GeezerVison

Summary

Fixes #49888

The and UTF8 fast paths (introduced in #48658 and #49884) only accepted lowercase encoding strings 'utf8' and 'utf-8'. The uppercase variants 'UTF8' and 'UTF-8' are valid encodings (accepted by Buffer.isEncoding()) but were not routed to the fast path, causing them to fall through to the slower generic code path.

Changes

• lib/fs.js: Extended the fast path checks in readFileSync and writeFileSync to also accept 'UTF8' and 'UTF-8'
• Added test file test/parallel/test-fs-utf8-fast-path-encoding.js verifying all four encoding variants work correctly with both string and object form options

Testing

New test covers:

• writeFileSync(path, data, encoding) — string form
• readFileSync(path, encoding) — string form
• readFileSync(path, { encoding }) — object form
• writeFileSync(path, data, { encoding }) — object form

All four encoding variants ('utf8', 'utf-8', 'UTF8', 'UTF-8') are tested with Unicode characters (CJK, emoji) to verify correctness.

node test/parallel/test-fs-utf8-fast-path-encoding.js