fix: fixed buffer length bug on string decoder

close #278

internal/decoder/string.go

@@ -239,14 +239,15 @@ func stringBytes(s *Stream) ([]byte, error) {
 			fallthrough
 		default:
 			// multi bytes character
-			r, _ := utf8.DecodeRune(s.buf[cursor:])
-			b := []byte(string(r))
+			r, size := utf8.DecodeRune(s.buf[cursor:])
 			if r == utf8.RuneError {
-				s.buf = append(append(append([]byte{}, s.buf[:cursor]...), b...), s.buf[cursor+1:]...)
+				s.buf = append(append(append([]byte{}, s.buf[:cursor]...), runeErrBytes...), s.buf[cursor+1:]...)
+				cursor += runeErrBytesLen
+				s.length += runeErrBytesLen
 				_, _, p = s.stat()
+			} else {
+				cursor += int64(size)
 			}
-			cursor += int64(len(b))
-			s.length += int64(len(b))
 			continue
 		}
 		cursor++

stream_test.go

@@ -14,7 +14,6 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"reflect"
-
 	"strings"
 	"testing"
 
@@ -502,3 +501,16 @@ func TestGzipStreaming(t *testing.T) {
 		t.Fatalf("Unexpected error: %v", err)
 	}
 }
+
+func TestIssue278(t *testing.T) {
+	a := `{"嗷嗷":"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\u55f7"}`
+	r := strings.NewReader(a)
+	var m map[string]string
+	if err := json.NewDecoder(r).Decode(&m); err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+	want := "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\u55f7"
+	if got := m["嗷嗷"]; got != want {
+		t.Errorf("string %q; want = %q", got, want)
+	}
+}