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 66.66667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.35%. Comparing base (37779fd) to head (f08ad6f).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/string_bytes.cc	66.66%	2 Missing and 3 partials ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #63587 +/- ##
=======================================
Coverage 90.34% 90.35% =======================================
Files 732 732 Lines 236689 236681 -8 Branches 44586 44584 -2 =======================================
+ Hits 213839 213842 +3 + Misses 14550 14548 -2 + Partials 8300 8291 -9 

Files with missing lines	Coverage Δ
src/string_bytes.h	80.00% <ø> (ø)
src/string_bytes.cc	75.73% <66.66%> (+2.17%)	⬆️

... and 23 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