build: move package sources from src/pkg to src

Preparation was in CL 134570043.
This CL contains only the effect of 'hg mv src/pkg/* src'.
For more about the move, see golang.org/s/go14nopkg.

17 files changed, 8111 insertions, 0 deletions

diff --git a/src/encoding/gob/codec_test.go b/src/encoding/gob/codec_test.go
new file mode 100644
index 0000000000..4f17a28931
--- /dev/null
+++ b/src/encoding/gob/codec_test.go
@@ -0,0 +1,1469 @@
+// 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 (
+	"bytes"
+	"errors"
+	"flag"
+	"math"
+	"math/rand"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+)
+
+var doFuzzTests = flag.Bool("gob.fuzz", false, "run the fuzz tests, which are large and very slow")
+
+// Guarantee encoding format by comparing some encodings to hand-written values
+type EncodeT struct {
+	x uint64
+	b []byte
+}
+
+var encodeT = []EncodeT{
+	{0x00, []byte{0x00}},
+	{0x0F, []byte{0x0F}},
+	{0xFF, []byte{0xFF, 0xFF}},
+	{0xFFFF, []byte{0xFE, 0xFF, 0xFF}},
+	{0xFFFFFF, []byte{0xFD, 0xFF, 0xFF, 0xFF}},
+	{0xFFFFFFFF, []byte{0xFC, 0xFF, 0xFF, 0xFF, 0xFF}},
+	{0xFFFFFFFFFF, []byte{0xFB, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}},
+	{0xFFFFFFFFFFFF, []byte{0xFA, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}},
+	{0xFFFFFFFFFFFFFF, []byte{0xF9, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}},
+	{0xFFFFFFFFFFFFFFFF, []byte{0xF8, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}},
+	{0x1111, []byte{0xFE, 0x11, 0x11}},
+	{0x1111111111111111, []byte{0xF8, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}},
+	{0x8888888888888888, []byte{0xF8, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88}},
+	{1 << 63, []byte{0xF8, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}},
+}
+
+// testError is meant to be used as a deferred function to turn a panic(gobError) into a
+// plain test.Error call.
+func testError(t *testing.T) {
+	if e := recover(); e != nil {
+		t.Error(e.(gobError).err) // Will re-panic if not one of our errors, such as a runtime error.
+	}
+	return
+}
+
+// Test basic encode/decode routines for unsigned integers
+func TestUintCodec(t *testing.T) {
+	defer testError(t)
+	b := new(bytes.Buffer)
+	encState := newEncoderState(b)
+	for _, tt := range encodeT {
+		b.Reset()
+		encState.encodeUint(tt.x)
+		if !bytes.Equal(tt.b, b.Bytes()) {
+			t.Errorf("encodeUint: %#x encode: expected % x got % x", tt.x, tt.b, b.Bytes())
+		}
+	}
+	decState := newDecodeState(b)
+	for u := uint64(0); ; u = (u + 1) * 7 {
+		b.Reset()
+		encState.encodeUint(u)
+		v := decState.decodeUint()
+		if u != v {
+			t.Errorf("Encode/Decode: sent %#x received %#x", u, v)
+		}
+		if u&(1<<63) != 0 {
+			break
+		}
+	}
+}
+
+func verifyInt(i int64, t *testing.T) {
+	defer testError(t)
+	var b = new(bytes.Buffer)
+	encState := newEncoderState(b)
+	encState.encodeInt(i)
+	decState := newDecodeState(b)
+	decState.buf = make([]byte, 8)
+	j := decState.decodeInt()
+	if i != j {
+		t.Errorf("Encode/Decode: sent %#x received %#x", uint64(i), uint64(j))
+	}
+}
+
+// Test basic encode/decode routines for signed integers
+func TestIntCodec(t *testing.T) {
+	for u := uint64(0); ; u = (u + 1) * 7 {
+		// Do positive and negative values
+		i := int64(u)
+		verifyInt(i, t)
+		verifyInt(-i, t)
+		verifyInt(^i, t)
+		if u&(1<<63) != 0 {
+			break
+		}
+	}
+	verifyInt(-1<<63, t) // a tricky case
+}
+
+// The result of encoding a true boolean with field number 7
+var boolResult = []byte{0x07, 0x01}
+
+// The result of encoding a number 17 with field number 7
+var signedResult = []byte{0x07, 2 * 17}
+var unsignedResult = []byte{0x07, 17}
+var floatResult = []byte{0x07, 0xFE, 0x31, 0x40}
+
+// The result of encoding a number 17+19i with field number 7
+var complexResult = []byte{0x07, 0xFE, 0x31, 0x40, 0xFE, 0x33, 0x40}
+
+// The result of encoding "hello" with field number 7
+var bytesResult = []byte{0x07, 0x05, 'h', 'e', 'l', 'l', 'o'}
+
+func newDecodeState(buf *bytes.Buffer) *decoderState {
+	d := new(decoderState)
+	d.b = buf
+	d.buf = make([]byte, uint64Size)
+	return d
+}
+
+func newEncoderState(b *bytes.Buffer) *encoderState {
+	b.Reset()
+	state := &encoderState{enc: nil, b: b}
+	state.fieldnum = -1
+	return state
+}
+
+// Test instruction execution for encoding.
+// Do not run the machine yet; instead do individual instructions crafted by hand.
+func TestScalarEncInstructions(t *testing.T) {
+	var b = new(bytes.Buffer)
+
+	// bool
+	{
+		var data bool = true
+		instr := &encInstr{encBool, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(boolResult, b.Bytes()) {
+			t.Errorf("bool enc instructions: expected % x got % x", boolResult, b.Bytes())
+		}
+	}
+
+	// int
+	{
+		b.Reset()
+		var data int = 17
+		instr := &encInstr{encInt, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(signedResult, b.Bytes()) {
+			t.Errorf("int enc instructions: expected % x got % x", signedResult, b.Bytes())
+		}
+	}
+
+	// uint
+	{
+		b.Reset()
+		var data uint = 17
+		instr := &encInstr{encUint, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(unsignedResult, b.Bytes()) {
+			t.Errorf("uint enc instructions: expected % x got % x", unsignedResult, b.Bytes())
+		}
+	}
+
+	// int8
+	{
+		b.Reset()
+		var data int8 = 17
+		instr := &encInstr{encInt, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(signedResult, b.Bytes()) {
+			t.Errorf("int8 enc instructions: expected % x got % x", signedResult, b.Bytes())
+		}
+	}
+
+	// uint8
+	{
+		b.Reset()
+		var data uint8 = 17
+		instr := &encInstr{encUint, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(unsignedResult, b.Bytes()) {
+			t.Errorf("uint8 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
+		}
+	}
+
+	// int16
+	{
+		b.Reset()
+		var data int16 = 17
+		instr := &encInstr{encInt, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(signedResult, b.Bytes()) {
+			t.Errorf("int16 enc instructions: expected % x got % x", signedResult, b.Bytes())
+		}
+	}
+
+	// uint16
+	{
+		b.Reset()
+		var data uint16 = 17
+		instr := &encInstr{encUint, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(unsignedResult, b.Bytes()) {
+			t.Errorf("uint16 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
+		}
+	}
+
+	// int32
+	{
+		b.Reset()
+		var data int32 = 17
+		instr := &encInstr{encInt, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(signedResult, b.Bytes()) {
+			t.Errorf("int32 enc instructions: expected % x got % x", signedResult, b.Bytes())
+		}
+	}
+
+	// uint32
+	{
+		b.Reset()
+		var data uint32 = 17
+		instr := &encInstr{encUint, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(unsignedResult, b.Bytes()) {
+			t.Errorf("uint32 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
+		}
+	}
+
+	// int64
+	{
+		b.Reset()
+		var data int64 = 17
+		instr := &encInstr{encInt, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(signedResult, b.Bytes()) {
+			t.Errorf("int64 enc instructions: expected % x got % x", signedResult, b.Bytes())
+		}
+	}
+
+	// uint64
+	{
+		b.Reset()
+		var data uint64 = 17
+		instr := &encInstr{encUint, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(unsignedResult, b.Bytes()) {
+			t.Errorf("uint64 enc instructions: expected % x got % x", unsignedResult, b.Bytes())
+		}
+	}
+
+	// float32
+	{
+		b.Reset()
+		var data float32 = 17
+		instr := &encInstr{encFloat, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(floatResult, b.Bytes()) {
+			t.Errorf("float32 enc instructions: expected % x got % x", floatResult, b.Bytes())
+		}
+	}
+
+	// float64
+	{
+		b.Reset()
+		var data float64 = 17
+		instr := &encInstr{encFloat, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(floatResult, b.Bytes()) {
+			t.Errorf("float64 enc instructions: expected % x got % x", floatResult, b.Bytes())
+		}
+	}
+
+	// bytes == []uint8
+	{
+		b.Reset()
+		data := []byte("hello")
+		instr := &encInstr{encUint8Array, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(bytesResult, b.Bytes()) {
+			t.Errorf("bytes enc instructions: expected % x got % x", bytesResult, b.Bytes())
+		}
+	}
+
+	// string
+	{
+		b.Reset()
+		var data string = "hello"
+		instr := &encInstr{encString, 6, nil, 0}
+		state := newEncoderState(b)
+		instr.op(instr, state, reflect.ValueOf(data))
+		if !bytes.Equal(bytesResult, b.Bytes()) {
+			t.Errorf("string enc instructions: expected % x got % x", bytesResult, b.Bytes())
+		}
+	}
+}
+
+func execDec(typ string, instr *decInstr, state *decoderState, t *testing.T, value reflect.Value) {
+	defer testError(t)
+	v := int(state.decodeUint())
+	if v+state.fieldnum != 6 {
+		t.Fatalf("decoding field number %d, got %d", 6, v+state.fieldnum)
+	}
+	instr.op(instr, state, value.Elem())
+	state.fieldnum = 6
+}
+
+func newDecodeStateFromData(data []byte) *decoderState {
+	b := bytes.NewBuffer(data)
+	state := newDecodeState(b)
+	state.fieldnum = -1
+	return state
+}
+
+// Test instruction execution for decoding.
+// Do not run the machine yet; instead do individual instructions crafted by hand.
+func TestScalarDecInstructions(t *testing.T) {
+	ovfl := errors.New("overflow")
+
+	// bool
+	{
+		var data bool
+		instr := &decInstr{decBool, 6, nil, ovfl}
+		state := newDecodeStateFromData(boolResult)
+		execDec("bool", instr, state, t, reflect.ValueOf(&data))
+		if data != true {
+			t.Errorf("bool a = %v not true", data)
+		}
+	}
+	// int
+	{
+		var data int
+		instr := &decInstr{decOpTable[reflect.Int], 6, nil, ovfl}
+		state := newDecodeStateFromData(signedResult)
+		execDec("int", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("int a = %v not 17", data)
+		}
+	}
+
+	// uint
+	{
+		var data uint
+		instr := &decInstr{decOpTable[reflect.Uint], 6, nil, ovfl}
+		state := newDecodeStateFromData(unsignedResult)
+		execDec("uint", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("uint a = %v not 17", data)
+		}
+	}
+
+	// int8
+	{
+		var data int8
+		instr := &decInstr{decInt8, 6, nil, ovfl}
+		state := newDecodeStateFromData(signedResult)
+		execDec("int8", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("int8 a = %v not 17", data)
+		}
+	}
+
+	// uint8
+	{
+		var data uint8
+		instr := &decInstr{decUint8, 6, nil, ovfl}
+		state := newDecodeStateFromData(unsignedResult)
+		execDec("uint8", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("uint8 a = %v not 17", data)
+		}
+	}
+
+	// int16
+	{
+		var data int16
+		instr := &decInstr{decInt16, 6, nil, ovfl}
+		state := newDecodeStateFromData(signedResult)
+		execDec("int16", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("int16 a = %v not 17", data)
+		}
+	}
+
+	// uint16
+	{
+		var data uint16
+		instr := &decInstr{decUint16, 6, nil, ovfl}
+		state := newDecodeStateFromData(unsignedResult)
+		execDec("uint16", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("uint16 a = %v not 17", data)
+		}
+	}
+
+	// int32
+	{
+		var data int32
+		instr := &decInstr{decInt32, 6, nil, ovfl}
+		state := newDecodeStateFromData(signedResult)
+		execDec("int32", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("int32 a = %v not 17", data)
+		}
+	}
+
+	// uint32
+	{
+		var data uint32
+		instr := &decInstr{decUint32, 6, nil, ovfl}
+		state := newDecodeStateFromData(unsignedResult)
+		execDec("uint32", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("uint32 a = %v not 17", data)
+		}
+	}
+
+	// uintptr
+	{
+		var data uintptr
+		instr := &decInstr{decOpTable[reflect.Uintptr], 6, nil, ovfl}
+		state := newDecodeStateFromData(unsignedResult)
+		execDec("uintptr", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("uintptr a = %v not 17", data)
+		}
+	}
+
+	// int64
+	{
+		var data int64
+		instr := &decInstr{decInt64, 6, nil, ovfl}
+		state := newDecodeStateFromData(signedResult)
+		execDec("int64", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("int64 a = %v not 17", data)
+		}
+	}
+
+	// uint64
+	{
+		var data uint64
+		instr := &decInstr{decUint64, 6, nil, ovfl}
+		state := newDecodeStateFromData(unsignedResult)
+		execDec("uint64", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("uint64 a = %v not 17", data)
+		}
+	}
+
+	// float32
+	{
+		var data float32
+		instr := &decInstr{decFloat32, 6, nil, ovfl}
+		state := newDecodeStateFromData(floatResult)
+		execDec("float32", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("float32 a = %v not 17", data)
+		}
+	}
+
+	// float64
+	{
+		var data float64
+		instr := &decInstr{decFloat64, 6, nil, ovfl}
+		state := newDecodeStateFromData(floatResult)
+		execDec("float64", instr, state, t, reflect.ValueOf(&data))
+		if data != 17 {
+			t.Errorf("float64 a = %v not 17", data)
+		}
+	}
+
+	// complex64
+	{
+		var data complex64
+		instr := &decInstr{decOpTable[reflect.Complex64], 6, nil, ovfl}
+		state := newDecodeStateFromData(complexResult)
+		execDec("complex", instr, state, t, reflect.ValueOf(&data))
+		if data != 17+19i {
+			t.Errorf("complex a = %v not 17+19i", data)
+		}
+	}
+
+	// complex128
+	{
+		var data complex128
+		instr := &decInstr{decOpTable[reflect.Complex128], 6, nil, ovfl}
+		state := newDecodeStateFromData(complexResult)
+		execDec("complex", instr, state, t, reflect.ValueOf(&data))
+		if data != 17+19i {
+			t.Errorf("complex a = %v not 17+19i", data)
+		}
+	}
+
+	// bytes == []uint8
+	{
+		var data []byte
+		instr := &decInstr{decUint8Slice, 6, nil, ovfl}
+		state := newDecodeStateFromData(bytesResult)
+		execDec("bytes", instr, state, t, reflect.ValueOf(&data))
+		if string(data) != "hello" {
+			t.Errorf(`bytes a = %q not "hello"`, string(data))
+		}
+	}
+
+	// string
+	{
+		var data string
+		instr := &decInstr{decString, 6, nil, ovfl}
+		state := newDecodeStateFromData(bytesResult)
+		execDec("bytes", instr, state, t, reflect.ValueOf(&data))
+		if data != "hello" {
+			t.Errorf(`bytes a = %q not "hello"`, data)
+		}
+	}
+}
+
+func TestEndToEnd(t *testing.T) {
+	type T2 struct {
+		T string
+	}
+	s1 := "string1"
+	s2 := "string2"
+	type T1 struct {
+		A, B, C  int
+		M        map[string]*float64
+		EmptyMap map[string]int // to check that we receive a non-nil map.
+		N        *[3]float64
+		Strs     *[2]string
+		Int64s   *[]int64
+		RI       complex64
+		S        string
+		Y        []byte
+		T        *T2
+	}
+	pi := 3.14159
+	e := 2.71828
+	t1 := &T1{
+		A:        17,
+		B:        18,
+		C:        -5,
+		M:        map[string]*float64{"pi": &pi, "e": &e},
+		EmptyMap: make(map[string]int),
+		N:        &[3]float64{1.5, 2.5, 3.5},
+		Strs:     &[2]string{s1, s2},
+		Int64s:   &[]int64{77, 89, 123412342134},
+		RI:       17 - 23i,
+		S:        "Now is the time",
+		Y:        []byte("hello, sailor"),
+		T:        &T2{"this is T2"},
+	}
+	b := new(bytes.Buffer)
+	err := NewEncoder(b).Encode(t1)
+	if err != nil {
+		t.Error("encode:", err)
+	}
+	var _t1 T1
+	err = NewDecoder(b).Decode(&_t1)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if !reflect.DeepEqual(t1, &_t1) {
+		t.Errorf("encode expected %v got %v", *t1, _t1)
+	}
+	// Be absolutely sure the received map is non-nil.
