js" autostart="false"></script>

in my Net8 App.Razor component as that's what's included in the VS2022 Net8 Blazor template.

As my app runs entirely in interactive server mode should I be using

<script src="/_framework/blazor.server.js" autostart="false"></script>

or is blazor.server.js now obsolete ? The app works fine in Local IIS btw.

[ryanbuening]

@jonrmorgan99 - did you ever find the answer to the question of whether to be using blazor.web.js or blazor.server.js if the app is interactive server only?