Improved how placeholder values are maintained and how the node is re…

…solved

hasher.go

@@ -128,7 +128,7 @@ func (th *trieHasher) parseInnerNode(data []byte) (leftData, rightData []byte) {
 
 func (th *trieHasher) parseSumInnerNode(data []byte) (leftData, rightData []byte) {
 	dataWithoutSum := data[:len(data)-sumSizeBits]
-	leftData = dataWithoutSum[len(innerNodePrefix) : th.hashSize()+sumSizeBits+len(innerNodePrefix)]
+	leftData = dataWithoutSum[len(innerNodePrefix) : len(innerNodePrefix)+th.hashSize()+sumSizeBits]
 	rightData = dataWithoutSum[len(innerNodePrefix)+th.hashSize()+sumSizeBits:]
 	return
 }

node_encoders.go

@@ -15,6 +15,8 @@ import (
 // NB: In this file, all references to the variable `data` should be treated as `encodedNodeData`.
 // It was abbreviated to `data` for brevity.
 
+// TODO_TECHDEBT: We can easily use `iota` and ENUMS to create a wait to have
+// more expressive code, and leverage switches statements throughout.
 var (
 	leafNodePrefix  = []byte{0}
 	innerNodePrefix = []byte{1}
@@ -114,22 +116,10 @@ func encodeExtensionNode(pathBounds [2]byte, path, childData []byte) (data []byt
 
 // encodeSumInnerNode encodes an inner node for an smst given the data for both children
 func encodeSumInnerNode(leftData, rightData []byte) (data []byte) {
-	// Retrieve the sum of the left subtree
-	leftSum := uint64(0)
-	leftSumBz := leftData[len(leftData)-sumSizeBits:]
-	if !bytes.Equal(leftSumBz, defaultEmptySum[:]) {
-		leftSum = binary.BigEndian.Uint64(leftSumBz)
-	}
-
-	// Retrieve the sum of the right subtree
-	rightSum := uint64(0)
-	rightSumBz := rightData[len(rightData)-sumSizeBits:]
-	if !bytes.Equal(rightSumBz, defaultEmptySum[:]) {
-		rightSum = binary.BigEndian.Uint64(rightSumBz)
-	}
-
 	// Compute the sum of the current node
 	var sum [sumSizeBits]byte
+	leftSum := parseSum(leftData)
+	rightSum := parseSum(rightData)
 	binary.BigEndian.PutUint64(sum[:], leftSum+rightSum)
 
 	// Prepare and return the encoded inner node data
@@ -157,3 +147,13 @@ func checkPrefix(data, prefix []byte) {
 		panic("invalid prefix")
 	}
 }
+
+// parseSum parses the sum from the encoded node data
+func parseSum(data []byte) uint64 {
+	sum := uint64(0)
+	sumBz := data[len(data)-sumSizeBits:]
+	if !bytes.Equal(sumBz, defaultEmptySum[:]) {
+		sum = binary.BigEndian.Uint64(sumBz)
+	}
+	return sum
+}

proofs.go

@@ -333,7 +333,7 @@ func verifyProofWithUpdates(proof *SparseMerkleProof, root []byte, key []byte, v
 	var currentHash, currentData []byte
 	if bytes.Equal(value, defaultEmptyValue) { // Non-membership proof.
 		if proof.NonMembershipLeafData == nil { // Leaf is a placeholder value.
-			currentHash = placeholder(spec)
+			currentHash = spec.placeholder()
 		} else { // Leaf is an unrelated leaf.
 			var actualPath, valueHash []byte
 			actualPath, valueHash = parseLeafNode(proof.NonMembershipLeafData, spec.ph)
@@ -412,7 +412,7 @@ func CompactProof(proof *SparseMerkleProof, spec *TrieSpec) (*SparseCompactMerkl
 	for i := 0; i < len(proof.SideNodes); i++ {
 		node := make([]byte, hashSize(spec))
 		copy(node, proof.SideNodes[i])
-		if bytes.Equal(node, placeholder(spec)) {
+		if bytes.Equal(node, spec.placeholder()) {
 			setPathBit(bitMask, i)
 		} else {
 			compactedSideNodes = append(compactedSideNodes, node)
@@ -438,7 +438,7 @@ func DecompactProof(proof *SparseCompactMerkleProof, spec *TrieSpec) (*SparseMer
 	position := 0
 	for i := 0; i < proof.NumSideNodes; i++ {
 		if getPathBit(proof.BitMask, i) == 1 {
-			decompactedSideNodes[i] = placeholder(spec)
+			decompactedSideNodes[i] = spec.placeholder()
 		} else {
 			decompactedSideNodes[i] = proof.SideNodes[position]
 			position++

