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fix: Form XObject text garbled when /Resources is an indirect reference #407

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fix: Form XObject text garbled when /Resources is an indirect reference #407

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264 changes: 242 additions & 22 deletions src/tounicode.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2077,10 +2077,17 @@ impl FontCMaps {
skip_truetype_fallback,
);

if !skip_truetype_fallback {
// Fonts inside Form XObjects referenced by this page
Self::collect_cmaps_from_xobjects(doc, page_id, &mut by_obj_num);
}
// Fonts inside Form XObjects referenced by this page. Always
// run — even in fast mode — so primary ToUnicode CMaps on Form
// XObject fonts are still discovered; skip_truetype_fallback
// only skips the *expensive* embedded-font fallback parsing
// for those fonts, not CMap discovery entirely. See #398.
Self::collect_cmaps_from_xobjects(
doc,
page_id,
&mut by_obj_num,
skip_truetype_fallback,
);
}

FontCMaps { by_obj_num }
Expand All @@ -2089,14 +2096,6 @@ impl FontCMaps {
/// Parse ToUnicode CMaps from a set of font dictionaries.
/// Also handles Identity-H/V CID fonts without ToUnicode by parsing
/// the embedded TrueType cmap from FontFile2.
fn collect_cmaps_from_fonts(
fonts: &std::collections::BTreeMap<Vec<u8>, &lopdf::Dictionary>,
doc: &Document,
by_obj_num: &mut HashMap<u32, CMapEntry>,
) {
Self::collect_cmaps_from_fonts_inner(fonts, doc, by_obj_num, false);
}

fn collect_cmaps_from_fonts_inner(
fonts: &std::collections::BTreeMap<Vec<u8>, &lopdf::Dictionary>,
doc: &Document,
Expand Down Expand Up @@ -2439,6 +2438,7 @@ impl FontCMaps {
doc: &Document,
page_id: ObjectId,
by_obj_num: &mut HashMap<u32, CMapEntry>,
skip_truetype_fallback: bool,
) {
let (resource_dict, resource_ids) = match doc.get_page_resources(page_id) {
Ok(r) => r,
Expand All @@ -2448,25 +2448,48 @@ impl FontCMaps {
let mut visited = HashSet::new();

if let Some(resources) = resource_dict {
Self::walk_xobject_fonts(resources, doc, by_obj_num, &mut visited);
Self::walk_xobject_fonts(
resources,
doc,
by_obj_num,
&mut visited,
skip_truetype_fallback,
);
}
for resource_id in resource_ids {
if let Ok(resources) = doc.get_dictionary(resource_id) {
Self::walk_xobject_fonts(resources, doc, by_obj_num, &mut visited);
Self::walk_xobject_fonts(
resources,
doc,
by_obj_num,
&mut visited,
skip_truetype_fallback,
);
}
}
}

/// Resolve a dictionary-or-reference-to-dictionary `Object`, matching
/// the two shapes the PDF spec allows for entries like `/Resources`
/// (inline dictionary, or an indirect reference to one).
fn resolve_dict<'a>(doc: &'a Document, obj: &'a Object) -> Option<&'a lopdf::Dictionary> {
match obj {
Object::Reference(id) => doc.get_object(*id).and_then(Object::as_dict).ok(),
Object::Dictionary(dict) => Some(dict),
_ => None,
}
}

