Keep bytes separate from text

Use list[u8] when data may contain invalid UTF-8. Encoding text copies its exact UTF-8 bytes; decoding validates every byte. Both operations observe their input, so you can keep the original data.

def main() -> Result[(), IoError]:
    text = "é\r\n"
    bytes = encode_utf8(text)?
    print(len(bytes))?
    print(decode_utf8(&bytes)? == text)?
    print(len(bytes))?
    invalid = encode_utf8("x")?
    mut raw = invalid
    raw[0] = 255u8
    match decode_utf8(&raw):
        case Ok(_):
            print("unexpected text")?
        case Err(error):
            print(error)?
    Ok(())

4
True
4
IoError.Data(DataError.InvalidUtf8)

On Unix, filenames and executable arguments can contain arbitrary bytes except NUL. Use args_bytes() to obtain those arguments, then pass a path byte list to read_bytes(path) or write_bytes(path, contents). These helpers preserve file contents and names without text decoding or newline conversion. They currently support Linux. write_bytes creates or replaces its destination.

For supplied paths on stdin, use input_bytes(0u8). It returns one NUL-delimited record as Some(record) or Nothing at EOF. Write records with write_stdout_bytes(&record) followed by write_stdout_bytes(b"\0"). Finish with flush_stdout()?. Empty records are distinct from EOF; a final nonempty unterminated record is accepted.

CR, LF, and invalid UTF-8 remain part of the path. Keep the original bytes when opening files, even if you separately decode or format them for display. The finder experiment includes a working --null mode. Its globs match bytes in that mode, so ? matches one byte.

See the binary I/O reference for partial effects, allocation failures, and remaining library limits.