libs/db: Fix the BoltDB Get and Iterator

BoltDB's accessors will return slices that are only valid for the
lifetime of the transaction.  This adds copies where required to prevent
hard to debug crashes (among other things).

CHANGELOG_PENDING.md

@@ -29,3 +29,4 @@
 
 ### BUG FIXES:
 - [libs/db] Fixed the BoltDB backend's Batch.Delete implementation (@Yawning)
+- [libs/db] Fixed the BoltDB backend's Get and Iterator implementation (@Yawning)

libs/db/boltdb.go

@@ -66,7 +66,9 @@ func (bdb *BoltDB) Get(key []byte) (value []byte) {
 	key = nonEmptyKey(nonNilBytes(key))
 	err := bdb.db.View(func(tx *bbolt.Tx) error {
 		b := tx.Bucket(bucket)
-		value = b.Get(key)
+		if v := b.Get(key); v != nil {
+			value = append([]byte{}, v...)
+		}
 		return nil
 	})
 	if err != nil {
@@ -312,12 +314,16 @@ func (itr *boltDBIterator) Next() {
 
 func (itr *boltDBIterator) Key() []byte {
 	itr.assertIsValid()
-	return itr.currentKey
+	return append([]byte{}, itr.currentKey...)
 }
 
 func (itr *boltDBIterator) Value() []byte {
 	itr.assertIsValid()
-	return itr.currentValue
+	var value []byte
+	if itr.currentValue != nil {
+		value = append([]byte{}, itr.currentValue...)
+	}
+	return value
 }
 
 func (itr *boltDBIterator) Close() {