Tendermint merkle hash (#21)

* tendermint_hash

* document and link to tree

* update to use less copy

* removed let binding and added a test

* Fix warnings

* Improve feature granularity in maybestd to fix warns

* fmt

---------

Co-authored-by: Connor O'Hara <[email protected]>
Co-authored-by: Preston Evans <[email protected]>

Cargo.toml

@@ -20,6 +20,7 @@ borsh = { version = "0.10.0", optional = true }
 borsh = { version = "0.10.0" }
 serde_json = "1.0.96"
 postcard = { version = "1.0.4" }
+tendermint = {version = "0.35.0"}
 
 [features]
 default = ["std"]

src/lib.rs

@@ -18,11 +18,15 @@ extern crate alloc;
 
 mod maybestd {
     #[cfg(not(feature = "std"))]
-    pub use alloc::{boxed, collections, format, string, vec};
+    pub use alloc::{boxed, vec};
+    #[cfg(all(not(feature = "std"), feature = "serde"))]
+    pub use alloc::{format, string};
     #[cfg(not(feature = "std"))]
     pub use core::{cmp, fmt, hash, marker, mem, ops};
     #[cfg(feature = "std")]
-    pub use std::{boxed, cmp, collections, fmt, format, hash, marker, mem, ops, string, vec};
+    pub use std::{boxed, cmp, fmt, hash, marker, mem, ops, vec};
+    #[cfg(all(feature = "std", feature = "serde"))]
+    pub use std::{format, string};
 
     pub mod hash_or_btree_map {
         #[cfg(not(feature = "std"))]
@@ -46,6 +50,9 @@ use simple_merkle::{
 mod namespaced_hash;
 pub use namespaced_hash::*;
 
+mod tendermint_hash;
+pub use tendermint_hash::*;
+
 // pub mod db;
 pub mod nmt_proof;
 pub mod simple_merkle;
@@ -414,7 +421,7 @@ pub enum RangeProofType {
 
 #[cfg(test)]
 mod tests {
-    use crate::maybestd::{format, vec::Vec};
+    use crate::maybestd::vec::Vec;
     use crate::NamespaceMerkleHasher;
     use crate::{
         namespaced_hash::{NamespaceId, NamespacedSha2Hasher},

src/tendermint_hash.rs

@@ -0,0 +1,72 @@
+use sha2::{Digest, Sha256};
+
+use crate::simple_merkle::tree::MerkleHash;
+
+const LEAF_PREFIX: &[u8] = &[0];
+const INNER_PREFIX: &[u8] = &[1];
+
+fn leaf_hash(bytes: &[u8]) -> [u8; 32] {
+    //hash([LEAF_PREFIX, bytes].concat().as_slice())
+    let mut hasher = Sha256::new();
+    hasher.update(LEAF_PREFIX);
+    hasher.update(bytes);
+    hasher.finalize().into()
+}
+
+fn inner_hash(left: &[u8], right: &[u8]) -> [u8; 32] {
+    let mut hasher = Sha256::new();
+    hasher.update(INNER_PREFIX);
+    hasher.update(left);
+    hasher.update(right);
+    hasher.finalize().into()
+}
+
+/// A sha256 hasher, compatible with [Tendermint merkle hash](https://github.com/informalsystems/tendermint-rs/blob/979456c9f33463944f97f7ea3900640e59f7ea6d/tendermint/src/merkle.rs)
+pub struct TmSha2Hasher;
+
+impl Default for TmSha2Hasher {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl TmSha2Hasher {
+    /// Create a new instance of the hasher
+    pub fn new() -> Self {
+        TmSha2Hasher
+    }
+}
+
+impl MerkleHash for TmSha2Hasher {
+    type Output = [u8; 32];
+
+    const EMPTY_ROOT: Self::Output = [
+        227, 176, 196, 66, 152, 252, 28, 20, 154, 251, 244, 200, 153, 111, 185, 36, 39, 174, 65,
+        228, 100, 155, 147, 76, 164, 149, 153, 27, 120, 82, 184, 85,
+    ];
+
+    fn hash_leaf(&self, data: &[u8]) -> Self::Output {
+        leaf_hash(data)
+    }
+    fn hash_nodes(&self, left: &Self::Output, right: &Self::Output) -> Self::Output {
+        inner_hash(left, right)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{MemDb, MerkleTree};
+    use tendermint::merkle::simple_hash_from_byte_vectors;
+    #[test]
+    fn test_tm_hash_matches_upstream() {
+        let leaves: Vec<&[u8]> = vec![b"leaf_1", b"leaf_2", b"leaf_3", b"leaf_4"];
+        let hasher = TmSha2Hasher {};
+        let mut tree: MerkleTree<MemDb<[u8; 32]>, TmSha2Hasher> = MerkleTree::with_hasher(hasher);
+        leaves.iter().for_each(|leaf| {
+            tree.push_raw_leaf(leaf);
+        });
+        let hash_from_byte_slices = simple_hash_from_byte_vectors::<Sha256>(leaves.as_slice());
+        assert_eq!(tree.root().as_ref(), &hash_from_byte_slices);
+    }
+}