How to troubleshoot unreachable blazor local server?

[MetacodeX7]

Hi,

I have been working on a blazor wasm project (.net 7) in visual studio 2022, for about 6 months. Never had an issue running the project, until now. After an accidental rebuild, my local server, at localhost:7290, just isn't reachable anymore - I get a 404 error in the browser. The blazor client never has a chance to boot. This has been going on for days, I tried everything I could think of, short of rebuilding the entire project from scratch, but I am getting nowhere.

How would you troubleshoot this kind of issue? How can I get more information about why the (local!) server can't be reached?

• There's no error displayed in the server console - as far as I can tell, the server is fine. I stepped into it and it seems to execute as I would expect.
• I pushed my changes anyway, and my app got deployed on AWS. It was working. It's only localhost that doesn't work.
• In the VS output, I get these errors, which tell me nothing useful: "The thread 0x1 has exited with code 0 (0x0).", "The program 'service-worker.js' has exited with code 4294967295 (0xffffffff).". Service worker is a small file, and it's the same for all my apps. No reason it would fail. Couldn't find any useful clue about this on google.
• I also get this error right after, which I assume is simply an error in the chrome 404 page. "Could not read source map for chrome-error://chromewebdata/: Unexpected 503 response from chrome-error://chromewebdata/neterror.rollup.js.map: Unsupported protocol "chrome-error:""
• I erased the bin and obj folders, cleaned, rebuilt many times, no luck. Release, debug, neither work.
• It's not a port issue: if I tell the broken project to use another port (from a working project), it doesn't work any better, and if I tell a working project to use 7290, that project works.
• It's not a browser-specific or cache issue: that local server doesn't work on any browser, and doesn't work in incognito.
• My other projects still work fine, and they are very similar, modified from an earlier copy of this one. But cloning the broken project doesn't lead to a working project. There must be something, somewhere, causing the issue.
• I double-checked all project files, program.cs files, settings etc, and can't find any meaningful difference.
• Note that all of this did follow a failed attempt to update from visual studio 17.7.3 to 17.8.4 or 5. I quickly reverted when it turned out something had gotten broken with blazor debugging - but even at that time the server was still reachable, so I don't think it's related. After reverting, I was able to work for a couple of days until the local server became unreachable.

[MetacodeX7]

I managed to find the cause after all. You will not find this answer (or this problem) anywhere else on the internet ;)

Turns out I had removed the client project dependency in the server project, thinking this was odd and likely a mistake I made previously. Even though I had restored the dependency by going into the solution's "Project Dependencies", that had not restored the actual client project reference in the server project. When I fixed that, my project worked again.