Function is_binary 

pub fn is_binary(bytes: &[u8]) -> bool

Git’s binary heuristic (buffer_is_binary): a NUL byte within the first BINARY_SNIFF_LEN bytes marks the blob binary, regardless of UTF-8 validity. bytes may be a full blob or just its leading BINARY_SNIFF_LEN-byte prefix — since this never looks past that many bytes, the result is identical either way.