eml-codec 0.1.2

Email enCOder DECoder in Rust. Support Internet Message Format and MIME (RFC 822, 5322, 2045, 2046, 2047, 2048, 2049).
Documentation 
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use nom::{
    bytes::complete::{tag, take},
    combinator::{map, opt, verify},
    sequence::tuple,
    IResult,
};

use crate::text::ascii;
use crate::text::whitespace::cfws;

#[derive(Debug, PartialEq)]
pub struct Version {
    pub major: u8,
    pub minor: u8,
}

pub fn version(input: &[u8]) -> IResult<&[u8], Version> {
    let (rest, (_, major, _, _, _, minor, _)) = tuple((
        opt(cfws),
        map(verify(take(1usize), is_digit), ascii_to_u8),
        opt(cfws),
        tag(b"."),
        opt(cfws),
        map(verify(take(1usize), is_digit), ascii_to_u8),
        opt(cfws),
    ))(input)?;
    Ok((rest, Version { major, minor }))
}

fn is_digit(c: &[u8]) -> bool {
    c[0] >= ascii::N0 && c[0] <= ascii::N9
}

fn ascii_to_u8(c: &[u8]) -> u8 {
    c[0] - ascii::N0
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_version() {
        assert_eq!(
            version(b"1.0"),
            Ok((&b""[..], Version { major: 1, minor: 0 })),
        );

        assert_eq!(
            version(b" 1.0 (produced by MetaSend Vx.x)"),
            Ok((&b""[..], Version { major: 1, minor: 0 })),
        );

        assert_eq!(
            version(b"(produced by MetaSend Vx.x) 1.0"),
            Ok((&b""[..], Version { major: 1, minor: 0 })),
        );

        assert_eq!(
            version(b"1.(produced by MetaSend Vx.x)0"),
            Ok((&b""[..], Version { major: 1, minor: 0 })),
        );
    }
}