[Enhancement] Add features related to the usage of the ClosestProof…

… method (#43)

errors.go

@@ -9,4 +9,7 @@ var (
 	ErrBadProof = errors.New("bad proof")
 	// ErrKeyNotFound is returned when a key is not found in the tree.
 	ErrKeyNotFound = errors.New("key not found")
+	// ErrInvalidClosestPath is returned when the path used in the ClosestProof
+	// method does not match the size of the trie's PathHasher
+	ErrInvalidClosestPath = errors.New("invalid path does not match path hasher size")
 )

hasher.go

@@ -29,6 +29,8 @@ type PathHasher interface {
 type ValueHasher interface {
 	// HashValue hashes value data to produce the digest stored in leaf node.
 	HashValue([]byte) []byte
+	// ValueHashSize returns the length (in bytes) of digests produced by this hasher.
+	ValueHashSize() int
 }
 
 type trieHasher struct {
@@ -59,10 +61,19 @@ func (ph *pathHasher) PathSize() int {
 	return ph.hasher.Size()
 }
 
+// HashValue hashes the producdes a digest of the data provided by the value hasher
 func (vh *valueHasher) HashValue(data []byte) []byte {
 	return vh.digest(data)
 }
 
+// ValueHashSize returns the length (in bytes) of digests produced by the value hasher
+func (vh *valueHasher) ValueHashSize() int {
+	if vh.hasher == nil {
+		return 0
+	}
+	return vh.hasher.Size()
+}
+
 func (th *trieHasher) digest(data []byte) []byte {
 	th.hasher.Write(data)
 	sum := th.hasher.Sum(nil)

proofs.go

@@ -61,7 +61,11 @@ func (proof *SparseMerkleProof) validateBasic(spec *TrieSpec) error {
 	// Check that leaf data for non-membership proofs is a valid size.
 	lps := len(leafPrefix) + spec.ph.PathSize()
 	if proof.NonMembershipLeafData != nil && len(proof.NonMembershipLeafData) < lps {
-		return fmt.Errorf("invalid non-membership leaf data size: got %d but min is %d", len(proof.NonMembershipLeafData), lps)
+		return fmt.Errorf(
+			"invalid non-membership leaf data size: got %d but min is %d",
+			len(proof.NonMembershipLeafData),
+			lps,
+		)
 	}
 
 	// Check that all supplied sidenodes are the correct size.
@@ -133,7 +137,11 @@ func (proof *SparseCompactMerkleProof) validateBasic(spec *TrieSpec) error {
 
 	// Compact proofs: check that NumSideNodes is within the right range.
 	if proof.NumSideNodes < 0 || proof.NumSideNodes > spec.ph.PathSize()*8 {
-		return fmt.Errorf("invalid number of side nodes: got %d, min is 0 and max is %d", len(proof.SideNodes), spec.ph.PathSize()*8)
+		return fmt.Errorf(
+			"invalid number of side nodes: got %d, min is 0 and max is %d",
+			len(proof.SideNodes),
+			spec.ph.PathSize()*8,
+		)
 	}
 
 	// Compact proofs: check that the length of the bit mask is as expected
@@ -185,7 +193,24 @@ func (proof *SparseMerkleClosestProof) Unmarshal(bz []byte) error {
 	return dec.Decode(proof)
 }
 
+// GetValueHash returns the value hash of the closest proof.
+func (proof *SparseMerkleClosestProof) GetValueHash(spec *TrieSpec) []byte {
+	if proof.ClosestValueHash == nil {
+		return nil
+	}
+	if spec.sumTrie {
+		return proof.ClosestValueHash[:len(proof.ClosestValueHash)-sumSize]
+	}
+	return proof.ClosestValueHash
+}
+
 func (proof *SparseMerkleClosestProof) validateBasic(spec *TrieSpec) error {
+	// ensure the proof length is the same size (in bytes) as the path
+	// hasher of the spec provided
+	if len(proof.Path) != spec.PathHasherSize() {
+		return fmt.Errorf("invalid path length: got %d, want %d", len(proof.Path), spec.PathHasherSize())
+	}
+
 	// ensure the depth of the leaf node being proven is within the path size
 	if proof.Depth < 0 || proof.Depth > spec.ph.PathSize()*8 {
 		return fmt.Errorf("invalid depth: got %d, outside of [0, %d]", proof.Depth, spec.ph.PathSize()*8)
@@ -231,6 +256,12 @@ type SparseCompactMerkleClosestProof struct {
 }
 
