add Serialized method to Proof

proof.go

@@ -19,6 +19,9 @@ type Proof interface {
 
 	// Get retrieves the given key if it's present in the key-value data store.
 	Get(key []byte) ([]byte, error)
+
+	// Serialize returns the serialized proof
+	Serialize() [][]byte
 }
 
 type ProofDB struct {
@@ -58,6 +61,14 @@ func (w *ProofDB) Get(key []byte) ([]byte, error) {
 	return val, nil
 }
 
+func (w *ProofDB) Serialize() [][]byte {
+	nodes := make([][]byte, 0, len(w.kv))
+	for _, value := range w.kv {
+		nodes = append(nodes, value)
+	}
+	return nodes
+}
+
 // Prove returns the merkle proof for the given key, which is
 func (t *Trie) Prove(key []byte) (Proof, bool) {
 	proof := NewProofDB()