+	if t1.EmptyMap == nil {
+		t.Errorf("nil map sent")
+	}
+	if _t1.EmptyMap == nil {
+		t.Errorf("nil map received")
+	}
+}
+
+func TestOverflow(t *testing.T) {
+	type inputT struct {
+		Maxi int64
+		Mini int64
+		Maxu uint64
+		Maxf float64
+		Minf float64
+		Maxc complex128
+		Minc complex128
+	}
+	var it inputT
+	var err error
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	dec := NewDecoder(b)
+
+	// int8
+	b.Reset()
+	it = inputT{
+		Maxi: math.MaxInt8 + 1,
+	}
+	type outi8 struct {
+		Maxi int8
+		Mini int8
+	}
+	var o1 outi8
+	enc.Encode(it)
+	err = dec.Decode(&o1)
+	if err == nil || err.Error() != `value for "Maxi" out of range` {
+		t.Error("wrong overflow error for int8:", err)
+	}
+	it = inputT{
+		Mini: math.MinInt8 - 1,
+	}
+	b.Reset()
+	enc.Encode(it)
+	err = dec.Decode(&o1)
+	if err == nil || err.Error() != `value for "Mini" out of range` {
+		t.Error("wrong underflow error for int8:", err)
+	}
+
+	// int16
+	b.Reset()
+	it = inputT{
+		Maxi: math.MaxInt16 + 1,
+	}
+	type outi16 struct {
+		Maxi int16
+		Mini int16
+	}
+	var o2 outi16
+	enc.Encode(it)
+	err = dec.Decode(&o2)
+	if err == nil || err.Error() != `value for "Maxi" out of range` {
+		t.Error("wrong overflow error for int16:", err)
+	}
+	it = inputT{
+		Mini: math.MinInt16 - 1,
+	}
+	b.Reset()
+	enc.Encode(it)
+	err = dec.Decode(&o2)
+	if err == nil || err.Error() != `value for "Mini" out of range` {
+		t.Error("wrong underflow error for int16:", err)
+	}
+
+	// int32
+	b.Reset()
+	it = inputT{
+		Maxi: math.MaxInt32 + 1,
+	}
+	type outi32 struct {
+		Maxi int32
+		Mini int32
+	}
+	var o3 outi32
+	enc.Encode(it)
+	err = dec.Decode(&o3)
+	if err == nil || err.Error() != `value for "Maxi" out of range` {
+		t.Error("wrong overflow error for int32:", err)
+	}
+	it = inputT{
+		Mini: math.MinInt32 - 1,
+	}
+	b.Reset()
+	enc.Encode(it)
+	err = dec.Decode(&o3)
+	if err == nil || err.Error() != `value for "Mini" out of range` {
+		t.Error("wrong underflow error for int32:", err)
+	}
+
+	// uint8
+	b.Reset()
+	it = inputT{
+		Maxu: math.MaxUint8 + 1,
+	}
+	type outu8 struct {
+		Maxu uint8
+	}
+	var o4 outu8
+	enc.Encode(it)
+	err = dec.Decode(&o4)
+	if err == nil || err.Error() != `value for "Maxu" out of range` {
+		t.Error("wrong overflow error for uint8:", err)
+	}
+
+	// uint16
+	b.Reset()
+	it = inputT{
+		Maxu: math.MaxUint16 + 1,
+	}
+	type outu16 struct {
+		Maxu uint16
+	}
+	var o5 outu16
+	enc.Encode(it)
+	err = dec.Decode(&o5)
+	if err == nil || err.Error() != `value for "Maxu" out of range` {
+		t.Error("wrong overflow error for uint16:", err)
+	}
+
+	// uint32
+	b.Reset()
+	it = inputT{
+		Maxu: math.MaxUint32 + 1,
+	}
+	type outu32 struct {
+		Maxu uint32
+	}
+	var o6 outu32
+	enc.Encode(it)
+	err = dec.Decode(&o6)
+	if err == nil || err.Error() != `value for "Maxu" out of range` {
+		t.Error("wrong overflow error for uint32:", err)
+	}
+
+	// float32
+	b.Reset()
+	it = inputT{
+		Maxf: math.MaxFloat32 * 2,
+	}
+	type outf32 struct {
+		Maxf float32
+		Minf float32
+	}
+	var o7 outf32
+	enc.Encode(it)
+	err = dec.Decode(&o7)
+	if err == nil || err.Error() != `value for "Maxf" out of range` {
+		t.Error("wrong overflow error for float32:", err)
+	}
+
+	// complex64
+	b.Reset()
+	it = inputT{
+		Maxc: complex(math.MaxFloat32*2, math.MaxFloat32*2),
+	}
+	type outc64 struct {
+		Maxc complex64
+		Minc complex64
+	}
+	var o8 outc64
+	enc.Encode(it)
+	err = dec.Decode(&o8)
+	if err == nil || err.Error() != `value for "Maxc" out of range` {
+		t.Error("wrong overflow error for complex64:", err)
+	}
+}
+
+func TestNesting(t *testing.T) {
+	type RT struct {
+		A    string
+		Next *RT
+	}
+	rt := new(RT)
+	rt.A = "level1"
+	rt.Next = new(RT)
+	rt.Next.A = "level2"
+	b := new(bytes.Buffer)
+	NewEncoder(b).Encode(rt)
+	var drt RT
+	dec := NewDecoder(b)
+	err := dec.Decode(&drt)
+	if err != nil {
+		t.Fatal("decoder error:", err)
+	}
+	if drt.A != rt.A {
+		t.Errorf("nesting: encode expected %v got %v", *rt, drt)
+	}
+	if drt.Next == nil {
+		t.Errorf("nesting: recursion failed")
+	}
+	if drt.Next.A != rt.Next.A {
+		t.Errorf("nesting: encode expected %v got %v", *rt.Next, *drt.Next)
+	}
+}
+
+// These three structures have the same data with different indirections
+type T0 struct {
+	A int
+	B int
+	C int
+	D int
+}
+type T1 struct {
+	A int
+	B *int
+	C **int
+	D ***int
+}
+type T2 struct {
+	A ***int
+	B **int
+	C *int
+	D int
+}
+
+func TestAutoIndirection(t *testing.T) {
+	// First transfer t1 into t0
+	var t1 T1
+	t1.A = 17
+	t1.B = new(int)
+	*t1.B = 177
+	t1.C = new(*int)
+	*t1.C = new(int)
+	**t1.C = 1777
+	t1.D = new(**int)
+	*t1.D = new(*int)
+	**t1.D = new(int)
+	***t1.D = 17777
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	enc.Encode(t1)
+	dec := NewDecoder(b)
+	var t0 T0
+	dec.Decode(&t0)
+	if t0.A != 17 || t0.B != 177 || t0.C != 1777 || t0.D != 17777 {
+		t.Errorf("t1->t0: expected {17 177 1777 17777}; got %v", t0)
+	}
+
+	// Now transfer t2 into t0
+	var t2 T2
+	t2.D = 17777
+	t2.C = new(int)
+	*t2.C = 1777
+	t2.B = new(*int)
+	*t2.B = new(int)
+	**t2.B = 177
+	t2.A = new(**int)
+	*t2.A = new(*int)
+	**t2.A = new(int)
+	***t2.A = 17
+	b.Reset()
+	enc.Encode(t2)
+	t0 = T0{}
+	dec.Decode(&t0)
+	if t0.A != 17 || t0.B != 177 || t0.C != 1777 || t0.D != 17777 {
+		t.Errorf("t2->t0 expected {17 177 1777 17777}; got %v", t0)
+	}
+
+	// Now transfer t0 into t1
+	t0 = T0{17, 177, 1777, 17777}
+	b.Reset()
+	enc.Encode(t0)
+	t1 = T1{}
+	dec.Decode(&t1)
+	if t1.A != 17 || *t1.B != 177 || **t1.C != 1777 || ***t1.D != 17777 {
+		t.Errorf("t0->t1 expected {17 177 1777 17777}; got {%d %d %d %d}", t1.A, *t1.B, **t1.C, ***t1.D)
+	}
+
+	// Now transfer t0 into t2
+	b.Reset()
+	enc.Encode(t0)
+	t2 = T2{}
+	dec.Decode(&t2)
+	if ***t2.A != 17 || **t2.B != 177 || *t2.C != 1777 || t2.D != 17777 {
+		t.Errorf("t0->t2 expected {17 177 1777 17777}; got {%d %d %d %d}", ***t2.A, **t2.B, *t2.C, t2.D)
+	}
+
+	// Now do t2 again but without pre-allocated pointers.
+	b.Reset()
+	enc.Encode(t0)
+	***t2.A = 0
+	**t2.B = 0
+	*t2.C = 0
+	t2.D = 0
+	dec.Decode(&t2)
+	if ***t2.A != 17 || **t2.B != 177 || *t2.C != 1777 || t2.D != 17777 {
+		t.Errorf("t0->t2 expected {17 177 1777 17777}; got {%d %d %d %d}", ***t2.A, **t2.B, *t2.C, t2.D)
+	}
+}
+
+type RT0 struct {
+	A int
+	B string
+	C float64
+}
+type RT1 struct {
+	C      float64
+	B      string
+	A      int
+	NotSet string
+}
+
+func TestReorderedFields(t *testing.T) {
+	var rt0 RT0
+	rt0.A = 17
+	rt0.B = "hello"
+	rt0.C = 3.14159
+	b := new(bytes.Buffer)
+	NewEncoder(b).Encode(rt0)
+	dec := NewDecoder(b)
+	var rt1 RT1
+	// Wire type is RT0, local type is RT1.
+	err := dec.Decode(&rt1)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if rt0.A != rt1.A || rt0.B != rt1.B || rt0.C != rt1.C {
+		t.Errorf("rt1->rt0: expected %v; got %v", rt0, rt1)
+	}
+}
+
+// Like an RT0 but with fields we'll ignore on the decode side.
+type IT0 struct {
+	A        int64
+	B        string
+	Ignore_d []int
+	Ignore_e [3]float64
+	Ignore_f bool
+	Ignore_g string
+	Ignore_h []byte
+	Ignore_i *RT1
+	Ignore_m map[string]int
+	C        float64
+}
+
+func TestIgnoredFields(t *testing.T) {
+	var it0 IT0
+	it0.A = 17
+	it0.B = "hello"
+	it0.C = 3.14159
+	it0.Ignore_d = []int{1, 2, 3}
+	it0.Ignore_e[0] = 1.0
+	it0.Ignore_e[1] = 2.0
+	it0.Ignore_e[2] = 3.0
+	it0.Ignore_f = true
+	it0.Ignore_g = "pay no attention"
+	it0.Ignore_h = []byte("to the curtain")
+	it0.Ignore_i = &RT1{3.1, "hi", 7, "hello"}
+	it0.Ignore_m = map[string]int{"one": 1, "two": 2}
+
+	b := new(bytes.Buffer)
+	NewEncoder(b).Encode(it0)
+	dec := NewDecoder(b)
+	var rt1 RT1
+	// Wire type is IT0, local type is RT1.
+	err := dec.Decode(&rt1)
+	if err != nil {
+		t.Error("error: ", err)
+	}
+	if int(it0.A) != rt1.A || it0.B != rt1.B || it0.C != rt1.C {
+		t.Errorf("rt0->rt1: expected %v; got %v", it0, rt1)
+	}
+}
+
+func TestBadRecursiveType(t *testing.T) {
+	type Rec ***Rec
+	var rec Rec
+	b := new(bytes.Buffer)
+	err := NewEncoder(b).Encode(&rec)
+	if err == nil {
+		t.Error("expected error; got none")
+	} else if strings.Index(err.Error(), "recursive") < 0 {
+		t.Error("expected recursive type error; got", err)
+	}
+	// Can't test decode easily because we can't encode one, so we can't pass one to a Decoder.
+}
+
+type Indirect struct {
+	A ***[3]int
+	S ***[]int
+	M ****map[string]int
+}
+
+type Direct struct {
+	A [3]int
+	S []int
+	M map[string]int
+}
+
+func TestIndirectSliceMapArray(t *testing.T) {
+	// Marshal indirect, unmarshal to direct.
+	i := new(Indirect)
+	i.A = new(**[3]int)
+	*i.A = new(*[3]int)
+	**i.A = new([3]int)
+	***i.A = [3]int{1, 2, 3}
+	i.S = new(**[]int)
+	*i.S = new(*[]int)
+	**i.S = new([]int)
+	***i.S = []int{4, 5, 6}
+	i.M = new(***map[string]int)
+	*i.M = new(**map[string]int)
+	**i.M = new(*map[string]int)
+	***i.M = new(map[string]int)
+	****i.M = map[string]int{"one": 1, "two": 2, "three": 3}
+	b := new(bytes.Buffer)
+	NewEncoder(b).Encode(i)
+	dec := NewDecoder(b)
+	var d Direct
+	err := dec.Decode(&d)
+	if err != nil {
+		t.Error("error: ", err)
+	}
+	if len(d.A) != 3 || d.A[0] != 1 || d.A[1] != 2 || d.A[2] != 3 {
+		t.Errorf("indirect to direct: d.A is %v not %v", d.A, ***i.A)
+	}
+	if len(d.S) != 3 || d.S[0] != 4 || d.S[1] != 5 || d.S[2] != 6 {
+		t.Errorf("indirect to direct: d.S is %v not %v", d.S, ***i.S)
+	}
+	if len(d.M) != 3 || d.M["one"] != 1 || d.M["two"] != 2 || d.M["three"] != 3 {
+		t.Errorf("indirect to direct: d.M is %v not %v", d.M, ***i.M)
+	}
+	// Marshal direct, unmarshal to indirect.
+	d.A = [3]int{11, 22, 33}
+	d.S = []int{44, 55, 66}
+	d.M = map[string]int{"four": 4, "five": 5, "six": 6}
+	i = new(Indirect)
+	b.Reset()
+	NewEncoder(b).Encode(d)
+	dec = NewDecoder(b)
+	err = dec.Decode(&i)
+	if err != nil {
+		t.Fatal("error: ", err)
+	}
+	if len(***i.A) != 3 || (***i.A)[0] != 11 || (***i.A)[1] != 22 || (***i.A)[2] != 33 {
+		t.Errorf("direct to indirect: ***i.A is %v not %v", ***i.A, d.A)
+	}
+	if len(***i.S) != 3 || (***i.S)[0] != 44 || (***i.S)[1] != 55 || (***i.S)[2] != 66 {
+		t.Errorf("direct to indirect: ***i.S is %v not %v", ***i.S, ***i.S)
+	}
+	if len(****i.M) != 3 || (****i.M)["four"] != 4 || (****i.M)["five"] != 5 || (****i.M)["six"] != 6 {
+		t.Errorf("direct to indirect: ****i.M is %v not %v", ****i.M, d.M)
+	}
+}
+
+// An interface with several implementations
+type Squarer interface {
+	Square() int
+}
+
+type Int int
+
+func (i Int) Square() int {
+	return int(i * i)
+}
+
+type Float float64
+
+func (f Float) Square() int {
+	return int(f * f)
+}
+
+type Vector []int
+
+func (v Vector) Square() int {
+	sum := 0
+	for _, x := range v {
+		sum += x * x
+	}
+	return sum
+}
+
+type Point struct {
+	X, Y int
+}
+
+func (p Point) Square() int {
+	return p.X*p.X + p.Y*p.Y
+}
+
+// A struct with interfaces in it.
+type InterfaceItem struct {
+	I             int
+	Sq1, Sq2, Sq3 Squarer
+	F             float64
+	Sq            []Squarer
+}
+
+// The same struct without interfaces
+type NoInterfaceItem struct {
+	I int
+	F float64
+}
+
+func TestInterface(t *testing.T) {
+	iVal := Int(3)
+	fVal := Float(5)
+	// Sending a Vector will require that the receiver define a type in the middle of
+	// receiving the value for item2.
+	vVal := Vector{1, 2, 3}
+	b := new(bytes.Buffer)
+	item1 := &InterfaceItem{1, iVal, fVal, vVal, 11.5, []Squarer{iVal, fVal, nil, vVal}}
+	// Register the types.
+	Register(Int(0))
+	Register(Float(0))
+	Register(Vector{})
+	err := NewEncoder(b).Encode(item1)
+	if err != nil {
+		t.Error("expected no encode error; got", err)
+	}
+
+	item2 := InterfaceItem{}
+	err = NewDecoder(b).Decode(&item2)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if item2.I != item1.I {
+		t.Error("normal int did not decode correctly")
+	}
+	if item2.Sq1 == nil || item2.Sq1.Square() != iVal.Square() {
+		t.Error("Int did not decode correctly")
+	}
+	if item2.Sq2 == nil || item2.Sq2.Square() != fVal.Square() {
+		t.Error("Float did not decode correctly")
+	}
+	if item2.Sq3 == nil || item2.Sq3.Square() != vVal.Square() {
+		t.Error("Vector did not decode correctly")
+	}
+	if item2.F != item1.F {
+		t.Error("normal float did not decode correctly")
+	}
+	// Now check that we received a slice of Squarers correctly, including a nil element
+	if len(item1.Sq) != len(item2.Sq) {
+		t.Fatalf("[]Squarer length wrong: got %d; expected %d", len(item2.Sq), len(item1.Sq))
+	}
+	for i, v1 := range item1.Sq {
+		v2 := item2.Sq[i]
+		if v1 == nil || v2 == nil {
+			if v1 != nil || v2 != nil {
+				t.Errorf("item %d inconsistent nils", i)
+			}
+		} else if v1.Square() != v2.Square() {
+			t.Errorf("item %d inconsistent values: %v %v", i, v1, v2)
+		}
+	}
+}
+
+// A struct with all basic types, stored in interfaces.
+type BasicInterfaceItem struct {
+	Int, Int8, Int16, Int32, Int64      interface{}
+	Uint, Uint8, Uint16, Uint32, Uint64 interface{}
+	Float32, Float64                    interface{}
+	Complex64, Complex128               interface{}
+	Bool                                interface{}
+	String                              interface{}
+	Bytes                               interface{}
+}
+
+func TestInterfaceBasic(t *testing.T) {
+	b := new(bytes.Buffer)
+	item1 := &BasicInterfaceItem{
+		int(1), int8(1), int16(1), int32(1), int64(1),
+		uint(1), uint8(1), uint16(1), uint32(1), uint64(1),
+		float32(1), 1.0,
+		complex64(1i), complex128(1i),
+		true,
+		"hello",
+		[]byte("sailor"),
+	}
+	err := NewEncoder(b).Encode(item1)
+	if err != nil {
+		t.Error("expected no encode error; got", err)
+	}
+
+	item2 := &BasicInterfaceItem{}
+	err = NewDecoder(b).Decode(&item2)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if !reflect.DeepEqual(item1, item2) {
+		t.Errorf("encode expected %v got %v", item1, item2)
+	}
+	// Hand check a couple for correct types.
+	if v, ok := item2.Bool.(bool); !ok || !v {
+		t.Error("boolean should be true")
+	}
+	if v, ok := item2.String.(string); !ok || v != item1.String.(string) {
+		t.Errorf("string should be %v is %v", item1.String, v)
+	}
+}
+
+type String string
+
+type PtrInterfaceItem struct {
+	Str1 interface{} // basic
+	Str2 interface{} // derived
+}
+
+// We'll send pointers; should receive values.
+// Also check that we can register T but send *T.
+func TestInterfacePointer(t *testing.T) {
+	b := new(bytes.Buffer)
+	str1 := "howdy"
+	str2 := String("kiddo")
+	item1 := &PtrInterfaceItem{
+		&str1,
+		&str2,
+	}
+	// Register the type.
+	Register(str2)
+	err := NewEncoder(b).Encode(item1)
+	if err != nil {
+		t.Error("expected no encode error; got", err)
+	}
+
+	item2 := &PtrInterfaceItem{}
+	err = NewDecoder(b).Decode(&item2)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	// Hand test for correct types and values.
+	if v, ok := item2.Str1.(string); !ok || v != str1 {
+		t.Errorf("basic string failed: %q should be %q", v, str1)
+	}
+	if v, ok := item2.Str2.(String); !ok || v != str2 {
+		t.Errorf("derived type String failed: %q should be %q", v, str2)
+	}
+}
+
+func TestIgnoreInterface(t *testing.T) {
+	iVal := Int(3)
+	fVal := Float(5)
+	// Sending a Point will require that the receiver define a type in the middle of
+	// receiving the value for item2.
+	pVal := Point{2, 3}
+	b := new(bytes.Buffer)
+	item1 := &InterfaceItem{1, iVal, fVal, pVal, 11.5, nil}
+	// Register the types.
+	Register(Int(0))
+	Register(Float(0))
+	Register(Point{})
+	err := NewEncoder(b).Encode(item1)
+	if err != nil {
+		t.Error("expected no encode error; got", err)
+	}
+
+	item2 := NoInterfaceItem{}
+	err = NewDecoder(b).Decode(&item2)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if item2.I != item1.I {
+		t.Error("normal int did not decode correctly")
+	}
+	if item2.F != item2.F {
+		t.Error("normal float did not decode correctly")
+	}
+}
+
+type U struct {
+	A int
+	B string
+	c float64
+	D uint
+}
+
+func TestUnexportedFields(t *testing.T) {
+	var u0 U
+	u0.A = 17
+	u0.B = "hello"
+	u0.c = 3.14159
+	u0.D = 23
+	b := new(bytes.Buffer)
+	NewEncoder(b).Encode(u0)
+	dec := NewDecoder(b)
+	var u1 U
+	u1.c = 1234.
+	err := dec.Decode(&u1)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if u0.A != u0.A || u0.B != u1.B || u0.D != u1.D {
+		t.Errorf("u1->u0: expected %v; got %v", u0, u1)
+	}
+	if u1.c != 1234. {
+		t.Error("u1.c modified")
+	}
+}
+
+var singletons = []interface{}{
+	true,
+	7,
+	3.2,
+	"hello",
+	[3]int{11, 22, 33},
+	[]float32{0.5, 0.25, 0.125},
+	map[string]int{"one": 1, "two": 2},
+}
+
+func TestDebugSingleton(t *testing.T) {
+	if debugFunc == nil {
+		return
+	}
+	b := new(bytes.Buffer)
+	// Accumulate a number of values and print them out all at once.
+	for _, x := range singletons {
+		err := NewEncoder(b).Encode(x)
+		if err != nil {
+			t.Fatal("encode:", err)
+		}
+	}
+	debugFunc(b)
+}
+
+// A type that won't be defined in the gob until we send it in an interface value.
+type OnTheFly struct {
+	A int
+}
+
+type DT struct {
+	//	X OnTheFly
+	A     int
+	B     string
+	C     float64
+	I     interface{}
+	J     interface{}
+	I_nil interface{}
+	M     map[string]int
+	T     [3]int
+	S     []string
+}
+
+func newDT() DT {
+	var dt DT
+	dt.A = 17
+	dt.B = "hello"
+	dt.C = 3.14159
+	dt.I = 271828
+	dt.J = OnTheFly{3}
+	dt.I_nil = nil
+	dt.M = map[string]int{"one": 1, "two": 2}
+	dt.T = [3]int{11, 22, 33}
+	dt.S = []string{"hi", "joe"}
+	return dt
+}
+
+func TestDebugStruct(t *testing.T) {
+	if debugFunc == nil {
+		return
+	}
+	Register(OnTheFly{})
+	dt := newDT()
+	b := new(bytes.Buffer)
+	err := NewEncoder(b).Encode(dt)
+	if err != nil {
+		t.Fatal("encode:", err)
+	}
+	debugBuffer := bytes.NewBuffer(b.Bytes())
+	dt2 := &DT{}
+	err = NewDecoder(b).Decode(&dt2)
+	if err != nil {
+		t.Error("decode:", err)
+	}
+	debugFunc(debugBuffer)
+}
+
+func encFuzzDec(rng *rand.Rand, in interface{}) error {
+	buf := new(bytes.Buffer)
+	enc := NewEncoder(buf)
+	if err := enc.Encode(&in); err != nil {
+		return err
+	}
+
+	b := buf.Bytes()
+	for i, bi := range b {
+		if rng.Intn(10) < 3 {
+			b[i] = bi + uint8(rng.Intn(256))
+		}
+	}
+
+	dec := NewDecoder(buf)
+	var e interface{}
+	if err := dec.Decode(&e); err != nil {
+		return err
+	}
+	return nil
+}
+
+// This does some "fuzz testing" by attempting to decode a sequence of random bytes.
+func TestFuzz(t *testing.T) {
+	if !*doFuzzTests {
+		t.Logf("disabled; run with -gob.fuzz to enable")
+		return
+	}
+
+	// all possible inputs
+	input := []interface{}{
+		new(int),
+		new(float32),
+		new(float64),
+		new(complex128),
+		&ByteStruct{255},
+		&ArrayStruct{},
+		&StringStruct{"hello"},
+		&GobTest1{0, &StringStruct{"hello"}},
+	}
+	testFuzz(t, time.Now().UnixNano(), 100, input...)
+}
+
+func TestFuzzRegressions(t *testing.T) {
+	if !*doFuzzTests {
+		t.Logf("disabled; run with -gob.fuzz to enable")
+		return
+	}
+
+	// An instance triggering a type name of length ~102 GB.
+	testFuzz(t, 1328492090837718000, 100, new(float32))
+	// An instance triggering a type name of 1.6 GB.
+	// Note: can take several minutes to run.
+	testFuzz(t, 1330522872628565000, 100, new(int))
+}
+
+func testFuzz(t *testing.T, seed int64, n int, input ...interface{}) {
+	for _, e := range input {
+		t.Logf("seed=%d n=%d e=%T", seed, n, e)
+		rng := rand.New(rand.NewSource(seed))
+		for i := 0; i < n; i++ {
+			encFuzzDec(rng, e)
+		}
+	}
+}
+
+// TestFuzzOneByte tries to decode corrupted input sequences
+// and checks that no panic occurs.
+func TestFuzzOneByte(t *testing.T) {
+	buf := new(bytes.Buffer)
+	Register(OnTheFly{})
+	dt := newDT()
+	if err := NewEncoder(buf).Encode(dt); err != nil {
+		t.Fatal(err)
+	}
+	s := buf.String()
+
+	indices := make([]int, 0, len(s))
+	for i := 0; i < len(s); i++ {
+		switch i {
+		case 14, 167, 231, 265: // a slice length, corruptions are not handled yet.
+			continue
+		}
+		indices = append(indices, i)
+	}
+	if testing.Short() {
+		indices = []int{1, 111, 178} // known fixed panics
+	}
+	for _, i := range indices {
+		for j := 0; j < 256; j += 3 {
+			b := []byte(s)
+			b[i] ^= byte(j)
+			var e DT
+			func() {
+				defer func() {
+					if p := recover(); p != nil {
+						t.Errorf("crash for b[%d] ^= 0x%x", i, j)
+						panic(p)
+					}
+				}()
+				err := NewDecoder(bytes.NewReader(b)).Decode(&e)
+				_ = err
+			}()
+		}
+	}
+}
diff --git a/src/encoding/gob/debug.go b/src/encoding/gob/debug.go
new file mode 100644
index 0000000000..536bbdb5ac
--- /dev/null
+++ b/src/encoding/gob/debug.go
@@ -0,0 +1,705 @@
+// 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.
+
+// Delete the next line to include in the gob package.
+// +build ignore
+
+package gob
+
+// This file is not normally included in the gob package.  Used only for debugging the package itself.
+// Except for reading uints, it is an implementation of a reader that is independent of
+// the one implemented by Decoder.
+// To enable the Debug function, delete the +build ignore line above and do
+//	go install
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+	"sync"
+)
+
+var dumpBytes = false // If true, print the remaining bytes in the input buffer at each item.
+
+// Init installs the debugging facility. If this file is not compiled in the
+// package, the tests in codec_test.go are no-ops.
+func init() {
+	debugFunc = Debug
+}
+
+var (
+	blanks = bytes.Repeat([]byte{' '}, 3*10)
+	empty  = []byte(": <empty>\n")
+	tabs   = strings.Repeat("\t", 100)
+)
+
+// tab indents itself when printed.
+type tab int
+
+func (t tab) String() string {
+	n := int(t)
+	if n > len(tabs) {
+		n = len(tabs)
+	}
+	return tabs[0:n]
+}
+
+func (t tab) print() {
+	fmt.Fprint(os.Stderr, t)
+}
+
+// A peekReader wraps an io.Reader, allowing one to peek ahead to see
+// what's coming without stealing the data from the client of the Reader.
+type peekReader struct {
+	r    io.Reader
+	data []byte // read-ahead data
+}
+
+// newPeekReader returns a peekReader that wraps r.
+func newPeekReader(r io.Reader) *peekReader {
+	return &peekReader{r: r}
+}
+
+// Read is the usual method. It will first take data that has been read ahead.
+func (p *peekReader) Read(b []byte) (n int, err error) {
+	if len(p.data) == 0 {
+		return p.r.Read(b)
+	}
+	// Satisfy what's possible from the read-ahead data.
+	n = copy(b, p.data)
+	// Move data down to beginning of slice, to avoid endless growth
+	copy(p.data, p.data[n:])
+	p.data = p.data[:len(p.data)-n]
+	return
+}
+
+// peek returns as many bytes as possible from the unread
+// portion of the stream, up to the length of b.
+func (p *peekReader) peek(b []byte) (n int, err error) {
+	if len(p.data) > 0 {
+		n = copy(b, p.data)
+		if n == len(b) {
+			return
+		}
+		b = b[n:]
+	}
+	if len(b) == 0 {
+		return
+	}
+	m, e := io.ReadFull(p.r, b)
+	if m > 0 {
+		p.data = append(p.data, b[:m]...)
+	}
+	n += m
+	if e == io.ErrUnexpectedEOF {
+		// That means m > 0 but we reached EOF. If we got data
+		// we won't complain about not being able to peek enough.
+		if n > 0 {
+			e = nil
+		} else {
+			e = io.EOF
+		}
+	}
+	return n, e
+}
+
+type debugger struct {
+	mutex          sync.Mutex
+	remain         int  // the number of bytes known to remain in the input
+	remainingKnown bool // the value of 'remain' is valid
+	r              *peekReader
+	wireType       map[typeId]*wireType
+	tmp            []byte // scratch space for decoding uints.
+}
+
+// dump prints the next nBytes of the input.
+// It arranges to print the output aligned from call to
+// call, to make it easy to see what has been consumed.
+func (deb *debugger) dump(format string, args ...interface{}) {
+	if !dumpBytes {
+		return
+	}
+	fmt.Fprintf(os.Stderr, format+" ", args...)
+	if !deb.remainingKnown {
+		return
+	}
+	if deb.remain < 0 {
+		fmt.Fprintf(os.Stderr, "remaining byte count is negative! %d\n", deb.remain)
+		return
+	}
+	data := make([]byte, deb.remain)
+	n, _ := deb.r.peek(data)
+	if n == 0 {
+		os.Stderr.Write(empty)
+		return
+	}
+	b := new(bytes.Buffer)
+	fmt.Fprintf(b, "[%d]{\n", deb.remain)
+	// Blanks until first byte
+	lineLength := 0
+	if n := len(data); n%10 != 0 {
+		lineLength = 10 - n%10
+		fmt.Fprintf(b, "\t%s", blanks[:lineLength*3])
+	}
+	// 10 bytes per line
+	for len(data) > 0 {
+		if lineLength == 0 {
+			fmt.Fprint(b, "\t")
+		}
+		m := 10 - lineLength
+		lineLength = 0
+		if m > len(data) {
+			m = len(data)
+		}
+		fmt.Fprintf(b, "% x\n", data[:m])
+		data = data[m:]
+	}
+	fmt.Fprint(b, "}\n")
+	os.Stderr.Write(b.Bytes())
+}
+
+// Debug prints a human-readable representation of the gob data read from r.
+// It is a no-op unless debugging was enabled when the package was built.
+func Debug(r io.Reader) {
+	err := debug(r)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "gob debug: %s\n", err)
+	}
+}
+
+// debug implements Debug, but catches panics and returns
+// them as errors to be printed by Debug.
+func debug(r io.Reader) (err error) {
+	defer catchError(&err)
+	fmt.Fprintln(os.Stderr, "Start of debugging")
+	deb := &debugger{
+		r:        newPeekReader(r),
+		wireType: make(map[typeId]*wireType),
+		tmp:      make([]byte, 16),
+	}
+	if b, ok := r.(*bytes.Buffer); ok {
+		deb.remain = b.Len()
+		deb.remainingKnown = true
+	}
+	deb.gobStream()
+	return
+}
+
+// note that we've consumed some bytes
+func (deb *debugger) consumed(n int) {
+	if deb.remainingKnown {
+		deb.remain -= n
+	}
+}
+
+// int64 decodes and returns the next integer, which must be present.
+// Don't call this if you could be at EOF.
+func (deb *debugger) int64() int64 {
+	return toInt(deb.uint64())
+}
+
+// uint64 returns and decodes the next unsigned integer, which must be present.
+// Don't call this if you could be at EOF.
+// TODO: handle errors better.
+func (deb *debugger) uint64() uint64 {
+	n, w, err := decodeUintReader(deb.r, deb.tmp)
+	if err != nil {
+		errorf("debug: read error: %s", err)
+	}
+	deb.consumed(w)
+	return n
+}
+
+// GobStream:
+//	DelimitedMessage* (until EOF)
+func (deb *debugger) gobStream() {
+	// Make sure we're single-threaded through here.
+	deb.mutex.Lock()
+	defer deb.mutex.Unlock()
+
+	for deb.delimitedMessage(0) {
+	}
+}
+
+// DelimitedMessage:
+//	uint(lengthOfMessage) Message
+func (deb *debugger) delimitedMessage(indent tab) bool {
+	for {
+		n := deb.loadBlock(true)
+		if n < 0 {
+			return false
+		}
+		deb.dump("Delimited message of length %d", n)
+		deb.message(indent)
+	}
+	return true
+}
+
+// loadBlock preps us to read a message
+// of the length specified next in the input. It returns
+// the length of the block. The argument tells whether
+// an EOF is acceptable now.  If it is and one is found,
+// the return value is negative.
+func (deb *debugger) loadBlock(eofOK bool) int {
+	n64, w, err := decodeUintReader(deb.r, deb.tmp) // deb.uint64 will error at EOF
+	if err != nil {
+		if eofOK && err == io.EOF {
+			return -1
+		}
+		errorf("debug: unexpected error: %s", err)
+	}
+	deb.consumed(w)
+	n := int(n64)
+	if n < 0 {
+		errorf("huge value for message length: %d", n64)
+	}
+	return int(n)
+}
+
+// Message:
+//	TypeSequence TypedValue
+// TypeSequence
+//	(TypeDefinition DelimitedTypeDefinition*)?
+// DelimitedTypeDefinition:
+//	uint(lengthOfTypeDefinition) TypeDefinition
+// TypedValue:
+//	int(typeId) Value
+func (deb *debugger) message(indent tab) bool {
+	for {
+		// Convert the uint64 to a signed integer typeId
+		uid := deb.int64()
+		id := typeId(uid)
+		deb.dump("type id=%d", id)
+		if id < 0 {
+			deb.typeDefinition(indent, -id)
+			n := deb.loadBlock(false)
+			deb.dump("Message of length %d", n)
+			continue
+		} else {
+			deb.value(indent, id)
+			break
+		}
+	}
+	return true
+}
+
+// Helper methods to make it easy to scan a type descriptor.
+
+// common returns the CommonType at the input point.
+func (deb *debugger) common() CommonType {
+	fieldNum := -1
+	name := ""
+	id := typeId(0)
+	for {
+		delta := deb.delta(-1)
+		if delta == 0 {
+			break
+		}
+		fieldNum += delta
+		switch fieldNum {
+		case 0:
+			name = deb.string()
+		case 1:
+			// Id typeId
+			id = deb.typeId()
+		default:
+			errorf("corrupted CommonType, delta is %d fieldNum is %d", delta, fieldNum)
+		}
+	}
+	return CommonType{name, id}
+}
+
+// uint returns the unsigned int at the input point, as a uint (not uint64).
+func (deb *debugger) uint() uint {
+	return uint(deb.uint64())
+}
+
+// int returns the signed int at the input point, as an int (not int64).
+func (deb *debugger) int() int {
+	return int(deb.int64())
+}
+
+// typeId returns the type id at the input point.
+func (deb *debugger) typeId() typeId {
+	return typeId(deb.int64())
+}
+
+// string returns the string at the input point.
+func (deb *debugger) string() string {
+	x := int(deb.uint64())
+	b := make([]byte, x)
+	nb, _ := deb.r.Read(b)
+	if nb != x {
+		errorf("corrupted type")
+	}
+	deb.consumed(nb)
+	return string(b)
+}
+
+// delta returns the field delta at the input point.  The expect argument,
+// if non-negative, identifies what the value should be.
+func (deb *debugger) delta(expect int) int {
+	delta := int(deb.uint64())
+	if delta < 0 || (expect >= 0 && delta != expect) {
+		errorf("decode: corrupted type: delta %d expected %d", delta, expect)
+	}
+	return delta
+}
+
+// TypeDefinition:
+//	[int(-typeId) (already read)] encodingOfWireType
+func (deb *debugger) typeDefinition(indent tab, id typeId) {
+	deb.dump("type definition for id %d", id)
+	// Encoding is of a wireType. Decode the structure as usual
+	fieldNum := -1
+	wire := new(wireType)
+	// A wireType defines a single field.
+	delta := deb.delta(-1)
+	fieldNum += delta
+	switch fieldNum {
+	case 0: // array type, one field of {{Common}, elem, length}
+		// Field number 0 is CommonType
+		deb.delta(1)
+		com := deb.common()
+		// Field number 1 is type Id of elem
+		deb.delta(1)
+		id := deb.typeId()
+		// Field number 3 is length
+		deb.delta(1)
+		length := deb.int()
+		wire.ArrayT = &arrayType{com, id, length}
+
+	case 1: // slice type, one field of {{Common}, elem}
+		// Field number 0 is CommonType
+		deb.delta(1)
+		com := deb.common()
+		// Field number 1 is type Id of elem
+		deb.delta(1)
+		id := deb.typeId()
+		wire.SliceT = &sliceType{com, id}
+
+	case 2: // struct type, one field of {{Common}, []fieldType}
+		// Field number 0 is CommonType
+		deb.delta(1)
+		com := deb.common()
+		// Field number 1 is slice of FieldType
+		deb.delta(1)
+		numField := int(deb.uint())
+		field := make([]*fieldType, numField)
+		for i := 0; i < numField; i++ {
+			field[i] = new(fieldType)
+			deb.delta(1) // field 0 of fieldType: name
+			field[i].Name = deb.string()
+			deb.delta(1) // field 1 of fieldType: id
+			field[i].Id = deb.typeId()
+			deb.delta(0) // end of fieldType
+		}
+		wire.StructT = &structType{com, field}
+
+	case 3: // map type, one field of {{Common}, key, elem}
+		// Field number 0 is CommonType
+		deb.delta(1)
+		com := deb.common()
+		// Field number 1 is type Id of key
+		deb.delta(1)
+		keyId := deb.typeId()
+		// Field number 2 is type Id of elem
+		deb.delta(1)
+		elemId := deb.typeId()
+		wire.MapT = &mapType{com, keyId, elemId}
+	case 4: // GobEncoder type, one field of {{Common}}
+		// Field number 0 is CommonType
+		deb.delta(1)
+		com := deb.common()
+		wire.GobEncoderT = &gobEncoderType{com}
+	case 5: // BinaryMarshaler type, one field of {{Common}}
+		// Field number 0 is CommonType
+		deb.delta(1)
+		com := deb.common()
+		wire.BinaryMarshalerT = &gobEncoderType{com}
+	case 6: // TextMarshaler type, one field of {{Common}}
+		// Field number 0 is CommonType
+		deb.delta(1)
+		com := deb.common()
+		wire.TextMarshalerT = &gobEncoderType{com}
+	default:
+		errorf("bad field in type %d", fieldNum)
+	}
+	deb.printWireType(indent, wire)
+	deb.delta(0) // end inner type (arrayType, etc.)
+	deb.delta(0) // end wireType
+	// Remember we've seen this type.
+	deb.wireType[id] = wire
+}
+
+// Value:
+//	SingletonValue | StructValue
+func (deb *debugger) value(indent tab, id typeId) {
+	wire, ok := deb.wireType[id]
+	if ok && wire.StructT != nil {
+		deb.structValue(indent, id)
+	} else {
+		deb.singletonValue(indent, id)
+	}
+}
+
+// SingletonValue:
+//	uint(0) FieldValue
+func (deb *debugger) singletonValue(indent tab, id typeId) {
+	deb.dump("Singleton value")
+	// is it a builtin type?
+	wire := deb.wireType[id]
+	_, ok := builtinIdToType[id]
+	if !ok && wire == nil {
+		errorf("type id %d not defined", id)
+	}
+	m := deb.uint64()
+	if m != 0 {
+		errorf("expected zero; got %d", m)
+	}
+	deb.fieldValue(indent, id)
+}
+
+// InterfaceValue:
+//	NilInterfaceValue | NonNilInterfaceValue
+func (deb *debugger) interfaceValue(indent tab) {
+	deb.dump("Start of interface value")
+	if nameLen := deb.uint64(); nameLen == 0 {
+		deb.nilInterfaceValue(indent)
+	} else {
+		deb.nonNilInterfaceValue(indent, int(nameLen))
+	}
+}
+
+// NilInterfaceValue:
+//	uint(0) [already read]
+func (deb *debugger) nilInterfaceValue(indent tab) int {
+	fmt.Fprintf(os.Stderr, "%snil interface\n", indent)
+	return 0
+}
+
+// NonNilInterfaceValue:
+//	ConcreteTypeName TypeSequence InterfaceContents
+// ConcreteTypeName:
+//	uint(lengthOfName) [already read=n] name
+// InterfaceContents:
+//	int(concreteTypeId) DelimitedValue
+// DelimitedValue:
+//	uint(length) Value
+func (deb *debugger) nonNilInterfaceValue(indent tab, nameLen int) {
+	// ConcreteTypeName
+	b := make([]byte, nameLen)
+	deb.r.Read(b) // TODO: CHECK THESE READS!!
+	deb.consumed(nameLen)
+	name := string(b)
+
+	for {
+		id := deb.typeId()
+		if id < 0 {
+			deb.typeDefinition(indent, -id)
+			n := deb.loadBlock(false)
+			deb.dump("Nested message of length %d", n)
+		} else {
+			// DelimitedValue
+			x := deb.uint64() // in case we want to ignore the value; we don't.
+			fmt.Fprintf(os.Stderr, "%sinterface value, type %q id=%d; valueLength %d\n", indent, name, id, x)
+			deb.value(indent, id)
+			break
+		}
+	}
+}
+
+// printCommonType prints a common type; used by printWireType.
+func (deb *debugger) printCommonType(indent tab, kind string, common *CommonType) {
+	indent.print()
+	fmt.Fprintf(os.Stderr, "%s %q id=%d\n", kind, common.Name, common.Id)
+}
+
+// printWireType prints the contents of a wireType.
+func (deb *debugger) printWireType(indent tab, wire *wireType) {
+	fmt.Fprintf(os.Stderr, "%stype definition {\n", indent)
+	indent++
+	switch {
+	case wire.ArrayT != nil:
+		deb.printCommonType(indent, "array", &wire.ArrayT.CommonType)
+		fmt.Fprintf(os.Stderr, "%slen %d\n", indent+1, wire.ArrayT.Len)
+		fmt.Fprintf(os.Stderr, "%selemid %d\n", indent+1, wire.ArrayT.Elem)
+	case wire.MapT != nil:
+		deb.printCommonType(indent, "map", &wire.MapT.CommonType)
+		fmt.Fprintf(os.Stderr, "%skey id=%d\n", indent+1, wire.MapT.Key)
+		fmt.Fprintf(os.Stderr, "%selem id=%d\n", indent+1, wire.MapT.Elem)
+	case wire.SliceT != nil:
+		deb.printCommonType(indent, "slice", &wire.SliceT.CommonType)
+		fmt.Fprintf(os.Stderr, "%selem id=%d\n", indent+1, wire.SliceT.Elem)
+	case wire.StructT != nil:
+		deb.printCommonType(indent, "struct", &wire.StructT.CommonType)
+		for i, field := range wire.StructT.Field {
+			fmt.Fprintf(os.Stderr, "%sfield %d:\t%s\tid=%d\n", indent+1, i, field.Name, field.Id)
+		}
+	case wire.GobEncoderT != nil:
+		deb.printCommonType(indent, "GobEncoder", &wire.GobEncoderT.CommonType)
+	}
+	indent--
+	fmt.Fprintf(os.Stderr, "%s}\n", indent)
+}
+
+// fieldValue prints a value of any type, such as a struct field.
+// FieldValue:
+//	builtinValue | ArrayValue | MapValue | SliceValue | StructValue | InterfaceValue
+func (deb *debugger) fieldValue(indent tab, id typeId) {
+	_, ok := builtinIdToType[id]
+	if ok {
+		if id == tInterface {
+			deb.interfaceValue(indent)
+		} else {
+			deb.printBuiltin(indent, id)
+		}
+		return
+	}
+	wire, ok := deb.wireType[id]
+	if !ok {
+		errorf("type id %d not defined", id)
+	}
+	switch {
+	case wire.ArrayT != nil:
+		deb.arrayValue(indent, wire)
+	case wire.MapT != nil:
+		deb.mapValue(indent, wire)
+	case wire.SliceT != nil:
+		deb.sliceValue(indent, wire)
+	case wire.StructT != nil:
+		deb.structValue(indent, id)
+	case wire.GobEncoderT != nil:
+		deb.gobEncoderValue(indent, id)
+	default:
+		panic("bad wire type for field")
+	}
+}
+
+// printBuiltin prints a value not of a fundamental type, that is,
+// one whose type is known to gobs at bootstrap time.
+func (deb *debugger) printBuiltin(indent tab, id typeId) {
+	switch id {
+	case tBool:
+		x := deb.int64()
+		if x == 0 {
+			fmt.Fprintf(os.Stderr, "%sfalse\n", indent)
+		} else {
+			fmt.Fprintf(os.Stderr, "%strue\n", indent)
+		}
+	case tInt:
+		x := deb.int64()
+		fmt.Fprintf(os.Stderr, "%s%d\n", indent, x)
+	case tUint:
+		x := deb.int64()
+		fmt.Fprintf(os.Stderr, "%s%d\n", indent, x)
+	case tFloat:
+		x := deb.uint64()
+		fmt.Fprintf(os.Stderr, "%s%g\n", indent, float64FromBits(x))
+	case tComplex:
+		r := deb.uint64()
+		i := deb.uint64()
+		fmt.Fprintf(os.Stderr, "%s%g+%gi\n", indent, float64FromBits(r), float64FromBits(i))
+	case tBytes:
+		x := int(deb.uint64())
+		b := make([]byte, x)
+		deb.r.Read(b)
+		deb.consumed(x)
+		fmt.Fprintf(os.Stderr, "%s{% x}=%q\n", indent, b, b)
+	case tString:
+		x := int(deb.uint64())
+		b := make([]byte, x)
+		deb.r.Read(b)
+		deb.consumed(x)
+		fmt.Fprintf(os.Stderr, "%s%q\n", indent, b)
+	default:
+		panic("unknown builtin")
+	}
+}
+
+// ArrayValue:
+//	uint(n) FieldValue*n
+func (deb *debugger) arrayValue(indent tab, wire *wireType) {
+	elemId := wire.ArrayT.Elem
+	u := deb.uint64()
+	length := int(u)
+	for i := 0; i < length; i++ {
+		deb.fieldValue(indent, elemId)
+	}
+	if length != wire.ArrayT.Len {
+		fmt.Fprintf(os.Stderr, "%s(wrong length for array: %d should be %d)\n", indent, length, wire.ArrayT.Len)
+	}
+}
+
+// MapValue:
+//	uint(n) (FieldValue FieldValue)*n  [n (key, value) pairs]
+func (deb *debugger) mapValue(indent tab, wire *wireType) {
+	keyId := wire.MapT.Key
+	elemId := wire.MapT.Elem
+	u := deb.uint64()
+	length := int(u)
+	for i := 0; i < length; i++ {
+		deb.fieldValue(indent+1, keyId)
+		deb.fieldValue(indent+1, elemId)
+	}
+}
+
+// SliceValue:
+//	uint(n) (n FieldValue)
+func (deb *debugger) sliceValue(indent tab, wire *wireType) {
+	elemId := wire.SliceT.Elem
+	u := deb.uint64()
+	length := int(u)
+	deb.dump("Start of slice of length %d", length)
+
+	for i := 0; i < length; i++ {
+		deb.fieldValue(indent, elemId)
+	}
+}
+
+// StructValue:
+//	(uint(fieldDelta) FieldValue)*
+func (deb *debugger) structValue(indent tab, id typeId) {
+	deb.dump("Start of struct value of %q id=%d\n<<\n", id.name(), id)
+	fmt.Fprintf(os.Stderr, "%s%s struct {\n", indent, id.name())
+	wire, ok := deb.wireType[id]
+	if !ok {
+		errorf("type id %d not defined", id)
+	}
+	strct := wire.StructT
+	fieldNum := -1
+	indent++
+	for {
+		delta := deb.uint64()
+		if delta == 0 { // struct terminator is zero delta fieldnum
+			break
+		}
+		fieldNum += int(delta)
+		if fieldNum < 0 || fieldNum >= len(strct.Field) {
+			deb.dump("field number out of range: prevField=%d delta=%d", fieldNum-int(delta), delta)
+			break
+		}
+		fmt.Fprintf(os.Stderr, "%sfield %d:\t%s\n", indent, fieldNum, wire.StructT.Field[fieldNum].Name)
+		deb.fieldValue(indent+1, strct.Field[fieldNum].Id)
+	}
+	indent--
+	fmt.Fprintf(os.Stderr, "%s} // end %s struct\n", indent, id.name())
+	deb.dump(">> End of struct value of type %d %q", id, id.name())
+}
+
+// GobEncoderValue:
+//	uint(n) byte*n
+func (deb *debugger) gobEncoderValue(indent tab, id typeId) {
+	len := deb.uint64()
+	deb.dump("GobEncoder value of %q id=%d, length %d\n", id.name(), id, len)
+	fmt.Fprintf(os.Stderr, "%s%s (implements GobEncoder)\n", indent, id.name())
+	data := make([]byte, len)
+	_, err := deb.r.Read(data)
+	if err != nil {
+		errorf("gobEncoder data read: %s", err)
+	}
+	fmt.Fprintf(os.Stderr, "%s[% .2x]\n", indent+1, data)
+}
diff --git a/src/encoding/gob/decode.go b/src/encoding/gob/decode.go
new file mode 100644
index 0000000000..2367650c8b
--- /dev/null
+++ b/src/encoding/gob/decode.go
@@ -0,0 +1,1146 @@
+// 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 (
+	"bytes"
+	"encoding"
+	"errors"
+	"io"
+	"math"
+	"reflect"
+)
+
+var (
+	errBadUint = errors.New("gob: encoded unsigned integer out of range")
+	errBadType = errors.New("gob: unknown type id or corrupted data")
+	errRange   = errors.New("gob: bad data: field numbers out of bounds")
+)
+
+// decoderState is the execution state of an instance of the decoder. A new state
+// is created for nested objects.
+type decoderState struct {
+	dec *Decoder
+	// The buffer is stored with an extra indirection because it may be replaced
+	// if we load a type during decode (when reading an interface value).
+	b        *bytes.Buffer
+	fieldnum int // the last field number read.
+	buf      []byte
+	next     *decoderState // for free list
+}
+
+// We pass the bytes.Buffer separately for easier testing of the infrastructure
+// without requiring a full Decoder.
+func (dec *Decoder) newDecoderState(buf *bytes.Buffer) *decoderState {
+	d := dec.freeList
+	if d == nil {
+		d = new(decoderState)
+		d.dec = dec
+		d.buf = make([]byte, uint64Size)
+	} else {
+		dec.freeList = d.next
+	}
+	d.b = buf
+	return d
+}
+
+func (dec *Decoder) freeDecoderState(d *decoderState) {
+	d.next = dec.freeList
+	dec.freeList = d
+}
+
+func overflow(name string) error {
+	return errors.New(`value for "` + name + `" out of range`)
+}
+
+// decodeUintReader reads an encoded unsigned integer from an io.Reader.
+// Used only by the Decoder to read the message length.
+func decodeUintReader(r io.Reader, buf []byte) (x uint64, width int, err error) {
+	width = 1
+	n, err := io.ReadFull(r, buf[0:width])
+	if n == 0 {
+		return
+	}
+	b := buf[0]
+	if b <= 0x7f {
+		return uint64(b), width, nil
+	}
+	n = -int(int8(b))
+	if n > uint64Size {
+		err = errBadUint
+		return
+	}
+	width, err = io.ReadFull(r, buf[0:n])
+	if err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		return
+	}
+	// Could check that the high byte is zero but it's not worth it.
+	for _, b := range buf[0:width] {
+		x = x<<8 | uint64(b)
+	}
+	width++ // +1 for length byte
+	return
+}
+
+// decodeUint reads an encoded unsigned integer from state.r.
+// Does not check for overflow.
+func (state *decoderState) decodeUint() (x uint64) {
+	b, err := state.b.ReadByte()
+	if err != nil {
+		error_(err)
+	}
+	if b <= 0x7f {
+		return uint64(b)
+	}
+	n := -int(int8(b))
+	if n > uint64Size {
+		error_(errBadUint)
+	}
+	width, err := state.b.Read(state.buf[0:n])
+	if err != nil {
+		error_(err)
+	}
+	// Don't need to check error; it's safe to loop regardless.
+	// Could check that the high byte is zero but it's not worth it.
+	for _, b := range state.buf[0:width] {
+		x = x<<8 | uint64(b)
+	}
+	return x
+}
+
+// decodeInt reads an encoded signed integer from state.r.
+// Does not check for overflow.
+func (state *decoderState) decodeInt() int64 {
+	x := state.decodeUint()
+	if x&1 != 0 {
+		return ^int64(x >> 1)
+	}
+	return int64(x >> 1)
+}
+
+// decOp is the signature of a decoding operator for a given type.
+type decOp func(i *decInstr, state *decoderState, v reflect.Value)
+
+// The 'instructions' of the decoding machine
+type decInstr struct {
+	op    decOp
+	field int   // field number of the wire type
+	index []int // field access indices for destination type
+	ovfl  error // error message for overflow/underflow (for arrays, of the elements)
+}
+
+// ignoreUint discards a uint value with no destination.
+func ignoreUint(i *decInstr, state *decoderState, v reflect.Value) {
+	state.decodeUint()
+}
+
+// ignoreTwoUints discards a uint value with no destination. It's used to skip
+// complex values.
+func ignoreTwoUints(i *decInstr, state *decoderState, v reflect.Value) {
+	state.decodeUint()
+	state.decodeUint()
+}
+
+// Since the encoder writes no zeros, if we arrive at a decoder we have
+// a value to extract and store.  The field number has already been read
+// (it's how we knew to call this decoder).
+// Each decoder is responsible for handling any indirections associated
+// with the data structure.  If any pointer so reached is nil, allocation must
+// be done.
+
+// decAlloc takes a value and returns a settable value that can
+// be assigned to. If the value is a pointer, decAlloc guarantees it points to storage.
+// The callers to the individual decoders are expected to have used decAlloc.
+// The individual decoders don't need to it.
+func decAlloc(v reflect.Value) reflect.Value {
+	for v.Kind() == reflect.Ptr {
+		if v.IsNil() {
+			v.Set(reflect.New(v.Type().Elem()))
+		}
+		v = v.Elem()
+	}
+	return v
+}
+
+// decBool decodes a uint and stores it as a boolean in value.
+func decBool(i *decInstr, state *decoderState, value reflect.Value) {
+	value.SetBool(state.decodeUint() != 0)
+}
+
+// decInt8 decodes an integer and stores it as an int8 in value.
+func decInt8(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeInt()
+	if v < math.MinInt8 || math.MaxInt8 < v {
+		error_(i.ovfl)
+	}
+	value.SetInt(v)
+}
+
+// decUint8 decodes an unsigned integer and stores it as a uint8 in value.
+func decUint8(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeUint()
+	if math.MaxUint8 < v {
+		error_(i.ovfl)
+	}
+	value.SetUint(v)
+}
+
+// decInt16 decodes an integer and stores it as an int16 in value.
+func decInt16(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeInt()
+	if v < math.MinInt16 || math.MaxInt16 < v {
+		error_(i.ovfl)
+	}
+	value.SetInt(v)
+}
+
+// decUint16 decodes an unsigned integer and stores it as a uint16 in value.
+func decUint16(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeUint()
+	if math.MaxUint16 < v {
+		error_(i.ovfl)
+	}
+	value.SetUint(v)
+}
+
+// decInt32 decodes an integer and stores it as an int32 in value.
+func decInt32(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeInt()
+	if v < math.MinInt32 || math.MaxInt32 < v {
+		error_(i.ovfl)
+	}
+	value.SetInt(v)
+}
+
+// decUint32 decodes an unsigned integer and stores it as a uint32 in value.
+func decUint32(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeUint()
+	if math.MaxUint32 < v {
+		error_(i.ovfl)
+	}
+	value.SetUint(v)
+}
+
+// decInt64 decodes an integer and stores it as an int64 in value.
+func decInt64(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeInt()
+	value.SetInt(v)
+}
+
+// decUint64 decodes an unsigned integer and stores it as a uint64 in value.
+func decUint64(i *decInstr, state *decoderState, value reflect.Value) {
+	v := state.decodeUint()
+	value.SetUint(v)
+}
+
+// Floating-point numbers are transmitted as uint64s holding the bits
+// of the underlying representation.  They are sent byte-reversed, with
+// the exponent end coming out first, so integer floating point numbers
+// (for example) transmit more compactly.  This routine does the
+// unswizzling.
+func float64FromBits(u uint64) float64 {
+	var v uint64
+	for i := 0; i < 8; i++ {
+		v <<= 8
+		v |= u & 0xFF
+		u >>= 8
+	}
+	return math.Float64frombits(v)
+}
+
+// float32FromBits decodes an unsigned integer, treats it as a 32-bit floating-point
+// number, and returns it. It's a helper function for float32 and complex64.
+// It returns a float64 because that's what reflection needs, but its return
+// value is known to be accurately representable in a float32.
+func float32FromBits(i *decInstr, u uint64) float64 {
+	v := float64FromBits(u)
+	av := v
+	if av < 0 {
+		av = -av
+	}
+	// +Inf is OK in both 32- and 64-bit floats.  Underflow is always OK.
