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|
//! Provides the MerkleTree structure and associated methods for creating and interacting
//! with binary Merkle trees using custom hashers.
use crate::{fs, hasher::Hasher, node::Node};
use rayon::prelude::*;
/// A binary Merkle tree implementation.
///
/// Merkle trees are hash-based data structures used for secure and efficient data verification.
/// Each leaf node contains the hash of a data item, and each internal node contains the hash
/// of the concatenation of its children's hashes.
pub struct MerkleTree {
/// Leaf nodes at the base of the tree (may include a duplicate for even pairing).
leaves: Vec<Node>,
/// Height of the tree (number of levels including root).
height: usize,
/// Root node of the Merkle tree.
root: Node,
}
impl MerkleTree {
/// Creates a new `MerkleTree` from a collection of data items and a hash function.
///
/// # Arguments
///
/// * `hasher` - A reference to an implementation of the `Hasher` trait.
/// * `data` - A vector of values to be converted into leaf nodes.
///
/// # Panics
///
/// Panics if the `data` vector is empty.
///
/// # Notes
///
/// If the number of leaf nodes is odd, the last node is duplicated to ensure all internal
/// nodes have exactly two children.
pub fn new<I, T, H>(hasher: H, data: I) -> Self
where
I: IntoIterator<Item = T>,
T: AsRef<[u8]>,
H: Hasher + 'static + std::marker::Sync,
{
let owned_data: Vec<T> = data.into_iter().collect();
let data_slices: Vec<&[u8]> = owned_data.iter().map(|item| item.as_ref()).collect();
assert!(
!data_slices.is_empty(),
"Merkle Tree requires at least one element"
);
let leaves: Vec<Node> = data_slices
.iter()
.map(|data| Node::new_leaf(hasher.hash(data)))
.collect();
Self::build(hasher, leaves)
}
/// Construct a Merkletree from an iter of String-s.
pub fn from_paths<H>(hasher: H, paths: Vec<String>) -> Self
where
H: Hasher + 'static + std::marker::Sync + Clone,
{
let leaves = fs::hash_dir(hasher.clone(), paths);
Self::build(hasher, leaves)
}
/// Constructs the internal nodes of the tree from the leaves upward and computes the root.
fn build<H>(hasher: H, leaves: Vec<Node>) -> Self
where
H: Hasher + 'static + std::marker::Sync,
{
let mut current_level = leaves.clone();
let mut next_level = Vec::with_capacity((current_level.len() + 1) / 2);
let mut height = 0;
while current_level.len() > 1 {
if current_level.len() % 2 != 0 {
// duplicate last node to make the count even
current_level.push(current_level.last().unwrap().clone());
}
next_level.clear();
next_level = current_level
.par_chunks(2)
.map(|pair| {
let (left, right) = (&pair[0], &pair[1]);
let (left_hash, right_hash) = (left.hash().as_bytes(), right.hash().as_bytes());
let mut buffer = Vec::with_capacity(left_hash.len() + right_hash.len());
buffer.extend_from_slice(left_hash);
buffer.extend_from_slice(right_hash);
let hash = hasher.hash(&buffer);
Node::new_internal(hash, left.clone(), right.clone())
})
.collect();
std::mem::swap(&mut current_level, &mut next_level);
height += 1;
}
let root = current_level.remove(0);
MerkleTree {
leaves,
height: height + 1,
root,
}
}
/// Returns the height (number of levels) of the tree.
pub fn height(&self) -> usize {
self.height
}
/// Returns true if the tree has no leaves (should never happen if `new()` was used).
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// Returns the number of leaf nodes in the tree.
pub fn len(&self) -> usize {
self.leaves.len()
}
/// Returns the tree' leaves.
pub fn leaves(&self) -> Vec<Node> {
self.leaves.clone()
}
/// Returns the root node of the tree.
pub fn root(&self) -> Node {
self.root.clone()
}
}
#[cfg(test)]
mod tests {
use super::*;
use crate::hasher::*;
#[test]
fn test_merkle_tree_with_default_hasher() {
let data = &["hello".as_bytes(), "world".as_bytes()];
let tree = MerkleTree::new(DummyHasher, data);
assert_eq!(tree.height(), 2);
assert_eq!(tree.root().hash(), "hash_539");
}
#[test]
fn test_merkle_tree_hashing() {
let data = &["hello".as_bytes(), "world".as_bytes()];
let tree = MerkleTree::new(SHA256Hasher::new(), data);
assert_eq!(tree.height(), 2);
assert_eq!(
tree.root().hash(),
"15e178b71fae8849ee562c9cc0d7ea322fba6cd495411329d47234479167cc8b"
);
}
#[test]
fn test_merkle_tree_single_leaf() {
let data = &["hello".as_bytes()];
let tree = MerkleTree::new(SHA256Hasher::new(), data);
assert_eq!(tree.height(), 1);
assert_eq!(tree.len(), 1);
assert_eq!(
tree.root().hash(),
"2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
);
}
#[test]
fn test_merkle_tree_with_10_elements() {
let inputs = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"];
let data: Vec<&[u8]> = inputs.iter().map(|s| s.as_bytes()).collect();
let tree = MerkleTree::new(SHA256Hasher::new(), &data);
assert_eq!(tree.height(), 5); // 10 elements padded to 16 → log2(16) + 1 = 5
// You can print the root hash if you're unsure what it should be:
println!("Merkle root hash: {}", tree.root().hash());
// If you know the expected hash, use:
assert_eq!(
tree.root().hash(),
"9da1ff0dfa79217bdbea9ec96407b1e693646cc493f64059fa27182a37cadf94"
);
}
}
|
