[EricKaden]

Split out of #1566 by @EULArule, who asked for it to be taken over in two PRs. The other part, required fields, is #4537.

What this changes

Some viewers save a dynamic XFA form with its pages drawn. They leave no /NeedsRendering and keep only the signature boxes as AcroForm fields. PdfCraft took such a file for a static form, because it has fields, and showed its pages as they were saved: nothing on them could be filled in, because the other fields live in the template.

Such a form is now laid out from its template when its configuration says <dynamicRender>required</dynamicRender>, as #1566 did. Designer writes that value for a dynamic form, as it writes forbidden for a static one (#3180).

Signed forms are left as saved. If one of the signature boxes is signed, the form opens exactly as before. Laying it out would replace the pages the signature covers. PdfCraft would then report that signature as broken, since the open-time layout is an appended revision. Another viewer would see changed pages after the signature too. #1566 noted this ("a signature made before the layout is reported as invalid because the pages changed"). Making a signed form fillable needs a save that keeps the signed revision's pages, the design question in #4309, so it is not attempted here.

The same rule is in both places that decide:

• pdfcraft_render::inspect, which sets DocInfo::xfa;
• pdfcraft_xfa::is_dynamic, which render_into checks.

The xfa crate reads only the configuration packet (config/acrobat/acrobat7/dynamicRender), never the same element in the template or data. It finds signed boxes by walking the AcroForm's fields, at most 32 levels deep and 10 000 fields.

How you verified it

• cargo fmt --check, clippy -D warnings and tests on pdfcraft-xfa, pdfcraft-render and pdfcraft-engine.
• New fixture saved_with_pages_shell(render, signed): a form saved with its pages drawn, its signature box the only field, and the configuration's dynamicRender value.
• engine::tests::a_form_saved_with_its_pages_that_requires_dynamic_rendering_is_laid_out_unless_signed:
  • unsigned, it opens laid out, and its text field takes a value;
  • signed, it opens as saved, with no revision appended.
  • It fails with the rule reverted, and with the signed exception taken out.
• xfa::tests::a_form_saved_with_its_pages_is_laid_out_when_it_requires_dynamic_rendering: is_dynamic for required, required and signed, no configuration, and forbidden. It also fails with the rule reverted.
• xfa::tests::dynamic_rendering_is_read_from_the_configuration_only: the value inside config/acrobat/acrobat7 only, and not:
  • <configuration>, the template, or another path;
  • a configuration with no end tag.

Never-crash

• No new panics, indexing or unsafe. Slices are taken with get. The configuration is parsed only from its own packet, and a malformed one counts as not required. The field walk is bounded by depth, by a visited set and by a 10 000-field budget.

Provenance

• dynamicRender from the XFA configuration specification; the approach from M12: XFA form fidelity: Latin Extended text, anchors, script objects, required fields #1566. No other implementation read.

Parity and reach

• parity/acrobat-features.toml (the XFA layout note and its evidence) and crates/xfa/README.md.
• Headless: opening through the tools takes the same path (doc_info reports xfa: dynamic and the layout).

Anything a reviewer should look at first

• The signed exception is deliberate. It keeps today's behavior for signed forms, which show their signature valid but can't be filled. A form signed in another viewer and passed on to be filled further is what Dynamic XFA forms: a save that only fills in the form keeps its usage rights valid #4309's save proposal is for.

Summary by CodeRabbit

• Bug Fixes
  • Unsigned XFA forms configured to require dynamic rendering now lay out fields from their template, even when the PDF already contains saved pages.
  • Signed XFA forms retain their saved layout and are not laid out again.
  • Forms without the required dynamic-rendering setting, or with rendering explicitly forbidden, remain static.
  • Unrelated or malformed configuration settings do not trigger dynamic rendering.
• Documentation
  • Clarified how saved pages, dynamic-rendering settings, and signatures affect XFA form layout.