/// Recursively collect font CMaps from XObjects in a resource dictionary.
fn walk_xobject_fonts(
resources: &lopdf::Dictionary,
doc: &Document,
by_obj_num: &mut HashMap<u32, CMapEntry>,
visited: &mut HashSet<ObjectId>,
skip_truetype_fallback: bool,
) {
let xobject_dict = match resources.get(b"XObject") {
Ok(Object::Reference(id)) => doc.get_object(*id).and_then(Object::as_dict).ok(),
Ok(Object::Dictionary(dict)) => Some(dict),
Ok(obj) => Self::resolve_dict(doc, obj),
_ => None,
};
let xobject_dict = match xobject_dict {
Expand Down Expand Up @@ -2494,12 +2517,20 @@ impl FontCMaps {
if !is_form {
continue;
}
// Collect fonts from this Form XObject's Resources
if let Ok(form_resources) = stream.dict.get(b"Resources").and_then(Object::as_dict) {
// Collect fonts from this Form XObject's Resources. /Resources
// can be an inline dictionary or an indirect reference to one
// (both are valid per spec) — resolve_dict handles both, where
// the old inline-only lookup silently skipped the latter,
// dropping the Form's ToUnicode CMap discovery entirely. See
// #398.
let form_resources = match stream.dict.get(b"Resources") {
Ok(obj) => Self::resolve_dict(doc, obj),
_ => None,
};
if let Some(form_resources) = form_resources {
// Extract font dict from the Form's resources
let font_dict_obj = match form_resources.get(b"Font") {
Ok(Object::Reference(id)) => doc.get_object(*id).and_then(Object::as_dict).ok(),
Ok(Object::Dictionary(dict)) => Some(dict),
Ok(obj) => Self::resolve_dict(doc, obj),
_ => None,
};
if let Some(font_dict) = font_dict_obj {
Expand All @@ -2514,10 +2545,21 @@ impl FontCMaps {
fonts.insert(name.clone(), font);
}
}
Self::collect_cmaps_from_fonts(&fonts, doc, by_obj_num);
Self::collect_cmaps_from_fonts_inner(
&fonts,
doc,
by_obj_num,
skip_truetype_fallback,
);
}
// Recurse into nested XObjects
Self::walk_xobject_fonts(form_resources, doc, by_obj_num, visited);
Self::walk_xobject_fonts(
form_resources,
doc,
by_obj_num,
visited,
skip_truetype_fallback,
);
}
}
}
Expand Down Expand Up @@ -2662,6 +2704,184 @@ fn build_fallback_cmap_for_simple(
mod tests {
use super::*;

/// Regression for #398: a Form XObject's `/Resources` entry can be an
/// indirect reference to a dictionary rather than an inline
/// dictionary — both are valid per spec. Builds a minimal PDF with a
/// page → Form XObject → indirect `/Resources` → Type0 font with a
/// ToUnicode CMap, and confirms `FontCMaps::from_doc` still discovers
/// that CMap.
#[test]
fn form_xobject_with_indirect_resources_discovers_tounicode_cmap() {
use lopdf::{dictionary, Stream};

let mut doc = Document::with_version("1.4");
let pages_id = doc.new_object_id();
let page_id = doc.new_object_id();

let cmap_content = b"\
/CIDInit /ProcSet findresource begin
12 dict begin
begincmap
1 begincodespacerange
<0000><FFFF>
endcodespacerange
1 beginbfchar
<0003> <0041>
endbfchar
endcmap"
.to_vec();
let tounicode_id =
doc.add_object(Object::Stream(Stream::new(dictionary! {}, cmap_content)));

let font_id = doc.add_object(dictionary! {
"Type" => "Font",
"Subtype" => Object::Name(b"Type0".to_vec()),
"BaseFont" => Object::Name(b"ABCDEF+Test".to_vec()),
"Encoding" => Object::Name(b"Identity-H".to_vec()),
"ToUnicode" => Object::Reference(tounicode_id),
});

// The Form's /Resources is stored as an indirect reference to a
// dictionary — the case the old inline-only lookup silently
// skipped.
let form_resources_id = doc.add_object(Object::Dictionary(dictionary! {
"Font" => dictionary! {
"F1" => Object::Reference(font_id),
},
}));

let form_stream_content = b"BT /F1 12 Tf (test) Tj ET".to_vec();
let mut form_dict = dictionary! {
"Type" => "XObject",
"Subtype" => Object::Name(b"Form".to_vec()),
"Resources" => Object::Reference(form_resources_id),
};
form_dict.set("Length", form_stream_content.len() as i64);
let form_id = doc.add_object(Object::Stream(Stream::new(form_dict, form_stream_content)));

