Merge pull request #72 from libsv/block-with-single-transaction

Fix calculating merkle path with only one transaction in the block. F…

merklepath.go

@@ -117,17 +117,25 @@ func (mp *MerklePath) CalculateRoot(txid string) (string, error) {
 	return StringFromBytesReverse(workingHash), nil
 }
 
-// getPathElements traverses the tree and returns the path to coinbase.
+// getPathElements traverses the tree and returns the path to Merkle root.
 func getPathElements(txIndex int, hashes []string) []string {
 	// if our hash index is odd the next hash of the path is the previous element in the array otherwise the next element.
 	var path []string
+	var hash string
 	if txIndex%2 == 0 {
-		path = append(path, hashes[txIndex+1])
+		hash = hashes[txIndex+1]
 	} else {
-		path = append(path, hashes[txIndex-1])
+		hash = hashes[txIndex-1]
 	}
 
-	// If we reach the coinbase hash stop path calculation.
+	// when generating path if the neighbour is empty we append itself
+	if hash == "" {
+		path = append(path, hashes[txIndex])
+	} else {
+		path = append(path, hash)
+	}
+
+	// If we reach the Merkle root hash stop path calculation.
 	if len(hashes) == 3 {
 		return path
 	}
@@ -137,8 +145,15 @@ func getPathElements(txIndex int, hashes []string) []string {
 
 // GetTxMerklePath with merkle tree we calculate the merkle path for a given transaction.
 func GetTxMerklePath(txIndex int, merkleTree []string) *MerklePath {
-	return &MerklePath{
+	merklePath := &MerklePath{
 		Index: uint64(txIndex),
-		Path:  getPathElements(txIndex, merkleTree),
+		Path:  nil,
 	}
+
+	// if we have only one transaction in the block there is no merkle path to calculate
+	if len(merkleTree) != 1 {
+		merklePath.Path = getPathElements(txIndex, merkleTree)
+	}
+
+	return merklePath
 }

merklepath_test.go

@@ -2,6 +2,7 @@ package bc_test
 
 import (
 	"encoding/hex"
+	"encoding/json"
 	"testing"
 
 	"github.com/libsv/go-bc"
@@ -94,3 +95,51 @@ func TestGetMerklePath(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, expected, root)
 }
+
+func TestGetMerklePathOddPosition(t *testing.T) {
+	txids := []string{
+		"b6d4d13aa08bb4b6cdb3b329cef29b5a5d55d85a85c330d56fddbce78d99c7d6",
+		"426f65f6a6ce79c909e54d8959c874a767db3076e76031be70942b896cc64052",
+		"adc23d36cc457d5847968c2e4d5f017a6f12a2f165102d10d2843f5276cfe68e",
+		"728714bbbddd81a54cae473835ae99eb92ed78191327eb11a9d7494273dcad2a",
+		"e3aa0230aa81abd483023886ad12790acf070e2a9f92d7f0ae3bebd90a904361",
+	}
+
+	merkles, err := bc.BuildMerkleTreeStore(txids)
+	assert.NoError(t, err)
+
+	// build path for tx index 4.
+	path := bc.GetTxMerklePath(4, merkles)
+	root, err := bc.MerkleRootFromBranches("e3aa0230aa81abd483023886ad12790acf070e2a9f92d7f0ae3bebd90a904361", int(path.Index), path.Path)
+	assert.NoError(t, err)
+	assert.Equal(t, merkles[len(merkles)-1], root)
+}
+
+func TestGetMerklePathEmptyPath(t *testing.T) {
+	txids := []string{
+		"b6d4d13aa08bb4b6cdb3b329cef29b5a5d55d85a85c330d56fddbce78d99c7d6",
+	}
+
+	merkles, err := bc.BuildMerkleTreeStore(txids)
+	assert.NoError(t, err)
+
+	// build path for tx index 4.
+	path := bc.GetTxMerklePath(0, merkles)
+	root, err := bc.MerkleRootFromBranches("b6d4d13aa08bb4b6cdb3b329cef29b5a5d55d85a85c330d56fddbce78d99c7d6", int(path.Index), path.Path)
+	assert.NoError(t, err)
+	assert.Equal(t, merkles[len(merkles)-1], root)
+	assert.Equal(t, ([]string)(nil), path.Path)
+	assert.Equal(t, uint64(0), path.Index)
+}
+
+func TestGetMerklePathEmptyPathJson(t *testing.T) {
+	txids := []string{
+		"b6d4d13aa08bb4b6cdb3b329cef29b5a5d55d85a85c330d56fddbce78d99c7d6",
+	}
+
+	merkles, _ := bc.BuildMerkleTreeStore(txids)
+	path := bc.GetTxMerklePath(0, merkles)
+	js, err := json.Marshal(path)
+	assert.NoError(t, err)
+	assert.Equal(t, string(js), "{\"index\":0,\"path\":null}")
+}