defensive copy + layout change

types/tx.go

@@ -211,17 +211,24 @@ func (t TxRecordSet) Validate(maxSizeBytes int64, otxs Txs) error {
 	// indexes can be preserved.
 	addedCopy := make([]Tx, len(t.added))
 	copy(addedCopy, t.added)
+	sort.Sort(Txs(addedCopy))
+
 	removedCopy := make([]Tx, len(t.removed))
 	copy(removedCopy, t.removed)
+	sort.Sort(Txs(removedCopy))
+
 	unmodifiedCopy := make([]Tx, len(t.unmodified))
 	copy(unmodifiedCopy, t.unmodified)
-
-	sort.Sort(otxs)
-	sort.Sort(Txs(addedCopy))
-	sort.Sort(Txs(removedCopy))
 	sort.Sort(Txs(unmodifiedCopy))
+
+	// make a defensive copy of otxs so that the order of
+	// the caller's data is not altered.
+	otxsCopy := make([]Tx, len(otxs))
+	copy(otxsCopy, otxs)
+	sort.Sort(Txs(otxsCopy))
+
 	unmodifiedIdx, addedIdx, removedIdx := 0, 0, 0
-	for i := 0; i < len(otxs); i++ {
+	for i := 0; i < len(otxsCopy); i++ {
 		if addedIdx == len(addedCopy) &&
 			removedIdx == len(removedCopy) &&
 			unmodifiedIdx == len(unmodifiedCopy) {
@@ -234,9 +241,9 @@ func (t TxRecordSet) Validate(maxSizeBytes int64, otxs Txs) error {
 		// iterate over the sorted addedIndex until we reach a value that sorts
 		// higher than the value we are examining in the original list.
 		for addedIdx < len(addedCopy) {
-			switch bytes.Compare(addedCopy[addedIdx], otxs[i]) {
+			switch bytes.Compare(addedCopy[addedIdx], otxsCopy[i]) {
 			case 0:
-				return fmt.Errorf("existing transaction incorrectly marked as added, transaction hash: %x", otxs[i].Hash())
+				return fmt.Errorf("existing transaction incorrectly marked as added, transaction hash: %x", otxsCopy[i].Hash())
 			case -1:
 				addedIdx++
 			case 1:
@@ -258,7 +265,7 @@ func (t TxRecordSet) Validate(maxSizeBytes int64, otxs Txs) error {
 		// The same logic applies for the unmodified check.
 
 		if removedIdx < len(removedCopy) {
-			switch bytes.Compare(removedCopy[removedIdx], otxs[i]) {
+			switch bytes.Compare(removedCopy[removedIdx], otxsCopy[i]) {
 			case 0:
 				removedIdx++
 			case -1:
@@ -266,7 +273,7 @@ func (t TxRecordSet) Validate(maxSizeBytes int64, otxs Txs) error {
 			}
 		}
 		if unmodifiedIdx < len(unmodifiedCopy) {
-			switch bytes.Compare(unmodifiedCopy[unmodifiedIdx], otxs[i]) {
+			switch bytes.Compare(unmodifiedCopy[unmodifiedIdx], otxsCopy[i]) {
 			case 0:
 				unmodifiedIdx++
 			case -1: