gtin-validate 1.3.0

Validate GTIN barcodes including UPC-A and EAN-13. This module has built-in support for GTIN-8, GTIN-12 (UPC-A), GTIN-13 (EAN-13), and GTIN-14 codes.
Documentation 
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/// Compute the check digit for a GTIN code as described on the
/// [GS1 website](http://www.gs1.org/how-calculate-check-digit-manually)
/// This function assumes that the passed in bytes are already
/// guaranteed to be ASCII digits (eg, by calling is_ascii_numeric).
pub fn compute_check_digit(bytes: &[u8]) -> u8 {
    let mut even: u16 = 0;
    let mut odd: u16 = 0;
    let mut check: u8;
    let mut curr: u8;

    // Read GTIN in reverse because the even/odd columns are defined
    // right-to-left, with the last non-check-digit column being odd.
    for i in 2..bytes.len() + 1 {
        curr = bytes[bytes.len() - i] - 48;
        if i % 2 == 0 {
            odd += u16::from(curr);
        } else {
            even += u16::from(curr);
        }
    }

    check = ((3 * odd + even) % 10) as u8;
    if check > 0 {
        check = 10 - check;
    }

    check
}

/// Add zeros to the left side of a string so that it matches the
/// desired length.
///
/// If the string is longer than the desired length, it is returned,
/// without modification.
pub fn zero_pad(upc: String, size: usize) -> String {
    if upc.len() >= size {
        return upc;
    }
    let mut padded = String::with_capacity(size);
    for _ in 0..size - upc.len() {
        padded.push('0');
    }
    padded.push_str(&upc);

    padded
}

pub fn is_ascii_numeric(s: &str) -> bool {
    s.chars().all(|c| c.is_ascii_digit())
}

#[cfg(test)]
mod tests {
    use super::compute_check_digit;
    use super::is_ascii_numeric;
    use super::zero_pad;

    use proptest::prelude::*;

    #[test]
    fn compute_check_digit_static_data() {
        assert_eq!(compute_check_digit("000000000000".as_bytes()), 0);
        assert_eq!(compute_check_digit("123456789012".as_bytes()), 2);
        assert_eq!(compute_check_digit("123456789081".as_bytes()), 1);
        assert_eq!(compute_check_digit("036000291452".as_bytes()), 2);
        assert_eq!(compute_check_digit("999999999993".as_bytes()), 3);
        assert_eq!(compute_check_digit("0000000000000".as_bytes()), 0);
        assert_eq!(compute_check_digit("1234123412344".as_bytes()), 4);
        assert_eq!(compute_check_digit("9249874313545".as_bytes()), 5);
        assert_eq!(compute_check_digit("00000000000000".as_bytes()), 0);
        assert_eq!(compute_check_digit("01010101010104".as_bytes()), 4);
        assert_eq!(compute_check_digit("92498743135447".as_bytes()), 7);
    }

    #[test]
    fn zero_pad_static_data() {
        assert_eq!(zero_pad("hello".to_string(), 6), "0hello".to_string());
        assert_eq!(zero_pad("".to_string(), 0), "".to_string());
    }

    #[test]
    fn zero_pad_string_longer_than_desired_length() {
        assert_eq!(zero_pad("hello".to_string(), 3), "hello".to_string());
        assert_eq!(zero_pad("hello".to_string(), 0), "hello".to_string());
    }

    #[test]
    fn is_ascii_numeric_valid_numbers() {
        assert_eq!(is_ascii_numeric("0"), true);
        assert_eq!(is_ascii_numeric("1"), true);
        assert_eq!(is_ascii_numeric("00"), true);
        assert_eq!(is_ascii_numeric("99"), true);
    }

    #[test]
    fn is_ascii_numeric_invalid_numbers() {
        assert_eq!(is_ascii_numeric("a"), false);
        assert_eq!(is_ascii_numeric("0a"), false);
        assert_eq!(is_ascii_numeric("-1"), false);
        assert_eq!(is_ascii_numeric("4.2"), false);
    }

    proptest! {
        #[test]
        fn compute_check_digit_doesnt_crash(ref code in "[0-9]*") {
            assert!(compute_check_digit(code.as_bytes()) < 10);
        }
    }
}