gob: add DecodeValue and EncodeValue

R=rsc
CC=golang-dev
https://golang.org/cl/1698045

src/pkg/gob/codec_test.go

@@ -1028,7 +1028,7 @@ func TestInvalidField(t *testing.T) {
 	var bad0 Bad0
 	bad0.inter = 17
 	b := new(bytes.Buffer)
-	err := encode(b, &bad0)
+	err := encode(b, reflect.NewValue(&bad0))
 	if err == nil {
 		t.Error("expected error; got none")
 	} else if strings.Index(err.String(), "interface") < 0 {

src/pkg/gob/decode.go

@@ -918,9 +918,9 @@ func (dec *Decoder) getIgnoreEnginePtr(wireId typeId) (enginePtr **decEngine, er
 	return
 }
 
-func (dec *Decoder) decode(wireId typeId, e interface{}) os.Error {
+func (dec *Decoder) decode(wireId typeId, val reflect.Value) os.Error {
 	// Dereference down to the underlying struct type.
-	rt, indir := indirect(reflect.Typeof(e))
+	rt, indir := indirect(val.Type())
 	enginePtr, err := dec.getDecEnginePtr(wireId, rt)
 	if err != nil {
 		return err
@@ -931,9 +931,9 @@ func (dec *Decoder) decode(wireId typeId, e interface{}) os.Error {
 			name := rt.Name()
 			return os.ErrorString("gob: type mismatch: no fields matched compiling decoder for " + name)
 		}
-		return decodeStruct(engine, st, dec.state.b, uintptr(reflect.NewValue(e).Addr()), indir)
+		return decodeStruct(engine, st, dec.state.b, uintptr(val.Addr()), indir)
 	}
-	return decodeSingle(engine, rt, dec.state.b, uintptr(reflect.NewValue(e).Addr()), indir)
+	return decodeSingle(engine, rt, dec.state.b, uintptr(val.Addr()), indir)
 }
 
 func init() {

src/pkg/gob/decoder.go

@@ -47,7 +47,7 @@ func (dec *Decoder) recvType(id typeId) {
 
 	// Type:
 	wire := new(wireType)
-	dec.state.err = dec.decode(tWireType, wire)
+	dec.state.err = dec.decode(tWireType, reflect.NewValue(wire))
 	// Remember we've seen this type.
 	dec.wireType[id] = wire
 }
@@ -55,7 +55,7 @@ func (dec *Decoder) recvType(id typeId) {
 // Decode reads the next value from the connection and stores
 // it in the data represented by the empty interface value.
 // The value underlying e must be the correct type for the next
-// data item received.
+// data item received, which must be a pointer.
 func (dec *Decoder) Decode(e interface{}) os.Error {
 	// If e represents a value, the answer won't get back to the
 	// caller.  Make sure it's a pointer.
@@ -63,7 +63,14 @@ func (dec *Decoder) Decode(e interface{}) os.Error {
 		dec.state.err = os.ErrorString("gob: attempt to decode into a non-pointer")
 		return dec.state.err
 	}
+	return dec.DecodeValue(reflect.NewValue(e))
+}
 
+// DecodeValue reads the next value from the connection and stores
+// it in the data represented by the reflection value.
+// The value must be the correct type for the next
+// data item received.
+func (dec *Decoder) DecodeValue(value reflect.Value) os.Error {
 	// Make sure we're single-threaded through here.
 	dec.mutex.Lock()
 	defer dec.mutex.Unlock()
@@ -114,7 +121,7 @@ func (dec *Decoder) Decode(e interface{}) os.Error {
 			dec.state.err = errBadType
 			break
 		}
-		dec.state.err = dec.decode(id, e)
+		dec.state.err = dec.decode(id, value)
 		break
 	}
 	return dec.state.err

src/pkg/gob/encode.go

@@ -798,12 +798,11 @@ func getEncEngine(rt reflect.Type) (*encEngine, os.Error) {
 	return info.encoder, err
 }
 
-func encode(b *bytes.Buffer, e interface{}) os.Error {
+func encode(b *bytes.Buffer, value reflect.Value) os.Error {
 	// Dereference down to the underlying object.
-	rt, indir := indirect(reflect.Typeof(e))
+	rt, indir := indirect(value.Type())
-	v := reflect.NewValue(e)
 	for i := 0; i < indir; i++ {
-		v = reflect.Indirect(v)
+		value = reflect.Indirect(value)
 	}
 	typeLock.Lock()
 	engine, err := getEncEngine(rt)
@@ -811,8 +810,8 @@ func encode(b *bytes.Buffer, e interface{}) os.Error {
 	if err != nil {
 		return err
 	}
-	if _, ok := v.(*reflect.StructValue); ok {
+	if _, ok := value.(*reflect.StructValue); ok {
-		return encodeStruct(engine, b, v.Addr())
+		return encodeStruct(engine, b, value.Addr())
 	}
-	return encodeSingle(engine, b, v.Addr())
+	return encodeSingle(engine, b, value.Addr())
 }

src/pkg/gob/encoder.go

@@ -115,7 +115,7 @@ func (enc *Encoder) sendType(origt reflect.Type) (sent bool) {
 	// Id:
 	encodeInt(enc.state, -int64(info.id))
 	// Type:
-	encode(enc.state.b, info.wire)
+	encode(enc.state.b, reflect.NewValue(info.wire))
 	enc.send()
 	if enc.state.err != nil {
 		return
@@ -140,13 +140,19 @@ func (enc *Encoder) sendType(origt reflect.Type) (sent bool) {
 // Encode transmits the data item represented by the empty interface value,
 // guaranteeing that all necessary type information has been transmitted first.
 func (enc *Encoder) Encode(e interface{}) os.Error {
+	return enc.EncodeValue(reflect.NewValue(e))
+}
+
+// EncodeValue transmits the data item represented by the reflection value,
+// guaranteeing that all necessary type information has been transmitted first.
+func (enc *Encoder) EncodeValue(value reflect.Value) os.Error {
 	// Make sure we're single-threaded through here, so multiple
 	// goroutines can share an encoder.
 	enc.mutex.Lock()
 	defer enc.mutex.Unlock()
 
 	enc.state.err = nil
-	rt, _ := indirect(reflect.Typeof(e))
+	rt, _ := indirect(value.Type())
 
 	// Sanity check only: encoder should never come in with data present.
 	if enc.state.b.Len() > 0 || enc.countState.b.Len() > 0 {
@@ -181,7 +187,7 @@ func (enc *Encoder) Encode(e interface{}) os.Error {
 	encodeInt(enc.state, int64(enc.sent[rt]))
 
 	// Encode the object.
-	err := encode(enc.state.b, e)
+	err := encode(enc.state.b, value)
 	if err != nil {
 		enc.setError(err)
 	} else {