+	if math.MaxFloat32 < av && av <= math.MaxFloat64 {
+		error_(i.ovfl)
+	}
+	return v
+}
+
+// decFloat32 decodes an unsigned integer, treats it as a 32-bit floating-point
+// number, and stores it in value.
+func decFloat32(i *decInstr, state *decoderState, value reflect.Value) {
+	value.SetFloat(float32FromBits(i, state.decodeUint()))
+}
+
+// decFloat64 decodes an unsigned integer, treats it as a 64-bit floating-point
+// number, and stores it in value.
+func decFloat64(i *decInstr, state *decoderState, value reflect.Value) {
+	value.SetFloat(float64FromBits(state.decodeUint()))
+}
+
+// decComplex64 decodes a pair of unsigned integers, treats them as a
+// pair of floating point numbers, and stores them as a complex64 in value.
+// The real part comes first.
+func decComplex64(i *decInstr, state *decoderState, value reflect.Value) {
+	real := float32FromBits(i, state.decodeUint())
+	imag := float32FromBits(i, state.decodeUint())
+	value.SetComplex(complex(real, imag))
+}
+
+// decComplex128 decodes a pair of unsigned integers, treats them as a
+// pair of floating point numbers, and stores them as a complex128 in value.
+// The real part comes first.
+func decComplex128(i *decInstr, state *decoderState, value reflect.Value) {
+	real := float64FromBits(state.decodeUint())
+	imag := float64FromBits(state.decodeUint())
+	value.SetComplex(complex(real, imag))
+}
+
+// decUint8Slice decodes a byte slice and stores in value a slice header
+// describing the data.
+// uint8 slices are encoded as an unsigned count followed by the raw bytes.
+func decUint8Slice(i *decInstr, state *decoderState, value reflect.Value) {
+	u := state.decodeUint()
+	n := int(u)
+	if n < 0 || uint64(n) != u {
+		errorf("length of %s exceeds input size (%d bytes)", value.Type(), u)
+	}
+	if n > state.b.Len() {
+		errorf("%s data too long for buffer: %d", value.Type(), n)
+	}
+	if value.Cap() < n {
+		value.Set(reflect.MakeSlice(value.Type(), n, n))
+	} else {
+		value.Set(value.Slice(0, n))
+	}
+	if _, err := state.b.Read(value.Bytes()); err != nil {
+		errorf("error decoding []byte: %s", err)
+	}
+}
+
+// decString decodes byte array and stores in value a string header
+// describing the data.
+// Strings are encoded as an unsigned count followed by the raw bytes.
+func decString(i *decInstr, state *decoderState, value reflect.Value) {
+	u := state.decodeUint()
+	n := int(u)
+	if n < 0 || uint64(n) != u || n > state.b.Len() {
+		errorf("length of %s exceeds input size (%d bytes)", value.Type(), u)
+	}
+	if n > state.b.Len() {
+		errorf("%s data too long for buffer: %d", value.Type(), n)
+	}
+	// Read the data.
+	data := make([]byte, n)
+	if _, err := state.b.Read(data); err != nil {
+		errorf("error decoding string: %s", err)
+	}
+	value.SetString(string(data))
+}
+
+// ignoreUint8Array skips over the data for a byte slice value with no destination.
+func ignoreUint8Array(i *decInstr, state *decoderState, value reflect.Value) {
+	b := make([]byte, state.decodeUint())
+	state.b.Read(b)
+}
+
+// Execution engine
+
+// The encoder engine is an array of instructions indexed by field number of the incoming
+// decoder.  It is executed with random access according to field number.
+type decEngine struct {
+	instr    []decInstr
+	numInstr int // the number of active instructions
+}
+
+// decodeSingle decodes a top-level value that is not a struct and stores it in value.
+// Such values are preceded by a zero, making them have the memory layout of a
+// struct field (although with an illegal field number).
+func (dec *Decoder) decodeSingle(engine *decEngine, ut *userTypeInfo, value reflect.Value) {
+	state := dec.newDecoderState(&dec.buf)
+	defer dec.freeDecoderState(state)
+	state.fieldnum = singletonField
+	if state.decodeUint() != 0 {
+		errorf("decode: corrupted data: non-zero delta for singleton")
+	}
+	instr := &engine.instr[singletonField]
+	instr.op(instr, state, value)
+}
+
+// decodeStruct decodes a top-level struct and stores it in value.
+// Indir is for the value, not the type.  At the time of the call it may
+// differ from ut.indir, which was computed when the engine was built.
+// This state cannot arise for decodeSingle, which is called directly
+// from the user's value, not from the innards of an engine.
+func (dec *Decoder) decodeStruct(engine *decEngine, ut *userTypeInfo, value reflect.Value) {
+	state := dec.newDecoderState(&dec.buf)
+	defer dec.freeDecoderState(state)
+	state.fieldnum = -1
+	for state.b.Len() > 0 {
+		delta := int(state.decodeUint())
+		if delta < 0 {
+			errorf("decode: corrupted data: negative delta")
+		}
+		if delta == 0 { // struct terminator is zero delta fieldnum
+			break
+		}
+		fieldnum := state.fieldnum + delta
+		if fieldnum >= len(engine.instr) {
+			error_(errRange)
+			break
+		}
+		instr := &engine.instr[fieldnum]
+		var field reflect.Value
+		if instr.index != nil {
+			// Otherwise the field is unknown to us and instr.op is an ignore op.
+			field = value.FieldByIndex(instr.index)
+			if field.Kind() == reflect.Ptr {
+				field = decAlloc(field)
+			}
+		}
+		instr.op(instr, state, field)
+		state.fieldnum = fieldnum
+	}
+}
+
+var noValue reflect.Value
+
+// ignoreStruct discards the data for a struct with no destination.
+func (dec *Decoder) ignoreStruct(engine *decEngine) {
+	state := dec.newDecoderState(&dec.buf)
+	defer dec.freeDecoderState(state)
+	state.fieldnum = -1
+	for state.b.Len() > 0 {
+		delta := int(state.decodeUint())
+		if delta < 0 {
+			errorf("ignore decode: corrupted data: negative delta")
+		}
+		if delta == 0 { // struct terminator is zero delta fieldnum
+			break
+		}
+		fieldnum := state.fieldnum + delta
+		if fieldnum >= len(engine.instr) {
+			error_(errRange)
+		}
+		instr := &engine.instr[fieldnum]
+		instr.op(instr, state, noValue)
+		state.fieldnum = fieldnum
+	}
+}
+
+// ignoreSingle discards the data for a top-level non-struct value with no
+// destination. It's used when calling Decode with a nil value.
+func (dec *Decoder) ignoreSingle(engine *decEngine) {
+	state := dec.newDecoderState(&dec.buf)
+	defer dec.freeDecoderState(state)
+	state.fieldnum = singletonField
+	delta := int(state.decodeUint())
+	if delta != 0 {
+		errorf("decode: corrupted data: non-zero delta for singleton")
+	}
+	instr := &engine.instr[singletonField]
+	instr.op(instr, state, noValue)
+}
+
+// decodeArrayHelper does the work for decoding arrays and slices.
+func (dec *Decoder) decodeArrayHelper(state *decoderState, value reflect.Value, elemOp decOp, length int, ovfl error) {
+	instr := &decInstr{elemOp, 0, nil, ovfl}
+	isPtr := value.Type().Elem().Kind() == reflect.Ptr
+	for i := 0; i < length; i++ {
+		if state.b.Len() == 0 {
+			errorf("decoding array or slice: length exceeds input size (%d elements)", length)
+		}
+		v := value.Index(i)
+		if isPtr {
+			v = decAlloc(v)
+		}
+		elemOp(instr, state, v)
+	}
+}
+
+// decodeArray decodes an array and stores it in value.
+// The length is an unsigned integer preceding the elements.  Even though the length is redundant
+// (it's part of the type), it's a useful check and is included in the encoding.
+func (dec *Decoder) decodeArray(atyp reflect.Type, state *decoderState, value reflect.Value, elemOp decOp, length int, ovfl error) {
+	if n := state.decodeUint(); n != uint64(length) {
+		errorf("length mismatch in decodeArray")
+	}
+	dec.decodeArrayHelper(state, value, elemOp, length, ovfl)
+}
+
+// decodeIntoValue is a helper for map decoding.
+func decodeIntoValue(state *decoderState, op decOp, isPtr bool, value reflect.Value, ovfl error) reflect.Value {
+	instr := &decInstr{op, 0, nil, ovfl}
+	v := value
+	if isPtr {
+		v = decAlloc(value)
+	}
+	op(instr, state, v)
+	return value
+}
+
+// decodeMap decodes a map and stores it in value.
+// Maps are encoded as a length followed by key:value pairs.
+// Because the internals of maps are not visible to us, we must
+// use reflection rather than pointer magic.
+func (dec *Decoder) decodeMap(mtyp reflect.Type, state *decoderState, value reflect.Value, keyOp, elemOp decOp, ovfl error) {
+	if value.IsNil() {
+		// Allocate map.
+		value.Set(reflect.MakeMap(mtyp))
+	}
+	n := int(state.decodeUint())
+	keyIsPtr := mtyp.Key().Kind() == reflect.Ptr
+	elemIsPtr := mtyp.Elem().Kind() == reflect.Ptr
+	for i := 0; i < n; i++ {
+		key := decodeIntoValue(state, keyOp, keyIsPtr, allocValue(mtyp.Key()), ovfl)
+		elem := decodeIntoValue(state, elemOp, elemIsPtr, allocValue(mtyp.Elem()), ovfl)
+		value.SetMapIndex(key, elem)
+	}
+}
+
+// ignoreArrayHelper does the work for discarding arrays and slices.
+func (dec *Decoder) ignoreArrayHelper(state *decoderState, elemOp decOp, length int) {
+	instr := &decInstr{elemOp, 0, nil, errors.New("no error")}
+	for i := 0; i < length; i++ {
+		elemOp(instr, state, noValue)
+	}
+}
+
+// ignoreArray discards the data for an array value with no destination.
+func (dec *Decoder) ignoreArray(state *decoderState, elemOp decOp, length int) {
+	if n := state.decodeUint(); n != uint64(length) {
+		errorf("length mismatch in ignoreArray")
+	}
+	dec.ignoreArrayHelper(state, elemOp, length)
+}
+
+// ignoreMap discards the data for a map value with no destination.
+func (dec *Decoder) ignoreMap(state *decoderState, keyOp, elemOp decOp) {
+	n := int(state.decodeUint())
+	keyInstr := &decInstr{keyOp, 0, nil, errors.New("no error")}
+	elemInstr := &decInstr{elemOp, 0, nil, errors.New("no error")}
+	for i := 0; i < n; i++ {
+		keyOp(keyInstr, state, noValue)
+		elemOp(elemInstr, state, noValue)
+	}
+}
+
+// decodeSlice decodes a slice and stores it in value.
+// Slices are encoded as an unsigned length followed by the elements.
+func (dec *Decoder) decodeSlice(state *decoderState, value reflect.Value, elemOp decOp, ovfl error) {
+	u := state.decodeUint()
+	n := int(u)
+	if n < 0 || uint64(n) != u {
+		// We don't check n against buffer length here because if it's a slice
+		// of interfaces, there will be buffer reloads.
+		errorf("length of %s is negative (%d bytes)", value.Type(), u)
+	}
+	if value.Cap() < n {
+		value.Set(reflect.MakeSlice(value.Type(), n, n))
+	} else {
+		value.Set(value.Slice(0, n))
+	}
+	dec.decodeArrayHelper(state, value, elemOp, n, ovfl)
+}
+
+// ignoreSlice skips over the data for a slice value with no destination.
+func (dec *Decoder) ignoreSlice(state *decoderState, elemOp decOp) {
+	dec.ignoreArrayHelper(state, elemOp, int(state.decodeUint()))
+}
+
+// decodeInterface decodes an interface value and stores it in value.
+// Interfaces are encoded as the name of a concrete type followed by a value.
+// If the name is empty, the value is nil and no value is sent.
+func (dec *Decoder) decodeInterface(ityp reflect.Type, state *decoderState, value reflect.Value) {
+	// Read the name of the concrete type.
+	nr := state.decodeUint()
+	if nr < 0 || nr > 1<<31 { // zero is permissible for anonymous types
+		errorf("invalid type name length %d", nr)
+	}
+	if nr > uint64(state.b.Len()) {
+		errorf("invalid type name length %d: exceeds input size", nr)
+	}
+	b := make([]byte, nr)
+	state.b.Read(b)
+	name := string(b)
+	// Allocate the destination interface value.
+	if name == "" {
+		// Copy the nil interface value to the target.
+		value.Set(reflect.Zero(value.Type()))
+		return
+	}
+	if len(name) > 1024 {
+		errorf("name too long (%d bytes): %.20q...", len(name), name)
+	}
+	// The concrete type must be registered.
+	registerLock.RLock()
+	typ, ok := nameToConcreteType[name]
+	registerLock.RUnlock()
+	if !ok {
+		errorf("name not registered for interface: %q", name)
+	}
+	// Read the type id of the concrete value.
+	concreteId := dec.decodeTypeSequence(true)
+	if concreteId < 0 {
+		error_(dec.err)
+	}
+	// Byte count of value is next; we don't care what it is (it's there
+	// in case we want to ignore the value by skipping it completely).
+	state.decodeUint()
+	// Read the concrete value.
+	v := allocValue(typ)
+	dec.decodeValue(concreteId, v)
+	if dec.err != nil {
+		error_(dec.err)
+	}
+	// Assign the concrete value to the interface.
+	// Tread carefully; it might not satisfy the interface.
+	if !typ.AssignableTo(ityp) {
+		errorf("%s is not assignable to type %s", typ, ityp)
+	}
+	// Copy the interface value to the target.
+	value.Set(v)
+}
+
+// ignoreInterface discards the data for an interface value with no destination.
+func (dec *Decoder) ignoreInterface(state *decoderState) {
+	// Read the name of the concrete type.
+	b := make([]byte, state.decodeUint())
+	_, err := state.b.Read(b)
+	if err != nil {
+		error_(err)
+	}
+	id := dec.decodeTypeSequence(true)
+	if id < 0 {
+		error_(dec.err)
+	}
+	// At this point, the decoder buffer contains a delimited value. Just toss it.
+	state.b.Next(int(state.decodeUint()))
+}
+
+// decodeGobDecoder decodes something implementing the GobDecoder interface.
+// The data is encoded as a byte slice.
+func (dec *Decoder) decodeGobDecoder(ut *userTypeInfo, state *decoderState, value reflect.Value) {
+	// Read the bytes for the value.
+	b := make([]byte, state.decodeUint())
+	_, err := state.b.Read(b)
+	if err != nil {
+		error_(err)
+	}
+	// We know it's one of these.
+	switch ut.externalDec {
+	case xGob:
+		err = value.Interface().(GobDecoder).GobDecode(b)
+	case xBinary:
+		err = value.Interface().(encoding.BinaryUnmarshaler).UnmarshalBinary(b)
+	case xText:
+		err = value.Interface().(encoding.TextUnmarshaler).UnmarshalText(b)
+	}
+	if err != nil {
+		error_(err)
+	}
+}
+
+// ignoreGobDecoder discards the data for a GobDecoder value with no destination.
+func (dec *Decoder) ignoreGobDecoder(state *decoderState) {
+	// Read the bytes for the value.
+	b := make([]byte, state.decodeUint())
+	_, err := state.b.Read(b)
+	if err != nil {
+		error_(err)
+	}
+}
+
+// Index by Go types.
+var decOpTable = [...]decOp{
+	reflect.Bool:       decBool,
+	reflect.Int8:       decInt8,
+	reflect.Int16:      decInt16,
+	reflect.Int32:      decInt32,
+	reflect.Int64:      decInt64,
+	reflect.Uint8:      decUint8,
+	reflect.Uint16:     decUint16,
+	reflect.Uint32:     decUint32,
+	reflect.Uint64:     decUint64,
+	reflect.Float32:    decFloat32,
+	reflect.Float64:    decFloat64,
+	reflect.Complex64:  decComplex64,
+	reflect.Complex128: decComplex128,
+	reflect.String:     decString,
+}
+
+// Indexed by gob types.  tComplex will be added during type.init().
+var decIgnoreOpMap = map[typeId]decOp{
+	tBool:    ignoreUint,
+	tInt:     ignoreUint,
+	tUint:    ignoreUint,
+	tFloat:   ignoreUint,
+	tBytes:   ignoreUint8Array,
+	tString:  ignoreUint8Array,
+	tComplex: ignoreTwoUints,
+}
+
+// decOpFor returns the decoding op for the base type under rt and
+// the indirection count to reach it.
+func (dec *Decoder) decOpFor(wireId typeId, rt reflect.Type, name string, inProgress map[reflect.Type]*decOp) *decOp {
+	ut := userType(rt)
+	// If the type implements GobEncoder, we handle it without further processing.
+	if ut.externalDec != 0 {
+		return dec.gobDecodeOpFor(ut)
+	}
+
+	// If this type is already in progress, it's a recursive type (e.g. map[string]*T).
+	// Return the pointer to the op we're already building.
+	if opPtr := inProgress[rt]; opPtr != nil {
+		return opPtr
+	}
+	typ := ut.base
+	var op decOp
+	k := typ.Kind()
+	if int(k) < len(decOpTable) {
+		op = decOpTable[k]
+	}
+	if op == nil {
+		inProgress[rt] = &op
+		// Special cases
+		switch t := typ; t.Kind() {
+		case reflect.Array:
+			name = "element of " + name
+			elemId := dec.wireType[wireId].ArrayT.Elem
+			elemOp := dec.decOpFor(elemId, t.Elem(), name, inProgress)
+			ovfl := overflow(name)
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.decodeArray(t, state, value, *elemOp, t.Len(), ovfl)
+			}
+
+		case reflect.Map:
+			keyId := dec.wireType[wireId].MapT.Key
+			elemId := dec.wireType[wireId].MapT.Elem
+			keyOp := dec.decOpFor(keyId, t.Key(), "key of "+name, inProgress)
+			elemOp := dec.decOpFor(elemId, t.Elem(), "element of "+name, inProgress)
+			ovfl := overflow(name)
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.decodeMap(t, state, value, *keyOp, *elemOp, ovfl)
+			}
+
+		case reflect.Slice:
+			name = "element of " + name
+			if t.Elem().Kind() == reflect.Uint8 {
+				op = decUint8Slice
+				break
+			}
+			var elemId typeId
+			if tt, ok := builtinIdToType[wireId]; ok {
+				elemId = tt.(*sliceType).Elem
+			} else {
+				elemId = dec.wireType[wireId].SliceT.Elem
+			}
+			elemOp := dec.decOpFor(elemId, t.Elem(), name, inProgress)
+			ovfl := overflow(name)
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.decodeSlice(state, value, *elemOp, ovfl)
+			}
+
+		case reflect.Struct:
+			// Generate a closure that calls out to the engine for the nested type.
