1 files changed, 248 insertions, 0 deletions
diff --git a/src/encoding/gob/encoder.go b/src/encoding/gob/encoder.go
new file mode 100644
index 000000000..a340e47b5
--- /dev/null
+++ b/src/encoding/gob/encoder.go
@@ -0,0 +1,248 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package gob
+
+import (
+	"io"
+	"reflect"
+	"sync"
+)
+
+// An Encoder manages the transmission of type and data information to the
+// other side of a connection.
+type Encoder struct {
+	mutex      sync.Mutex              // each item must be sent atomically
+	w          []io.Writer             // where to send the data
+	sent       map[reflect.Type]typeId // which types we've already sent
+	countState *encoderState           // stage for writing counts
+	freeList   *encoderState           // list of free encoderStates; avoids reallocation
+	byteBuf    encBuffer               // buffer for top-level encoderState
+	err        error
+}
+
+// Before we encode a message, we reserve space at the head of the
+// buffer in which to encode its length. This means we can use the
+// buffer to assemble the message without another allocation.
+const maxLength = 9 // Maximum size of an encoded length.
+var spaceForLength = make([]byte, maxLength)
+
+// NewEncoder returns a new encoder that will transmit on the io.Writer.
+func NewEncoder(w io.Writer) *Encoder {
+	enc := new(Encoder)
+	enc.w = []io.Writer{w}
+	enc.sent = make(map[reflect.Type]typeId)
+	enc.countState = enc.newEncoderState(new(encBuffer))
+	return enc
+}
+
+// writer() returns the innermost writer the encoder is using
+func (enc *Encoder) writer() io.Writer {
+	return enc.w[len(enc.w)-1]
+}
+
+// pushWriter adds a writer to the encoder.
+func (enc *Encoder) pushWriter(w io.Writer) {
+	enc.w = append(enc.w, w)
+}
+
+// popWriter pops the innermost writer.
+func (enc *Encoder) popWriter() {
+	enc.w = enc.w[0 : len(enc.w)-1]
+}
+
+func (enc *Encoder) setError(err error) {
+	if enc.err == nil { // remember the first.
+		enc.err = err
+	}
+}
+
+// writeMessage sends the data item preceded by a unsigned count of its length.
+func (enc *Encoder) writeMessage(w io.Writer, b *encBuffer) {
+	// Space has been reserved for the length at the head of the message.
+	// This is a little dirty: we grab the slice from the bytes.Buffer and massage
+	// it by hand.
+	message := b.Bytes()
+	messageLen := len(message) - maxLength
+	// Encode the length.
+	enc.countState.b.Reset()
+	enc.countState.encodeUint(uint64(messageLen))
+	// Copy the length to be a prefix of the message.
+	offset := maxLength - enc.countState.b.Len()
+	copy(message[offset:], enc.countState.b.Bytes())
+	// Write the data.
+	_, err := w.Write(message[offset:])
+	// Drain the buffer and restore the space at the front for the count of the next message.
+	b.Reset()
+	b.Write(spaceForLength)
+	if err != nil {
+		enc.setError(err)
+	}
+}
+
+// sendActualType sends the requested type, without further investigation, unless
+// it's been sent before.
+func (enc *Encoder) sendActualType(w io.Writer, state *encoderState, ut *userTypeInfo, actual reflect.Type) (sent bool) {
+	if _, alreadySent := enc.sent[actual]; alreadySent {
+		return false
+	}
+	info, err := getTypeInfo(ut)
+	if err != nil {
+		enc.setError(err)
+		return
+	}
+	// Send the pair (-id, type)
+	// Id:
+	state.encodeInt(-int64(info.id))
+	// Type:
+	enc.encode(state.b, reflect.ValueOf(info.wire), wireTypeUserInfo)
+	enc.writeMessage(w, state.b)
+	if enc.err != nil {
+		return
+	}
+
+	// Remember we've sent this type, both what the user gave us and the base type.
+	enc.sent[ut.base] = info.id
+	if ut.user != ut.base {
+		enc.sent[ut.user] = info.id
+	}
+	// Now send the inner types
+	switch st := actual; st.Kind() {
+	case reflect.Struct:
+		for i := 0; i < st.NumField(); i++ {
+			if isExported(st.Field(i).Name) {
+				enc.sendType(w, state, st.Field(i).Type)
+			}
+		}
+	case reflect.Array, reflect.Slice:
+		enc.sendType(w, state, st.Elem())
+	case reflect.Map:
+		enc.sendType(w, state, st.Key())
+		enc.sendType(w, state, st.Elem())
+	}
+	return true
+}
+
+// sendType sends the type info to the other side, if necessary.
