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Sort table records when parsing the table directory #29

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Merged
laurmaedje merged 1 commit into from
Jul 23, 2026
Merged

Sort table records when parsing the table directory #29

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34 changes: 34 additions & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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 })
}

Expand Down Expand Up @@ -693,6 +697,36 @@ mod tests {
assert_eq!(result, Err(Error::CFFError));
}

#[test]
fn unsorted_table_directory_is_searchable() {

@LaurenzV LaurenzV Jul 22, 2026

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Did you make sure that this test fails before this commit? AFAIK it might depend on where exactly the binary search starts right?

@dcalvo dcalvo Jul 22, 2026

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Yes. With the sort reverted, the test fails (table(Tag::HEAD) returns None). It's also pivot-independent because the fixture is a swapped pair, so searching for one of the two tags always gets steered into an empty range, and one of the two asserts always fails.

// 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 {
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