9adca4a8e5
* craft-tiff: keep shared child IFDs and every string of a multi-string ASCII value Two pointers to the same child IFD (two SubIFDs entries, or an Exif IFD shared by two directories) were treated as a loop and the second was dropped. Loops are now detected on the current parent path only; a shared IFD is parsed once and copied for later pointers, and each copy is charged its IFDs, entries and value bytes so max_ifds, max_entries_total and the value budget still hold. ASCII values keep every NUL-separated string (Value::as_strings); as_str and as_bytes return the first. Ported from storytold/lightcraft#3002. * craft-tiff: parse_with_status reports whether the whole IFD structure was read The reader is best effort: truncated tables, over-budget values, dangling pointers and unfollowed children are skipped silently. A caller that must tell a clean absence from something it could not inspect (a privacy scan for GPS data) gets the same tree plus a completeness flag. Also adds the PHOTOSHOP_IMAGE_RESOURCES and GPS destination tag constants. Ported from storytold/lightcraft#3766. On top of the shared-child change, a second pointer to an IFD already read counts as read, and a next pointer that loops back to the chain is incomplete. --------- Co-authored-by: Andrew Frahn <andrew@emmertex.com> Co-authored-by: ronibalthazar <61232335+ronibalthazar@users.noreply.github.com>
3.5 KiB
craft-tiff
The TIFF / IFD reader and writer underneath raw decoding (DNG, CR2, NEF, ARW…) and Exif. Moved from
LightCraft's lightcraft-tiff as the first step of shared RAW support (craft-libs#783, #587). It depends
on no other Craft crate.
Features
- Classic TIFF and BigTIFF, little- and big-endian (
II/MM). Also accepts the TIFF-like magic numbers of some raw formats (ORFIIRO/IIRS, RW2IIU) whenParseOptions::accept_raw_magicis set (default). - Every field type: BYTE, ASCII, SHORT, LONG, RATIONAL, SBYTE, UNDEFINED, SSHORT, SLONG, SRATIONAL, FLOAT, DOUBLE, IFD, LONG8, SLONG8, IFD8.
- IFD chain +
SubIFDs(330) + Exif (34665) / GPS (34853) / Interoperability (40965) pointer IFDs, resolved into a tree (Ifd::sub_ifds,exif,gps,interop).Entry::offsetrecords the absolute position of each value (needed for maker notes and embedded blobs). Tiff::parse_with_statusreturns the best-effort tree with a completeness flag for callers that must distinguish a clean absence from an IFD, entry, or pointer that could not be inspected.parse_ifd_at(data, offset, order, base, bigtiff, opts)parses an IFD whose offsets are relative to an arbitrary base;makernote::parse_makernoteknows the header / byte-order / offset-base conventions of Canon, Nikon (types 1 and 3), Sony, Fujifilm, Olympus (old and new), Panasonic and Pentax notes.image::ImageInfo— width/height, bits, samples, compression, photometric, planar config, predictor, sample format and the strip or tile chunk list (chunks(),chunk_bytes()); missing byte counts are inferred.directory_entries,entry_span,ParseOptions::budget_foranddecode_valueare the reader's own rules (directory layout and entry limit, which entries it reads, its value budget, value decoding), for callers that must select entries exactly asparse_ifd_atwould without decoding the whole directory (e.g. a raw decoder's SonySR2Privatelookup).TiffWriterwrites IFD chains with strips or tiles,SubIFDsand pointer IFDs, in either byte order, classic or BigTIFF;writer::rational/srationalapproximate floats as rationals.
Robustness
The reader never panics on malformed input (proptests feed random and mutated files): offsets are
bounds-checked; out-of-range or unknown-type entries are skipped; IFD loops are detected; IFD count,
nesting depth and entries per IFD are limited; at most 65,536 directory entry slots
(ParseOptions::max_entries_total) are accepted across the main IFD chain and all child IFDs, even when tables
overlap at distinct offsets, and an IFD past that bound ends the chain or is skipped like any other bad IFD after
the first; a next-IFD pointer is followed only when every declared entry was read, with the counts compared as
64-bit numbers (a BigTIFF declaring 4,294,967,297 entries but holding one can't pass for a whole directory on a
32-bit target); the total bytes of decoded values are capped at
8 × input + 1 MiB so a file cannot make us allocate far more than its own size. parse_with_status reports
truncated tables, skipped values, unresolved pointers and incomplete IFD chains without changing the parser's
best-effort tree.
Sources
Public specifications only: TIFF 6.0 (Adobe, 1992), the TIFF 6.0 supplements (IFD type, SubIFDs), the BigTIFF format description (AWare Systems), Adobe DNG Specification 1.7 (tag numbers), CIPA DC-008 Exif 2.32, and the ExifTool tag-name documentation (maker-note header conventions, prose only). No third-party code was consulted.