Y.js backend enhancements and debug helpers

[juliushaertl]

• chore: Add helpful comments and code bits for y.js debugging
• chore: Basic backend y.js message decoder

📝 Summary

While looking into #4309 I thought it might be nicer to actually decode parts of the y.js message to perform relevant checks on it. This is now done in the YjsMessage class where so far only the relevant bits for extracting the message type is implemented. Upstream references are left in the code.

In addition I added a few logging parts in comments that might be useful in future debugging/development.

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• Documentation (README or documentation) has been updated or is not required

[cypress]

3 failed and 4 flaky tests on run #12081 ↗︎

3	137	18	0	4
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Details:

Y.js backend enhancements and debug helpers
Project: Text	Commit: d7d78107e4
Status: Failed	Duration: 29:01 💡
Started: Sep 11, 2023 3:30 PM	Ended: Sep 11, 2023 3:59 PM

_{This comment has been generated by cypress-bot as a result of this project's GitHub integration settings.}

[mejo-]

Nice! The code looks good to me, but I'd prefer if we could get a second review - especially of readVarUint() in lib/YjsMessage.php 🤓

[juliushaertl]

Conflicts resolved, @max-nextcloud any chance you find some time? Not urgent but trying to get my open pr count down a bit 🙈

[max-nextcloud]

The parsing of the base64 encoded messages and extraction of the first bits to get the types is nicely covered with tests. So I'm confident it's good as it is.