Hamza
ab7b584811
A form past the pass's depth limit is removed rather than walked. That
is the fail-safe choice for a redaction -- marked content inside a form
we cannot read would otherwise survive -- but it also removes whatever
else that form drew, marked or not. At a limit of 12, a page with a
13-deep chain lost the text of its innermost form with nothing in it
marked.
Measured on a page that draws HEAD, a chain of forms whose innermost
draws DEEP, then TAIL, with only HEAD marked:
chain before after (12) after (50)
1 HEAD DEEP TAIL DEEP TAIL DEEP TAIL
12 HEAD DEEP TAIL DEEP TAIL DEEP TAIL
13 HEAD DEEP TAIL TAIL DEEP TAIL
14 HEAD DEEP TAIL TAIL DEEP TAIL
50 HEAD DEEP TAIL TAIL DEEP TAIL
51 HEAD TAIL TAIL TAIL
The limit is now 50, which is what the renderer follows
(MAX_NESTED_INTERPRETATION_DEPTH) and what Edit text's reader follows
(text::MAX_FORM_DEPTH). So anything a reader can see, this pass can
walk. The last row is why 50 and not more: at 51 the renderer does not
draw DEEP either, so removing that form costs nothing visible and the
fail-safe still holds.
Fixes #3645's data loss. The other half of that report -- that nothing
tells the user when a form is removed -- is untouched: Report.forms_removed
is counted but the engine's edit pipeline does not carry it out, and the
one channel that reaches the result (doc.edit_notices) is typed
TextNotice, for text that could not be drawn. Widening that type or
adding a channel is a design choice for the maintainers rather than
something to slip into this fix.
pdfcraft-redact
Layer L4 (may use edit): redaction, architecture §11.2.
// Marks are Redact annotations (pdfcraft-annot: Shape::Redact { quads, overlay }).
let marks: Vec<Mark> = marks(&doc); // page, areas (user space), fill, overlay text
let report = apply(&mut doc, None)?; // everything, or Some(&[pages])
clear_marks(&mut doc, None)?; // remove marks without applying
apply removes, under every marked area:
- text: glyphs are cut out of
Tj/TJ/'/"and replaced by aTJdisplacement of the same advance, so the rest of the line keeps its exact position. Widths come from/Widths,/W//DW(composite fonts, embedded CMaps with codespace and CID ranges), Type 3 font matrices, and approximations for the standard 14. A glyph goes when it overlaps an area by more than a fifth of its size (or a point) both ways; zero-size text goes when its origin is inside; - images: fully covered → removed; partly covered → a copy with the covered pixels cleared
(8/16-bit and 1/2/4-bit images, image masks; Flate/LZW/RL/A85/AHx). Codecs PdfCraft can't
re-encode (DCT, JPX, JBIG2, CCITT) are removed whole (fail-closed); inline images under an
area are removed. Images with separate
/SMaskor/Maskdata are removed whole; cleared copies drop/Alternatesso alternate pixels cannot survive; - vectors: covered paths are removed; partly covered paths and shadings are clipped so nothing paints inside the areas;
- form XObjects: rewritten recursively into new objects (pages sharing the original keep it);
- annotations whose rectangle overlaps (with their pop-ups and their replies,
/IRT), and form fields with a widget under a mark; - the marks themselves, replaced by boxes in their fill colour (and overlay text) drawn into the
page as a
/PCMark /Redactionstream.
A verification pass re-reads each redacted page and fails the operation if any glyph or inline image is still under an area. Content that can't be decoded makes the operation fail rather than leave it unredacted.
Before changing any page, apply prepares the redaction appearances with a shared 8 MiB
budget for their uncompressed PDF content across the selected pages. It bounds repeated-text
counts and working line buffers before allocating them, and measures and encodes each repeated
line once. Invalid or excessive appearances return RedactError::OverlayLimit without changing
the document. Reduce the marked area, disable repeated text, or apply fewer pages at a time.
This limits appearance generation; it is not a limit on the input PDF or the whole process's memory.
Structure cleanup resolves named MCIDs and indirect content references. Form content references are updated to the cleaned copy; unchanged sibling descriptions remain.
Replacement descriptions are removed only from marked-content spans changed by cleanup. Unchanged spans retain their descriptions; unused property entries are retired during redaction and hidden-content cleanup, including aliases in shared/inherited resources. Descriptions still used by surviving pages or forms are kept.
A redacted page that inherits /Resources from the page tree gets them pinned (by reference;
a direct inherited dictionary is made one shared object first) before it is rewritten. The parent's
/Resources is then retired unless another page still inherits it, so it cannot keep a removed
XObject reachable. Pages that aren't redacted are left untouched.
Remove hidden information / Sanitize
let found = sanitize::scan(&doc); // [(Hidden, count)] per category
sanitize::remove_hidden(&mut doc, &[Hidden::Comments])?; // chosen categories
sanitize::sanitize(&mut doc)?; // all of them
Categories: metadata (/Info, XMP), file attachments, comments, form fields (flattened so the
values stay visible), hidden text (render modes 3 and 7, or wholly off the page), hidden layers
(content of off optional-content groups, then the groups), bookmarks, links/actions/JavaScript,
and /PieceInfo private data. Both make the next save a full rewrite.
patterns finds phone numbers, e-mail addresses, credit card numbers (Luhn-checked), US Social
Security numbers and dates for Search & Redact.
codes holds the redaction code sets (U.S. FOIA and U.S. Privacy Act exemptions):
CodeSet::from_id("foia")?.overlay(&["(b)(6)"]) gives the overlay text for the picked codes.
Custom code sets aren't supported yet.
Not yet: pattern locales, struct-tree/alt-text cleanup, metadata and hidden-information sanitising (M8.4), re-encoding of DCT images (they are removed instead).