M12: a picture an XFA form links is drawn from the PDF's XFAImages name tree

crates/xfa/src/fixtures.rs

@@ -739,3 +739,42 @@ if (this.rawValue == "1") {
 "##
     .to_string()
 }
+
+/// A form whose two draws link their pictures instead of embedding them: `.\logo.png`, which the
+/// PDF keeps in its `XFAImages` name tree (a [`tiny_png`], under a `Kids` node, as producers
+/// split the tree), and `.\missing.png`, which it doesn't (XFA 3.3 pp. 257–258).
+pub fn linked_image_shell() -> Vec<u8> {
+    linked_image_shell_with(b"<< /Kids [7 0 R] >>", br"<< /Limits [(.\\logo.png) (.\\logo.png)] /Names [(.\\logo.png) 8 0 R] >>")
+}
+
+/// [`linked_image_shell`] with its own name tree: `root` is object 6 (the tree the catalog names),
+/// `kid` object 7, and object 8 the PNG.
+pub fn linked_image_shell_with(root: &[u8], kid: &[u8]) -> Vec<u8> {
+    let xdp = r##"<?xml version="1.0" encoding="UTF-8"?>
+<xdp:xdp xmlns:xdp="http://ns.adobe.com/xdp/">
+<template xmlns="http://www.xfa.org/schema/xfa-template/3.3/">
+<subform name="form" layout="tb">
+ <pageSet><pageArea name="front"><contentArea x="0.5in" y="0.5in" w="7.5in" h="10in"/><medium short="8.5in" long="11in"/></pageArea></pageSet>
+ <subform name="page1" layout="tb">
+  <draw name="logo" w="1in" h="1in"><value><image contentType="image/png" href=".\logo.png"/></value></draw>
+  <draw name="gone" w="1in" h="1in"><value><image contentType="image/png" href=".\missing.png"/></value></draw>
+ </subform>
+</subform>
+</template>
+</xdp:xdp>
+"##;
+    let mut png = format!("<< /Length {} >>\nstream\n", TINY_PNG.len()).into_bytes();
+    png.extend_from_slice(TINY_PNG);
+    png.extend_from_slice(b"\nendstream");
+    let objs: Vec<Vec<u8>> = vec![
+        b"<< /Type /Catalog /Pages 2 0 R /NeedsRendering true /AcroForm << /XFA 5 0 R /Fields [] >> /Names << /XFAImages 6 0 R >> >>".to_vec(),
+        b"<< /Type /Pages /Kids [3 0 R] /Count 1 >>".to_vec(),
+        b"<< /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] /Contents 4 0 R >>".to_vec(),
+        b"<< /Length 44 >>\nstream\nBT /F1 12 Tf 72 700 Td (Please wait...) Tj ET\nendstream".to_vec(),
+        format!("<< /Length {} >>\nstream\n{xdp}\nendstream", xdp.len()).into_bytes(),
+        root.to_vec(),
+        kid.to_vec(),
+        png,
+    ];
+    assemble(objs)
+}

crates/xfa/src/layout/draw.rs

@@ -233,7 +233,7 @@ impl Layouter<'_> {
         let inner = rect.inset(&d.common.margin);
         match &d.value {
             Value::Text(_) | Value::Rich(_) => self.draw_value_text(&d.value, inner, &ctx.font, &ctx.para),
-            Value::Image { content_type, data } => self.draw_image(data, content_type, inner),
+            Value::Image { content_type, data, .. } => self.draw_image(data, content_type, inner),
             Value::Line { slope_up, edge } => {
                 if !edge.visible() {
                     return Ok(());

crates/xfa/src/layout/field.rs

@@ -95,7 +95,7 @@ impl Layouter<'_> {
                 let box_ = ui.inset(&f.ui_margin);
                 match (&from_data, &f.value) {
                     (Some(d), _) => self.draw_image(d, "", box_)?,
-                    (None, Value::Image { content_type, data }) => self.draw_image(data, content_type, box_)?,
+                    (None, Value::Image { content_type, data, .. }) => self.draw_image(data, content_type, box_)?,
                     _ => {}
                 }
                 // Then the field itself, which clicking gives a new picture.