smst_example_test.go

@@ -82,15 +82,15 @@ func exportToCSV(
 	nodeStore kvstore.MapStore,
 ) {
 	t.Helper()
-	// rootHash := smst.Root()
-	// rootNode, err := nodeStore.Get(rootHash)
-	// require.NoError(t, err)
-
-	// Testing
-	// fmt.Println(isExtNode(rootNode), isLeafNode(rootNode), isInnerNode(rootNode))
-	// leftChild, rightChild := smst.Spec().th.parseInnerNode(rootNode)
-	// // fmt.Println(isExtNode(leftChild), isExtNode(rightChild), rightChild, leftChild)
-	// fmt.Println(leftChild[:1], isExtNode(leftChild), isInnerNode(leftChild), isLeafNode(leftChild))
+	rootHash := smst.Root()
+	rootNode, err := nodeStore.Get(rootHash)
+	require.NoError(t, err)
+
+	leftChild, rightChild := smst.Spec().th.parseSumInnerNode(rootNode)
+	fmt.Println("Prefix", "isExt", "isLeaf", "isInner")
+	fmt.Println(rootNode[:1], isExtNode(rootNode), isLeafNode(rootNode), isInnerNode(rootNode))
+	fmt.Println(leftChild[:1], isExtNode(leftChild), isLeafNode(leftChild), isInnerNode(leftChild))
+	fmt.Println(rightChild[:1], isExtNode(rightChild), isLeafNode(rightChild), isInnerNode(rightChild))
 	// path, value := parseLeafNode(rightChild, smst.Spec().ph)
 	// path2, value2 := parseLeafNode(leftChild, smst.Spec().ph)
 	// fmt.Println(path, "~~~", value, "~~~", path2, "~~~", value2)

smst_proofs_test.go

@@ -33,7 +33,7 @@ func TestSMST_Proof_Operations(t *testing.T) {
 	proof, err = smst.Prove([]byte("testKey3"))
 	require.NoError(t, err)
 	checkCompactEquivalence(t, proof, base)
-	result, err = VerifySumProof(proof, placeholder(base), []byte("testKey3"), defaultEmptyValue, 0, base)
+	result, err = VerifySumProof(proof, base.placeholder(), []byte("testKey3"), defaultEmptyValue, 0, base)
 	require.NoError(t, err)
 	require.True(t, result)
 	result, err = VerifySumProof(proof, root, []byte("testKey3"), []byte("badValue"), 5, base)
@@ -377,7 +377,7 @@ func TestSMST_ProveClosest_Empty(t *testing.T) {
 		Path:         path[:],
 		FlippedBits:  []int{0},
 		Depth:        0,
-		ClosestPath:  placeholder(smst.Spec()),
+		ClosestPath:  smst.placeholder(),
 		ClosestProof: &SparseMerkleProof{},
 	})
 

