Rust Core

Rust Core

rust/pdftool_core — the only implemented, tested part of this repository.

Crate facts

Edition	2021
Crate types	cdylib, rlib
Licence	MPL-2.0
#![forbid(unsafe_code)]	yes
Lines (src/lib.rs)	~1030
Unit tests	6

Dependencies

Crate	Version	Why
lopdf	0.34	PDF object model, parsing, serialisation
serde	1 (derive)	Block serialisation across the WASM boundary
serde-wasm-bindgen	0.6	serde ↔ JsValue
wasm-bindgen	0.2	export surface
js-sys	0.3	Uint8Array return type

Nothing else. Cargo.lock is committed and CI runs with --locked.

Public surface

Two #[wasm_bindgen] exports, plus the Block struct they share:

pub struct Block { pub label: String, pub x: f32, pub y: f32,
                   pub width: f32, pub height: f32 }

Everything else in the crate is private. resolve_object, object_to_number, rect_from_object, object_to_text, dict_text, the field-descriptor walkers and apply_field_value are internal machinery.

What fill_blocks does, in order

1. Reject empty input (BW_PDF_EMPTY).
2. Document::load_mem (BW_PDF_INVALID).
3. Resolve trailer.Root (BW_PDF_ROOT_MISSING / BW_PDF_ROOT_INVALID).
4. Resolve or materialise catalog.AcroForm (BW_FORM_*).
5. Set NeedAppearances = true so viewers regenerate appearances.
6. Walk AcroForm.Fields recursively, cycle-guarded by a seen set.
7. Build a FieldDescriptor per field: partial name, fully-qualified dotted name, inherited field type, and the widget ids underneath it.
8. Look each name up in the caller's map — fully-qualified first, then partial.
9. Dispatch on field type: Tx/Ch → text writeback, Btn → appearance-state writeback, anything else → BW_FILL_UNSUPPORTED_FIELD_TYPE.
10. If nothing matched and something was supplied → BW_FILL_NO_MATCHING_FIELDS.
11. doc.save_to (BW_FILL_SAVE_FAILED).

Known limitations

• Only Tx, Ch and Btn field types are written. Signatures (Sig) are not.
• detect_blocks reports widget rectangles only. It does not detect ruled lines, per-character cells or baselines — the "hand spacing" case the project is named for is not implemented yet.
• Recursion depth is capped at 48 to bound hostile or cyclic field trees.
• field_full_name uses . as the separator, per the PDF convention.

Running the checks

cargo fmt    --manifest-path rust/pdftool_core/Cargo.toml -- --check
cargo test   --manifest-path rust/pdftool_core/Cargo.toml --locked
cargo clippy --manifest-path rust/pdftool_core/Cargo.toml --locked --all-targets -- -D warnings

There is no Rust toolchain in most sandboxes, so if you cannot run these, say so in the PR rather than implying you did. CI is the only authority on green.