net: handle undefined parent in _unrefTimer and _destroy

[haggholm]

The fix and approach are from #64491 by @Shivay-98; opening from a fresh branch to land it, since that PR stalled awaiting the requested changes (unrelated commit dropped, failing test addressed, Signed-off-by added).

Socket.prototype._unrefTimer and Socket.prototype._destroy both walk the socket _parent chain with a strict !== null check. When teardown leaves a socket's _parent as undefined (for example a TLS socket layered over another stream), the loop steps onto undefined and throws

TypeError: Cannot read properties of undefined (reading 'Symbol(timeout)')
    at TLSSocket._unrefTimer (node:net)
    at TLSWrap.onStreamRead (node:internal/stream_base_commons)

from an uncaught I/O callback, crashing the process. Switching both loops to a nullish != null check stops the walk on undefined as well.

The original PR fixed only _unrefTimer; its regression test also calls destroy(), which hits the same unpatched loop in _destroy, so that path is fixed and covered here too.

Fixes: #64490
Refs: #64491

Checklist

• make -j4 test (UNIX) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines

[nodejs-github-bot]

Review requested:

• @nodejs/net

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.14%. Comparing base (ed63b19) to head (6b91d30).
⚠️ Report is 56 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64644      +/-   ##
==========================================
- Coverage   92.01%   90.14%   -1.88%     
==========================================
  Files         381      741     +360     
  Lines      170167   242095   +71928     
  Branches    26075    45552   +19477     
==========================================
+ Hits       156585   218239   +61654     
- Misses      13291    15364    +2073     
- Partials      291     8492    +8201     

Files with missing lines	Coverage Δ
lib/net.js	94.37% <100.00%> (+3.37%)	⬆️

... and 514 files with indirect coverage changes

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[haggholm]

Cc. @aduh95 who was active in the original PR.

Note: I've never contributed to Node and basically do not know what I am doing.

[pimterry]

Actual change and tests look good! 👍

My one concern is the overall description of this, and these comments specifically, because as far as I can tell we never set _parent to undefined. It's exclusively an external thing, where libraries mess with these internals, is that right? It's a bit unclear in the context given, but AFAICT that's the real problem here.

I understand that they do indeed do that (I'd be interested if you have specific examples) and this is unfortunately de-facto public API now so it would be good to defend against this where it's cheap to do it, but I'd rather avoid documenting undefined as expected behaviour, so we stick with just null internally. It's useful if we don't lead future readers on a wild goose chase.

How about changing both comments to something like:

_parent may be null, we use loose != null checks in case external code sets it to undefined

[pimterry]

Note: I've never contributed to Node and basically do not know what I am doing.

Thanks for the PR @haggholm, no worries, this looks good to me and all going in the right direction. Very helpful picking up stalled work like this. I have a minor comment here that it'd be nice to clean up (you can just push another commit and they'll be squashed together at merge automatically) but otherwise everything looks great.

Don't worry too much about the test-internet failure, I strongly suspect something flaky is going on there... Could be us, could be github actions, hard to say.