Grzegorz MartensandClaude Opus 5.5 b16f0c0a77 M8: redaction reads an operator's operands from the end, as the renderer does ...

An operator takes its operands from the end, and the renderer ignores a
surplus before them: `(x) /OC /MC0 BDC` marks a layer's block, and
`(x) /GS1 gs` selects `/GS1`. Redaction read some of them from the front,
so a surplus stood in for them and what they named went unseen. Found in
review of #6882, where Remove Hidden Information left the text of a
hidden layer in `(x) /OC /MC0 BDC (LAYERSECRET) Tj EMC`, which both the
app's renderer and Poppler hide.

In what Apply Redactions and Remove Hidden Information decide:
- the layers walk read a block's tag and property list from the front,
  and kept a hidden layer's block;
- the cleanup of `/ActualText`, `/Alt`, `/E` and `/T` in a block whose
  paint was removed read (and wrote) the property list from the front,
  and kept the name that still read the removed word;
- the tags cleanup read a block's `MCID` from the front, and left the
  removed text in its structure element's `/ActualText` and `/Alt`; and a
  `TJ`'s array, so a block that still drew was taken for empty and its
  structure element lost the content the page still shows;
- the property cleanups read the name of a `BDC` or `DP` property list
  from the front, and retired a property list the page still draws with;
- the walk read the ExtGState a `gs` selects from the front, so a font set
  only that way was not set, and `cs`/`CS` the same for a pattern space;
- the Type 3 cleanup's reads of `cs`, `gs`, `Tf`, `BDC` and `DP`, which
  decide which resources and fonts are still used.
The redaction proof read `Tc`, `Tw`, `Tz`, `TL`, `Ts`, `Tf`, `"`, `TJ` and
`Do` from the front too. `pdfcraft_content::Op` gains `back`, `name_back`
and `num_back`: operand `k` counted from the end.

Tests (`crates/redact/src/tests/operands_from_the_end.rs`): a hidden
layer's block, `/ActualText` on removed paint, a tag's `MCID`, a tagged
`TJ` that still draws, a property list still drawn with, a font from an
ExtGState, the pattern a `/Pattern cs` keeps, and a Type 3 font with the
ExtGState, colour space, property list and font its glyph uses, each
after a surplus operand. In `tests_verify.rs`,
`the_proof_reads_operands_from_the_end` (`Tf`, `TJ`, and `Do` of a form
and of images), `the_proof_reads_the_text_states_operands_from_the_end`
(`Tc`, `Tw`, `Tz`, `TL`, `Ts` and `"`) and
`an_image_a_type3_glyph_draws_after_a_surplus_operand_is_found`. And
`operands_are_counted_from_the_end` in the content crate.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AmsdeUCdTaD72jkDw2pJKY

2026-11-10 22:22:09 +01:00

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lib.rs

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tests.rs

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