smt.go

@@ -490,7 +490,7 @@ func (smt *SMT) ProveClosest(path []byte) (
 
 	// Retrieve the closest path and value hash if found
 	if node == nil { // trie was empty
-		proof.ClosestPath, proof.ClosestValueHash = placeholder(smt.Spec()), nil
+		proof.ClosestPath, proof.ClosestValueHash = smt.placeholder(), nil
 		proof.ClosestProof = &SparseMerkleProof{}
 		return proof, nil
 	}
@@ -529,66 +529,99 @@ func (smt *SMT) resolveLazy(node trieNode) (trieNode, error) {
 		return node, nil
 	}
 	if smt.sumTrie {
-		return smt.resolveSum(stub.digest)
+		return smt.resolveSumNode(stub.digest)
 	}
-	return smt.resolve(stub.digest)
+	return smt.resolveNode(stub.digest)
 }
 
-func (smt *SMT) resolve(hash []byte) (trieNode, error) {
-	if bytes.Equal(smt.th.placeholder(), hash) {
+// resolveNode returns a trieNode (inner, leaf, or extension) based on what they
+// keyHash points to.
+func (smt *SMT) resolveNode(digest []byte) (trieNode, error) {
+	// Check if the keyHash is the empty zero value of an empty subtree
+	if bytes.Equal(smt.placeholder(), digest) {
 		return nil, nil
 	}
-	data, err := smt.nodes.Get(hash)
+
+	// Retrieve the encoded noe data
+	data, err := smt.nodes.Get(digest)
 	if err != nil {
 		return nil, err
 	}
+
+	// Return the appropriate node type based on the first byte of the data
 	if isLeafNode(data) {
-		leaf := leafNode{persisted: true, digest: hash}
-		leaf.path, leaf.valueHash = parseLeafNode(data, smt.ph)
-		return &leaf, nil
-	}
-	if isExtNode(data) {
-		extNode := extensionNode{persisted: true, digest: hash}
-		pathBounds, path, childHash := parseExtNode(data, smt.ph)
-		extNode.path = path
-		copy(extNode.pathBounds[:], pathBounds)
-		extNode.child = &lazyNode{childHash}
-		return &extNode, nil
-	}
-	leftHash, rightHash := smt.th.parseInnerNode(data)
-	inner := innerNode{persisted: true, digest: hash}
-	inner.leftChild = &lazyNode{leftHash}
-	inner.rightChild = &lazyNode{rightHash}
-	return &inner, nil
+		path, valueHash := parseLeafNode(data, smt.ph)
+		return &leafNode{
+			path:      path,
+			valueHash: valueHash,
+			persisted: true,
+			digest:    digest,
+		}, nil
+	} else if isExtNode(data) {
+		pathBounds, path, childData := parseExtNode(data, smt.ph)
+		return &extensionNode{
+			path:       path,
+			pathBounds: [2]byte(pathBounds),
+			child:      &lazyNode{childData},
+			persisted:  true,
+			digest:     digest,
+		}, nil
+	} else if isInnerNode(data) {
+		leftHash, rightHash := smt.th.parseInnerNode(data)
+		return &innerNode{
+			leftChild:  &lazyNode{leftHash},
+			rightChild: &lazyNode{rightHash},
+			persisted:  true,
+			digest:     digest,
+		}, nil
+	} else {
+		panic("invalid node type")
+	}
 }
 