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Walkthrough

Unsigned saved XFA forms with dynamicRender set to required are classified as dynamic despite existing rendered pages. Signed forms remain static. New fixtures and tests cover classification, layout, and signed-form handling.

Changes: Saved XFA dynamic rendering

Layer / File(s)	Summary
Dynamic-render and signature classification crates/xfa/src/packets.rs, crates/xfa/src/lib.rs, crates/render/src/inspect.rs	Packet helpers detect the required dynamicRender setting and valued signature fields. XFA and render classification use these results alongside existing rendering conditions.
Saved-form fixtures and behavior coverage crates/xfa/src/fixtures.rs, crates/xfa/src/tests.rs, crates/engine/src/tests.rs	Fixtures and tests cover dynamic layout for unsigned saved forms and static handling for signed forms. Tests also cover configuration parsing, nested signature detection, and text-field input after layout.
Classification documentation and parity evidence crates/xfa/README.md, parity/acrobat-features.toml	The documentation and parity evidence describe required dynamic rendering for saved forms and the signed-form exception.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant Inspector
  participant XFAPackets
  participant XFAClassifier
  participant Layout
  Inspector->>XFAPackets: Read dynamicRender configuration
  Inspector->>XFAPackets: Check signature fields
  XFAPackets-->>Inspector: Return configuration and signature status
  Inspector->>XFAClassifier: Classify saved XFA form
  XFAClassifier-->>Layout: Select dynamic layout for unsigned required form

Loading

Possibly related issues

• Signed dynamic XFA forms always show as invalid #4621 — The issue concerns layout after opening a signed dynamic XFA form. This change keeps signed forms in their saved page state.
• Dynamic XFA forms: a save that only fills in the form keeps its usage rights valid #4309 — The issue concerns an open-time XFA layout revision and usage rights. This change alters when saved forms enter dynamic layout.

Possibly related PRs

• storytold/pdfcraft#4527 — Its XFA event-ordering and relayout changes apply to forms newly classified for dynamic layout.
• storytold/pdfcraft#4507 — Its nested signature-field structure relates to this change’s signature detection through /Kids.

Suggested reviewers: mtlcl410, aiongg, fredapps

Merge Risk: Moderate · previous review c85e9

Required-dynamic-render forms with very deeply nested or very numerous fields can be classified differently by the renderer and the XFA crate. A signed form could then be laid out again and its saved pages changed. Align the renderer's signature scan with the XFA crate's limits before merging.

Security architecture risk: Low · up to c85e9

A narrow signed-document integrity gap remains for callers that lay out forms directly. Normal document opening has an additional check, while automatic processing retains existing script restrictions and failure recovery.

Retained concerns

• Medium · security · inferred: The public XFA layout guard does not preserve signed pages when a signature field's /FT is an indirect reference to /Sig. has_signature uses Dict::name, which accepts only direct names. For a saved form with nonempty fields, required dynamic rendering, no /NeedsRendering and no existing layout, this can make is_dynamic return true despite a valued signature; render_into then replaces the page tree. The base rejected that same form because it had fields. Normal engine opening is protected by its separate classifier, which resolves /FT. Exposure is therefore bounded to callers relying directly on the public XFA classification and layout contract, rather than a demonstrated bypass of normal opening.

Security review details

Security Blast Radius

• inferred — The identified integrity issue affects the document passed to a direct XFA layout caller. It can replace signed pages if the caller subsequently persists the result; it does not demonstrate signature forgery, cross-document access or elevated host authority. The normal engine classifier provides counterevidence against broader exposure.

Security Findings and Attack Paths

• inferred — An input-controlled indirect field-type representation can cross the public layout API's signed-state guard: unresolved /FT becomes an unrecognized type, the required-render branch admits the form, and the writer replaces its pages. This is a source-derived integrity concern, not an executed exploit or a retained finding from the supplied security assessment.

