[Code Health] refactor: SMST#Root(), #Sum(), & #Count() (#51)

Signed-off-by: Bryan White <[email protected]>

root.go

@@ -5,18 +5,11 @@ import (
 	"fmt"
 )
 
-const (
-	// These are intentionally exposed to allow for for testing and custom
-	// implementations of downstream applications.
-	SmtRootSizeBytes  = 32
-	SmstRootSizeBytes = SmtRootSizeBytes + sumSizeBytes + countSizeBytes
-)
-
 // MustSum returns the uint64 sum of the merkle root, it checks the length of the
 // merkle root and if it is no the same as the size of the SMST's expected
 // root hash it will panic.
-func (r MerkleRoot) MustSum() uint64 {
-	sum, err := r.Sum()
+func (root MerkleSumRoot) MustSum() uint64 {
+	sum, err := root.Sum()
 	if err != nil {
 		panic(err)
 	}
@@ -27,28 +20,76 @@ func (r MerkleRoot) MustSum() uint64 {
 // Sum returns the uint64 sum of the merkle root, it checks the length of the
 // merkle root and if it is no the same as the size of the SMST's expected
 // root hash it will return an error.
-func (r MerkleRoot) Sum() (uint64, error) {
-	if len(r)%SmtRootSizeBytes == 0 {
-		return 0, fmt.Errorf("root#sum: not a merkle sum trie")
+func (root MerkleSumRoot) Sum() (uint64, error) {
+	if err := root.validateBasic(); err != nil {
+		return 0, err
 	}
 
-	firstSumByteIdx, firstCountByteIdx := getFirstMetaByteIdx([]byte(r))
+	return root.sum(), nil
+}
+
+// MustCount returns the uint64 count of the merkle root, a cryptographically secure
+// count of the number of non-empty leafs in the tree. It panics if the root length
+// is invalid.
+func (root MerkleSumRoot) MustCount() uint64 {
+	count, err := root.Count()
+	if err != nil {
+		panic(err)
+	}
 
-	var sumBz [sumSizeBytes]byte
-	copy(sumBz[:], []byte(r)[firstSumByteIdx:firstCountByteIdx])
-	return binary.BigEndian.Uint64(sumBz[:]), nil
+	return count
 }
 
 // Count returns the uint64 count of the merkle root, a cryptographically secure
-// count of the number of non-empty leafs in the tree.
-func (r MerkleRoot) Count() uint64 {
-	if len(r)%SmtRootSizeBytes == 0 {
-		panic("root#sum: not a merkle sum trie")
+// count of the number of non-empty leafs in the tree. It returns an error if the
+// root length is invalid.
+func (root MerkleSumRoot) Count() (uint64, error) {
+	if err := root.validateBasic(); err != nil {
+		return 0, err
 	}
 
-	_, firstCountByteIdx := getFirstMetaByteIdx([]byte(r))
+	return root.count(), nil
+}
+
+// DigestSize returns the length of the digest portion of the root.
+func (root MerkleSumRoot) DigestSize() int {
+	return len(root) - countSizeBytes - sumSizeBytes
+}
+
+// HasDigestSize returns true if the root digest size is the same as
+// that of the size of the given hasher.
+func (root MerkleSumRoot) HasDigestSize(size int) bool {
+	return root.DigestSize() == size
+}
 
-	var countBz [countSizeBytes]byte
-	copy(countBz[:], []byte(r)[firstCountByteIdx:])
-	return binary.BigEndian.Uint64(countBz[:])
+// validateBasic returns an error if the root digest size is not a power of two.
+func (root MerkleSumRoot) validateBasic() error {
+	if !isPowerOfTwo(root.DigestSize()) {
+		return fmt.Errorf("MerkleSumRoot#validateBasic: invalid root length")
+	}
+
+	return nil
+}
+
+// sum returns the sum of the node stored in the root.
+func (root MerkleSumRoot) sum() uint64 {
+	firstSumByteIdx, firstCountByteIdx := getFirstMetaByteIdx(root)
+
+	return binary.BigEndian.Uint64(root[firstSumByteIdx:firstCountByteIdx])
+}
+
+// count returns the count of the node stored in the root.
+func (root MerkleSumRoot) count() uint64 {
+	_, firstCountByteIdx := getFirstMetaByteIdx(root)
+
+	return binary.BigEndian.Uint64(root[firstCountByteIdx:])
+}
+
+// isPowerOfTwo function returns true if the input n is a power of 2
+func isPowerOfTwo(n int) bool {
+	// A power of 2 has only one bit set in its binary representation
+	if n <= 0 {
+		return false
+	}
+	return (n & (n - 1)) == 0
 }

root_test.go

@@ -13,64 +13,82 @@ import (
 	"github.com/pokt-network/smt/kvstore/simplemap"
 )
 
