tendermint 0.10.1

Tendermint is a high-performance blockchain consensus engine that powers Byzantine fault tolerant applications written in any programming language. This crate provides core types for representing information about Tendermint blockchain networks, including chain information types, secret connections, and remote procedure calls (JSONRPC).
Documentation 
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//! Merkle tree used in Tendermint networks

use sha2::{Digest, Sha256};

/// Size of Merkle root hash
pub const HASH_SIZE: usize = 32;

/// Compute a simple Merkle root from the arbitrary sized byte slices
pub fn simple_hash_from_byte_slices(byte_slices: &[&[u8]]) -> [u8; HASH_SIZE] {
    let length = byte_slices.len();
    match length {
        0 => [0; HASH_SIZE],
        1 => leaf_hash(byte_slices[0]),
        _ => {
            let k = get_split_point(length);
            let left = simple_hash_from_byte_slices(&byte_slices[..k]);
            let right = simple_hash_from_byte_slices(&byte_slices[k..]);
            inner_hash(&left, &right)
        }
    }
}

// returns the largest power of 2 less than length
fn get_split_point(length: usize) -> usize {
    match length {
        0 => panic!("tree is empty!"),
        1 => panic!("tree has only one element!"),
        2 => 1,
        _ => length.next_power_of_two() / 2,
    }
}

// tmhash(0x00 || leaf)
fn leaf_hash(bytes: &[u8]) -> [u8; HASH_SIZE] {
    // make a new array starting with 0 and copy in the bytes
    let mut leaf_bytes = Vec::with_capacity(bytes.len() + 1);
    leaf_bytes.push(0x00);
    leaf_bytes.extend_from_slice(bytes);

    // hash it !
    let digest = Sha256::digest(&leaf_bytes);

    // copy the GenericArray out
    let mut hash_bytes = [0u8; HASH_SIZE];
    hash_bytes.copy_from_slice(&digest);
    hash_bytes
}

// tmhash(0x01 || left || right)
fn inner_hash(left: &[u8], right: &[u8]) -> [u8; HASH_SIZE] {
    // make a new array starting with 0x1 and copy in the bytes
    let mut inner_bytes = Vec::with_capacity(left.len() + right.len() + 1);
    inner_bytes.push(0x01);
    inner_bytes.extend_from_slice(left);
    inner_bytes.extend_from_slice(right);

    // hash it !
    let digest = Sha256::digest(&inner_bytes);

    // copy the GenericArray out
    let mut hash_bytes = [0u8; HASH_SIZE];
    hash_bytes.copy_from_slice(&digest);
    hash_bytes
}

#[cfg(test)]
mod tests {
    use super::*;
    use subtle_encoding::hex; // TODO: use non-subtle ?

    #[test]
    fn test_get_split_point() {
        assert_eq!(get_split_point(2), 1);
        assert_eq!(get_split_point(3), 2);
        assert_eq!(get_split_point(4), 2);
        assert_eq!(get_split_point(5), 4);
        assert_eq!(get_split_point(10), 8);
        assert_eq!(get_split_point(20), 16);
        assert_eq!(get_split_point(100), 64);
        assert_eq!(get_split_point(255), 128);
        assert_eq!(get_split_point(256), 128);
        assert_eq!(get_split_point(257), 256);
    }

    #[test]
    fn test_rfc6962_empty_leaf() {
        let empty_leaf_root_hex =
            "6e340b9cffb37a989ca544e6bb780a2c78901d3fb33738768511a30617afa01d";
        let empty_leaf_root = &hex::decode(empty_leaf_root_hex).unwrap();
        let empty_tree: &[&[u8]] = &[&[]];
        let root = simple_hash_from_byte_slices(empty_tree);
        assert_eq!(empty_leaf_root, &root);
    }

    #[test]
    fn test_rfc6962_leaf() {
        let leaf_root_hex = "395aa064aa4c29f7010acfe3f25db9485bbd4b91897b6ad7ad547639252b4d56";
        let leaf_string = "L123456";

        let leaf_root = &hex::decode(leaf_root_hex).unwrap();
        let leaf_tree: &[&[u8]] = &[leaf_string.as_bytes()];
        let root = simple_hash_from_byte_slices(leaf_tree);
        assert_eq!(leaf_root, &root);
    }

    #[test]
    fn test_rfc6962_node() {
        let node_hash_hex = "aa217fe888e47007fa15edab33c2b492a722cb106c64667fc2b044444de66bbb";
        let left_string = "N123";
        let right_string = "N456";

        let node_hash = &hex::decode(node_hash_hex).unwrap();
        let hash = inner_hash(left_string.as_bytes(), right_string.as_bytes());
        assert_eq!(node_hash, &hash);
    }
}