Crate zenmeta 

zenmeta

Shared metadata implementation for image codecs, using zencodec’s interchange types. Metadata operations do not require zenpipe, zencodecs or a pixel decoder.

The default build supports metadata/EXIF filtering and serialization, plus rendering-preserving retention for an already parsed ISO gain map. Optional xmp and audit features enable namespace-aware XML inspection and structural metadata reports independently. apple enables MakerNote and binary-plist inspection without XML or audit. inventory enables the TIFF/BigTIFF walker used with codec-specific consumption rules. All features support no_std + alloc; no unsafe code is used.

use zencodec::{GainMapParams, Metadata, MetadataPolicy};

let metadata = Metadata::none();
let params = GainMapParams::default();
let retained = zenmeta::display::filter_for_gain_map(
    &metadata, &params, &MetadataPolicy::PreserveExact,
)?;
assert_eq!(retained, metadata);

An audit reports its coverage limits and opaque content. It does not certify privacy. Container framing, packet reassembly and rewriting belong to codecs; an inventory is not a safe generic deletion recipe.

See source provenance and the workspace design.

The xmp feature also provides gain-map XMP parsing/generation and Google container-directory inspection under zenmeta::xmp::{gainmap, container}. JPEG APP framing and packet reassembly remain codec responsibilities.

Optional rewrite supplies bounded EXIF processing and fallible plan assembly for codec-owned rewriters. Requests, services and completed plans are zencodec types, so a codec need not expose zenmeta types in its public API.

xmp::container::Directory validates a complete GContainer packet and updates secondary lengths by semantic while preserving unrelated source bytes. It rejects ambiguous directories and missing carried payloads. Codecs still own MPF offsets, payload layout and APP/box framing.

Basic EXIF reading, orientation, ICC/CICP and ISO gain-map interpretation remain available in zencodec without zenmeta. New processing callers use zenmeta::metadata::filter and zenmeta::exif::{filter, retain, serialize}. The published zencodec writers are deprecated compatibility implementations; these entry points delegate to that single implementation until a breaking release can physically relocate it without a dependency cycle.

Rewrite requests carry policy, services and budgets but do not execute them. zenmeta::rewrite::Context::new performs admission checks; packet processing and bounded plan assembly also live here. PreserveExact can retain XMP without an editor. Explicit XMP editing still requires a service, and keeping descriptive bytes does not certify their privacy or make unsupported container edits valid.

The TIFF inventory walker follows external old-style JPEG tables (519–521). Quantization tables have 64 bytes; Huffman extents use the 16 code counts and their declared symbol lengths, under the walk’s scan budget. Null and shared offsets, Classic TIFF/BigTIFF, relative bases and truncation are handled without decoding pixels. Rules::jpeg_table defaults to Unknown: a structural reference does not prove decoder consumption, JPEG validity or privacy. Codec rules must match their enabled decoder and its actual use of external versus embedded tables. The remaining consumer and shared-stream requirements are tracked in issue 171.

Modules

apple

Apple iOS MakerNote HDR gain-map metadata extraction.

audit

Explicit metadata inspection and structural diffing.

bplist

Minimal Apple binary property list (bplist00) reader.

display

Retention checks for a pipeline retaining a gain-map rendition. Extract vendor/XMP parameters into GainMapParams before calling this. Container writers must regenerate gain-map discovery/parameters separately from source XMP, and filter metadata inside encoded auxiliary images too.

exif

EXIF rewrite entry points using zencodec’s published interchange types.

ifd

Shared TIFF/BigTIFF inventory traversal. Each codec supplies its decoder’s consumption rules through walk::Rules; no pixels are decoded here. This module is available only with the inventory feature.

metadata

Retention implementation entry points for already extracted metadata.

rewrite

Common bounded packet processing for codec-owned metadata rewrite planners. Public codec signatures use zencodec’s request and plan types; these helpers remain implementation details that can evolve with zenmeta independently.

xmp

Namespace-aware XMP inspection. XML prefixes are aliases, never identities.