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54 lines
2.9 KiB
Markdown
54 lines
2.9 KiB
Markdown
# printcraft-redact
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Layer L4 (may use `edit`): redaction, architecture §11.2.
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```rust
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// Marks are Redact annotations (printcraft-annot: Shape::Redact { quads, overlay }).
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let marks: Vec<Mark> = marks(&doc); // page, areas (user space), fill, overlay text
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let report = apply(&mut doc, None)?; // everything, or Some(&[pages])
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clear_marks(&mut doc, None)?; // remove marks without applying
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```
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`apply` removes, under every marked area:
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- **text**: glyphs are cut out of `Tj`/`TJ`/`'`/`"` and replaced by a `TJ` displacement of the
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same advance, so the rest of the line keeps its exact position. Widths come from `/Widths`,
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`/W`/`/DW` (composite fonts, embedded CMaps with codespace and CID ranges), Type 3 font
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matrices, and approximations for the standard 14. A glyph goes when it overlaps an area by
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more than a fifth of its size (or a point) both ways; zero-size text goes when its origin is
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inside;
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- **images**: fully covered → removed; partly covered → a copy with the covered pixels cleared
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(8/16-bit and 1/2/4-bit images, image masks; Flate/LZW/RL/A85/AHx). Codecs PrintCraft can't
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re-encode (DCT, JPX, JBIG2, CCITT) are removed whole (fail-closed); inline images under an
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area are removed;
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- **vectors**: covered paths are removed; partly covered paths and shadings are clipped so
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nothing paints inside the areas;
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- **form XObjects**: rewritten recursively into new objects (pages sharing the original keep it);
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- **annotations** whose rectangle overlaps (with their pop-ups), and **form fields** with a
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widget under a mark;
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- the marks themselves, replaced by boxes in their fill colour (and overlay text) drawn into the
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page as a `/PCMark /Redaction` stream.
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A verification pass re-reads each redacted page and fails the operation if any glyph or inline
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image is still under an area. Content that can't be decoded makes the operation fail rather than
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leave it unredacted.
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## Remove hidden information / Sanitize
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```rust
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let found = sanitize::scan(&doc); // [(Hidden, count)] per category
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sanitize::remove_hidden(&mut doc, &[Hidden::Comments])?; // chosen categories
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sanitize::sanitize(&mut doc)?; // all of them
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```
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Categories: metadata (`/Info`, XMP), file attachments, comments, form fields (flattened so the
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values stay visible), hidden text (render modes 3 and 7, or wholly off the page), hidden layers
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(content of off optional-content groups, then the groups), bookmarks, links/actions/JavaScript,
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and `/PieceInfo` private data. Both make the next save a full rewrite.
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`patterns` finds phone numbers, e-mail addresses, credit card numbers (Luhn-checked), US Social
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Security numbers and dates for Search & Redact.
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Not yet: pattern locales, struct-tree/alt-text cleanup, metadata and hidden-information
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sanitising (M8.4), re-encoding of DCT images (they are removed instead).
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