The fixture wrote each row as one literal run of w bytes, which PackBits
can't express past 128 (a 160-pixel row's header byte read as a repeat
run). The old decoder clipped such rows silently; with the PSD fix in
this batch an overrun is an error, as it should be, and the fixture now
splits rows into valid runs.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01912WaK6Rmew3wxZuPyX7E8
The import probe of a non-raw image decoded it (at a 64 px fit, which for
JPEG still entropy-decodes every block and for PNG inflates everything)
only to learn its stored size and orientation: ~95 % of import CPU.
lightcraft-codecs gets `read_header(bytes) -> Header { format, width,
height, orientation }`: JPEG from its markers (EXIF orientation), PNG from
its chunks (IHDR, eXIf anywhere), TIFF from the first IFD (tiff crate,
no strips read), WebP from its RIFF chunks / bitstream header (image-webp),
PSD from its header and image resources. GIF, BMP and JPEG XL keep the
small decode. `files::probe_bytes` uses it; raw handling is unchanged.
The TIFF colour-layout check is shared with the decoder (`layout`).
Measured (release, 4 cores, throwaway benchmark, per file, bytes in
memory): 200 generated 4000x3000 JPEGs (3.6 MB): 72.7 ms -> 2.1 ms
(read_header alone 1.05 ms; the rest is the content hash and metadata);
20 PNGs (30.8 MB): 236-265 ms -> 9.0-9.6 ms.
Corrupt files (behaviour note): the header readers also refuse what a
decode refuses before the pixels (unsupported layout, compression, frame
type, bad IHDR, ...) and truncated files: a JPEG whose markers don't reach
its EOI, a PNG cut before the chunk after its IDAT run, TIFF strips/tiles
that start past the end, a WebP image chunk or PSD merged data past the
end. So truncated files (interrupted copies, partial downloads) are still
marked `error` in the import review, as before; tests check that whenever
the old decode accepted a (cut or byte-mutated) file the header agrees.
Changed: damage *inside* compressed data that is all present (flipped or
garbled bytes) was refused at scan and is now imported, and shows as
unreadable ("!" in the grid) when rendered. Also: tiny JPEGs (< 128 px)
were decoded leniently by the old probe, so a truncated one imported; it
is now refused. A TIFF truncated inside its last strip is not detected
(StripByteCounts are often overstated, so only strip starts are checked).
Tests: header readers vs decode on generated JPEG/PNG/TIFF/WebP/PSD/BMP
with and without EXIF/TIFF orientation; truncations and random mutations
agree with decode; hostile headers (zero/absurd sizes, bad lengths,
truncation, garbage) are errors; read_header added to the fuzz tests;
probe_bytes oriented dims match the decode-based values.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01912WaK6Rmew3wxZuPyX7E8
Claude