src: refactor EncodeValidUtf8 to reuse non-ASCII UTF-8 path

[araujogui]

Upstream PR #63231 added StringBytes::EncodeValidUtf8 but duplicated the EncodeTwoByteString block already present in StringBytes::Encode.

This PR refactors that by extracting a shared EncodeValidNonAsciiUtf8 helper, called from both EncodeValidUtf8 and the existing Encode UTF-8 path.

[Copilot]

Pull request overview

Note

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This PR optimizes UTF-8 decoding in the encoding binding by avoiding redundant UTF-8 validation when input has already been validated.

Changes:

• Added StringBytes::EncodeValidatedUTF8() API for encoding already-validated UTF-8.
• Refactored the fast UTF-8→UTF-16 conversion into a shared helper (EncodeKnownValidNonAsciiUTF8).
• Updated BindingData::DecodeUTF8() to use the new API after performing UTF-8 validation.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/string_bytes.h	Declares a new EncodeValidatedUTF8() entry point for already-validated UTF-8.
src/string_bytes.cc	Implements EncodeValidatedUTF8() and factors out the fast conversion helper used by both code paths.
src/encoding_binding.cc	Uses EncodeValidatedUTF8() after explicit UTF-8 validation to avoid re-validation overhead.

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[codecov]

Codecov Report

❌ Patch coverage is 62.50000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.34%. Comparing base (79def6d) to head (c02c51d).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/string_bytes.cc	62.50%	4 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63587      +/-   ##
==========================================
+ Coverage   90.32%   90.34%   +0.02%     
==========================================
  Files         732      732              
  Lines      236435   236444       +9     
  Branches    44527    44524       -3     
==========================================
+ Hits       213563   213621      +58     
+ Misses      14589    14521      -68     
- Partials     8283     8302      +19     

Files with missing lines	Coverage Δ
src/string_bytes.h	80.00% <ø> (ø)
src/string_bytes.cc	74.22% <62.50%> (+2.87%)	⬆️

... and 34 files with indirect coverage changes

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[araujogui]

CC @nodejs/performance

[mertcanaltin]

I also tried to fix this in #63231, but this pr more generally, good work!

[araujogui]

I also tried to fix this in #63231, but this pr more generally, good work!

Uh, my bad, I haven't seen it. I'm okay with closing this PR in favour of yours.

[mertcanaltin]

No problem at all, thanks for your effort. This PR seems like a better solution to me, @addaleax, Do you have any thoughts?

[araujogui]

@mertcanaltin @addaleax I rebased the branch, it's just a small DRY refactoring now