-// resolveSum resolves
-func (smt *SMT) resolveSum(hash []byte) (trieNode, error) {
-	if bytes.Equal(placeholder(smt.Spec()), hash) {
+// resolveNode returns a trieNode (inner, leaf, or extension) based on what they
+// keyHash points to.
+func (smt *SMT) resolveSumNode(digest []byte) (trieNode, error) {
+	// Check if the keyHash is the empty zero value of an empty subtree
+	if bytes.Equal(smt.placeholder(), digest) {
 		return nil, nil
 	}
-	data, err := smt.nodes.Get(hash)
+
+	// Retrieve the encoded noe data
+	data, err := smt.nodes.Get(digest)
 	if err != nil {
 		return nil, err
 	}
+
+	// Return the appropriate node type based on the first byte of the data
 	if isLeafNode(data) {
-		leaf := leafNode{persisted: true, digest: hash}
-		leaf.path, leaf.valueHash = parseLeafNode(data, smt.ph)
-		return &leaf, nil
-	}
-	if isExtNode(data) {
-		extNode := extensionNode{persisted: true, digest: hash}
-		pathBounds, path, childHash, _ := parseSumExtNode(data, smt.ph)
-		extNode.path = path
-		copy(extNode.pathBounds[:], pathBounds)
-		extNode.child = &lazyNode{childHash}
-		return &extNode, nil
-	}
-	leftHash, rightHash := smt.th.parseSumInnerNode(data)
-	inner := innerNode{persisted: true, digest: hash}
-	inner.leftChild = &lazyNode{leftHash}
-	inner.rightChild = &lazyNode{rightHash}
-	return &inner, nil
+		path, valueHash := parseLeafNode(data, smt.ph)
+		return &leafNode{
+			path:      path,
+			valueHash: valueHash,
+			persisted: true,
+			digest:    digest,
+		}, nil
+	} else if isExtNode(data) {
+		pathBounds, path, childData, _ := parseSumExtNode(data, smt.ph)
+		return &extensionNode{
+			path:       path,
+			pathBounds: [2]byte(pathBounds),
+			child:      &lazyNode{childData},
+			persisted:  true,
+			digest:     digest,
+		}, nil
+	} else if isInnerNode(data) {
+		leftHash, rightHash := smt.th.parseSumInnerNode(data)
+		return &innerNode{
+			leftChild:  &lazyNode{leftHash},
+			rightChild: &lazyNode{rightHash},
+			persisted:  true,
+			digest:     digest,
+		}, nil
+	} else {
+		panic("invalid node type")
+	}
 }
 
 // Commit persists all dirty nodes in the trie, deletes all orphaned

smt_proofs_test.go

@@ -332,7 +332,7 @@ func TestSMT_ProveClosest_Empty(t *testing.T) {
 		Path:         path[:],
 		FlippedBits:  []int{0},
 		Depth:        0,
-		ClosestPath:  placeholder(smt.Spec()),
+		ClosestPath:  smt.placeholder(),
 		ClosestProof: &SparseMerkleProof{},
 	})
 

types.go

@@ -106,6 +106,16 @@ func (spec *TrieSpec) Spec() *TrieSpec {
 	return spec
 }
 
+// placeholder returns the default placeholder value depending on the trie type
+func (spec *TrieSpec) placeholder() []byte {
+	if spec.sumTrie {
+		placeholder := spec.th.placeholder()
+		placeholder = append(placeholder, defaultEmptySum[:]...)
+		return placeholder
+	}
+	return spec.th.placeholder()
+}
+
 // depth returns the maximum depth of the trie.
 // Since this tree is a binary tree, the depth is the number of bits in the path
 // TODO_IN_THIS_PR: Try to understand why we're not taking the log of the output
@@ -190,7 +200,7 @@ func (spec *TrieSpec) sumSerialize(node trieNode) (preImage []byte) {
 // digest = [node hash]+[8 byte sum]
 func (spec *TrieSpec) hashSumNode(node trieNode) []byte {
 	if node == nil {
-		return placeholder(spec)
+		return spec.placeholder()
 	}
 	var cache *[]byte
 	switch n := node.(type) {

utils.go

@@ -106,16 +106,6 @@ func bytesToInt(bz []byte) int {
 	return int(u)
 }
 
-// placeholder returns the default placeholder value depending on the trie type
-func placeholder(spec *TrieSpec) []byte {
-	if spec.sumTrie {
-		placeholder := spec.th.placeholder()
-		placeholder = append(placeholder, defaultEmptySum[:]...)
-		return placeholder
-	}
-	return spec.th.placeholder()
-}
-
 // hashSize returns the hash size depending on the trie type
 func hashSize(spec *TrieSpec) int {
 	if spec.sumTrie {