Trust Boundaries and Controls

• observed — Newly eligible documents inherit existing active-content controls. Open-time XFA scripts respect the JavaScript-off setting; print, save and URL-launch effects require click activity, and unsolicited scripts receive tighter loop, recursion and timeout limits.

Resilience and Maintainability Implications

• observed — The added engine test asserts that an ordinary signed saved-form fixture remains static and byte-identical on open. The added XFA test checks conservative rejection beyond the signature traversal depth limit. These support the intended invariant but do not establish protection for indirect field-type identity at the direct API.

Pre-merge checks: 5

Check name	Status	Explanation
Title check		The title clearly and concisely states the primary behavior change: saved XFA forms require dynamic rendering unless they are signed.
Description check		The description covers the behavior change, signed-form exception, implementation scope, verification results, safety limits, provenance, parity, reach, and reviewer focus. It is sufficiently complete…
Docstring Coverage		Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 6 files. (2 skipped: 2 …
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description covers the behavior change, signed-form exception, implementation scope, verification results, safety limits, provenance, parity, reach, and reviewer focus. It is sufficiently complete, although it does not reproduce the individual verification checklist items from the template.

Full details: Docstring Coverage

Explanation

Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 20 functions across 6 files. (2 skipped: 2 unsupported.)

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at @crates/xfa/src/packets.rs:
- Around line 100-124: Update requires_dynamic_render to select the actual
config packet instead of the first textual “config” element: use the named
config packet for XFA array streams and only the direct config child of the xdp
root for whole-XDP streams. Parse the selected packet and preserve the existing
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⚠️ Outside diff range comments (1)

Minor · Fail closed when signature traversal is truncated. · packets.rs:131-162

crates/xfa/src/packets.rs:131-162
🗄️ Data Integrity & Integration | 🟡 Minor | ⚡ Quick win

Fail closed when signature traversal is truncated.

has_signature skips fields past depth 32 or after 10,000 visited fields, then returns false. The AcroForm field walker also follows nested /Kids entries without these limits, so a valued /Sig field can be valid and reachable beyond either cap.

The required-render branch can then classify the saved form as dynamic. The engine can call render_into, which writes the laid-out form over the saved pages. This can change pages covered by the signature.

Treat a truncated traversal as signed, or return an unknown result and block dynamic rendering unless traversal completes.

Suggested fix

-        if budget == 0 || depth > 32 || f.as_ref().is_some_and(|r| !seen.insert(r)) {
+        if budget == 0 || depth > 32 {
+            return true;
+        }
+        if f.as_ref().is_some_and(|r| !seen.insert(r)) {
             continue;
         }

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only still-valid issues, skip the rest with a brief reason, keep changes
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Review comment at @crates/xfa/src/packets.rs around lines 131 - 162:
Update has_signature so reaching the depth or field-count limit returns true
rather than skipping the field and potentially returning false; keep
duplicate-field handling unchanged. This treats an incomplete traversal as
signed and prevents truncated results from allowing dynamic rendering.

---

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Outside diff comments:
Review comments at @crates/xfa/src/packets.rs:
- Around line 131-162: Update has_signature so reaching the depth or field-count
limit returns true rather than skipping the field and potentially returning
false; keep duplicate-field handling unchanged. This treats an incomplete
traversal as signed and prevents truncated results from allowing dynamic
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[EricKaden]

@coderabbitai On the outside-diff finding about has_signature (crates/xfa/src/packets.rs:131-162): fixed. Reaching the 32-level depth limit or the 10 000-field budget now returns true: the form counts as signed and stays as saved. A field already visited is still just skipped. A new fixture deep_saved_with_pages_shell(depth) puts the box under nested fields. a_form_saved_with_its_pages_is_laid_out_when_it_requires_dynamic_rendering checks two depths:

• 5 levels: the form is still laid out;
• 40 levels: it is left as saved. That case fails with the old walk.

