sstable 0.11.1

Sorted String Tables, an on-disk format for storing immutable maps consisting of string,string pairs, and retrieving values by key efficiently. This crate also features bloom filters, checksums and skipping bad blocks. It is based on the code implemented for the rusty_leveldb crate.
Documentation 
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use std::cmp::Ordering;

/// Comparator trait, supporting types that can be nested (i.e., add additional functionality on
/// top of an inner comparator)
pub trait Cmp: Sync + Send {
    /// Compare to byte strings, bytewise.
    fn cmp(&self, _: &[u8], _: &[u8]) -> Ordering;

    /// Return the shortest byte string that compares "Greater" to the first argument and "Less" to
    /// the second one.
    fn find_shortest_sep(&self, _: &[u8], _: &[u8]) -> Vec<u8>;
    /// Return the shortest byte string that compares "Greater" to the argument.
    fn find_short_succ(&self, _: &[u8]) -> Vec<u8>;

    /// A unique identifier for a comparator. A comparator wrapper (like InternalKeyCmp) may
    /// return the id of its inner comparator.
    fn id(&self) -> &'static str;
}

/// Lexical comparator.
#[derive(Clone)]
pub struct DefaultCmp;

impl Cmp for DefaultCmp {
    fn cmp(&self, a: &[u8], b: &[u8]) -> Ordering {
        a.cmp(b)
    }

    fn id(&self) -> &'static str {
        "leveldb.BytewiseComparator"
    }

    fn find_shortest_sep(&self, a: &[u8], b: &[u8]) -> Vec<u8> {
        if a == b {
            return a.to_vec();
        }

        let min = if a.len() < b.len() { a.len() } else { b.len() };
        let mut diff_at = 0;

        while diff_at < min && a[diff_at] == b[diff_at] {
            diff_at += 1;
        }

        while diff_at < min {
            let diff = a[diff_at];
            if diff < 0xff && diff + 1 < b[diff_at] {
                let mut sep = Vec::from(&a[0..diff_at + 1]);
                sep[diff_at] += 1;
                assert!(self.cmp(&sep, b) == Ordering::Less);
                return sep;
            }

            diff_at += 1;
        }
        // Backup case: either `a` is full of 0xff, or all different places are less than 2
        // characters apart.
        // The result is not necessarily short, but a good separator: e.g., "abc" vs "abd" ->
        // "abc\0", which is greater than "abc" and lesser than "abd".
        let mut sep = Vec::with_capacity(a.len() + 1);
        sep.extend_from_slice(a);
        // Append a 0 byte; by making it longer than a, it will compare greater to it.
        sep.extend_from_slice(&[0]);
        return sep;
    }

    fn find_short_succ(&self, a: &[u8]) -> Vec<u8> {
        let mut result = a.to_vec();
        for i in 0..a.len() {
            if a[i] != 0xff {
                result[i] += 1;
                result.resize(i + 1, 0);
                return result;
            }
        }
        // Rare path
        result.push(255);
        return result;
    }
}

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

    #[test]
    fn test_cmp_defaultcmp_shortest_sep() {
        assert_eq!(
            DefaultCmp.find_shortest_sep("abcd".as_bytes(), "abcf".as_bytes()),
            "abce".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_shortest_sep("abc".as_bytes(), "acd".as_bytes()),
            "abc\0".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_shortest_sep("abcdefghi".as_bytes(), "abcffghi".as_bytes()),
            "abce".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_shortest_sep("a".as_bytes(), "a".as_bytes()),
            "a".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_shortest_sep("a".as_bytes(), "b".as_bytes()),
            "a\0".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_shortest_sep("abc".as_bytes(), "zzz".as_bytes()),
            "b".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_shortest_sep("yyy".as_bytes(), "z".as_bytes()),
            "yyy\0".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_shortest_sep("".as_bytes(), "".as_bytes()),
            "".as_bytes()
        );
    }

    #[test]
    fn test_cmp_defaultcmp_short_succ() {
        assert_eq!(
            DefaultCmp.find_short_succ("abcd".as_bytes()),
            "b".as_bytes()
        );
        assert_eq!(
            DefaultCmp.find_short_succ("zzzz".as_bytes()),
            "{".as_bytes()
        );
        assert_eq!(DefaultCmp.find_short_succ(&[]), &[0xff]);
        assert_eq!(
            DefaultCmp.find_short_succ(&[0xff, 0xff, 0xff]),
            &[0xff, 0xff, 0xff, 0xff]
        );
    }
}