crates/xfa/src/lib.rs

@@ -11,6 +11,7 @@ pub mod data;
 pub mod fixtures;
 pub mod image;
 pub mod layout;
+pub mod linked_images;
 pub mod model;
 pub mod packets;
 pub mod parse;
@@ -156,7 +157,8 @@ pub fn render_into(doc: &mut Document) -> Result<Report, XfaError> {
     if packets.xdp.trim().is_empty() {
         return Err(XfaError::Malformed("the XFA packets hold no template".into()));
     }
-    let (tpl, parse_warnings) = parse(&packets.xdp)?;
+    let (mut tpl, mut parse_warnings) = parse(&packets.xdp)?;
+    parse_warnings.extend(linked_images::resolve(&mut tpl, doc));
     let data = parse_datasets(&packets.xdp);
     let laid = apply_overrides(&tpl, &overrides(doc));
     let mut form = layout(&laid, data.as_ref())?;

crates/xfa/src/linked_images.rs

@@ -0,0 +1,207 @@
+//! Pictures a template links instead of embedding (`<image href="…">`). Since XFA 2.6 a form
+//! keeps them in its PDF: each image file is a stream holding the file's bytes, named in the
+//! `XFAImages` name tree of the catalog's `Names` dictionary by the URI the template writes (XFA
+//! 3.3 pp. 257–258, "Storing Images Inside PDF"). Only that tree is looked in: as the spec warns,
+//! a form that isn't trusted must not have its links followed outside the file.
+
+use std::collections::{HashMap, HashSet};
+
+use pdfcraft_cos::{Document, ObjRef, Object};
+
+use crate::model::{Field, Node, Subform, Template, Value};
+
+/// Most nodes of the name tree visited, and most names kept from it.
+const MAX_TREE_NODES: usize = 4096;
+const MAX_NAMES: usize = 4096;
+/// Deepest the name tree is followed.
+const MAX_DEPTH: usize = 32;
+/// Largest picture taken from the file, as for a picture written into the template.
+const MAX_IMAGE: usize = 32 << 20;
+/// Most bytes of pictures taken from the file in all, each place a picture is used counted (a
+/// picture is held once per place). Small in tests, so a test can reach it.
+#[cfg(not(test))]
+const MAX_TOTAL: usize = 128 << 20;
+#[cfg(test)]
+const MAX_TOTAL: usize = 1 << 10;
+/// Deepest the template is walked.
+const MAX_TEMPLATE_DEPTH: usize = 256;
+
+/// The `XFAImages` name tree: each name, as text, and the object it names.
+fn names(doc: &Document) -> HashMap<String, Object> {
+    let mut out = HashMap::new();
+    let Some(root) = doc.root() else { return out };
+    let catalog = doc.get(root);
+    let tree =
+        catalog.as_dict().and_then(|c| c.get(b"Names")).map(|n| doc.resolve(n)).and_then(|n| n.as_dict().and_then(|d| d.get(b"XFAImages")).cloned());
+    let Some(tree) = tree else { return out };
+    let mut seen: HashSet<ObjRef> = HashSet::new();
+    let mut visited = 0usize;
+    let mut stack = vec![(tree, 0usize)];
+    while let Some((node, depth)) = stack.pop() {
+        if visited >= MAX_TREE_NODES || out.len() >= MAX_NAMES {
+            break;
+        }
+        // Too deep: this branch is left, the others are still walked.
+        if depth > MAX_DEPTH {
+            continue;
+        }
+        visited += 1;
+        if let Some(r) = node.as_ref()
+            && !seen.insert(r)
+        {
+            continue;
+        }
+        let node = doc.resolve(&node);
+        let Some(d) = node.as_dict() else { continue };
+        if let Some(pairs) = d.get(b"Names").map(|n| doc.resolve(n)).and_then(|n| n.as_array().cloned()) {
+            for pair in pairs.chunks(2) {
+                if let [key, value] = pair
+                    && let Some(key) = doc.resolve(key).as_string()
+                {
+                    out.entry(key.to_text()).or_insert_with(|| value.clone());
+                    if out.len() >= MAX_NAMES {
+                        break;
+                    }
+                }
+            }
+        }
+        if let Some(kids) = d.get(b"Kids").map(|k| doc.resolve(k)).and_then(|k| k.as_array().cloned()) {
+            stack.extend(kids.into_iter().map(|k| (k, depth + 1)));
+        }
+    }
+    out
+}
+
+/// Pictures found so far by their link, read from the file once each.
+struct Found<'a> {
+    doc: &'a Document,
+    names: HashMap<String, Object>,
+    read: HashMap<String, Option<Vec<u8>>>,
+    /// Bytes of the pictures in `read`, and of the copies put in places: each at most
+    /// [`MAX_TOTAL`], however many names the tree holds.
+    kept: usize,
+    total: usize,
+    warnings: Vec<String>,
+}
+
+impl Found<'_> {
+    /// A copy of the picture linked as `href` for one more place, when the file holds it and the
