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lib: call normalizeEncoding in fs.writeFileSync and fs.readFileSync#60539

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JonasBa:fix-utf8-encoding-case-sensitivity
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lib: call normalizeEncoding in fs.writeFileSync and fs.readFileSync#60539
JonasBa wants to merge 1 commit intonodejs:mainfrom
JonasBa:fix-utf8-encoding-case-sensitivity

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@JonasBa JonasBa commented Nov 1, 2025

Fixes #49888 by adding calls to normalizeEncoding.

Benchmarks between #f46152fdb3 and CL from this PR

                                                                                                                 confidence improvement accuracy (*)    (**)   (***)
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1024 useFd='false' encoding='utf8'                    1.34 %       ±5.41%  ±7.22%  ±9.43%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1024 useFd='false' encoding='UTF8'                   -0.50 %       ±2.76%  ±3.67%  ±4.78%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1024 useFd='true' encoding='utf8'                    -0.39 %       ±3.46%  ±4.61%  ±6.01%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1024 useFd='true' encoding='UTF8'            ***     57.52 %       ±4.34%  ±5.79%  ±7.55%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=102400 useFd='false' encoding='utf8'                 -0.39 %       ±3.91%  ±5.21%  ±6.78%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=102400 useFd='false' encoding='UTF8'         ***     66.76 %       ±5.95%  ±7.98% ±10.52%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=102400 useFd='true' encoding='utf8'                   0.93 %       ±1.54%  ±2.05%  ±2.67%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=102400 useFd='true' encoding='UTF8'          ***    288.37 %       ±5.84%  ±7.79% ±10.20%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1048576 useFd='false' encoding='utf8'                 1.45 %       ±3.28%  ±4.38%  ±5.74%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1048576 useFd='false' encoding='UTF8'        ***     99.65 %       ±5.43%  ±7.29%  ±9.61%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1048576 useFd='true' encoding='utf8'                  2.30 %       ±5.30%  ±7.07%  ±9.24%
fs/bench-writeFileSync.js n=1000 func='writeFile' useBuffer='false' length=1048576 useFd='true' encoding='UTF8'         ***    246.19 %      ±17.91% ±24.14% ±32.04%

Be aware that when doing many comparisons the risk of a false-positive result increases.
In this case, there are 12 comparisons, you can thus expect the following amount of false-positive results:
  0.60 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.12 false positives, when considering a   1% risk acceptance (**, ***),
  0.01 false positives, when considering a 0.1% risk acceptance (***)

I am open to suggestions here, but given that in the case of fast paths, the only encoding we care about is utf8, would it perhaps make more sense to have a isUTF8Encoding() which would return a bool?

Reviews and suggestions are much appreciated 🙏🏼

@JonasBa JonasBa requested review from CanadaHonk and anonrig November 1, 2025 22:19
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nodejs-github-bot commented Nov 1, 2025

Review requested:

  • @nodejs/performance

@nodejs-github-bot nodejs-github-bot added fs Issues and PRs related to the fs subsystem / file system. needs-ci PRs that need a full CI run. labels Nov 1, 2025
@JonasBa JonasBa force-pushed the fix-utf8-encoding-case-sensitivity branch 3 times, most recently from 9143536 to 121725f Compare November 1, 2025 22:27
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Looks good see next comment

normalizeEncoding has already a short-cut for utf8 and utf-8 (which were directly checked here before), so this should not have any measurable negative effect for those common cases, but optimizes non-common ones

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This breaks default encoding to be buffer

normalizeEncoding normalizes undefined to 'utf8', but readFileSync does not set options.encoding to a default value at that point, unlike writeFileSync, and the expectation is to read Buffers by default, not strings

@JonasBa JonasBa force-pushed the fix-utf8-encoding-case-sensitivity branch from 121725f to 862df86 Compare November 2, 2025 14:11
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@JonasBa JonasBa force-pushed the fix-utf8-encoding-case-sensitivity branch from 862df86 to 771bd39 Compare November 2, 2025 14:27
@RafaelGSS RafaelGSS added the performance Issues and PRs related to the performance of Node.js. label Nov 2, 2025
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eeeh

this also demonstrates how flush option is broken in fast write path
it's does not appear to be the fault of this PR but an existing bug though

upd: #60552

@ChALkeR ChALkeR mentioned this pull request Nov 2, 2025
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codecov bot commented Nov 2, 2025 •
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.56%. Comparing base (f46152f) to head (771bd39).
⚠️ Report is 5 commits behind head on main.

Additional details and impacted files 
@@            Coverage Diff             @@
##             main   #60539      +/-   ##
==========================================
- Coverage   88.58%   88.56%   -0.03%     
==========================================
  Files         704      704              
  Lines      207839   207844       +5     
  Branches    40051    40043       -8     
==========================================
- Hits       184117   184076      -41     
- Misses      15791    15809      +18     
- Partials     7931     7959      +28
Files with missing lines Coverage Δ
lib/fs.js 98.18% <100.00%> (+<0.01%) ⬆️

... and 44 files with indirect coverage changes

🚀 New features to boost your workflow:
  • ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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ChALkeR commented Nov 2, 2025 •
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CI is going to fail unless #60552 is fixed first, which is though unrelated directly
Usage which only supplies { flush: true } in options, but relies on default encoding, will be negatively affected by this PR until that gets resolved

Basically, #60552 fix has to go in first. (Upd: #60553)
This PR is not at fault though and should not need further changes except for rebase

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JonasBa commented Nov 2, 2025 •
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@ChALkeR, I appreciate the thorough review and explanation here, thank you so much!

@ChALkeR ChALkeR mentioned this pull request Jan 17, 2026
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fs: utf8 fast paths don't accept all valid utf8 values

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