http: fix just-merged change that could silently truncate responses

[pimterry]

This fixes an issue introduced 2 days ago in #64278. With that change, errors that emit after HTTP response headers are received but before the response is completed are swallowed silently.

This PR preserves the core change there, but covers the "response set but not yet completed" window properly so errors here still fire as expected.

[nodejs-github-bot]

Review requested:

• @nodejs/http
• @nodejs/net

[github-actions]

Fast-track has been requested by @pimterry. Please 👍 to approve.

[bjohansebas]

LGTM!

[mcollina]

lgtm

[mcollina]

I'm also ok to revert #64278.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/74823/

[pimterry]

I'm also ok to revert

I think we can roll forwards instead. The issue is real, and the fix is roughly correct, it just misses a couple of cases en route. AFAICT with some small changes this'll work as intended.

That said, I say "cases" plural because I've found another one: if the response is completed but the request is still going, this will now swallow errors we previously emitted on the still open request.

That can happen because request/response lifetimes are surprisingly independent, servers can finish responding while the request is still going. Most plausible example: the server could send an HTTP 202 to confirm an upload based on headers alone, before the body is fully delivered, expecting the request to keep writing it out even though the response side is closed. It's definitely weird, but it's valid HTTP AFAICT and I wouldn't be surprised at all if somebody does it and expects to get errors if it goes wrong.

Bonus fix for that incoming now.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.23%. Comparing base (3ac95f2) to head (30901e2).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #64507 +/- ##
==========================================
- Coverage 90.23% 90.23% -0.01% 
==========================================
Files 741 739 -2 Lines 241692 241668 -24 Branches 45541 45547 +6 ==========================================
- Hits 218097 218073 -24 - Misses 15113 15152 +39 + Partials 8482 8443 -39 

Files with missing lines	Coverage Δ
lib/_http_client.js	97.63% <100.00%> (-0.01%)	⬇️

... and 37 files with indirect coverage changes

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[pimterry]

@Archkon I'm assuming from your comments on #64511 that you're happy to open a new PR for this once it's reverted? That would be great if so, I'll close this once that's open.

Just for reference, I think there's a few key things to cover:

• The original test was covering useful behaviour, but not the exact problem from the reported issue: it fails on the affected versions and previous Node versions (e.g. v24.15). I tried to tweak it further here, but I'm not sure the current state is right either. The test for this should cover the actual issue if possible, meaning it should pass on v24.15, fail on v24.16, and then pass with the fix applied.
• I think if read or write are still incomplete in any way (read not completed or writable not flushed) we do need to expose the error. Any failure at that stage is a real problem that should be exposed.
• The MacOS difference seems to be due to flushing timing. writableFinished resolves when the OS confirms that the full write has been flushed (as opposed to Ended which resolves immediately, but doesn't actually confirm the data was sent). The flush happens async and timing depends on OS & network behaviour. It is the right gate I think, but the test here was still wrong, it was a quick fix on my part and it needs more thought. That needs fixing, but I don't think the error code is the issue - the failing test isn't supposed to error at all! I think the problem is that the server doesn't read the request body, so the write doesn't fully flush in some environments - req.resume() on the server might resolve that.

I think the correct logic for the code is now clear enough, the tricky part is writing tests that carefully wait for the write events so they properly cover the original issue, and also validate the various different cases here. It turns out it's quite a complex set of behaviours! In terms of testing it, see what you can come up with to try to fix this, and then open the PR and we can run CI manually to validate it there.

Thanks for your work on this. Sorry for all the back and forth but hopefully we'll get something working nicely soon. Feel free to ping if you have questions or want any help.

[pimterry]

I will but I don't completely understand that what do you mean by the failing test isn't supposed to error at all

Ah, there are at least two failing tests, that's the confusion. macOS fails on that error test, but aarch64-darwin fails here in the test-http-client-complete-response-reset.js test that shouldn't error at all, that's what I meant.

For the error test case, yes being flexible on the error codes if they're all reasonable is OK I think.

[pimterry]

I think I understand, interesting! I don't have a mac easily available for testing unfortunately.

There will just be some difference in packet processing or delivery at the OS level. You'll need to break down smaller repros until you work out exactly where macos differs. Once we know where the timing difference is we can write a test that is stable under those conditions. My expectation is that this is purely a testing issue - it's just hard to reproduce the problem in a clean way without hitting these timing issues.