+			ut := userType(typ)
+			enginePtr, err := dec.getDecEnginePtr(wireId, ut)
+			if err != nil {
+				error_(err)
+			}
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				// indirect through enginePtr to delay evaluation for recursive structs.
+				dec.decodeStruct(*enginePtr, ut, value)
+			}
+		case reflect.Interface:
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.decodeInterface(t, state, value)
+			}
+		}
+	}
+	if op == nil {
+		errorf("decode can't handle type %s", rt)
+	}
+	return &op
+}
+
+// decIgnoreOpFor returns the decoding op for a field that has no destination.
+func (dec *Decoder) decIgnoreOpFor(wireId typeId) decOp {
+	op, ok := decIgnoreOpMap[wireId]
+	if !ok {
+		if wireId == tInterface {
+			// Special case because it's a method: the ignored item might
+			// define types and we need to record their state in the decoder.
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.ignoreInterface(state)
+			}
+			return op
+		}
+		// Special cases
+		wire := dec.wireType[wireId]
+		switch {
+		case wire == nil:
+			errorf("bad data: undefined type %s", wireId.string())
+		case wire.ArrayT != nil:
+			elemId := wire.ArrayT.Elem
+			elemOp := dec.decIgnoreOpFor(elemId)
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.ignoreArray(state, elemOp, wire.ArrayT.Len)
+			}
+
+		case wire.MapT != nil:
+			keyId := dec.wireType[wireId].MapT.Key
+			elemId := dec.wireType[wireId].MapT.Elem
+			keyOp := dec.decIgnoreOpFor(keyId)
+			elemOp := dec.decIgnoreOpFor(elemId)
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.ignoreMap(state, keyOp, elemOp)
+			}
+
+		case wire.SliceT != nil:
+			elemId := wire.SliceT.Elem
+			elemOp := dec.decIgnoreOpFor(elemId)
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.ignoreSlice(state, elemOp)
+			}
+
+		case wire.StructT != nil:
+			// Generate a closure that calls out to the engine for the nested type.
+			enginePtr, err := dec.getIgnoreEnginePtr(wireId)
+			if err != nil {
+				error_(err)
+			}
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				// indirect through enginePtr to delay evaluation for recursive structs
+				state.dec.ignoreStruct(*enginePtr)
+			}
+
+		case wire.GobEncoderT != nil, wire.BinaryMarshalerT != nil, wire.TextMarshalerT != nil:
+			op = func(i *decInstr, state *decoderState, value reflect.Value) {
+				state.dec.ignoreGobDecoder(state)
+			}
+		}
+	}
+	if op == nil {
+		errorf("bad data: ignore can't handle type %s", wireId.string())
+	}
+	return op
+}
+
+// gobDecodeOpFor returns the op for a type that is known to implement
+// GobDecoder.
+func (dec *Decoder) gobDecodeOpFor(ut *userTypeInfo) *decOp {
+	rcvrType := ut.user
+	if ut.decIndir == -1 {
+		rcvrType = reflect.PtrTo(rcvrType)
+	} else if ut.decIndir > 0 {
+		for i := int8(0); i < ut.decIndir; i++ {
+			rcvrType = rcvrType.Elem()
+		}
+	}
+	var op decOp
+	op = func(i *decInstr, state *decoderState, value reflect.Value) {
+		// We now have the base type. We need its address if the receiver is a pointer.
+		if value.Kind() != reflect.Ptr && rcvrType.Kind() == reflect.Ptr {
+			value = value.Addr()
+		}
+		state.dec.decodeGobDecoder(ut, state, value)
+	}
+	return &op
+}
+
+// compatibleType asks: Are these two gob Types compatible?
+// Answers the question for basic types, arrays, maps and slices, plus
+// GobEncoder/Decoder pairs.
+// Structs are considered ok; fields will be checked later.
+func (dec *Decoder) compatibleType(fr reflect.Type, fw typeId, inProgress map[reflect.Type]typeId) bool {
+	if rhs, ok := inProgress[fr]; ok {
+		return rhs == fw
+	}
+	inProgress[fr] = fw
+	ut := userType(fr)
+	wire, ok := dec.wireType[fw]
+	// If wire was encoded with an encoding method, fr must have that method.
+	// And if not, it must not.
+	// At most one of the booleans in ut is set.
+	// We could possibly relax this constraint in the future in order to
+	// choose the decoding method using the data in the wireType.
+	// The parentheses look odd but are correct.
+	if (ut.externalDec == xGob) != (ok && wire.GobEncoderT != nil) ||
+		(ut.externalDec == xBinary) != (ok && wire.BinaryMarshalerT != nil) ||
+		(ut.externalDec == xText) != (ok && wire.TextMarshalerT != nil) {
+		return false
+	}
+	if ut.externalDec != 0 { // This test trumps all others.
+		return true
+	}
+	switch t := ut.base; t.Kind() {
+	default:
+		// chan, etc: cannot handle.
+		return false
+	case reflect.Bool:
+		return fw == tBool
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return fw == tInt
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return fw == tUint
+	case reflect.Float32, reflect.Float64:
+		return fw == tFloat
+	case reflect.Complex64, reflect.Complex128:
+		return fw == tComplex
+	case reflect.String:
+		return fw == tString
+	case reflect.Interface:
+		return fw == tInterface
+	case reflect.Array:
+		if !ok || wire.ArrayT == nil {
+			return false
+		}
+		array := wire.ArrayT
+		return t.Len() == array.Len && dec.compatibleType(t.Elem(), array.Elem, inProgress)
+	case reflect.Map:
+		if !ok || wire.MapT == nil {
+			return false
+		}
+		MapType := wire.MapT
+		return dec.compatibleType(t.Key(), MapType.Key, inProgress) && dec.compatibleType(t.Elem(), MapType.Elem, inProgress)
+	case reflect.Slice:
+		// Is it an array of bytes?
+		if t.Elem().Kind() == reflect.Uint8 {
+			return fw == tBytes
+		}
+		// Extract and compare element types.
+		var sw *sliceType
+		if tt, ok := builtinIdToType[fw]; ok {
+			sw, _ = tt.(*sliceType)
+		} else if wire != nil {
+			sw = wire.SliceT
+		}
+		elem := userType(t.Elem()).base
+		return sw != nil && dec.compatibleType(elem, sw.Elem, inProgress)
+	case reflect.Struct:
+		return true
+	}
+}
+
+// typeString returns a human-readable description of the type identified by remoteId.
+func (dec *Decoder) typeString(remoteId typeId) string {
+	if t := idToType[remoteId]; t != nil {
+		// globally known type.
+		return t.string()
+	}
+	return dec.wireType[remoteId].string()
+}
+
+// compileSingle compiles the decoder engine for a non-struct top-level value, including
+// GobDecoders.
+func (dec *Decoder) compileSingle(remoteId typeId, ut *userTypeInfo) (engine *decEngine, err error) {
+	rt := ut.user
+	engine = new(decEngine)
+	engine.instr = make([]decInstr, 1) // one item
+	name := rt.String()                // best we can do
+	if !dec.compatibleType(rt, remoteId, make(map[reflect.Type]typeId)) {
+		remoteType := dec.typeString(remoteId)
+		// Common confusing case: local interface type, remote concrete type.
+		if ut.base.Kind() == reflect.Interface && remoteId != tInterface {
+			return nil, errors.New("gob: local interface type " + name + " can only be decoded from remote interface type; received concrete type " + remoteType)
+		}
+		return nil, errors.New("gob: decoding into local type " + name + ", received remote type " + remoteType)
+	}
+	op := dec.decOpFor(remoteId, rt, name, make(map[reflect.Type]*decOp))
+	ovfl := errors.New(`value for "` + name + `" out of range`)
+	engine.instr[singletonField] = decInstr{*op, singletonField, nil, ovfl}
+	engine.numInstr = 1
+	return
+}
+
+// compileIgnoreSingle compiles the decoder engine for a non-struct top-level value that will be discarded.
+func (dec *Decoder) compileIgnoreSingle(remoteId typeId) (engine *decEngine, err error) {
+	engine = new(decEngine)
+	engine.instr = make([]decInstr, 1) // one item
+	op := dec.decIgnoreOpFor(remoteId)
+	ovfl := overflow(dec.typeString(remoteId))
+	engine.instr[0] = decInstr{op, 0, nil, ovfl}
+	engine.numInstr = 1
+	return
+}
+
+// compileDec compiles the decoder engine for a value.  If the value is not a struct,
+// it calls out to compileSingle.
+func (dec *Decoder) compileDec(remoteId typeId, ut *userTypeInfo) (engine *decEngine, err error) {
+	rt := ut.base
+	srt := rt
+	if srt.Kind() != reflect.Struct || ut.externalDec != 0 {
+		return dec.compileSingle(remoteId, ut)
+	}
+	var wireStruct *structType
+	// Builtin types can come from global pool; the rest must be defined by the decoder.
+	// Also we know we're decoding a struct now, so the client must have sent one.
+	if t, ok := builtinIdToType[remoteId]; ok {
+		wireStruct, _ = t.(*structType)
+	} else {
+		wire := dec.wireType[remoteId]
+		if wire == nil {
+			error_(errBadType)
+		}
+		wireStruct = wire.StructT
+	}
+	if wireStruct == nil {
+		errorf("type mismatch in decoder: want struct type %s; got non-struct", rt)
+	}
+	engine = new(decEngine)
+	engine.instr = make([]decInstr, len(wireStruct.Field))
+	seen := make(map[reflect.Type]*decOp)
+	// Loop over the fields of the wire type.
+	for fieldnum := 0; fieldnum < len(wireStruct.Field); fieldnum++ {
+		wireField := wireStruct.Field[fieldnum]
+		if wireField.Name == "" {
+			errorf("empty name for remote field of type %s", wireStruct.Name)
+		}
+		ovfl := overflow(wireField.Name)
+		// Find the field of the local type with the same name.
+		localField, present := srt.FieldByName(wireField.Name)
+		// TODO(r): anonymous names
+		if !present || !isExported(wireField.Name) {
+			op := dec.decIgnoreOpFor(wireField.Id)
+			engine.instr[fieldnum] = decInstr{op, fieldnum, nil, ovfl}
+			continue
+		}
+		if !dec.compatibleType(localField.Type, wireField.Id, make(map[reflect.Type]typeId)) {
+			errorf("wrong type (%s) for received field %s.%s", localField.Type, wireStruct.Name, wireField.Name)
+		}
+		op := dec.decOpFor(wireField.Id, localField.Type, localField.Name, seen)
+		engine.instr[fieldnum] = decInstr{*op, fieldnum, localField.Index, ovfl}
+		engine.numInstr++
+	}
+	return
+}
+
+// getDecEnginePtr returns the engine for the specified type.
+func (dec *Decoder) getDecEnginePtr(remoteId typeId, ut *userTypeInfo) (enginePtr **decEngine, err error) {
+	rt := ut.user
+	decoderMap, ok := dec.decoderCache[rt]
+	if !ok {
+		decoderMap = make(map[typeId]**decEngine)
+		dec.decoderCache[rt] = decoderMap
+	}
+	if enginePtr, ok = decoderMap[remoteId]; !ok {
+		// To handle recursive types, mark this engine as underway before compiling.
+		enginePtr = new(*decEngine)
+		decoderMap[remoteId] = enginePtr
+		*enginePtr, err = dec.compileDec(remoteId, ut)
+		if err != nil {
+			delete(decoderMap, remoteId)
+		}
+	}
+	return
+}
+
+// emptyStruct is the type we compile into when ignoring a struct value.
+type emptyStruct struct{}
+
+var emptyStructType = reflect.TypeOf(emptyStruct{})
+
+// getDecEnginePtr returns the engine for the specified type when the value is to be discarded.
+func (dec *Decoder) getIgnoreEnginePtr(wireId typeId) (enginePtr **decEngine, err error) {
+	var ok bool
+	if enginePtr, ok = dec.ignorerCache[wireId]; !ok {
+		// To handle recursive types, mark this engine as underway before compiling.
+		enginePtr = new(*decEngine)
+		dec.ignorerCache[wireId] = enginePtr
+		wire := dec.wireType[wireId]
+		if wire != nil && wire.StructT != nil {
+			*enginePtr, err = dec.compileDec(wireId, userType(emptyStructType))
+		} else {
+			*enginePtr, err = dec.compileIgnoreSingle(wireId)
+		}
+		if err != nil {
+			delete(dec.ignorerCache, wireId)
+		}
+	}
+	return
+}
+
+// decodeValue decodes the data stream representing a value and stores it in value.
+func (dec *Decoder) decodeValue(wireId typeId, value reflect.Value) {
+	defer catchError(&dec.err)
+	// If the value is nil, it means we should just ignore this item.
+	if !value.IsValid() {
+		dec.decodeIgnoredValue(wireId)
+		return
+	}
+	// Dereference down to the underlying type.
+	ut := userType(value.Type())
+	base := ut.base
+	var enginePtr **decEngine
+	enginePtr, dec.err = dec.getDecEnginePtr(wireId, ut)
+	if dec.err != nil {
+		return
+	}
+	value = decAlloc(value)
+	engine := *enginePtr
+	if st := base; st.Kind() == reflect.Struct && ut.externalDec == 0 {
+		if engine.numInstr == 0 && st.NumField() > 0 &&
+			dec.wireType[wireId] != nil && len(dec.wireType[wireId].StructT.Field) > 0 {
+			name := base.Name()
+			errorf("type mismatch: no fields matched compiling decoder for %s", name)
+		}
+		dec.decodeStruct(engine, ut, value)
+	} else {
+		dec.decodeSingle(engine, ut, value)
+	}
+}
+
+// decodeIgnoredValue decodes the data stream representing a value of the specified type and discards it.
+func (dec *Decoder) decodeIgnoredValue(wireId typeId) {
+	var enginePtr **decEngine
+	enginePtr, dec.err = dec.getIgnoreEnginePtr(wireId)
+	if dec.err != nil {
+		return
+	}
+	wire := dec.wireType[wireId]
+	if wire != nil && wire.StructT != nil {
+		dec.ignoreStruct(*enginePtr)
+	} else {
+		dec.ignoreSingle(*enginePtr)
+	}
+}
+
+func init() {
+	var iop, uop decOp
+	switch reflect.TypeOf(int(0)).Bits() {
+	case 32:
+		iop = decInt32
+		uop = decUint32
+	case 64:
+		iop = decInt64
+		uop = decUint64
+	default:
+		panic("gob: unknown size of int/uint")
+	}
+	decOpTable[reflect.Int] = iop
+	decOpTable[reflect.Uint] = uop
+
+	// Finally uintptr
+	switch reflect.TypeOf(uintptr(0)).Bits() {
+	case 32:
+		uop = decUint32
+	case 64:
+		uop = decUint64
+	default:
+		panic("gob: unknown size of uintptr")
+	}
+	decOpTable[reflect.Uintptr] = uop
+}
+
+// Gob depends on being able to take the address
+// of zeroed Values it creates, so use this wrapper instead
+// of the standard reflect.Zero.
+// Each call allocates once.
+func allocValue(t reflect.Type) reflect.Value {
+	return reflect.New(t).Elem()
+}
diff --git a/src/encoding/gob/decoder.go b/src/encoding/gob/decoder.go
new file mode 100644
index 0000000000..3a769ec125
--- /dev/null
+++ b/src/encoding/gob/decoder.go
@@ -0,0 +1,237 @@
+// 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 (
+	"bufio"
+	"bytes"
+	"errors"
+	"io"
+	"reflect"
+	"sync"
+)
+
+// A Decoder manages the receipt of type and data information read from the
+// remote side of a connection.
+type Decoder struct {
+	mutex        sync.Mutex                              // each item must be received atomically
+	r            io.Reader                               // source of the data
+	buf          bytes.Buffer                            // buffer for more efficient i/o from r
+	wireType     map[typeId]*wireType                    // map from remote ID to local description
+	decoderCache map[reflect.Type]map[typeId]**decEngine // cache of compiled engines
+	ignorerCache map[typeId]**decEngine                  // ditto for ignored objects
+	freeList     *decoderState                           // list of free decoderStates; avoids reallocation
+	countBuf     []byte                                  // used for decoding integers while parsing messages
+	tmp          []byte                                  // temporary storage for i/o; saves reallocating
+	err          error
+}
+
+// NewDecoder returns a new decoder that reads from the io.Reader.
+// If r does not also implement io.ByteReader, it will be wrapped in a
+// bufio.Reader.
+func NewDecoder(r io.Reader) *Decoder {
+	dec := new(Decoder)
+	// We use the ability to read bytes as a plausible surrogate for buffering.
+	if _, ok := r.(io.ByteReader); !ok {
+		r = bufio.NewReader(r)
+	}
+	dec.r = r
+	dec.wireType = make(map[typeId]*wireType)
+	dec.decoderCache = make(map[reflect.Type]map[typeId]**decEngine)
+	dec.ignorerCache = make(map[typeId]**decEngine)
+	dec.countBuf = make([]byte, 9) // counts may be uint64s (unlikely!), require 9 bytes
+
+	return dec
+}
+
+// recvType loads the definition of a type.
+func (dec *Decoder) recvType(id typeId) {
+	// Have we already seen this type?  That's an error
+	if id < firstUserId || dec.wireType[id] != nil {
+		dec.err = errors.New("gob: duplicate type received")
+		return
+	}
+
+	// Type:
+	wire := new(wireType)
+	dec.decodeValue(tWireType, reflect.ValueOf(wire))
+	if dec.err != nil {
+		return
+	}
+	// Remember we've seen this type.
+	dec.wireType[id] = wire
+}
+
+var errBadCount = errors.New("invalid message length")
+
+// recvMessage reads the next count-delimited item from the input. It is the converse
+// of Encoder.writeMessage. It returns false on EOF or other error reading the message.
+func (dec *Decoder) recvMessage() bool {
+	// Read a count.
+	nbytes, _, err := decodeUintReader(dec.r, dec.countBuf)
+	if err != nil {
+		dec.err = err
+		return false
+	}
+	// Upper limit of 1GB, allowing room to grow a little without overflow.
+	// TODO: We might want more control over this limit.
+	if nbytes >= 1<<30 {
+		dec.err = errBadCount
+		return false
+	}
+	dec.readMessage(int(nbytes))
+	return dec.err == nil
+}
+
+// readMessage reads the next nbytes bytes from the input.
+func (dec *Decoder) readMessage(nbytes int) {
+	// Allocate the dec.tmp buffer, up to 10KB.
+	const maxBuf = 10 * 1024
+	nTmp := nbytes
+	if nTmp > maxBuf {
+		nTmp = maxBuf
+	}
+	if cap(dec.tmp) < nTmp {
+		nAlloc := nTmp + 100 // A little extra for growth.
