WbunkerandClaude Sonnet 5.5
a711c61840
Writer::add rejected a duplicate name by comparing the new name with every sibling through compare_names, which allocates two Vec<u16> per call, so n children in one storage cost O(n^2) allocating comparisons. An AAF export puts every marker and component in one storage: 20 000 markers took 58 s, 20 000 clips 56 s, 20 000 connected clips 87 s and 100 000 markers never finished (an FCPXML of 1 MB is enough). Doubling the input quadrupled the time; every other exporter stayed linear. Each storage keeps a set of its children's names as sibling order compares them (UTF-16 code units, upper-cased), so the duplicate check is a hash lookup. Same result: case-insensitive, also beyond ASCII, per storage. 20 000 markers now export to AAF in 0.38 s, 100 000 in 2.0 s, 20 000 clips in 0.23 s and 20 000 connected clips in 0.45 s. Tests: adding 40 000 children must take under 3 s (0.02 s now, 21 s before) and the duplicate rules are unchanged. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
filmcraft-cfb
A clean-room reader and writer for the Compound File Binary format (Microsoft "structured
storage"), the low-level container of AAF files. Layer L0: no dependencies beyond std, no
unsafe, builds for wasm32-unknown-unknown. No third-party implementation (the AAF SDK's
structured storage code, libgsf, olefile, POI…) was consulted.
Specification
| Document | Edition | Used for |
|---|---|---|
| [MS-CFB] Compound File Binary File Format (Microsoft Open Specifications) | revision 10.0 (the format is unchanged since 1.0) | header, sector chains, FAT / DIFAT / mini FAT, directory entries, red-black sibling trees, name comparison, version 3 and 4 files |
Reading
let bytes = std::fs::read("sequence.aaf")?;
let cf = filmcraft_cfb::CompoundFile::open(&bytes)?;
let header = cf.find("Header-2")?; // a storage
println!("{:02x?}", cf.entries[header].clsid); // its class id
let props = cf.read_path("Header-2/properties")?; // a stream
for &child in &cf.entries[header].children { /* sorted siblings */ }
- Accepts version 3 (512-byte sectors) and version 4 (4096-byte sectors) files; other sector shifts between 7 and 16 are tolerated.
- Every chain (DIFAT, FAT, mini FAT, directory, streams) is bounds-checked and cycle-checked; a
directory tree that references an entry twice is rejected. Damaged or truncated files return
Error::Invalid, never panic or loop. - Version 3 stream sizes ignore the high 32 bits (§2.6.3).
Writing
let mut w = filmcraft_cfb::Writer::new(filmcraft_cfb::Version::V4);
w.set_clsid(filmcraft_cfb::Writer::ROOT, root_class);
let h = w.storage(filmcraft_cfb::Writer::ROOT, "Header-2", header_class)?;
w.stream(h, "properties", bytes)?;
let file: Vec<u8> = w.finish();
Layout: stream sectors (streams ≥ 4096 bytes), mini stream, mini FAT, directory, FAT, DIFAT. Each
chain is contiguous. Sibling trees are balanced binary search trees in [MS-CFB] name order
(length first, then upper-cased code units) coloured as valid red-black trees. Names are checked
(1–31 UTF-16 code units, none of / \ : !, unique per storage, case-insensitively).
Tests
src/tests.rs: round trips for both versions with empty, mini, boundary (63/64/65, 4095/4096/4097
bytes) and multi-sector streams and up to 40 siblings; red-black invariants of every sibling tree;
a 7.5 MB stream that needs DIFAT sectors; Unicode and case-insensitive names; truncation at every
29 bytes and 1500 random mutations never panic and only return complete streams.
The writer rejects a duplicate sibling name with an O(1) hash lookup on the upper-cased name (a scan over the
siblings made n children cost O(n^2): 20 000 AAF markers took a minute); adding_many_children_is_not_quadratic
and duplicate_names_are_still_rejected (tests/writer_scale.rs) cover it.