-func TestMerkleRoot_TrieTypes(t *testing.T) {
+func TestMerkleSumRoot_SumAndCountSuccess(t *testing.T) {
 	tests := []struct {
-		desc          string
-		sumTree       bool
-		hasher        hash.Hash
-		expectedPanic string
+		desc   string
+		hasher hash.Hash
 	}{
 		{
-			desc:          "successfully: gets sum of sha256 hasher SMST",
-			sumTree:       true,
-			hasher:        sha256.New(),
-			expectedPanic: "",
+			desc:   "sha256 hasher",
+			hasher: sha256.New(),
 		},
 		{
-			desc:          "successfully: gets sum of sha512 hasher SMST",
-			sumTree:       true,
-			hasher:        sha512.New(),
-			expectedPanic: "",
+			desc:   "sha512 hasher",
+			hasher: sha512.New(),
 		},
+	}
+
+	nodeStore := simplemap.NewSimpleMap()
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			t.Cleanup(func() {
+				require.NoError(t, nodeStore.ClearAll())
+			})
+			trie := smt.NewSparseMerkleSumTrie(nodeStore, test.hasher)
+			for i := uint64(0); i < 10; i++ {
+				require.NoError(t, trie.Update([]byte(fmt.Sprintf("key%d", i)), []byte(fmt.Sprintf("value%d", i)), i))
+			}
+
+			sum, sumErr := trie.Sum()
+			require.NoError(t, sumErr)
+
+			count, countErr := trie.Count()
+			require.NoError(t, countErr)
+
+			require.EqualValues(t, uint64(45), sum)
+			require.EqualValues(t, uint64(10), count)
+		})
+	}
+}
+
+func TestMekleRoot_SumAndCountError(t *testing.T) {
+	tests := []struct {
+		desc   string
+		hasher hash.Hash
+	}{
 		{
-			desc:          "failure: panics for sha256 hasher SMT",
-			sumTree:       false,
-			hasher:        sha256.New(),
-			expectedPanic: "roo#sum: not a merkle sum trie",
+			desc:   "sha256 hasher",
+			hasher: sha256.New(),
 		},
 		{
-			desc:          "failure: panics for sha512 hasher SMT",
-			sumTree:       false,
-			hasher:        sha512.New(),
-			expectedPanic: "roo#sum: not a merkle sum trie",
+			desc:   "sha512 hasher",
+			hasher: sha512.New(),
 		},
 	}
 
 	nodeStore := simplemap.NewSimpleMap()
-	for _, tt := range tests {
-		tt := tt
-		t.Run(tt.desc, func(t *testing.T) {
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
 			t.Cleanup(func() {
 				require.NoError(t, nodeStore.ClearAll())
 			})
-			if tt.sumTree {
-				trie := smt.NewSparseMerkleSumTrie(nodeStore, tt.hasher)
-				for i := uint64(0); i < 10; i++ {
-					require.NoError(t, trie.Update([]byte(fmt.Sprintf("key%d", i)), []byte(fmt.Sprintf("value%d", i)), i))
-				}
-				require.NotNil(t, trie.Sum())
-				require.EqualValues(t, 45, trie.Sum())
-				require.EqualValues(t, 10, trie.Count())
-
-				return
-			}
-			trie := smt.NewSparseMerkleTrie(nodeStore, tt.hasher)
-			for i := 0; i < 10; i++ {
-				require.NoError(t, trie.Update([]byte(fmt.Sprintf("key%d", i)), []byte(fmt.Sprintf("value%d", i))))
-			}
-			if panicStr := recover(); panicStr != nil {
-				require.Equal(t, tt.expectedPanic, panicStr)
+			trie := smt.NewSparseMerkleSumTrie(nodeStore, test.hasher)
+			for i := uint64(0); i < 10; i++ {
+				require.NoError(t, trie.Update([]byte(fmt.Sprintf("key%d", i)), []byte(fmt.Sprintf("value%d", i)), i))
 			}
+
+			root := trie.Root()
+
+			// Mangle the root bytes.
+			root = root[:len(root)-1]
+
+			sum, sumErr := root.Sum()
+			require.Error(t, sumErr)
+			require.Equal(t, uint64(0), sum)
+
+			count, countErr := root.Count()
+			require.Error(t, countErr)
+			require.Equal(t, uint64(0), count)
 		})
 	}
 }

smst.go

@@ -3,6 +3,7 @@ package smt
 import (
 	"bytes"
 	"encoding/binary"
+	"fmt"
 	"hash"
 