+		if nAlloc > maxBuf {
+			nAlloc = maxBuf
+		}
+		dec.tmp = make([]byte, nAlloc)
+	}
+	dec.tmp = dec.tmp[:nTmp]
+
+	// Read the data
+	dec.buf.Grow(nbytes)
+	for nbytes > 0 {
+		if nbytes < nTmp {
+			dec.tmp = dec.tmp[:nbytes]
+		}
+		var nRead int
+		nRead, dec.err = io.ReadFull(dec.r, dec.tmp)
+		if dec.err != nil {
+			if dec.err == io.EOF {
+				dec.err = io.ErrUnexpectedEOF
+			}
+			return
+		}
+		dec.buf.Write(dec.tmp)
+		nbytes -= nRead
+	}
+}
+
+// toInt turns an encoded uint64 into an int, according to the marshaling rules.
+func toInt(x uint64) int64 {
+	i := int64(x >> 1)
+	if x&1 != 0 {
+		i = ^i
+	}
+	return i
+}
+
+func (dec *Decoder) nextInt() int64 {
+	n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
+	if err != nil {
+		dec.err = err
+	}
+	return toInt(n)
+}
+
+func (dec *Decoder) nextUint() uint64 {
+	n, _, err := decodeUintReader(&dec.buf, dec.countBuf)
+	if err != nil {
+		dec.err = err
+	}
+	return n
+}
+
+// decodeTypeSequence parses:
+// TypeSequence
+//	(TypeDefinition DelimitedTypeDefinition*)?
+// and returns the type id of the next value.  It returns -1 at
+// EOF.  Upon return, the remainder of dec.buf is the value to be
+// decoded.  If this is an interface value, it can be ignored by
+// resetting that buffer.
+func (dec *Decoder) decodeTypeSequence(isInterface bool) typeId {
+	for dec.err == nil {
+		if dec.buf.Len() == 0 {
+			if !dec.recvMessage() {
+				break
+			}
+		}
+		// Receive a type id.
+		id := typeId(dec.nextInt())
+		if id >= 0 {
+			// Value follows.
+			return id
+		}
+		// Type definition for (-id) follows.
+		dec.recvType(-id)
+		// When decoding an interface, after a type there may be a
+		// DelimitedValue still in the buffer.  Skip its count.
+		// (Alternatively, the buffer is empty and the byte count
+		// will be absorbed by recvMessage.)
+		if dec.buf.Len() > 0 {
+			if !isInterface {
+				dec.err = errors.New("extra data in buffer")
+				break
+			}
+			dec.nextUint()
+		}
+	}
+	return -1
+}
+
+// Decode reads the next value from the input stream and stores
+// it in the data represented by the empty interface value.
+// If e is nil, the value will be discarded. Otherwise,
+// the value underlying e must be a pointer to the
+// correct type for the next data item received.
+// If the input is at EOF, Decode returns io.EOF and
+// does not modify e.
+func (dec *Decoder) Decode(e interface{}) error {
+	if e == nil {
+		return dec.DecodeValue(reflect.Value{})
+	}
+	value := reflect.ValueOf(e)
+	// If e represents a value as opposed to a pointer, the answer won't
+	// get back to the caller.  Make sure it's a pointer.
+	if value.Type().Kind() != reflect.Ptr {
+		dec.err = errors.New("gob: attempt to decode into a non-pointer")
+		return dec.err
+	}
+	return dec.DecodeValue(value)
+}
+
+// DecodeValue reads the next value from the input stream.
+// If v is the zero reflect.Value (v.Kind() == Invalid), DecodeValue discards the value.
+// Otherwise, it stores the value into v.  In that case, v must represent
+// a non-nil pointer to data or be an assignable reflect.Value (v.CanSet())
+// If the input is at EOF, DecodeValue returns io.EOF and
+// does not modify e.
+func (dec *Decoder) DecodeValue(v reflect.Value) error {
+	if v.IsValid() {
+		if v.Kind() == reflect.Ptr && !v.IsNil() {
+			// That's okay, we'll store through the pointer.
+		} else if !v.CanSet() {
+			return errors.New("gob: DecodeValue of unassignable value")
+		}
+	}
+	// Make sure we're single-threaded through here.
+	dec.mutex.Lock()
+	defer dec.mutex.Unlock()
+
+	dec.buf.Reset() // In case data lingers from previous invocation.
+	dec.err = nil
+	id := dec.decodeTypeSequence(false)
+	if dec.err == nil {
+		dec.decodeValue(id, v)
+	}
+	return dec.err
+}
+
+// If debug.go is compiled into the program , debugFunc prints a human-readable
+// representation of the gob data read from r by calling that file's Debug function.
+// Otherwise it is nil.
+var debugFunc func(io.Reader)
diff --git a/src/encoding/gob/doc.go b/src/encoding/gob/doc.go
new file mode 100644
index 0000000000..d0acaba1ad
--- /dev/null
+++ b/src/encoding/gob/doc.go
@@ -0,0 +1,386 @@
+// 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 manages streams of gobs - binary values exchanged between an
+Encoder (transmitter) and a Decoder (receiver).  A typical use is transporting
+arguments and results of remote procedure calls (RPCs) such as those provided by
+package "rpc".
+
+The implementation compiles a custom codec for each data type in the stream and
+is most efficient when a single Encoder is used to transmit a stream of values,
+amortizing the cost of compilation.
+
+Basics
+
+A stream of gobs is self-describing.  Each data item in the stream is preceded by
+a specification of its type, expressed in terms of a small set of predefined
+types.  Pointers are not transmitted, but the things they point to are
+transmitted; that is, the values are flattened.  Recursive types work fine, but
+recursive values (data with cycles) are problematic.  This may change.
+
+To use gobs, create an Encoder and present it with a series of data items as
+values or addresses that can be dereferenced to values.  The Encoder makes sure
+all type information is sent before it is needed.  At the receive side, a
+Decoder retrieves values from the encoded stream and unpacks them into local
+variables.
+
+Types and Values
+
+The source and destination values/types need not correspond exactly.  For structs,
+fields (identified by name) that are in the source but absent from the receiving
+variable will be ignored.  Fields that are in the receiving variable but missing
+from the transmitted type or value will be ignored in the destination.  If a field
+with the same name is present in both, their types must be compatible. Both the
+receiver and transmitter will do all necessary indirection and dereferencing to
+convert between gobs and actual Go values.  For instance, a gob type that is
+schematically,
+
+	struct { A, B int }
+
+can be sent from or received into any of these Go types:
+
+	struct { A, B int }	// the same
+	*struct { A, B int }	// extra indirection of the struct
+	struct { *A, **B int }	// extra indirection of the fields
+	struct { A, B int64 }	// different concrete value type; see below
+
+It may also be received into any of these:
+
+	struct { A, B int }	// the same
+	struct { B, A int }	// ordering doesn't matter; matching is by name
+	struct { A, B, C int }	// extra field (C) ignored
+	struct { B int }	// missing field (A) ignored; data will be dropped
+	struct { B, C int }	// missing field (A) ignored; extra field (C) ignored.
+
+Attempting to receive into these types will draw a decode error:
+
+	struct { A int; B uint }	// change of signedness for B
+	struct { A int; B float }	// change of type for B
+	struct { }			// no field names in common
+	struct { C, D int }		// no field names in common
+
+Integers are transmitted two ways: arbitrary precision signed integers or
+arbitrary precision unsigned integers.  There is no int8, int16 etc.
+discrimination in the gob format; there are only signed and unsigned integers.  As
+described below, the transmitter sends the value in a variable-length encoding;
+the receiver accepts the value and stores it in the destination variable.
+Floating-point numbers are always sent using IEEE-754 64-bit precision (see
+below).
+
+Signed integers may be received into any signed integer variable: int, int16, etc.;
+unsigned integers may be received into any unsigned integer variable; and floating
+point values may be received into any floating point variable.  However,
+the destination variable must be able to represent the value or the decode
+operation will fail.
+
+Structs, arrays and slices are also supported. Structs encode and decode only
+exported fields. Strings and arrays of bytes are supported with a special,
+efficient representation (see below). When a slice is decoded, if the existing
+slice has capacity the slice will be extended in place; if not, a new array is
+allocated. Regardless, the length of the resulting slice reports the number of
+elements decoded.
+
+Functions and channels will not be sent in a gob. Attempting to encode such a value
+at top the level will fail. A struct field of chan or func type is treated exactly
+like an unexported field and is ignored.
+
+Gob can encode a value of any type implementing the GobEncoder or
+encoding.BinaryMarshaler interfaces by calling the corresponding method,
+in that order of preference.
+
+Gob can decode a value of any type implementing the GobDecoder or
+encoding.BinaryUnmarshaler interfaces by calling the corresponding method,
+again in that order of preference.
+
+Encoding Details
+
+This section documents the encoding, details that are not important for most
+users. Details are presented bottom-up.
+
+An unsigned integer is sent one of two ways.  If it is less than 128, it is sent
+as a byte with that value.  Otherwise it is sent as a minimal-length big-endian
+(high byte first) byte stream holding the value, preceded by one byte holding the
+byte count, negated.  Thus 0 is transmitted as (00), 7 is transmitted as (07) and
+256 is transmitted as (FE 01 00).
+
+A boolean is encoded within an unsigned integer: 0 for false, 1 for true.
+
+A signed integer, i, is encoded within an unsigned integer, u.  Within u, bits 1
+upward contain the value; bit 0 says whether they should be complemented upon
+receipt.  The encode algorithm looks like this:
+
+	uint u;
+	if i < 0 {
+		u = (^i << 1) | 1	// complement i, bit 0 is 1
+	} else {
+		u = (i << 1)	// do not complement i, bit 0 is 0
+	}
+	encodeUnsigned(u)
+
+The low bit is therefore analogous to a sign bit, but making it the complement bit
+instead guarantees that the largest negative integer is not a special case.  For
+example, -129=^128=(^256>>1) encodes as (FE 01 01).
+
+Floating-point numbers are always sent as a representation of a float64 value.
+That value is converted to a uint64 using math.Float64bits.  The uint64 is then
+byte-reversed and sent as a regular unsigned integer.  The byte-reversal means the
+exponent and high-precision part of the mantissa go first.  Since the low bits are
+often zero, this can save encoding bytes.  For instance, 17.0 is encoded in only
+three bytes (FE 31 40).
+
+Strings and slices of bytes are sent as an unsigned count followed by that many
+uninterpreted bytes of the value.
+
+All other slices and arrays are sent as an unsigned count followed by that many
+elements using the standard gob encoding for their type, recursively.
+
+Maps are sent as an unsigned count followed by that many key, element
+pairs. Empty but non-nil maps are sent, so if the sender has allocated
+a map, the receiver will allocate a map even if no elements are
+transmitted.
+
+Structs are sent as a sequence of (field number, field value) pairs.  The field
+value is sent using the standard gob encoding for its type, recursively.  If a
+field has the zero value for its type, it is omitted from the transmission.  The
+field number is defined by the type of the encoded struct: the first field of the
+encoded type is field 0, the second is field 1, etc.  When encoding a value, the
+field numbers are delta encoded for efficiency and the fields are always sent in
+order of increasing field number; the deltas are therefore unsigned.  The
+initialization for the delta encoding sets the field number to -1, so an unsigned
+integer field 0 with value 7 is transmitted as unsigned delta = 1, unsigned value
+= 7 or (01 07).  Finally, after all the fields have been sent a terminating mark
+denotes the end of the struct.  That mark is a delta=0 value, which has
+representation (00).
+
+Interface types are not checked for compatibility; all interface types are
+treated, for transmission, as members of a single "interface" type, analogous to
+int or []byte - in effect they're all treated as interface{}.  Interface values
+are transmitted as a string identifying the concrete type being sent (a name
+that must be pre-defined by calling Register), followed by a byte count of the
+length of the following data (so the value can be skipped if it cannot be
+stored), followed by the usual encoding of concrete (dynamic) value stored in
+the interface value.  (A nil interface value is identified by the empty string
+and transmits no value.) Upon receipt, the decoder verifies that the unpacked
+concrete item satisfies the interface of the receiving variable.
+
+The representation of types is described below.  When a type is defined on a given
+connection between an Encoder and Decoder, it is assigned a signed integer type
+id.  When Encoder.Encode(v) is called, it makes sure there is an id assigned for
+the type of v and all its elements and then it sends the pair (typeid, encoded-v)
+where typeid is the type id of the encoded type of v and encoded-v is the gob
+encoding of the value v.
+
+To define a type, the encoder chooses an unused, positive type id and sends the
+pair (-type id, encoded-type) where encoded-type is the gob encoding of a wireType
+description, constructed from these types:
+
+	type wireType struct {
+		ArrayT  *ArrayType
+		SliceT  *SliceType
+		StructT *StructType
+		MapT    *MapType
+	}
+	type arrayType struct {
+		CommonType
+		Elem typeId
+		Len  int
+	}
+	type CommonType struct {
+		Name string // the name of the struct type
+		Id  int    // the id of the type, repeated so it's inside the type
+	}
+	type sliceType struct {
+		CommonType
+		Elem typeId
+	}
+	type structType struct {
+		CommonType
+		Field []*fieldType // the fields of the struct.
+	}
+	type fieldType struct {
+		Name string // the name of the field.
+		Id   int    // the type id of the field, which must be already defined
+	}
+	type mapType struct {
+		CommonType
+		Key  typeId
+		Elem typeId
+	}
+
+If there are nested type ids, the types for all inner type ids must be defined
+before the top-level type id is used to describe an encoded-v.
+
+For simplicity in setup, the connection is defined to understand these types a
+priori, as well as the basic gob types int, uint, etc.  Their ids are:
+
+	bool        1
+	int         2
+	uint        3
+	float       4
+	[]byte      5
+	string      6
+	complex     7
+	interface   8
+	// gap for reserved ids.
+	WireType    16
+	ArrayType   17
+	CommonType  18
+	SliceType   19
+	StructType  20
+	FieldType   21
+	// 22 is slice of fieldType.
+	MapType     23
+
+Finally, each message created by a call to Encode is preceded by an encoded
+unsigned integer count of the number of bytes remaining in the message.  After
+the initial type name, interface values are wrapped the same way; in effect, the
+interface value acts like a recursive invocation of Encode.
+
+In summary, a gob stream looks like
+
+	(byteCount (-type id, encoding of a wireType)* (type id, encoding of a value))*
+
+where * signifies zero or more repetitions and the type id of a value must
+be predefined or be defined before the value in the stream.
+
+See "Gobs of data" for a design discussion of the gob wire format:
+http://golang.org/doc/articles/gobs_of_data.html
+*/
+package gob
+
+/*
+Grammar:
+
+Tokens starting with a lower case letter are terminals; int(n)
+and uint(n) represent the signed/unsigned encodings of the value n.
+
+GobStream:
+	DelimitedMessage*
+DelimitedMessage:
+	uint(lengthOfMessage) Message
+Message:
+	TypeSequence TypedValue
+TypeSequence
+	(TypeDefinition DelimitedTypeDefinition*)?
+DelimitedTypeDefinition:
+	uint(lengthOfTypeDefinition) TypeDefinition
+TypedValue:
+	int(typeId) Value
+TypeDefinition:
+	int(-typeId) encodingOfWireType
+Value:
+	SingletonValue | StructValue
+SingletonValue:
+	uint(0) FieldValue
+FieldValue:
+	builtinValue | ArrayValue | MapValue | SliceValue | StructValue | InterfaceValue
+InterfaceValue:
+	NilInterfaceValue | NonNilInterfaceValue
+NilInterfaceValue:
+	uint(0)
+NonNilInterfaceValue:
+	ConcreteTypeName TypeSequence InterfaceContents
+ConcreteTypeName:
+	uint(lengthOfName) [already read=n] name
+InterfaceContents:
+	int(concreteTypeId) DelimitedValue
+DelimitedValue:
+	uint(length) Value
+ArrayValue:
+	uint(n) FieldValue*n [n elements]
+MapValue:
+	uint(n) (FieldValue FieldValue)*n  [n (key, value) pairs]
+SliceValue:
+	uint(n) FieldValue*n [n elements]
+StructValue:
+	(uint(fieldDelta) FieldValue)*
+*/
+
+/*
+For implementers and the curious, here is an encoded example.  Given
+	type Point struct {X, Y int}
+and the value
+	p := Point{22, 33}
+the bytes transmitted that encode p will be:
+	1f ff 81 03 01 01 05 50 6f 69 6e 74 01 ff 82 00
+	01 02 01 01 58 01 04 00 01 01 59 01 04 00 00 00
+	07 ff 82 01 2c 01 42 00
+They are determined as follows.
+
+Since this is the first transmission of type Point, the type descriptor
+for Point itself must be sent before the value.  This is the first type
+we've sent on this Encoder, so it has type id 65 (0 through 64 are
+reserved).
+
+	1f	// This item (a type descriptor) is 31 bytes long.
+	ff 81	// The negative of the id for the type we're defining, -65.
+		// This is one byte (indicated by FF = -1) followed by
+		// ^-65<<1 | 1.  The low 1 bit signals to complement the
+		// rest upon receipt.
+
+	// Now we send a type descriptor, which is itself a struct (wireType).
+	// The type of wireType itself is known (it's built in, as is the type of
+	// all its components), so we just need to send a *value* of type wireType
+	// that represents type "Point".
+	// Here starts the encoding of that value.
+	// Set the field number implicitly to -1; this is done at the beginning
+	// of every struct, including nested structs.
+	03	// Add 3 to field number; now 2 (wireType.structType; this is a struct).
+		// structType starts with an embedded CommonType, which appears
+		// as a regular structure here too.
+	01	// add 1 to field number (now 0); start of embedded CommonType.
+	01	// add 1 to field number (now 0, the name of the type)
+	05	// string is (unsigned) 5 bytes long
+	50 6f 69 6e 74	// wireType.structType.CommonType.name = "Point"
+	01	// add 1 to field number (now 1, the id of the type)
+	ff 82	// wireType.structType.CommonType._id = 65
+	00	// end of embedded wiretype.structType.CommonType struct
+	01	// add 1 to field number (now 1, the field array in wireType.structType)
+	02	// There are two fields in the type (len(structType.field))
+	01	// Start of first field structure; add 1 to get field number 0: field[0].name
+	01	// 1 byte
+	58	// structType.field[0].name = "X"
+	01	// Add 1 to get field number 1: field[0].id
+	04	// structType.field[0].typeId is 2 (signed int).
+	00	// End of structType.field[0]; start structType.field[1]; set field number to -1.
+	01	// Add 1 to get field number 0: field[1].name
+	01	// 1 byte
+	59	// structType.field[1].name = "Y"
+	01	// Add 1 to get field number 1: field[1].id
+	04	// struct.Type.field[1].typeId is 2 (signed int).
+	00	// End of structType.field[1]; end of structType.field.
+	00	// end of wireType.structType structure
+	00	// end of wireType structure
+
+Now we can send the Point value.  Again the field number resets to -1:
+
+	07	// this value is 7 bytes long
+	ff 82	// the type number, 65 (1 byte (-FF) followed by 65<<1)
+	01	// add one to field number, yielding field 0
+	2c	// encoding of signed "22" (0x22 = 44 = 22<<1); Point.x = 22
+	01	// add one to field number, yielding field 1
+	42	// encoding of signed "33" (0x42 = 66 = 33<<1); Point.y = 33
+	00	// end of structure
+
+The type encoding is long and fairly intricate but we send it only once.
