fs: validate position argument before length === 0 early return

[geeksilva97]

Move position validation upwards to match documented behavior.

Fixes #62638

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.80%. Comparing base (68d7b6f) to head (de1c243).
⚠️ Report is 539 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #62674      +/-   ##
==========================================
+ Coverage   89.77%   89.80%   +0.03%     
==========================================
  Files         673      699      +26     
  Lines      203820   216235   +12415     
  Branches    39175    41331    +2156     
==========================================
+ Hits       182987   194199   +11212     
- Misses      13152    14148     +996     
- Partials     7681     7888     +207     

Files with missing lines	Coverage Δ
lib/fs.js	98.19% <100.00%> (+<0.01%)	⬆️
lib/internal/fs/promises.js	92.94% <100.00%> (-5.79%)	⬇️

... and 321 files with indirect coverage changes

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[afurm]

Moving validatePosition before the length === 0 early return is a good catch — it means invalid positions are rejected even for zero-length reads, which is more consistent.

One question on the validation ordering: Previously, validateOffsetLengthRead ran before the position normalization, and validatePosition ran after. The relative ordering of validateOffsetLengthRead vs validatePosition changed — do these validations have any ordering dependencies or could they produce different error messages depending on which runs first? For example, if position is valid but offset + length is out of bounds, which error should the user see first?

On the new test cases: The tests with empty buffer and an invalid position object are good — but note that validatePosition will throw ERR_INVALID_ARG_TYPE for non-number objects. The existing tests in the same file use ERR_INVALID_ARG_TYPE for invalid positions, so this is consistent — just making sure that is the intended behavior.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/72642/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/72676/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/72680/

[nodejs-github-bot]

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----------------------------------- PR info ------------------------------------
Title      fs: validate position argument before length === 0 early return (#62674)
Author     Edy Silva <edigleyssonsilva@gmail.com> (@geeksilva97)
Branch     geeksilva97:fix-fs-read-sync -> nodejs:main
Labels     fs, author ready, needs-ci
Commits    1
 - fs: validate position argument before length === 0 early return
Committers 1
 - Edy Silva <edigleyssonsilva@gmail.com>
PR-URL: https://github.com/nodejs/node/pull/62674
Reviewed-By: Aviv Keller <me@aviv.sh>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/62674
Reviewed-By: Aviv Keller <me@aviv.sh>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
--------------------------------------------------------------------------------
   ℹ  This PR was created on Fri, 10 Apr 2026 16:46:18 GMT
   ✔  Approvals: 2
   ✔  - Aviv Keller (@avivkeller): https://github.com/nodejs/node/pull/62674#pullrequestreview-4094424429
   ✔  - Luigi Pinca (@lpinca): https://github.com/nodejs/node/pull/62674#pullrequestreview-4101570935
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   ℹ  Last Full PR CI on 2026-04-14T09:32:37Z: https://ci.nodejs.org/job/node-test-pull-request/72680/
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 * branch                  main       -> FETCH_HEAD
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--------------------------------------------------------------------------------
Auto-merging lib/fs.js
Auto-merging lib/internal/fs/promises.js
[main d32bcd2881] fs: validate position argument before length === 0 early return
 Author: Edy Silva <edigleyssonsilva@gmail.com>
 Date: Fri Apr 10 13:42:53 2026 -0300
 5 files changed, 84 insertions(+), 19 deletions(-)
   ✔  Patches applied
--------------------------------------------------------------------------------
--------------------------------- New Message ----------------------------------
PR-URL: https://github.com/nodejs/node/pull/62674
Reviewed-By: Aviv Keller <me@aviv.sh>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
--------------------------------------------------------------------------------
[main 908808fa7e] PR-URL: https://github.com/nodejs/node/pull/62674 Reviewed-By: Aviv Keller <me@aviv.sh> Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
 Author: Edy Silva <edigleyssonsilva@gmail.com>
 Date: Fri Apr 10 13:42:53 2026 -0300
 5 files changed, 84 insertions(+), 19 deletions(-)
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