lzvn¶

A safe, dependency-free, no_std pure-Rust LZVN decompressor that reads real macOS files — length-tolerant where strict decoders reject them.

let block = [0xe5, b'h', b'e', b'l', b'l', b'o', 0x06, 0, 0, 0, 0, 0, 0, 0];
let mut out = [0u8; 5];
let n = lzvn::decode_into(&block, &mut out)?;
assert_eq!(&out[..n], b"hello");
# Ok::<(), lzvn::Error>(())

[dependencies]
lzvn = { package = "lzvn-core", version = "0.1" }

Why length-tolerance matters¶

LZVN is Apple's codec for HFS+/APFS transparent compression (decmpfs types 7 and 8) and the bvxn block inside an LZFSE stream. Real macOS decmpfs resource-fork blocks end with the LZVN end-of-stream opcode (0x06) and are then followed by 80–300 bytes of trailing data. Apple's kernel ignores those bytes; strict whole-stream Rust decoders reject them — and so fail on genuine macOS system files. lzvn stops at end-of-stream and returns.

See Validation for the oracle methodology and the real macOS 26.5 (Tahoe) results.

Trust, but verify¶

#![forbid(unsafe_code)], zero dependencies, no_std, typed errors.
Fixtures encoded by Apple's own COMPRESSION_LZVN; decoder additionally validated against 25 genuine macOS 26.5 system-file blocks (0/25 strict, 25/25 here).
Fuzz target decode clean over 1.37M executions.