lightcraft/crates/meta

lightcraft-meta (L1)

Photo metadata: EXIF, XMP (read + write), IPTC-IIM, and the containers that carry them.

API

Function	Purpose
read_exif(&[u8]) -> Metadata	TIFF-structured Exif block (whole TIFF/DNG/raw file, or JPEG APP1 payload with/without Exif\0\0). try_read_exif reports header errors.
from_tiff(&Tiff) -> Metadata	Same, from an already parsed stream (used by lightcraft-raw).
embedded(&[u8]) -> Embedded	Sniffs JPEG / PNG / WebP / TIFF / PSD / PSB and returns the Exif, XMP (+ extended XMP), ICC and IPTC blocks. PSD/PSB EXIF resource 1058 and XMP resource 1060 are read from the bounded image-resource section without decoding pixels. jpeg_segments, png_chunks, webp_chunks are the per-container walkers.
parse_xmp(&str) -> Result<XmpData>	Metadata + the opaque lc:settings JSON + every property (prefix:name, structs flattened as a:b/c:d).
write_xmp(&Metadata, Option<&str>) -> String	Complete <?xpacket?> packet; the second argument is LightCraft's full develop settings JSON.
parse_iptc(&[u8]) -> Metadata	IIM record 2: title (2:5), keywords (2:25), by-line (2:80), copyright (2:116), caption (2:120), date/time created (2:55/2:60).
extract(&[u8]) -> Metadata	Everything for a whole file. Precedence: EXIF → IPTC fills gaps → XMP overrides user fields (rating, label, title, caption, artist, copyright, keywords, GPS) and fills the rest.
try_extract(&[u8]) -> Result<Metadata, ExtractError>	Like extract, but reports malformed PSD/PSB headers, image-resource sections, or embedded EXIF/XMP structure (including duplicate EXIF/XMP resources) so callers can fail closed when location absence cannot be established. Other formats remain best-effort.

Metadata carries camera (make, model, serial, software), lens (make, model, serial, specification), capture (date-time with UTC offset and milliseconds, exposure time, f-number, ISO incl. extended ISO, focal length and 35 mm equivalent, flash, exposure bias, program, metering, white balance), orientation, GPS, dimensions and the user fields (artist, copyright, title, caption, keywords, hierarchical keywords, rating −1…5, colour label).

XMP namespaces

Written: dc, xmp, photoshop, exif, exifEX, tiff, lr (hierarchicalSubject) and ours, lc = http://ns.lightcraft.app/lc/1.0/ (lc:settings, an opaque JSON string). Reading canonicalises prefixes by namespace URI, handles attribute and element forms, rdf:Seq/Bag/Alt (x-default first), rdf:parseType="Resource" and nested-description structs, predefined and numeric entities. Nesting depth and node count are limited.

An explicitly foreign namespace using a recognized prefix (for example lc or xmp) cannot supply recognized properties. Its keys use Q{hex-encoded namespace URI}local in properties and values; hex encoding keeps / reserved for struct paths. Other unknown prefixes keep their existing QName keys. Merging preserves the original foreign XML rather than writing these opaque keys into the packet. The parser and merge scanner each cap generated opaque names at 8 MiB per packet, returning TooComplex if repeated use of a long namespace URI would exceed that budget.

Robustness

No panics on malformed input: proptests feed random bytes to every container walker and random text to the XMP parser; truncation tests cut a sample JPEG at every byte and exercise truncated PSD/PSB headers and image-resource records with hostile declared lengths. PSD/PSB XMP resources require valid UTF-8; trailing NUL padding is trimmed after validation.

Sources

CIPA DC-008 (Exif 2.32), TIFF 6.0, Adobe DNG 1.7 (tag numbers), ISO 16684-1 / Adobe XMP Specification Parts 1–3 (packet, RDF serialisation, standard schemas, JPEG extended XMP), IPTC-IIM 4.2 and the IPTC Photo Metadata Standard, ITU-T T.81 (JPEG markers), ICC.1 (APP2 embedding), PNG Specification 3rd ed. (eXIf, iTXt), the WebP RIFF container specification, Adobe Photoshop File Format Specification (image resource blocks). XML parsing: quick-xml (MIT). No third-party metadata code was consulted.