add trustMarshaler option to JSON encoder aimed at improving precomputed performance.

Author: qingyu31

src/encoding/json/encode.go

@@ -349,6 +349,8 @@ type encOpts struct {
 	quoted bool
 	// escapeHTML causes '<', '>', and '&' to be escaped in JSON strings.
 	escapeHTML bool
+	// trustMarshaler causes Marshaler not to be compacted, escaped and validated.
+	trustMarshaler bool
 }
 
 type encoderFunc func(e *encodeState, v reflect.Value, opts encOpts)
@@ -462,8 +464,12 @@ func marshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	}
 	b, err := m.MarshalJSON()
 	if err == nil {
-		// copy JSON into buffer, checking validity.
-		err = compact(&e.Buffer, b, opts.escapeHTML)
+		// copy JSON in to buffer.
+		if opts.trustMarshaler {
+			_, err = e.Buffer.Write(b)
+		} else {
+			err = compact(&e.Buffer, b, opts.escapeHTML)
+		}
 	}
 	if err != nil {
 		e.error(&MarshalerError{v.Type(), err, "MarshalJSON"})
@@ -479,8 +485,12 @@ func addrMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	m := va.Interface().(Marshaler)
 	b, err := m.MarshalJSON()
 	if err == nil {
-		// copy JSON into buffer, checking validity.
-		err = compact(&e.Buffer, b, opts.escapeHTML)
+		// copy JSON in to buffer.
+		if opts.trustMarshaler {
+			_, err = e.Buffer.Write(b)
+		} else {
+			err = compact(&e.Buffer, b, opts.escapeHTML)
+		}
 	}
 	if err != nil {
 		e.error(&MarshalerError{v.Type(), err, "MarshalJSON"})

src/encoding/json/stream.go

@@ -179,9 +179,10 @@ func nonSpace(b []byte) bool {
 
 // An Encoder writes JSON values to an output stream.
 type Encoder struct {
-	w          io.Writer
-	err        error
-	escapeHTML bool
+	w              io.Writer
+	err            error
+	escapeHTML     bool
+	trustMarshaler bool
 
 	indentBuf    *bytes.Buffer
 	indentPrefix string
@@ -203,7 +204,7 @@ func (enc *Encoder) Encode(v interface{}) error {
 		return enc.err
 	}
 	e := newEncodeState()
-	err := e.marshal(v, encOpts{escapeHTML: enc.escapeHTML})
+	err := e.marshal(v, encOpts{escapeHTML: enc.escapeHTML, trustMarshaler: enc.trustMarshaler})
 	if err != nil {
 		return err
 	}
@@ -254,6 +255,15 @@ func (enc *Encoder) SetEscapeHTML(on bool) {
 	enc.escapeHTML = on
 }
 
+// SetTrustMarshaler specifies whether fields implement Marshaler
+// should be computed such as escape, compact.
+// The default behavior is to run compact on output of Marshaler.
+// SetTrustMarshaler(true) just copies output of Marshaler
+// and makes better performance.
+func (enc *Encoder) SetTrustMarshaler(on bool) {
+	enc.trustMarshaler = on
+}
+
 // RawMessage is a raw encoded JSON value.
 // It implements Marshaler and Unmarshaler and can
 // be used to delay JSON decoding or precompute a JSON encoding.