+    /// pictures kept and the copies so far leave room for it under [`MAX_TOTAL`].
+    fn get(&mut self, href: &str) -> Option<Vec<u8>> {
+        if !self.read.contains_key(href) {
+            // Past the total, a picture not read yet is neither read nor kept.
+            let data = if self.kept >= MAX_TOTAL { None } else { self.load(href) };
+            let data = match data {
+                Some(d) if self.kept.saturating_add(d.len()) > MAX_TOTAL => {
+                    self.over_total();
+                    None
+                }
+                Some(d) => {
+                    self.kept = self.kept.saturating_add(d.len());
+                    Some(d)
+                }
+                None => {
+                    if self.kept >= MAX_TOTAL && self.names.contains_key(href) {
+                        self.over_total();
+                    }
+                    None
+                }
+            };
+            self.read.insert(href.to_string(), data);
+        }
+        let len = self.read.get(href).and_then(Option::as_ref).map(Vec::len)?;
+        if self.total.saturating_add(len) > MAX_TOTAL {
+            self.over_total();
+            return None;
+        }
+        self.total = self.total.saturating_add(len);
+        self.read.get(href).cloned().flatten()
+    }
+
+    fn over_total(&mut self) {
+        self.warnings.push("the pictures the form keeps in the file take too much memory in all; the rest are left out".into());
+    }
+
+    /// Bytes of the pictures read so far and kept for reuse.
+    #[cfg(test)]
+    fn kept(&self) -> usize {
+        self.read.values().flatten().map(Vec::len).sum()
+    }
+
+    fn load(&mut self, href: &str) -> Option<Vec<u8>> {
+        let object = self.names.get(href)?;
+        let object = self.doc.resolve(object);
+        let Object::Stream(s) = &*object else { return None };
+        let data = match s.decoded_within(MAX_IMAGE) {
+            Ok(d) => d,
+            Err(_) => {
+                self.warnings.push(format!("a picture the form keeps in the file ({href}) could not be read; it is left out"));
+                return None;
+            }
+        };
+        Some(data)
+    }
+
+    fn value(&mut self, v: &mut Value) {
+        if let Value::Image { data, href: Some(href), .. } = v
+            && data.is_empty()
+            && let Some(found) = self.get(href)
+        {
+            *data = found;
+        }
+    }
+
+    fn field(&mut self, f: &mut Field) {
+        self.value(&mut f.value);
+        if let Some(c) = f.caption.as_mut() {
+            self.value(&mut c.value);
+        }
+    }
+
+    fn nodes(&mut self, nodes: &mut [Node], depth: usize) {
+        if depth > MAX_TEMPLATE_DEPTH {
+            return;
+        }
+        for n in nodes {
+            match n {
+                Node::Subform(s) => self.subform(s, depth + 1),
+                Node::Area(a) => self.nodes(&mut a.children, depth + 1),
+                Node::Field(f) => self.field(f),
+                Node::Draw(d) => self.value(&mut d.value),
+                Node::ExclGroup(g) => g.fields.iter_mut().for_each(|f| self.field(f)),
+            }
+        }
+    }
+
+    fn subform(&mut self, s: &mut Subform, depth: usize) {
+        if let Some(set) = s.page_set.as_mut() {
+            for area in &mut set.areas {
+                self.nodes(&mut area.items, depth + 1);
+            }
+        }
+        self.nodes(&mut s.children, depth);
+    }
+}
+
+/// Give the pictures `tpl` links to (and doesn't embed) the data `doc` keeps for them. A link
+/// the file holds nothing for stays empty. What couldn't be read is returned as warnings.
+pub fn resolve(tpl: &mut Template, doc: &Document) -> Vec<String> {
+    resolve_found(tpl, doc).map(|f| f.warnings).unwrap_or_default()
+}
+
+fn resolve_found<'a>(tpl: &mut Template, doc: &'a Document) -> Option<Found<'a>> {
+    let names = names(doc);
+    if names.is_empty() {
+        return None;
+    }
+    let mut found = Found { doc, names, read: HashMap::new(), kept: 0, total: 0, warnings: Vec::new() };
+    found.subform(&mut tpl.root, 0);
+    found.warnings.dedup();
+    Some(found)
+}
+
+/// [`resolve`], and the bytes of pictures it held for reuse at the end.
+#[cfg(test)]
+pub(crate) fn resolve_keeping(tpl: &mut Template, doc: &Document) -> (Vec<String>, usize) {
+    resolve_found(tpl, doc).map_or((Vec::new(), 0), |f| (f.warnings.clone(), f.kept()))
+}

