encoding/json: optimize marshal for quoted string

breml · breml · commit b4da9fd8b042 · 2019-09-09T22:45:16.000+02:00
Since Go 1.2 every string can be marshaled to JSON without error even if it contains invalid UTF-8 byte sequences. Therefore there is no need to use Marshal again for the only reason of enclosing the string in double quotes. Not using Marshal here also removes the error check as there has not been a way for Marshal to fail anyway. Additionally, this code runs significantly faster for quoted string fields (30 - 45% in my measurements, depending on the length of the string that is processed). Fixes: #34154
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
@@ -601,11 +601,11 @@ func stringEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 		return
 	}
 	if opts.quoted {
-		sb, err := Marshal(v.String())
-		if err != nil {
-			e.error(err)
-		}
-		e.string(string(sb), opts.escapeHTML)
+		b := make([]byte, 0, v.Len()+2)
+		b = append(b, '"')
+		b = append(b, []byte(v.String())...)
+		b = append(b, '"')
+		e.stringBytes(b, opts.escapeHTML)
 	} else {
 		e.string(v.String(), opts.escapeHTML)
 	}
diff --git a/src/encoding/json/stream_test.go b/src/encoding/json/stream_test.go
@@ -158,6 +158,27 @@ func TestEncoderSetEscapeHTML(t *testing.T) {
 	}
 }
 
+// https://golang.org/issue/34154
+func TestEncoderStringOptionSetEscapeHTMLFalse(t *testing.T) {
+	value := struct {
+		Bar string `json:"bar,string"`
+	}{
+		Bar: `<html>foobar</html>`,
+	}
+	want := `{"bar":"\"<html>foobar</html>\""}`
+
+	var buf bytes.Buffer
+	enc := NewEncoder(&buf)
+	enc.SetEscapeHTML(false)
+	if err := enc.Encode(value); err != nil {
+		t.Fatalf("Encode: %s", err)
+	}
+	if got := strings.TrimSpace(buf.String()); got != want {
+		t.Errorf("SetEscapeHTML(false) Encode = %#q, want %#q",
+			got, want)
+	}
+}
+
 func TestDecoder(t *testing.T) {
 	for i := 0; i <= len(streamTest); i++ {
 		// Use stream without newlines as input,