🤖 Addressed by Claude Code

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🏁 Script executed:

#!/bin/bash
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for f in AGENTS.md CLAUDE.md; do
  if [ -f "$f" ]; then printf '\n--- %s ---\n' "$f"; sed -n '1,240p' "$f"; fi
done
fd -H '^(AGENTS|CLAUDE)\.md$' crates
ast-grep outline crates/xfa/src/packets.rs --match has_signature --view expanded
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rg -n -C 18 'fn deep_saved_with_pages_shell\b' crates/xfa/src/fixtures.rs
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Length of output: 42170

---

@EricKaden I checked the updated code. has_signature now returns true when traversal exceeds depth 32 or exhausts the 10,000-field budget. Repeated references are still skipped within those limits.

The regression test checks that depth 5 remains dynamic and depth 40 stays as saved. This addresses the reported traversal-limit concern.

I inspected the test source but did not run it. CI still needs to confirm that it passes.

---

🧠 Learnings used

Learnt from: CR
Repo: storytold/pdfcraft PR: 0
File: CLAUDE.md:0-0
Timestamp: 2026-10-20T18:53:40.819Z
Learning: Applicability reference:
AGENTS.md: # AGENTS.md — rules for every agent and contributor
These rules bind every AI agent and every human contributor working in this repository. They come before any task, instruction or deadline. `CLAUDE.md` holds the day-to-day working instructions. If the two ever disagree, **this file wins.**

AGENTS.md: # AGENTS.md — rules for every agent and contributor
Some sections link to **craftrules**, the standards shared by the Crafting Apps. That repository is internal to the storytold team, so outside contributors can't open it. Every rule a contributor here must follow is stated in this file and `CLAUDE.md`; the craftrules links give team members the background.

AGENTS.md: # AGENTS.md — rules for every agent and contributor
## 2. Clean-room rules (summary; details in `CLAUDE.md` and `plan/adr/0001`)
## 2. Clean-room rules (summary; details in `CLAUDE.md` and `plan/adr/0001`)

AGENTS.md: # AGENTS.md — rules for every agent and contributor
## 4. Never crash
- **Fail with `Result`.** Non-test code returns errors through the crate's error type and `?`. Where readers are lenient by design, fall back gracefully and record the repair (see Fidelity in `CLAUDE.md`).

AGENTS.md: # AGENTS.md — rules for every agent and contributor
## 5. Everything else
Follow `CLAUDE.md`. It covers quality gates, layering, commit rules and how to run and look at the app.

Source excerpt:
# PdfCraft — instructions for agents

## Non-negotiables

- **Never panic.** Every PDF, script, MCP call, settings file and keystroke is untrusted input, and none of it may crash the app or lose the user's work. This outranks feature work. Return `Result` (the crate's error enum) and propagate with `?`, or fall back leniently and record it. In non-test code:
  - No `unwrap`/`expect`/`panic!`/`unreachable!`/`todo!` unless it is provably infallible, with a comment saying why.
  - No indexing or slicing with input-derived positions (use `get`, and slice strings only at char boundaries).
  - Use checked or saturating arithmetic on input-derived numbers, and guard against division by zero and NaN/inf casts.
  - Cap allocations sized by input, and bound recursion with depth limits or seen-sets.
  - Handle lock poisoning.
  - No `unsafe` (`unsafe_code = "forbid"`).
  - Every crash fix gets a synthetic regression test. See `AGENTS.md` §4 (and, for team members, the internal `craftrules/standards/never-crash.md`).

