lib: implement WHATWG-spec Big5 decoder in js - #65458
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #65458 +/- ##
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- Coverage 90.12% 90.05% -0.08%
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Files 752 770 +18
Lines 252315 261455 +9140
Branches 47438 49665 +2227
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+ Hits 227411 235444 +8033
- Misses 16212 17050 +838
- Partials 8692 8961 +269
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TextDecoder('big5') was routed through ICU's Big5 converter, whose
table includes vendor/PUA mappings the WHATWG Encoding Standard does
not define. Byte sequences the standard defines as invalid (and
which must decode to U+FFFD, or throw when fatal) instead decoded to
those extra ICU-only characters, e.g. bytes 0x83 0x5C decoded to
U+F00E instead of U+FFFD U+005C, even with `fatal: true`.
This adds a small, self-contained decoder for the 'big5' label (and
its aliases, which the standard maps to the same decoder) that
implements the algorithm and index table from the Encoding Standard
directly, mirroring how single-byte.js already reimplements the
legacy single-byte encodings instead of relying on ICU for them. It
does not touch the ICU-backed path used by any other encoding.
The decoder module is required lazily from internal/encoding.js, only
when a Big5 TextDecoder is constructed, so its large base64 index
table is not pulled into the startup snapshot; internal/encoding.js
itself is loaded during bootstrap.
Refs: https://encoding.spec.whatwg.org/#big5-decoder
Refs: nodejs#61041
Fixes: nodejs#40091
Signed-off-by: agape1225 <[email protected]>
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TextDecoder('big5') was routed through ICU's Big5 converter, whose table includes vendor/PUA mappings the WHATWG Encoding Standard does not define. Byte sequences the standard defines as invalid (and which must decode to U+FFFD, or throw when fatal) instead decoded to those extra ICU-only characters, e.g. bytes 0x83 0x5C decoded to U+F00E instead of U+FFFD U+005C, even with
fatal: true.This adds a small, self-contained decoder for the 'big5' label (and its aliases, which the standard maps to the same decoder) that implements the algorithm and index table from the Encoding Standard directly, mirroring how single-byte.js already reimplements the legacy single-byte encodings instead of relying on ICU for them. It does not touch the ICU-backed path used by any other encoding.
Refs: https://encoding.spec.whatwg.org/#big5-decoder
Refs: #61041
Fixes: #40091