948135af72
Tables are generated from the Unicode Consortium's Microsoft mappings (VENDORS/MICSFT/PC), vendored in data/ and regenerated by tools/gen_tables.py. Decode is fallible because 857/864/869/874 leave byte values undefined; decode_lossy substitutes U+FFFD. Every table is a verified bijection, so defined bytes round-trip exactly.
67 lines
2.2 KiB
Markdown
67 lines
2.2 KiB
Markdown
# msdos-encodings
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Bidirectional, emulator-grade conversion between MS-DOS code pages and Unicode —
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without linking ICU. The crate owns the canonical Microsoft tables, so it stays
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small, self-contained, and cross-compiles cleanly.
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These are strictly **Microsoft's** mappings as published by the Unicode
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Consortium (`VENDORS/MICSFT/PC/`) — not the IBM or Oracle variants, which
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differ in a handful of slots.
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```rust
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use msdos_encodings::DosEncoding;
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let enc = DosEncoding::default(); // code page 437
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assert_eq!(enc.decode(b"Caf\x82").unwrap(), "Café");
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assert_eq!(enc.encode("Café").unwrap(), b"Caf\x82");
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// Pick by numeric code page (e.g. from CHCP or locale data):
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let enc = DosEncoding::from_code_page(866).unwrap();
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assert_eq!(enc.decode(&[0x80]).unwrap(), "А"); // DOS Cyrillic Russian
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// Four pages leave bytes undefined; decode is fallible, or go lossy:
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assert!(DosEncoding::Cp874.decode(&[0xFF]).is_err());
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assert_eq!(DosEncoding::Cp874.decode_lossy(&[0xFF]), "\u{FFFD}");
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```
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## Status
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- **All sixteen single-byte DOS pages** — implemented, decode + encode:
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437, 737, 775, 850, 852, 855, 857, 860, 861, 862, 863, 864, 865, 866, 869, 874.
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- **Double-byte CJK pages** (932 Shift-JIS, 936 GBK, 949 Korean, 950 Big5) —
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planned, to be codegen'd the same way and feature-gated.
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## Fidelity notes
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- Every table is a verified bijection: anything a page decodes re-encodes to
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the identical bytes.
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- Code pages 857, 864, 869, and 874 leave some byte values undefined, so
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`decode` returns a `Result`; `decode_lossy` substitutes U+FFFD.
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- Microsoft's CP864 (DOS Arabic) maps `0x25` to ARABIC PERCENT SIGN — the low
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half is *not* pure ASCII, and `%` itself is unmappable. This is faithful to
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the source table.
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## Regenerating tables
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`src/tables.rs` is generated from the vendored mapping files in `data/`
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(needs Python ≥ 3.10 and `rustfmt` on `PATH`):
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```sh
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uv run tools/gen_tables.py
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```
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## Scope
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Text-encoding conversion only. Filename conventions (8.3 space padding,
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case folding, the 0x05/0xE5 deleted-entry dance) are deliberately **out of
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scope** and left to consumers.
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## Consumers
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Designed to be shared by `fsinspect` and friends via path (and later git)
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dependency.
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## License
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MIT
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