_{You are interacting with an AI system.}

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Inline comments:
Review comments at @crates/xfa/src/fixtures.rs:
- Line 692: Update the depth-40 fixture assembly around the `objs.get_mut(5)`
replacement so the page’s `/Annots` reference points to the appended signature
widget’s new object number, while preserving the nested fields’ `/Parent`
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[FredApps]

Read the whole non-test change. A dynamic XFA form saved with its pages drawn and a configuration of dynamicRender required is now treated as dynamic, in both the inspector and the xfa crate is_dynamic, unless it holds a signed signature field, because laying it out would change what was signed. requires_dynamic_render parses the XDP with no DTD and a node limit, accepts the config packet only as the xdp child or a bare config root, and requires the text to be exactly required. has_signature walks the AcroForm fields iteratively with a seen set, a depth cap of 32 and a budget of 10 000, and treats an exhausted limit as signed, which is the safe side; it inherits FT from the parents and counts a non-null V. The inspector uses the fields it already has with the same rule, and the fixtures pin signed, unsigned, none and deeply nested boxes. The gate and SonarCloud pass at this head. I read the code and CI and did not open a form.

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Inline comments:
Review comments at @crates/render/src/inspect.rs:
- Around line 887-901: Update the `Inspector::fill` signature check so it uses
the XFA crate’s depth and field-count limits when scanning for valued `/FT /Sig`
fields, and treats either exhausted limit as signed; keep the existing
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[Harrison-Booth]

Review notes (comment only; nothing here is an approval or a request for changes).

What I checked:

• Read the source diff (xfa/src/packets.rs, xfa/src/lib.rs, render/src/inspect/core.rs, fixtures). requires_dynamic_render parses the XDP with allow_dtd: false and a node limit, and reads config/acrobat/acrobat7/dynamicRender == "required" only from the config child of the root. XML that does not parse, has a DTD, or puts the element elsewhere (data, template) asks for nothing.
• Signed forms are left as saved: has_signature (xfa crate) and signed_form (render crate) walk the field tree with the inherited /FT, a seen set, a depth limit of 32 and a budget of 10,000 fields, and treat a form past either limit as signed. That means a form too big to read is left as saved rather than laid out over a signature. The inspect code is written to give the same answer as the xfa crate, and both are bounded.
• Slicing and indexing are by get; the only subtraction (budget -= 1) follows a budget == 0 check.
• Checked out the PR head and ran on Linux (CARGO_BUILD_JOBS=2): pdfcraft-xfa full suite 130 passed, 0 failed, including a_form_saved_with_its_pages_is_laid_out_when_it_requires_dynamic_rendering and dynamic_rendering_is_read_from_the_configuration_only. In the engine, a_form_saved_with_its_pages_that_requires_dynamic_rendering_is_laid_out_unless_signed and a_saved_form_too_deep_to_read_through_is_left_as_saved pass.
• GitHub reports the branch as mergeable with main and CI is green.

Not checked: I did not run the pdfcraft-render suite beyond the saved filter. I did not test against a form actually saved by Acrobat or Designer (only the synthetic fixtures in the PR), so whether real files carry <dynamicRender>required</dynamicRender> this way rests on the PR's description. The signature check and the inspect copy of the field-tree walk are two copies of the same logic that have to be kept in step. I did not revert the fix to confirm the new tests fail without it.

[EricKaden]

Thanks @Harrison-Booth. On the two copies of the field-tree walk, agreed: they have to stay in step. They're two because the renderer still inspects files through lopdf (bootstrap debt, to go with the move to cos), while the xfa crate reads them through cos, so neither can call the other.

87f348d adds a test in the engine, which depends on both: the_renderer_and_the_xfa_crate_agree_on_which_saved_forms_are_laid_out. It checks that inspect's verdict (Xfa::Dynamic) and pdfcraft_xfa::is_dynamic agree for every saved-with-pages fixture:

• required, forbidden or no configuration, each signed and unsigned;
• the signature box nested 1, 5, 30, 31, 32, 33, 34 and 40 deep, around the 32-level limit.

With only the renderer's limit changed to 31, it fails at 32 deep, so a limit changed on one side alone is caught. (bca7f87 also merges the latest main.)

On the revert checks: "How you verified it" has them. a_form_saved_with_its_pages_that_requires_dynamic_rendering_is_laid_out_unless_signed fails with the rule reverted and with the signed exception taken out, and the xfa test fails with the rule reverted.