crates/xfa/src/model.rs

@@ -598,6 +598,9 @@ pub enum Value {
     Image {
         content_type: String,
         data: Vec<u8>,
+        /// Where the template links the picture from (`href`), when it does: its data is then
+        /// found in the PDF ([`crate::linked_images`]).
+        href: Option<String>,
     },
     /// A diagonal line through the box: `\` (top-left to bottom-right) or `/`.
     Line {

crates/xfa/src/parse.rs

@@ -401,7 +401,8 @@ fn parse_value(n: Option<XmlNode>, warnings: &mut Vec<String>) -> Value {
                     warnings.push("an image is larger than 32 MB; it is left out".into());
                     return Value::Empty;
                 }
-                return Value::Image { content_type: c.attribute("contentType").unwrap_or("").to_string(), data };
+                let href = c.attribute("href").map(str::trim).filter(|h| !h.is_empty()).map(str::to_string);
+                return Value::Image { content_type: c.attribute("contentType").unwrap_or("").to_string(), data, href };
             }
             "line" => {
                 return Value::Line { slope_up: c.attribute("slope") == Some("/"), edge: child(c, "edge").map(parse_edge).unwrap_or_default() };

crates/xfa/src/script.rs

@@ -656,7 +656,9 @@ pub fn template_of(doc: &Document) -> Result<Template, XfaError> {
     if packets.xdp.trim().is_empty() {
         return Err(XfaError::Malformed("the XFA packets hold no template".into()));
     }
-    crate::parse(&packets.xdp).map(|(t, _)| t)
+    let (mut tpl, _) = crate::parse(&packets.xdp)?;
+    crate::linked_images::resolve(&mut tpl, doc);
+    Ok(tpl)
 }
 
 /// Whether the template field at `som` is multiline text without a fixed height.