The Inspect page will read a chosen file entirely in the browser, and the
record it shows must equal what Images shows for the same bytes. This adds
to web/js/png-metadata.js (loaded by the legacy pages as before, with
parsePngTextChunks unchanged):
- readPngMetadataFile(file, {signal, prefix, yieldControl, decompress}):
a port of utils/prompt_inspector.py's _png_metadata, _PngRecords,
_png_text, _inflate and _batch_normalized. It slices only chunk headers,
80-byte keyword prefixes and the retained prompt, workflow, parameters
and comfyassets_prompt_pairs records, CRC-checks what it keeps, applies
the same budgets (2 MiB shared role budget encoded and decoded, 4 MiB
workflow that becomes limited, 8 MiB and 4 MiB duplicate budgets, 4 MiB
duplicate decoded parameters, 10,000 chunks, the batch-index rule for
parameters copies) and compares duplicate chunks byte for byte. Every
range is checked against file.size before slicing and charged against a
19,794,389-byte ceiling, so a multi-gigabyte PNG costs only its metadata.
Compressed text inflates through DecompressionStream with one 256-byte
write in flight and the output capped at the record's allowance; an
AbortSignal rejects the read with an AbortError and leaves no unhandled
rejection; yieldControl runs about every 8 ms of work.
- classifyPrefix(bytes): png, jpeg, webp, iso-bmff, matroska, avi, asf or
null from the first 32 bytes.
- readImageHeader(file, kind): JPEG (SOFn walk as Pillow) and WebP (VP8,
VP8L, VP8X) dimensions from at most 64 KiB.
tests/test_local_inspect_parity.py drives tests/js/support/local-inspect-
oracle.mjs over the committed and test-time inspection parity corpus plus
compressed, oversized, Latin-1, batch-duplicate and all-four-record shapes,
and asserts records, record formats, dimensions and readability equal
read_inspection_file on each file; the two JPEG/WebP fixtures are checked
against Pillow. tests/js/png-local-reader.test.js pins each server rule,
the sparse 3 GiB read, the prefix reuse, inflation back-pressure and abort.
tests/fixtures/local-inspect/tiny.{jpg,webp} are CC0 FFmpeg test patterns.
Vito Sansevero
05e7dd512c