+func (enc *Encoder) sendType(w io.Writer, state *encoderState, origt reflect.Type) (sent bool) {
+	ut := userType(origt)
+	if ut.externalEnc != 0 {
+		// The rules are different: regardless of the underlying type's representation,
+		// we need to tell the other side that the base type is a GobEncoder.
+		return enc.sendActualType(w, state, ut, ut.base)
+	}
+
+	// It's a concrete value, so drill down to the base type.
+	switch rt := ut.base; rt.Kind() {
+	default:
+		// Basic types and interfaces do not need to be described.
+		return
+	case reflect.Slice:
+		// If it's []uint8, don't send; it's considered basic.
+		if rt.Elem().Kind() == reflect.Uint8 {
+			return
+		}
+		// Otherwise we do send.
+		break
+	case reflect.Array:
+		// arrays must be sent so we know their lengths and element types.
+		break
+	case reflect.Map:
+		// maps must be sent so we know their lengths and key/value types.
+		break
+	case reflect.Struct:
+		// structs must be sent so we know their fields.
+		break
+	case reflect.Chan, reflect.Func:
+		// If we get here, it's a field of a struct; ignore it.
+		return
+	}
+
+	return enc.sendActualType(w, state, ut, ut.base)
+}
+
+// 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{}) error {
+	return enc.EncodeValue(reflect.ValueOf(e))
+}
+
+// sendTypeDescriptor makes sure the remote side knows about this type.
+// It will send a descriptor if this is the first time the type has been
+// sent.
+func (enc *Encoder) sendTypeDescriptor(w io.Writer, state *encoderState, ut *userTypeInfo) {
+	// Make sure the type is known to the other side.
+	// First, have we already sent this type?
+	rt := ut.base
+	if ut.externalEnc != 0 {
+		rt = ut.user
+	}
+	if _, alreadySent := enc.sent[rt]; !alreadySent {
+		// No, so send it.
+		sent := enc.sendType(w, state, rt)
+		if enc.err != nil {
+			return
+		}
+		// If the type info has still not been transmitted, it means we have
+		// a singleton basic type (int, []byte etc.) at top level.  We don't
+		// need to send the type info but we do need to update enc.sent.
+		if !sent {
+			info, err := getTypeInfo(ut)
+			if err != nil {
+				enc.setError(err)
+				return
+			}
+			enc.sent[rt] = info.id
+		}
+	}
+}
+
+// sendTypeId sends the id, which must have already been defined.
+func (enc *Encoder) sendTypeId(state *encoderState, ut *userTypeInfo) {
+	// Identify the type of this top-level value.
+	state.encodeInt(int64(enc.sent[ut.base]))
+}
+
+// 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) error {
+	// Gobs contain values. They cannot represent nil pointers, which
+	// have no value to encode.
+	if value.Kind() == reflect.Ptr && value.IsNil() {
+		panic("gob: cannot encode nil pointer of type " + value.Type().String())
+	}
+
+	// Make sure we're single-threaded through here, so multiple
+	// goroutines can share an encoder.
+	enc.mutex.Lock()
+	defer enc.mutex.Unlock()
+
+	// Remove any nested writers remaining due to previous errors.
+	enc.w = enc.w[0:1]
+
+	ut, err := validUserType(value.Type())
+	if err != nil {
+		return err
+	}
+
+	enc.err = nil
+	enc.byteBuf.Reset()
+	enc.byteBuf.Write(spaceForLength)
+	state := enc.newEncoderState(&enc.byteBuf)
+
+	enc.sendTypeDescriptor(enc.writer(), state, ut)
+	enc.sendTypeId(state, ut)
+	if enc.err != nil {
+		return enc.err
+	}
+
+	// Encode the object.
+	enc.encode(state.b, value, ut)
+	if enc.err == nil {
+		enc.writeMessage(enc.writer(), state.b)
+	}
+
+	enc.freeEncoderState(state)
+	return enc.err
+}