fs: fix writeFile[Sync] for non-seekable files

[mildsunrise]

Currently writeFile and writeFileSync perform a positioned write at the beginning of the file, which prevents them from working with non-seekable files (#31926).

Positioned writes were first removed for createWriteStream (#19329) and for custom FDs (#23433, #23709) as well as for files opened in append mode... but they're still used for filenames in normal mode. This PR removes positioned writes completely, as they're not needed for this case either.

This also makes it consistent with readFile (which does work with non-seekable files).

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included ← I'd like to test for this, but I can't find an OS-independent way of doing it...
• documentation is changed or added ← should we mention this change?
• commit message follows commit guidelines

[addaleax]

This variant is the one that does change behaviour in the custom-FD use case, right? I feel like 99.9 % of people wouldn’t be affected, but maybe we could still keep that for a separate PR?

[mildsunrise]

Nope, that behaviour change was already done in #23433 / #23709 (you voted for that option), i.e. the current code never does positioned writes on FDs:

node/lib/fs.js

Lines 1289 to 1293 in 3d894d0

	if (isFd(path)) {
	const isUserFd = true;
	writeAll(path, isUserFd, data, 0, data.byteLength, null, callback);
	return;
	}

So this is a patch/minor change (unless I'm missing something)

[addaleax]

Right, thanks for reminding me :)

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/29439/

[mildsunrise]

No prob! It was more than a year ago, I'd have forgotten too 😹

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/29452/ (:white_check_mark:)

[codecov-io]

Codecov Report

Merging #32006 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #32006   +/-   ##
=======================================
  Coverage   96.16%   96.16%           
=======================================
  Files         196      196           
  Lines       64918    64918           
=======================================
  Hits        62429    62429           
  Misses       2489     2489

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[addaleax]

Landed in f69de13 🎉

[MylesBorins]

This does not land cleanly on v13.x. Should it be backported?

[addaleax]

@MylesBorins Wrong label? And, yes, it should be backported. 👍