let page_resources = dictionary! {
"XObject" => dictionary! {
"X1" => Object::Reference(form_id),
},
};
doc.objects.insert(
page_id,
Object::Dictionary(dictionary! {
"Type" => "Page",
"Parent" => Object::Reference(pages_id),
"Resources" => page_resources,
}),
);
doc.objects.insert(
pages_id,
Object::Dictionary(dictionary! {
"Type" => "Pages",
"Kids" => vec![Object::Reference(page_id)],
"Count" => Object::Integer(1),
}),
);
let catalog_id = doc.add_object(dictionary! {
"Type" => "Catalog",
"Pages" => Object::Reference(pages_id),
});
doc.trailer.set("Root", Object::Reference(catalog_id));

let cmaps = FontCMaps::from_doc(&doc);
let entry = cmaps.get_by_obj(tounicode_id.0);
assert!(
entry.is_some(),
"ToUnicode CMap on a Form XObject font should be discovered even when \
the Form's /Resources is an indirect reference"
);
assert_eq!(entry.unwrap().primary.lookup(0x0003), Some("A".to_string()));
}

/// Same fixture as above, but via the fast/page-selected extraction
/// path (`from_doc_pages_fast`) — primary ToUnicode CMaps on Form
/// XObject fonts must still be discovered there too, even though the
/// expensive TrueType embedded-font fallback is skipped in that mode.
#[test]
fn form_xobject_indirect_resources_discovered_in_fast_mode_too() {
use lopdf::{dictionary, Stream};

let mut doc = Document::with_version("1.4");
let pages_id = doc.new_object_id();
let page_id = doc.new_object_id();

let cmap_content = b"\
/CIDInit /ProcSet findresource begin
12 dict begin
begincmap
1 begincodespacerange
<0000><FFFF>
endcodespacerange
1 beginbfchar
<0003> <0041>
endbfchar
endcmap"
.to_vec();
let tounicode_id =
doc.add_object(Object::Stream(Stream::new(dictionary! {}, cmap_content)));

let font_id = doc.add_object(dictionary! {
"Type" => "Font",
"Subtype" => Object::Name(b"Type0".to_vec()),
"BaseFont" => Object::Name(b"ABCDEF+Test".to_vec()),
"Encoding" => Object::Name(b"Identity-H".to_vec()),
"ToUnicode" => Object::Reference(tounicode_id),
});

let form_resources_id = doc.add_object(Object::Dictionary(dictionary! {
"Font" => dictionary! {
"F1" => Object::Reference(font_id),
},
}));

let form_stream_content = b"BT /F1 12 Tf (test) Tj ET".to_vec();
let mut form_dict = dictionary! {
"Type" => "XObject",
"Subtype" => Object::Name(b"Form".to_vec()),
"Resources" => Object::Reference(form_resources_id),
};
form_dict.set("Length", form_stream_content.len() as i64);
let form_id = doc.add_object(Object::Stream(Stream::new(form_dict, form_stream_content)));

let page_resources = dictionary! {
"XObject" => dictionary! {
"X1" => Object::Reference(form_id),
},
};
doc.objects.insert(
page_id,
Object::Dictionary(dictionary! {
"Type" => "Page",
"Parent" => Object::Reference(pages_id),
"Resources" => page_resources,
}),
);
doc.objects.insert(
pages_id,
Object::Dictionary(dictionary! {
"Type" => "Pages",
"Kids" => vec![Object::Reference(page_id)],
"Count" => Object::Integer(1),
}),
);
let catalog_id = doc.add_object(dictionary! {
"Type" => "Catalog",
"Pages" => Object::Reference(pages_id),
});
doc.trailer.set("Root", Object::Reference(catalog_id));

let cmaps = FontCMaps::from_doc_pages_fast(&doc, None);
let entry = cmaps.get_by_obj(tounicode_id.0);
assert!(
entry.is_some(),
"primary ToUnicode CMap on a Form XObject font should still be \
discovered in fast mode, even with indirect /Resources"
);
}

#[test]
fn test_parse_bfchar_2byte() {
let cmap_content = r#"
Expand Down