dd: allow B as a suffix for count, seek, and skip

[jfinkels]

Allow uppercase "B" on its own as a unit specifier for the count, seek, and skip arguments to dd.

For example,

$ printf "abcdef" | dd count=3B status=none
abc

This should fix GNU test suite file tests/dd/bytes.sh.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/dd/bytes is no longer failing!
Congrats! The gnu test tests/misc/timeout is no longer failing!

[jfinkels]

Looks like this doesn't quite work as-is:

run: /home/runner/work/coreutils/coreutils/target/debug/coreutils truncate -s 0B file
thread 'test_truncate::test_invalid_numbers' panicked at 'Command was expected to fail.

[tertsdiepraam]

Maybe we could report it back to GNU? Seems like an oversight on their part to not support B on truncate.

On our end, parse_size is due for a refactor that allows for specifying some options on how it should work. So that we don't end up with stuff like this:

fn parse_byte_count(input: &str) -> Result<usize, ParseSizeError> {
    // GNU sort (8.32)   valid: 1b,        k, K, m, M, g, G, t, T, P, E, Z, Y
    // GNU sort (8.32) invalid:  b, B, 1B,                         p, e, z, y
    const ALLOW_LIST: &[char] = &[
        'b', 'k', 'K', 'm', 'M', 'g', 'G', 't', 'T', 'P', 'E', 'Z', 'Y',
    ];
    let mut size_string = input.trim().to_string();

    if size_string.ends_with(|c: char| ALLOW_LIST.contains(&c) || c.is_ascii_digit()) {
        // b 1, K 1024 (default)
        if size_string.ends_with(|c: char| c.is_ascii_digit()) {
            size_string.push('K');
        } else if size_string.ends_with('b') {
            size_string.pop();
        }
        let size = parse_size(&size_string)?;
        usize::try_from(size).map_err(|_| {
            ParseSizeError::SizeTooBig(format!(
                "Buffer size {} does not fit in address space",
                size
            ))
        })
    } else if size_string.starts_with(|c: char| c.is_ascii_digit()) {
        Err(ParseSizeError::InvalidSuffix("invalid suffix".to_string()))
    } else {
        Err(ParseSizeError::ParseFailure("parse failure".to_string()))
    }
}

We'd need some configuration on what the allowed suffixes are, what the default factor is etc.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/dd/bytes is no longer failing!
Congrats! The gnu test tests/misc/timeout is no longer failing!

[jfinkels]

Okay, I've updated this pull request to add a uucore::parse_size::Parser struct, which has a parse() method, and the parse_size() function now delegates to Parser::default().parse(s). If we merge this pull request, then we can add more options to the Parse struct to cover the needs of parse_byte_count in a future pull request.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/dd/bytes is no longer failing!

[tertsdiepraam]

Even better than what I had in mind!