stackitem: escape control characters in ToJSON()

Decoding uses `json.Decoder` which handles everything for us.

pkg/vm/stackitem/json.go

@@ -66,16 +66,8 @@ func toJSON(buf *io.BufBinWriter, item Item) {
 		for i := range it.value {
 			// map key can always be converted to []byte
 			// but are not always a valid UTF-8.
-			key, err := ToString(it.value[i].Key)
+			writeJSONString(buf.BinWriter, it.value[i].Key)
-			if err != nil {
+			w.WriteBytes([]byte(`:`))
-				if buf.Err == nil {
-					buf.Err = err
-				}
-				return
-			}
-			w.WriteB('"')
-			w.WriteBytes([]byte(key))
-			w.WriteBytes([]byte(`":`))
 			toJSON(buf, it.value[i].Value)
 			if i < len(it.value)-1 {
 				w.WriteB(',')
@@ -89,16 +81,7 @@ func toJSON(buf *io.BufBinWriter, item Item) {
 		}
 		w.WriteBytes([]byte(it.value.String()))
 	case *ByteArray, *Buffer:
-		w.WriteB('"')
+		writeJSONString(w, it)
-		s, err := ToString(it)
-		if err != nil {
-			if buf.Err == nil {
-				buf.Err = err
-			}
-			return
-		}
-		w.WriteBytes([]byte(s))
-		w.WriteB('"')
 	case *Bool:
 		if it.value {
 			w.WriteBytes([]byte("true"))
@@ -116,6 +99,21 @@ func toJSON(buf *io.BufBinWriter, item Item) {
 	}
 }
 
+// writeJSONString converts it to string and writes it to w as JSON value
+// surrounded in quotes with control characters escaped.
+func writeJSONString(w *io.BinWriter, it Item) {
+	if w.Err != nil {
+		return
+	}
+	s, err := ToString(it)
+	if err != nil {
+		w.Err = err
+		return
+	}
+	data, _ := json.Marshal(s) // error never occurs because `ToString` checks for validity
+	w.WriteBytes(data)
+}
+
 // FromJSON decodes Item from JSON.
 // It behaves as following:
 //   string -> ByteArray from base64

pkg/vm/stackitem/json_test.go

@@ -30,6 +30,7 @@ func TestFromToJSON(t *testing.T) {
 	t.Run("ByteString", func(t *testing.T) {
 		t.Run("Empty", getTestDecodeFunc(`""`, []byte{}))
 		t.Run("Base64", getTestDecodeFunc(`"test"`, "test"))
+		t.Run("Escape", getTestDecodeFunc(`"\"quotes\""`, `"quotes"`))
 	})
 	t.Run("BigInteger", func(t *testing.T) {
 		t.Run("ZeroFloat", getTestDecodeFunc(`12.000`, 12, nil))
@@ -58,6 +59,10 @@ func TestFromToJSON(t *testing.T) {
 		t.Run("Empty", getTestDecodeFunc(`{}`, NewMap()))
 		t.Run("Small", getTestDecodeFunc(`{"a":3}`, small))
 		t.Run("Big", getTestDecodeFunc(`{"3":{"a":3},"arr":["test"]}`, large))
+
+		m := NewMap()
+		m.Add(NewByteArray([]byte("\t")), NewBool(true))
+		t.Run("escape keys", getTestDecodeFunc(`{"\t":true}`, m))
 	})
 	t.Run("Invalid", func(t *testing.T) {
 		t.Run("Empty", getTestDecodeFunc(``, nil))