encoding/json: fix and optimize marshal for quoted string

breml · breml · commit 9b0ac1d4c531 · 2019-09-10T20:45:51.000+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. name old time/op new time/op delta Issue34127-4 360ns ± 3% 200ns ± 3% -44.56% (p=0.008 n=5+5) name old alloc/op new alloc/op delta Issue34127-4 56.0B ± 0% 40.0B ± 0% -28.57% (p=0.008 n=5+5) name old allocs/op new allocs/op delta Issue34127-4 3.00 ± 0% 2.00 ± 0% -33.33% (p=0.008 n=5+5) Fixes #34154
diff --git a/src/encoding/json/bench_test.go b/src/encoding/json/bench_test.go
@@ -297,6 +297,22 @@ func BenchmarkIssue10335(b *testing.B) {
 	})
 }
 
+func BenchmarkIssue34127(b *testing.B) {
+	b.ReportAllocs()
+	j := struct {
+		Bar string `json:"bar,string"`
+	}{
+		Bar: `foobar`,
+	}
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			if _, err := Marshal(&j); err != nil {
+				b.Fatal(err)
+			}
+		}
+	})
+}
+
 func BenchmarkUnmapped(b *testing.B) {
 	b.ReportAllocs()
 	j := []byte(`{"s": "hello", "y": 2, "o": {"x": 0}, "a": [1, 99, {"x": 1}]}`)
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
@@ -118,6 +118,11 @@ func TestEncoderSetEscapeHTML(t *testing.T) {
 		Ptr    strPtrMarshaler
 	}{`"<str>"`, `"<str>"`}
 
+	// https://golang.org/issue/34154
+	stringOption := struct {
+		Bar string `json:"bar,string"`
+	}{`<html>foobar</html>`}
+
 	for _, tt := range []struct {
 		name       string
 		v          interface{}
@@ -137,6 +142,11 @@ func TestEncoderSetEscapeHTML(t *testing.T) {
 			`{"NonPtr":"\u003cstr\u003e","Ptr":"\u003cstr\u003e"}`,
 			`{"NonPtr":"<str>","Ptr":"<str>"}`,
 		},
+		{
+			"stringOption", stringOption,
+			`{"bar":"\"\u003chtml\u003efoobar\u003c/html\u003e\""}`,
+			`{"bar":"\"<html>foobar</html>\""}`,
+		},
 	} {
 		var buf bytes.Buffer
 		enc := NewEncoder(&buf)
