fix(extractor): bound CID /W range expansion

Type0 /W parsing and the Unicode-CID heuristic expanded every CID in every
range. Repeating a full-width [0 65535 w] entry therefore re-materialized
the same 65,536-key domain on every copy, growing a temporary vector and
HashMap work without bound.

Cap expansion at the 16-bit CID domain, collect unique CIDs for the
median heuristic, and stop width assignment once that many entries have
been written. Legitimate compact /W arrays are unchanged.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/extractor/fonts.rs

@@ -482,7 +482,11 @@ pub(crate) fn parse_cid_w_array(
     widths: &mut HashMap<u16, u16>,
 ) {
     let mut i = 0;
+    let mut assigned = 0usize;
     while i < w_array.len() {
+        if assigned >= crate::tounicode::MAX_CID_W_EXPANSION {
+            return;
+        }
         let start_cid = match &w_array[i] {
             Object::Integer(n) => *n as u16,
             Object::Real(n) => *n as u16,
@@ -501,12 +505,14 @@ pub(crate) fn parse_cid_w_array(
             Object::Array(arr) => {
                 // [c [w1 w2 ...]] — consecutive widths starting at c
                 for (j, w_obj) in arr.iter().enumerate() {
-                    let w = match w_obj {
-                        Object::Integer(n) => *n as u16,
-                        Object::Real(n) => *n as u16,
-                        _ => continue,
-                    };
-                    widths.insert(start_cid + j as u16, w);
+                    if !assign_cid_width(
+                        widths,
+                        start_cid.wrapping_add(j as u16),
+                        w_obj,
+                        &mut assigned,
+                    ) {
+                        return;
+                    }
                 }
                 i += 1;
             }
@@ -514,12 +520,14 @@ pub(crate) fn parse_cid_w_array(
                 // Could be a reference to an array
                 if let Ok(Object::Array(arr)) = doc.get_object(*r) {
                     for (j, w_obj) in arr.iter().enumerate() {
-                        let w = match w_obj {
-                            Object::Integer(n) => *n as u16,
-                            Object::Real(n) => *n as u16,
-                            _ => continue,
-                        };
-                        widths.insert(start_cid + j as u16, w);
+                        if !assign_cid_width(
+                            widths,
+                            start_cid.wrapping_add(j as u16),
+                            w_obj,
+                            &mut assigned,
+                        ) {
+                            return;
+                        }
                     }
                     i += 1;
                 } else {
@@ -542,8 +550,8 @@ pub(crate) fn parse_cid_w_array(
                         continue;
                     }
                 };
-                for cid in start_cid..=end {
-                    widths.insert(cid, w);
+                if !assign_cid_width_range(widths, start_cid, end, w, &mut assigned) {
+                    return;
                 }
                 i += 1;
             }
@@ -561,8 +569,8 @@ pub(crate) fn parse_cid_w_array(
                         continue;
                     }
                 };
-                for cid in start_cid..=end {
-                    widths.insert(cid, w);
+                if !assign_cid_width_range(widths, start_cid, end, w, &mut assigned) {
+                    return;
                 }
                 i += 1;
             }
@@ -573,6 +581,45 @@ pub(crate) fn parse_cid_w_array(
     }
 }
 
