feat: add parent node iterator for SimpleSMT

src/merkle/simple_smt/mod.rs

@@ -1,5 +1,6 @@
 use super::{
-    BTreeMap, EmptySubtreeRoots, MerkleError, MerklePath, NodeIndex, Rpo256, RpoDigest, Vec, Word,
+    BTreeMap, EmptySubtreeRoots, InnerNodeInfo, MerkleError, MerklePath, NodeIndex, Rpo256,
+    RpoDigest, Vec, Word,
 };
 
 #[cfg(test)]
@@ -15,14 +16,20 @@ pub struct SimpleSmt {
     depth: u8,
     root: Word,
     leaves: BTreeMap<u64, Word>,
-    pub(crate) branches: BTreeMap<NodeIndex, BranchNode>,
+    branches: BTreeMap<NodeIndex, BranchNode>,
     empty_hashes: Vec<RpoDigest>,
 }
 
 #[derive(Debug, Default, Clone, PartialEq, Eq)]
-pub(crate) struct BranchNode {
-    pub(crate) left: RpoDigest,
-    pub(crate) right: RpoDigest,
+struct BranchNode {
+    left: RpoDigest,
+    right: RpoDigest,
+}
+
+impl BranchNode {
+    fn parent(&self) -> RpoDigest {
+        Rpo256::merge(&[self.left, self.right])
+    }
 }
 
 impl SimpleSmt {
@@ -171,6 +178,15 @@ impl SimpleSmt {
         self.get_path(NodeIndex::new(self.depth(), key))
     }
 
+    /// Iterator over the inner nodes of the [SimpleSmt].
+    pub fn inner_nodes(&self) -> impl Iterator<Item = InnerNodeInfo> + '_ {
+        self.branches.values().map(|e| InnerNodeInfo {
+            value: e.parent().into(),
+            left: e.left.into(),
+            right: e.right.into(),
+        })
+    }
+
     // STATE MUTATORS
     // --------------------------------------------------------------------------------------------
 

src/merkle/simple_smt/tests.rs

@@ -1,5 +1,5 @@
 use super::{
-    super::{int_to_node, MerkleTree, RpoDigest, SimpleSmt},
+    super::{int_to_node, InnerNodeInfo, MerkleError, MerkleTree, RpoDigest, SimpleSmt},
     NodeIndex, Rpo256, Vec, Word,
 };
 use proptest::prelude::*;
@@ -138,6 +138,51 @@ fn get_path() {
     assert_eq!(vec![node2], *tree.get_path(NodeIndex::new(1, 1)).unwrap());
 }
 
+#[test]
+fn test_parent_node_iterator() -> Result<(), MerkleError> {
+    let tree = SimpleSmt::new(2)
+        .unwrap()
+        .with_leaves(KEYS4.into_iter().zip(VALUES4.into_iter()))
+        .unwrap();
+
+    // check depth 2
+    assert_eq!(VALUES4[0], tree.get_node(&NodeIndex::new(2, 0)).unwrap());
+    assert_eq!(VALUES4[1], tree.get_node(&NodeIndex::new(2, 1)).unwrap());
+    assert_eq!(VALUES4[2], tree.get_node(&NodeIndex::new(2, 2)).unwrap());
+    assert_eq!(VALUES4[3], tree.get_node(&NodeIndex::new(2, 3)).unwrap());
+
+    // get parent nodes
+    let root = tree.root();
+    let l1n0 = tree.get_node(&NodeIndex::new(1, 0))?;
+    let l1n1 = tree.get_node(&NodeIndex::new(1, 1))?;
+    let l2n0 = tree.get_node(&NodeIndex::new(2, 0))?;
+    let l2n1 = tree.get_node(&NodeIndex::new(2, 1))?;
+    let l2n2 = tree.get_node(&NodeIndex::new(2, 2))?;
+    let l2n3 = tree.get_node(&NodeIndex::new(2, 3))?;
+
+    let nodes: Vec<InnerNodeInfo> = tree.inner_nodes().collect();
+    let expected = vec![
+        InnerNodeInfo {
+            value: root.into(),
+            left: l1n0.into(),
+            right: l1n1.into(),
+        },
+        InnerNodeInfo {
+            value: l1n0.into(),
+            left: l2n0.into(),
+            right: l2n1.into(),
+        },
+        InnerNodeInfo {
+            value: l1n1.into(),
+            left: l2n2.into(),
+            right: l2n3.into(),
+        },
+    ];
+    assert_eq!(nodes, expected);
+
+    Ok(())
+}
+
 #[test]
 fn update_leaf() {
     let mut tree = SimpleSmt::new(3)

src/merkle/store/mod.rs

@@ -281,13 +281,12 @@ impl MerkleStore {
         I: Iterator<Item = (u64, Word)> + ExactSizeIterator,
     {
         let smt = SimpleSmt::new(depth)?.with_leaves(entries)?;
-        for branch in smt.branches.values() {
-            let parent = Rpo256::merge(&[branch.left, branch.right]);
+        for node in smt.inner_nodes() {
             self.nodes.insert(
-                parent,
+                node.value.into(),
                 Node {
-                    left: branch.left,
-                    right: branch.right,
+                    left: node.left.into(),
+                    right: node.right.into(),
                 },
             );
         }