Write directly into the underlying writer without temporary buffer when generating json ouptut

Author: valyala

jsonstring.go

@@ -1,52 +1,69 @@
 package quicktemplate
 
-// appendJSONString is a synonym to strconv.AppendQuote, but works 3x faster.
-func appendJSONString(dst []byte, s string) []byte {
-	j := 0
+import (
+	"io"
+)
+
+func writeJSONString(w io.Writer, s string) {
+	write := w.Write
 	b := unsafeStrToBytes(s)
+	j := 0
 	for i, n := 0, len(b); i < n; i++ {
 		switch b[i] {
 		case '"':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\"`...)
+			write(b[j:i])
+			write(strBackslashQuote)
 			j = i + 1
 		case '\\':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\\`...)
+			write(b[j:i])
+			write(strBackslashBackslash)
 			j = i + 1
 		case '\n':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\n`...)
+			write(b[j:i])
+			write(strBackslashN)
 			j = i + 1
 		case '\r':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\r`...)
+			write(b[j:i])
+			write(strBackslashR)
 			j = i + 1
 		case '\t':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\t`...)
+			write(b[j:i])
+			write(strBackslashT)
 			j = i + 1
 		case '\f':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\u000c`...)
+			write(b[j:i])
+			write(strBackslashF)
 			j = i + 1
 		case '\b':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\u0008`...)
+			write(b[j:i])
+			write(strBackslashB)
 			j = i + 1
 		case '<':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\u003c`...)
+			write(b[j:i])
+			write(strBackslashLT)
 			j = i + 1
 		case '\'':
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\u0027`...)
+			write(b[j:i])
+			write(strBackslashQ)
 			j = i + 1
 		case 0:
-			dst = append(dst, b[j:i]...)
-			dst = append(dst, `\u0000`...)
+			write(b[j:i])
+			write(strBackslashZero)
 			j = i + 1
 		}
 	}
-	return append(dst, b[j:]...)
+	write(b[j:])
 }
+
+var (
+	strBackslashQuote     = []byte(`\"`)
+	strBackslashBackslash = []byte(`\\`)
+	strBackslashN         = []byte(`\n`)
+	strBackslashR         = []byte(`\r`)
+	strBackslashT         = []byte(`\t`)
+	strBackslashF         = []byte(`\u000c`)
+	strBackslashB         = []byte(`\u0008`)
+	strBackslashLT        = []byte(`\u003c`)
+	strBackslashQ         = []byte(`\u0027`)
+	strBackslashZero      = []byte(`\u0000`)
+)

jsonstring_test.go

@@ -6,30 +6,34 @@ import (
 	"testing"
 )
 
-func TestAppendJSONString(t *testing.T) {
-	testAppendJSONString(t, ``)
-	testAppendJSONString(t, `f`)
-	testAppendJSONString(t, `"`)
-	testAppendJSONString(t, `<`)
-	testAppendJSONString(t, "\x00\n\r\t\b\f"+`"\`)
-	testAppendJSONString(t, `"foobar`)
-	testAppendJSONString(t, `foobar"`)
-	testAppendJSONString(t, `foo "bar"
+func TestWriteJSONString(t *testing.T) {
+	testWriteJSONString(t, ``)
+	testWriteJSONString(t, `f`)
+	testWriteJSONString(t, `"`)
+	testWriteJSONString(t, `<`)
+	testWriteJSONString(t, "\x00\n\r\t\b\f"+`"\`)
+	testWriteJSONString(t, `"foobar`)
+	testWriteJSONString(t, `foobar"`)
+	testWriteJSONString(t, `foo "bar"
 		baz`)
-	testAppendJSONString(t, `this is a "тест"`)
-	testAppendJSONString(t, `привет test`)
+	testWriteJSONString(t, `this is a "тест"`)
+	testWriteJSONString(t, `привет test`)
 
-	testAppendJSONString(t, `</script><script>alert('evil')</script>`)
+	testWriteJSONString(t, `</script><script>alert('evil')</script>`)
 }
 
-func testAppendJSONString(t *testing.T, s string) {
+func testWriteJSONString(t *testing.T, s string) {
 	expectedResult, err := json.Marshal(s)
 	if err != nil {
 		t.Fatalf("unexpected error when encoding string %q: %s", s, err)
 	}
 	expectedResult = expectedResult[1 : len(expectedResult)-1]
 
-	result := string(appendJSONString(nil, s))
+	bb := AcquireByteBuffer()
+	writeJSONString(bb, s)
+	result := string(bb.B)
+	ReleaseByteBuffer(bb)
+
 	if strings.Contains(result, "'") {
 		t.Fatalf("json string shouldn't contain single quote: %q, src %q", result, s)
 	}

writer.go

@@ -98,13 +98,14 @@ func (w *QWriter) FPrec(f float64, prec int) {
 
 // Q writes quoted json-safe s to w.
 func (w *QWriter) Q(s string) {
-	writeQuick(w.w, func(dst []byte) []byte {
-		dst = append(dst, '"')
-		dst = appendJSONString(dst, s)
-		return append(dst, '"')
-	})
+	ww := w.w
+	ww.Write(strQuote)
+	writeJSONString(w.w, s)
+	ww.Write(strQuote)
 }
 
+var strQuote = []byte(`"`)
+
 // QZ writes quoted json-safe z to w.
 func (w *QWriter) QZ(z []byte) {
 	w.Q(unsafeBytesToStr(z))
@@ -114,9 +115,7 @@ func (w *QWriter) QZ(z []byte) {
 //
 // Unlike Q it doesn't qoute resulting s.
 func (w *QWriter) J(s string) {
-	writeQuick(w.w, func(dst []byte) []byte {
-		return appendJSONString(dst, s)
-	})
+	writeJSONString(w.w, s)
 }
 
 // JZ writes json-safe z to w.