Sort table records when parsing so unsorted table directories remain searchable (#29)

Author: dcalvo

src/lib.rs

@@ -280,6 +280,10 @@ fn parse(data: &[u8], index: u32) -> Result<Face<'_>> {
         records.push(r.read::<TableRecord>().ok_or(MalformedFont)?);
     }
 
+    // `Face::table` binary-searches by tag, but fonts in the wild violate
+    // the spec's requirement that the directory be sorted.
+    records.sort_by_key(|record| record.tag);
+
     Ok(Face { data, records })
 }
 
@@ -693,6 +697,36 @@ mod tests {
         assert_eq!(result, Err(Error::CFFError));
     }
 
+    #[test]
+    fn unsorted_table_directory_is_searchable() {
+        // Two table records deliberately stored in non-alphabetical order
+        // (`head` before `cmap`): the directory violates the spec's sort
+        // requirement, but both tables must still be found.
+        let mut font = Vec::new();
+        font.extend(0x00010000u32.to_be_bytes());
+        font.extend(2u16.to_be_bytes());
+        font.extend(0u16.to_be_bytes());
+        font.extend(0u16.to_be_bytes());
+        font.extend(0u16.to_be_bytes());
+        // Directory (2 records à 16 bytes; data starts at 12 + 32 = 44).
+        font.extend(*b"head");
+        font.extend(0u32.to_be_bytes());
+        font.extend(44u32.to_be_bytes());
+        font.extend(4u32.to_be_bytes());
+        font.extend(*b"cmap");
+        font.extend(0u32.to_be_bytes());
+        font.extend(48u32.to_be_bytes());
+        font.extend(4u32.to_be_bytes());
+        // Table payloads.
+        font.extend([1, 2, 3, 4]);
+        font.extend([5, 6, 7, 8]);
+
+        let face = parse(&font, 0).unwrap();
+
+        assert_eq!(face.table(Tag::HEAD), Some([1, 2, 3, 4].as_slice()));
+        assert_eq!(face.table(Tag::CMAP), Some([5, 6, 7, 8].as_slice()));
+    }
+
     #[test]
     fn table_record_with_invalid_bounds_returns_none() {
         let face = Face {