 func (proof *SparseCompactMerkleClosestProof) validateBasic(spec *TrieSpec) error {
+	// Ensure the proof length is the same size (in bytes) as the path
+	// hasher of the spec provided
+	if len(proof.Path) != spec.PathHasherSize() {
+		return fmt.Errorf("invalid path length: got %d, want %d", len(proof.Path), spec.PathHasherSize())
+	}
+
 	// Do a basic sanity check on the proof on the fields of the proof specific to
 	// the compact proof only.
 	//
@@ -246,7 +277,12 @@ func (proof *SparseCompactMerkleClosestProof) validateBasic(spec *TrieSpec) erro
 	}
 	for i, b := range proof.FlippedBits {
 		if len(b) > maxSliceLen {
-			return fmt.Errorf("invalid compressed flipped bit index %d: got length %d, max is %d]", i, bytesToInt(b), maxSliceLen)
+			return fmt.Errorf(
+				"invalid compressed flipped bit index %d: got length %d, max is %d]",
+				i,
+				bytesToInt(b),
+				maxSliceLen,
+			)
 		}
 	}
 	// perform a sanity check on the closest proof
@@ -320,7 +356,13 @@ func VerifyClosestProof(proof *SparseMerkleClosestProof, root []byte, spec *Trie
 	return VerifySumProof(proof.ClosestProof, root, proof.ClosestPath, valueHash, sum, spec)
 }
 
-func verifyProofWithUpdates(proof *SparseMerkleProof, root []byte, key []byte, value []byte, spec *TrieSpec) (bool, [][][]byte, error) {
+func verifyProofWithUpdates(
+	proof *SparseMerkleProof,
+	root []byte,
+	key []byte,
+	value []byte,
+	spec *TrieSpec,
+) (bool, [][][]byte, error) {
 	path := spec.ph.Path(key)
 
 	if err := proof.validateBasic(spec); err != nil {
@@ -384,7 +426,13 @@ func VerifyCompactProof(proof *SparseCompactMerkleProof, root []byte, key, value
 }
 
 // VerifyCompactSumProof is similar to VerifySumProof but for a compacted Merkle proof.
-func VerifyCompactSumProof(proof *SparseCompactMerkleProof, root []byte, key, value []byte, sum uint64, spec *TrieSpec) (bool, error) {
+func VerifyCompactSumProof(
+	proof *SparseCompactMerkleProof,
+	root []byte,
+	key, value []byte,
+	sum uint64,
+	spec *TrieSpec,
+) (bool, error) {
 	decompactedProof, err := DecompactProof(proof, spec)
 	if err != nil {
 		return false, errors.Join(ErrBadProof, err)

smt.go

@@ -407,6 +407,11 @@ func (smt *SMT) ProveClosest(path []byte) (
 	proof *SparseMerkleClosestProof, // proof of the key-value pair found
 	err error, // the error value encountered
 ) {
+	// Ensure the path provided is the correct length for the path hasher.
+	if len(path) != smt.Spec().PathHasherSize() {
+		return nil, ErrInvalidClosestPath
+	}
+
 	workingPath := make([]byte, len(path))
 	copy(workingPath, path)
 	var siblings []trieNode

types.go

@@ -98,6 +98,18 @@ func newTrieSpec(hasher hash.Hash, sumTrie bool) TrieSpec {
 // Spec returns the TrieSpec associated with the given trie
 func (spec *TrieSpec) Spec() *TrieSpec { return spec }
 
+// PathHasherSize returns the length (in bytes) of digests produced by the
+// path hasher
+func (spec *TrieSpec) PathHasherSize() int { return spec.ph.PathSize() }
+
+// ValueHasherSize returns the length (in bytes) of digests produced by the
+// value hasher
+func (spec *TrieSpec) ValueHasherSize() int { return spec.vh.ValueHashSize() }
+
+// TrieHasherSize returns the length (in bytes) of digests produced by the
+// trie hasher
+func (spec *TrieSpec) TrieHasherSize() int { return spec.th.hashSize() }
+
 func (spec *TrieSpec) depth() int { return spec.ph.PathSize() * 8 }
 func (spec *TrieSpec) digestValue(data []byte) []byte {
 	if spec.vh == nil {