+fn assign_cid_width(
+    widths: &mut HashMap<u16, u16>,
+    cid: u16,
+    w_obj: &Object,
+    assigned: &mut usize,
+) -> bool {
+    let w = match w_obj {
+        Object::Integer(n) => *n as u16,
+        Object::Real(n) => *n as u16,
+        _ => return true,
+    };
+    if *assigned >= crate::tounicode::MAX_CID_W_EXPANSION {
+        return false;
+    }
+    widths.insert(cid, w);
+    *assigned += 1;
+    true
+}
+
+fn assign_cid_width_range(
+    widths: &mut HashMap<u16, u16>,
+    start: u16,
+    end: u16,
+    w: u16,
+    assigned: &mut usize,
+) -> bool {
+    if start > end {
+        return true;
+    }
+    for cid in start..=end {
+        if *assigned >= crate::tounicode::MAX_CID_W_EXPANSION {
+            return false;
+        }
+        widths.insert(cid, w);
+        *assigned += 1;
+    }
+    true
+}
+
 /// Compute the width of a string in text space units,
 /// given raw bytes and font width info.
 /// Returns width in text space units (font_units * units_scale * font_size).
@@ -2313,4 +2360,48 @@ end",
         // invalid CMap result — so it must not clear the gid flag.
         assert!(gid_flagged(Some("<01> <FFFD>\n<02> <FFFD>")));
     }
+
+    #[test]
+    fn parse_cid_w_array_range_and_consecutive() {
+        use super::parse_cid_w_array;
+        use lopdf::{Document, Object};
+        use std::collections::HashMap;
+
+        let doc = Document::new();
+        let mut widths = HashMap::new();
+        let w = vec![
+            Object::Integer(10),
+            Object::Integer(12),
+            Object::Integer(500),
+            Object::Integer(20),
+            Object::Array(vec![Object::Integer(100), Object::Integer(200)]),
+        ];
+        parse_cid_w_array(&doc, &w, &mut widths);
+        assert_eq!(widths.get(&10), Some(&500));
+        assert_eq!(widths.get(&11), Some(&500));
+        assert_eq!(widths.get(&12), Some(&500));
+        assert_eq!(widths.get(&20), Some(&100));
+        assert_eq!(widths.get(&21), Some(&200));
+    }
+
+    #[test]
+    fn parse_cid_w_array_repeated_full_ranges_stay_bounded() {
+        use super::parse_cid_w_array;
+        use crate::tounicode::MAX_CID_W_EXPANSION;
+        use lopdf::{Document, Object};
+        use std::collections::HashMap;
+
+        let doc = Document::new();
+        let mut widths = HashMap::new();
+        let mut w = Vec::new();
+        for _ in 0..5_000 {
+            w.push(Object::Integer(0));
+            w.push(Object::Integer(65535));
+            w.push(Object::Integer(500));
+        }
+        parse_cid_w_array(&doc, &w, &mut widths);
+        assert!(widths.len() <= MAX_CID_W_EXPANSION);
+        assert_eq!(widths.get(&0), Some(&500));
+        assert_eq!(widths.get(&65535), Some(&500));
+    }
 }

src/tounicode.rs

@@ -1832,6 +1832,11 @@ fn merge_cmaps(mut base: ToUnicodeCMap, overlay: ToUnicodeCMap) -> ToUnicodeCMap
     base
 }
 
+/// Upper bound on CID `/W` range expansion. The CID domain is 16-bit, so more
+/// than 65,536 unique keys cannot exist; repeating full-width ranges must not
+/// re-expand the same domain.
+pub(crate) const MAX_CID_W_EXPANSION: usize = 65_536;
+
 /// Check if a CIDFont's /W (widths) array contains CID values that look like
 /// Unicode codepoints rather than low-value GIDs.
 ///
@@ -1843,20 +1848,23 @@ pub(crate) fn cid_values_look_like_unicode(cid_font_dict: &lopdf::Dictionary) ->
         _ => return false,
     };
 