 	"github.com/pokt-network/smt/kvstore"
@@ -170,39 +171,48 @@ func (smst *SMST) Commit() error {
 }
 
 // Root returns the root hash of the trie with the total sum bytes appended
-func (smst *SMST) Root() MerkleRoot {
-	return smst.SMT.Root() // [digest]+[binary sum]
+func (smst *SMST) Root() MerkleSumRoot {
+	return MerkleSumRoot(smst.SMT.Root()) // [digest]+[binary sum]+[binary count]
 }
 
-// Sum returns the sum of the entire trie stored in the root.
+// MustSum returns the sum of the entire trie stored in the root.
 // If the tree is not a sum tree, it will panic.
-func (smst *SMST) Sum() uint64 {
-	rootDigest := []byte(smst.Root())
+func (smst *SMST) MustSum() uint64 {
+	sum, err := smst.Sum()
+	if err != nil {
+		panic(err)
+	}
+	return sum
+}
 
+// Sum returns the sum of the entire trie stored in the root.
+// If the tree is not a sum tree, it will return an error.
+func (smst *SMST) Sum() (uint64, error) {
 	if !smst.Spec().sumTrie {
-		panic("SMST: not a merkle sum trie")
+		return 0, fmt.Errorf("SMST: not a merkle sum trie")
 	}
 
-	firstSumByteIdx, firstCountByteIdx := getFirstMetaByteIdx(rootDigest)
+	return smst.Root().Sum()
+}
 
-	var sumBz [sumSizeBytes]byte
-	copy(sumBz[:], rootDigest[firstSumByteIdx:firstCountByteIdx])
-	return binary.BigEndian.Uint64(sumBz[:])
+// MustCount returns the number of non-empty nodes in the entire trie stored in the root.
+// If the tree is not a sum tree, it will panic.
+func (smst *SMST) MustCount() uint64 {
+	count, err := smst.Count()
+	if err != nil {
+		panic(err)
+	}
+	return count
 }
 
 // Count returns the number of non-empty nodes in the entire trie stored in the root.
-func (smst *SMST) Count() uint64 {
-	rootDigest := []byte(smst.Root())
-
+// If the tree is not a sum tree, it will return an error.
+func (smst *SMST) Count() (uint64, error) {
 	if !smst.Spec().sumTrie {
-		panic("SMST: not a merkle sum trie")
+		return 0, fmt.Errorf("SMST: not a merkle sum trie")
 	}
 
-	_, firstCountByteIdx := getFirstMetaByteIdx(rootDigest)
-
-	var countBz [countSizeBytes]byte
-	copy(countBz[:], rootDigest[firstCountByteIdx:])
-	return binary.BigEndian.Uint64(countBz[:])
+	return smst.Root().Count()
 }
 
 // getFirstMetaByteIdx returns the index of the first count byte and the first sum byte
@@ -211,5 +221,5 @@ func (smst *SMST) Count() uint64 {
 func getFirstMetaByteIdx(data []byte) (firstSumByteIdx, firstCountByteIdx int) {
 	firstCountByteIdx = len(data) - countSizeBytes
 	firstSumByteIdx = firstCountByteIdx - sumSizeBytes
-	return
+	return firstSumByteIdx, firstCountByteIdx
 }

smst_example_test.go

@@ -28,7 +28,7 @@ func TestExampleSMST(t *testing.T) {
 	_ = trie.Commit()
 
 	// Calculate the total sum of the trie
-	_ = trie.Sum() // 20
+	_ = trie.MustSum() // 20
 
 	// Generate a Merkle proof for "foo"
 	proof1, _ := trie.Prove([]byte("foo"))
@@ -52,8 +52,8 @@ func TestExampleSMST(t *testing.T) {
 	require.False(t, valid_false1)
 
 	// Verify the total sum of the trie
-	require.EqualValues(t, 20, trie.Sum())
+	require.EqualValues(t, 20, trie.MustSum())
 
 	// Verify the number of non-empty leafs in the trie
-	require.EqualValues(t, 3, trie.Count())
+	require.EqualValues(t, 3, trie.MustCount())
 }