util: optimize toASCIILower function using V8's native toLowerCase

[mertcanaltin]

benchmark results (mimetype-instantiation.js):

application/ecmascript +54%
text/html charset=gbk +24%
text/html long...=x charset=gbk +21%

[ChALkeR]

This is not identical (and there is a reason why the function checks character ranges)

This function is supposed to do ASCII lowercasing, not Unicode lowercasing

TextDecoder has the same issue for label normalization btw, as it incorrectly uses .toLowerCase at

node/lib/internal/encoding.js

Line 332 in b1c01fc

return encodings.get(trimAsciiWhitespace(label.toLowerCase()));

See spec: https://tc39.es/ecma262/#sec-string.prototype.tolowercase and notes there

As an example, '\u212A'.toLowerCase() === 'k'

toLowerCase can convert non-ascii characters into ascii characters (which makes e.g. current TextDecoder label handling incorrect, among all its other bugs)

text/html charset=gb\u212A should not turn into text/html charset=gbk

[ChALkeR]

What would be helpful is to move toASCIILower out to some helper lib and to fix TextDecoder label handling to use it instead of .toLowerCase.

[mertcanaltin]

What would be helpful is to move toASCIILower out to some helper lib and to fix TextDecoder label handling to use it instead of .toLowerCase.

Thanks I will try this idea

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.52%. Comparing base (4f24aff) to head (34692cf).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@ ## main #61107 +/- ## ========================================== - Coverage 88.53% 88.52% -0.01%  ========================================== Files 703 703 Lines 208546 208548 +2 Branches 40217 40224 +7 ========================================== - Hits 184634 184620 -14  - Misses 15926 15958 +32  + Partials 7986 7970 -16 

Files with missing lines	Coverage Δ
lib/internal/mime.js	98.48% <100.00%> (+<0.01%)	⬆️

... and 43 files with indirect coverage changes

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[RafaelGSS]

LGTM. With green CI and confirmed by benchmark CI.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70533/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70557/