-    // The /W array format: [cid [w1 w2 ...]] or [cid_start cid_end w]
-    // We extract all CID values (the first element of each group).
-    let mut cids: Vec<u16> = Vec::new();
+    // The /W array format: [cid [w1 w2 ...]] or [cid_start cid_end w].
+    // Collect unique CIDs only: repeating a full-width range must not grow a
+    // temporary vector (or the sort) with the range length on every copy.
+    let mut seen = HashSet::new();
     let mut i = 0;
-    while i < w_arr.len() {
+    while i < w_arr.len() && seen.len() < MAX_CID_W_EXPANSION {
         if let Ok(cid) = w_arr[i].as_i64() {
-            cids.push(cid as u16);
-            // Skip the width data
+            let start = cid as u16;
             if i + 1 < w_arr.len() {
                 match &w_arr[i + 1] {
                     Object::Array(widths) => {
                         // [cid [w1 w2 ...]] — CIDs are cid, cid+1, ..., cid+len-1
-                        for j in 1..widths.len() {
-                            cids.push((cid as u16).wrapping_add(j as u16));
+                        for j in 0..widths.len() {
+                            if seen.len() >= MAX_CID_W_EXPANSION {
+                                break;
+                            }
+                            seen.insert(start.wrapping_add(j as u16));
                         }
                         i += 2;
                     }
@@ -1864,9 +1872,7 @@ pub(crate) fn cid_values_look_like_unicode(cid_font_dict: &lopdf::Dictionary) ->
                         // [cid_start cid_end w] — range of CIDs
                         if i + 2 < w_arr.len() {
                             if let Ok(cid_end) = w_arr[i + 1].as_i64() {
-                                for c in (cid as u16)..=(cid_end as u16) {
-                                    cids.push(c);
-                                }
+                                record_unique_cid_range(start, cid_end as u16, &mut seen);
                             }
                             i += 3;
                         } else {
@@ -1875,6 +1881,7 @@ pub(crate) fn cid_values_look_like_unicode(cid_font_dict: &lopdf::Dictionary) ->
                     }
                 }
             } else {
+                seen.insert(start);
                 i += 1;
             }
         } else {
@@ -1882,10 +1889,11 @@ pub(crate) fn cid_values_look_like_unicode(cid_font_dict: &lopdf::Dictionary) ->
         }
     }
 
-    if cids.is_empty() {
+    if seen.is_empty() {
         return false;
     }
 
+    let mut cids: Vec<u16> = seen.into_iter().collect();
     cids.sort_unstable();
     let median = cids[cids.len() / 2];
     // Unicode text CIDs are typically >= 0x20 (space) with letters at 0x41+.
@@ -1894,6 +1902,18 @@ pub(crate) fn cid_values_look_like_unicode(cid_font_dict: &lopdf::Dictionary) ->
     median >= 0x41
 }
 
+fn record_unique_cid_range(start: u16, end: u16, seen: &mut HashSet<u16>) {
+    if start > end {
+        return;
+    }
+    for cid in start..=end {
+        if seen.len() >= MAX_CID_W_EXPANSION {
+            return;
+        }
+        seen.insert(cid);
+    }
+}
+
 /// Build a ToUnicodeCMap from predefined CID→Unicode mapping based on CIDSystemInfo.
 ///
 /// Supports Adobe-Korea1 (Korean) character collection. Can be extended for
@@ -3298,4 +3318,45 @@ endbfrange
             "An indirect /Subtype naming CIDFontType2 must still reach the remap"
         );
     }
+
+    #[test]
+    fn cid_values_look_like_unicode_letter_range() {
+        let mut dict = lopdf::Dictionary::new();
+        dict.set(
+            "W",
+            Object::Array(vec![
+                Object::Integer(0x41),
+                Object::Integer(0x5A),
+                Object::Integer(500),
+            ]),
+        );
+        assert!(cid_values_look_like_unicode(&dict));
+    }
+
+    #[test]
+    fn cid_values_look_like_unicode_low_gids() {
+        let mut dict = lopdf::Dictionary::new();
+        dict.set(
+            "W",
+            Object::Array(vec![
+                Object::Integer(0),
+                Object::Array(vec![Object::Integer(500); 10]),
+            ]),
+        );
+        assert!(!cid_values_look_like_unicode(&dict));
+    }
+
+    #[test]
+    fn cid_values_look_like_unicode_repeated_full_ranges_stay_bounded() {
+        // Repeating `[0 65535 w]` must not materialize 65,536 CIDs per copy.
+        let mut w = Vec::new();
+        for _ in 0..5_000 {
+            w.push(Object::Integer(0));
+            w.push(Object::Integer(65535));
+            w.push(Object::Integer(500));
+        }
+        let mut dict = lopdf::Dictionary::new();
+        dict.set("W", Object::Array(w));
+        assert!(cid_values_look_like_unicode(&dict));
+    }
 }