+If p is transmitted a second time, the type is already known so the
+output will be just:
+
+	07 ff 82 01 2c 01 42 00
+
+A single non-struct value at top level is transmitted like a field with
+delta tag 0.  For instance, a signed integer with value 3 presented as
+the argument to Encode will emit:
+
+	03 04 00 06
+
+Which represents:
+
+	03	// this value is 3 bytes long
+	04	// the type number, 2, represents an integer
+	00	// tag delta 0
+	06	// value 3
+
+*/
diff --git a/src/encoding/gob/dump.go b/src/encoding/gob/dump.go
new file mode 100644
index 0000000000..17238c98df
--- /dev/null
+++ b/src/encoding/gob/dump.go
@@ -0,0 +1,29 @@
+// 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.
+
+// +build ignore
+
+package main
+
+// Need to compile package gob with debug.go to build this program.
+// See comments in debug.go for how to do this.
+
+import (
+	"encoding/gob"
+	"fmt"
+	"os"
+)
+
+func main() {
+	var err error
+	file := os.Stdin
+	if len(os.Args) > 1 {
+		file, err = os.Open(os.Args[1])
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "dump: %s\n", err)
+			os.Exit(1)
+		}
+	}
+	gob.Debug(file)
+}
diff --git a/src/encoding/gob/encode.go b/src/encoding/gob/encode.go
new file mode 100644
index 0000000000..5d35db20e6
--- /dev/null
+++ b/src/encoding/gob/encode.go
@@ -0,0 +1,661 @@
+// 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 (
+	"bytes"
+	"encoding"
+	"math"
+	"reflect"
+)
+
+const uint64Size = 8
+
+// encoderState is the global execution state of an instance of the encoder.
+// Field numbers are delta encoded and always increase. The field
+// number is initialized to -1 so 0 comes out as delta(1). A delta of
+// 0 terminates the structure.
+type encoderState struct {
+	enc      *Encoder
+	b        *bytes.Buffer
+	sendZero bool                 // encoding an array element or map key/value pair; send zero values
+	fieldnum int                  // the last field number written.
+	buf      [1 + uint64Size]byte // buffer used by the encoder; here to avoid allocation.
+	next     *encoderState        // for free list
+}
+
+func (enc *Encoder) newEncoderState(b *bytes.Buffer) *encoderState {
+	e := enc.freeList
+	if e == nil {
+		e = new(encoderState)
+		e.enc = enc
+	} else {
+		enc.freeList = e.next
+	}
+	e.sendZero = false
+	e.fieldnum = 0
+	e.b = b
+	return e
+}
+
+func (enc *Encoder) freeEncoderState(e *encoderState) {
+	e.next = enc.freeList
+	enc.freeList = e
+}
+
+// Unsigned integers have a two-state encoding.  If the number is less
+// than 128 (0 through 0x7F), its value is written directly.
+// Otherwise the value is written in big-endian byte order preceded
+// by the byte length, negated.
+
+// encodeUint writes an encoded unsigned integer to state.b.
+func (state *encoderState) encodeUint(x uint64) {
+	if x <= 0x7F {
+		err := state.b.WriteByte(uint8(x))
+		if err != nil {
+			error_(err)
+		}
+		return
+	}
+	i := uint64Size
+	for x > 0 {
+		state.buf[i] = uint8(x)
+		x >>= 8
+		i--
+	}
+	state.buf[i] = uint8(i - uint64Size) // = loop count, negated
+	_, err := state.b.Write(state.buf[i : uint64Size+1])
+	if err != nil {
+		error_(err)
+	}
+}
+
+// encodeInt writes an encoded signed integer to state.w.
+// The low bit of the encoding says whether to bit complement the (other bits of the)
+// uint to recover the int.
+func (state *encoderState) encodeInt(i int64) {
+	var x uint64
+	if i < 0 {
+		x = uint64(^i<<1) | 1
+	} else {
+		x = uint64(i << 1)
+	}
+	state.encodeUint(uint64(x))
+}
+
+// encOp is the signature of an encoding operator for a given type.
+type encOp func(i *encInstr, state *encoderState, v reflect.Value)
+
+// The 'instructions' of the encoding machine
+type encInstr struct {
+	op    encOp
+	field int   // field number in input
+	index []int // struct index
+	indir int   // how many pointer indirections to reach the value in the struct
+}
+
+// update emits a field number and updates the state to record its value for delta encoding.
+// If the instruction pointer is nil, it does nothing
+func (state *encoderState) update(instr *encInstr) {
+	if instr != nil {
+		state.encodeUint(uint64(instr.field - state.fieldnum))
+		state.fieldnum = instr.field
+	}
+}
+
+// Each encoder for a composite is responsible for handling any
+// indirections associated with the elements of the data structure.
+// If any pointer so reached is nil, no bytes are written.  If the
+// data item is zero, no bytes are written.  Single values - ints,
+// strings etc. - are indirected before calling their encoders.
+// Otherwise, the output (for a scalar) is the field number, as an
+// encoded integer, followed by the field data in its appropriate
+// format.
+
+// encIndirect dereferences pv indir times and returns the result.
+func encIndirect(pv reflect.Value, indir int) reflect.Value {
+	for ; indir > 0; indir-- {
+		if pv.IsNil() {
+			break
+		}
+		pv = pv.Elem()
+	}
+	return pv
+}
+
+// encBool encodes the bool referenced by v as an unsigned 0 or 1.
+func encBool(i *encInstr, state *encoderState, v reflect.Value) {
+	b := v.Bool()
+	if b || state.sendZero {
+		state.update(i)
+		if b {
+			state.encodeUint(1)
+		} else {
+			state.encodeUint(0)
+		}
+	}
+}
+
+// encInt encodes the signed integer (int int8 int16 int32 int64) referenced by v.
+func encInt(i *encInstr, state *encoderState, v reflect.Value) {
+	value := v.Int()
+	if value != 0 || state.sendZero {
+		state.update(i)
+		state.encodeInt(value)
+	}
+}
+
+// encUint encodes the unsigned integer (uint uint8 uint16 uint32 uint64 uintptr) referenced by v.
+func encUint(i *encInstr, state *encoderState, v reflect.Value) {
+	value := v.Uint()
+	if value != 0 || state.sendZero {
+		state.update(i)
+		state.encodeUint(value)
+	}
+}
+
+// floatBits returns a uint64 holding the bits of a floating-point number.
+// Floating-point numbers are transmitted as uint64s holding the bits
+// of the underlying representation.  They are sent byte-reversed, with
+// the exponent end coming out first, so integer floating point numbers
+// (for example) transmit more compactly.  This routine does the
+// swizzling.
+func floatBits(f float64) uint64 {
+	u := math.Float64bits(f)
+	var v uint64
+	for i := 0; i < 8; i++ {
+		v <<= 8
+		v |= u & 0xFF
+		u >>= 8
+	}
+	return v
+}
+
+// encFloat encodes the floating point value (float32 float64) referenced by v.
+func encFloat(i *encInstr, state *encoderState, v reflect.Value) {
+	f := v.Float()
+	if f != 0 || state.sendZero {
+		bits := floatBits(f)
+		state.update(i)
+		state.encodeUint(bits)
+	}
+}
+
+// encComplex encodes the complex value (complex64 complex128) referenced by v.
+// Complex numbers are just a pair of floating-point numbers, real part first.
+func encComplex(i *encInstr, state *encoderState, v reflect.Value) {
+	c := v.Complex()
+	if c != 0+0i || state.sendZero {
+		rpart := floatBits(real(c))
+		ipart := floatBits(imag(c))
+		state.update(i)
+		state.encodeUint(rpart)
+		state.encodeUint(ipart)
+	}
+}
+
+// encUint8Array encodes the byte array referenced by v.
+// Byte arrays are encoded as an unsigned count followed by the raw bytes.
+func encUint8Array(i *encInstr, state *encoderState, v reflect.Value) {
+	b := v.Bytes()
+	if len(b) > 0 || state.sendZero {
+		state.update(i)
+		state.encodeUint(uint64(len(b)))
+		state.b.Write(b)
+	}
+}
+
+// encString encodes the string referenced by v.
+// Strings are encoded as an unsigned count followed by the raw bytes.
+func encString(i *encInstr, state *encoderState, v reflect.Value) {
+	s := v.String()
+	if len(s) > 0 || state.sendZero {
+		state.update(i)
+		state.encodeUint(uint64(len(s)))
+		state.b.WriteString(s)
+	}
+}
+
+// encStructTerminator encodes the end of an encoded struct
+// as delta field number of 0.
+func encStructTerminator(i *encInstr, state *encoderState, v reflect.Value) {
+	state.encodeUint(0)
+}
+
+// Execution engine
+
+// encEngine an array of instructions indexed by field number of the encoding
+// data, typically a struct.  It is executed top to bottom, walking the struct.
+type encEngine struct {
+	instr []encInstr
+}
+
+const singletonField = 0
+
+// valid reports whether the value is valid and a non-nil pointer.
+// (Slices, maps, and chans take care of themselves.)
+func valid(v reflect.Value) bool {
+	switch v.Kind() {
+	case reflect.Invalid:
+		return false
+	case reflect.Ptr:
+		return !v.IsNil()
+	}
+	return true
+}
+
+// encodeSingle encodes a single top-level non-struct value.
+func (enc *Encoder) encodeSingle(b *bytes.Buffer, engine *encEngine, value reflect.Value) {
+	state := enc.newEncoderState(b)
+	defer enc.freeEncoderState(state)
+	state.fieldnum = singletonField
+	// There is no surrounding struct to frame the transmission, so we must
+	// generate data even if the item is zero.  To do this, set sendZero.
+	state.sendZero = true
+	instr := &engine.instr[singletonField]
+	if instr.indir > 0 {
+		value = encIndirect(value, instr.indir)
+	}
+	if valid(value) {
+		instr.op(instr, state, value)
+	}
+}
+
+// encodeStruct encodes a single struct value.
+func (enc *Encoder) encodeStruct(b *bytes.Buffer, engine *encEngine, value reflect.Value) {
+	if !valid(value) {
+		return
+	}
+	state := enc.newEncoderState(b)
+	defer enc.freeEncoderState(state)
+	state.fieldnum = -1
+	for i := 0; i < len(engine.instr); i++ {
+		instr := &engine.instr[i]
+		if i >= value.NumField() {
+			// encStructTerminator
+			instr.op(instr, state, reflect.Value{})
+			break
+		}
+		field := value.FieldByIndex(instr.index)
+		if instr.indir > 0 {
+			field = encIndirect(field, instr.indir)
+		}
+		if !valid(field) {
+			continue
+		}
+		instr.op(instr, state, field)
+	}
+}
+
+// encodeArray encodes the array whose 0th element is at p.
+func (enc *Encoder) encodeArray(b *bytes.Buffer, value reflect.Value, op encOp, elemIndir int, length int) {
+	state := enc.newEncoderState(b)
+	defer enc.freeEncoderState(state)
+	state.fieldnum = -1
+	state.sendZero = true
+	state.encodeUint(uint64(length))
+	for i := 0; i < length; i++ {
+		elem := value.Index(i)
+		if elemIndir > 0 {
+			elem = encIndirect(elem, elemIndir)
+			if !valid(elem) {
+				errorf("encodeArray: nil element")
+			}
+		}
+		op(nil, state, elem)
+	}
+}
+
+// encodeReflectValue is a helper for maps. It encodes the value v.
+func encodeReflectValue(state *encoderState, v reflect.Value, op encOp, indir int) {
+	for i := 0; i < indir && v.IsValid(); i++ {
+		v = reflect.Indirect(v)
+	}
+	if !v.IsValid() {
+		errorf("encodeReflectValue: nil element")
+	}
+	op(nil, state, v)
+}
+
+// encodeMap encodes a map as unsigned count followed by key:value pairs.
+func (enc *Encoder) encodeMap(b *bytes.Buffer, mv reflect.Value, keyOp, elemOp encOp, keyIndir, elemIndir int) {
+	state := enc.newEncoderState(b)
+	state.fieldnum = -1
+	state.sendZero = true
+	keys := mv.MapKeys()
+	state.encodeUint(uint64(len(keys)))
+	for _, key := range keys {
+		encodeReflectValue(state, key, keyOp, keyIndir)
+		encodeReflectValue(state, mv.MapIndex(key), elemOp, elemIndir)
+	}
+	enc.freeEncoderState(state)
+}
+
+// encodeInterface encodes the interface value iv.
+// To send an interface, we send a string identifying the concrete type, followed
+// by the type identifier (which might require defining that type right now), followed
+// by the concrete value.  A nil value gets sent as the empty string for the name,
+// followed by no value.
+func (enc *Encoder) encodeInterface(b *bytes.Buffer, iv reflect.Value) {
+	// Gobs can encode nil interface values but not typed interface
+	// values holding nil pointers, since nil pointers point to no value.
+	elem := iv.Elem()
+	if elem.Kind() == reflect.Ptr && elem.IsNil() {
+		errorf("gob: cannot encode nil pointer of type %s inside interface", iv.Elem().Type())
+	}
+	state := enc.newEncoderState(b)
+	state.fieldnum = -1
+	state.sendZero = true
+	if iv.IsNil() {
+		state.encodeUint(0)
+		return
+	}
+
+	ut := userType(iv.Elem().Type())
+	registerLock.RLock()
+	name, ok := concreteTypeToName[ut.base]
+	registerLock.RUnlock()
+	if !ok {
+		errorf("type not registered for interface: %s", ut.base)
+	}
+	// Send the name.
+	state.encodeUint(uint64(len(name)))
+	_, err := state.b.WriteString(name)
+	if err != nil {
+		error_(err)
+	}
+	// Define the type id if necessary.
+	enc.sendTypeDescriptor(enc.writer(), state, ut)
+	// Send the type id.
+	enc.sendTypeId(state, ut)
+	// Encode the value into a new buffer.  Any nested type definitions
+	// should be written to b, before the encoded value.
+	enc.pushWriter(b)
+	data := new(bytes.Buffer)
+	data.Write(spaceForLength)
+	enc.encode(data, elem, ut)
+	if enc.err != nil {
+		error_(enc.err)
+	}
+	enc.popWriter()
+	enc.writeMessage(b, data)
+	if enc.err != nil {
+		error_(err)
+	}
+	enc.freeEncoderState(state)
+}
+
+// isZero reports whether the value is the zero of its type.
+func isZero(val reflect.Value) bool {
+	switch val.Kind() {
+	case reflect.Array:
+		for i := 0; i < val.Len(); i++ {
+			if !isZero(val.Index(i)) {
+				return false
+			}
+		}
+		return true
+	case reflect.Map, reflect.Slice, reflect.String:
+		return val.Len() == 0
+	case reflect.Bool:
+		return !val.Bool()
+	case reflect.Complex64, reflect.Complex128:
+		return val.Complex() == 0
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Ptr:
+		return val.IsNil()
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return val.Int() == 0
+	case reflect.Float32, reflect.Float64:
+		return val.Float() == 0
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return val.Uint() == 0
+	case reflect.Struct:
+		for i := 0; i < val.NumField(); i++ {
+			if !isZero(val.Field(i)) {
+				return false
+			}
+		}
+		return true
+	}
+	panic("unknown type in isZero " + val.Type().String())
+}
+
+// encGobEncoder encodes a value that implements the GobEncoder interface.
+// The data is sent as a byte array.
+func (enc *Encoder) encodeGobEncoder(b *bytes.Buffer, ut *userTypeInfo, v reflect.Value) {
+	// TODO: should we catch panics from the called method?
+
+	var data []byte
+	var err error
+	// We know it's one of these.
+	switch ut.externalEnc {
+	case xGob:
+		data, err = v.Interface().(GobEncoder).GobEncode()
+	case xBinary:
+		data, err = v.Interface().(encoding.BinaryMarshaler).MarshalBinary()
+	case xText:
+		data, err = v.Interface().(encoding.TextMarshaler).MarshalText()
+	}
+	if err != nil {
+		error_(err)
+	}
+	state := enc.newEncoderState(b)
+	state.fieldnum = -1
+	state.encodeUint(uint64(len(data)))
+	state.b.Write(data)
+	enc.freeEncoderState(state)
+}
+
+var encOpTable = [...]encOp{
+	reflect.Bool:       encBool,
+	reflect.Int:        encInt,
+	reflect.Int8:       encInt,
+	reflect.Int16:      encInt,
+	reflect.Int32:      encInt,
+	reflect.Int64:      encInt,
+	reflect.Uint:       encUint,
+	reflect.Uint8:      encUint,
+	reflect.Uint16:     encUint,
+	reflect.Uint32:     encUint,
+	reflect.Uint64:     encUint,
+	reflect.Uintptr:    encUint,
+	reflect.Float32:    encFloat,
+	reflect.Float64:    encFloat,
+	reflect.Complex64:  encComplex,
+	reflect.Complex128: encComplex,
+	reflect.String:     encString,
+}
+
+// encOpFor returns (a pointer to) the encoding op for the base type under rt and
+// the indirection count to reach it.
+func encOpFor(rt reflect.Type, inProgress map[reflect.Type]*encOp) (*encOp, int) {
+	ut := userType(rt)
+	// If the type implements GobEncoder, we handle it without further processing.
+	if ut.externalEnc != 0 {
+		return gobEncodeOpFor(ut)
+	}
+	// If this type is already in progress, it's a recursive type (e.g. map[string]*T).
+	// Return the pointer to the op we're already building.
+	if opPtr := inProgress[rt]; opPtr != nil {
+		return opPtr, ut.indir
+	}
+	typ := ut.base
+	indir := ut.indir
+	k := typ.Kind()
+	var op encOp
+	if int(k) < len(encOpTable) {
+		op = encOpTable[k]
+	}
+	if op == nil {
+		inProgress[rt] = &op
+		// Special cases
+		switch t := typ; t.Kind() {
+		case reflect.Slice:
+			if t.Elem().Kind() == reflect.Uint8 {
+				op = encUint8Array
+				break
+			}
+			// Slices have a header; we decode it to find the underlying array.
+			elemOp, elemIndir := encOpFor(t.Elem(), inProgress)
+			op = func(i *encInstr, state *encoderState, slice reflect.Value) {
+				if !state.sendZero && slice.Len() == 0 {
+					return
+				}
+				state.update(i)
+				state.enc.encodeArray(state.b, slice, *elemOp, elemIndir, slice.Len())
+			}
+		case reflect.Array:
+			// True arrays have size in the type.
+			elemOp, elemIndir := encOpFor(t.Elem(), inProgress)
+			op = func(i *encInstr, state *encoderState, array reflect.Value) {
+				state.update(i)
+				state.enc.encodeArray(state.b, array, *elemOp, elemIndir, array.Len())
+			}
+		case reflect.Map:
+			keyOp, keyIndir := encOpFor(t.Key(), inProgress)
+			elemOp, elemIndir := encOpFor(t.Elem(), inProgress)
+			op = func(i *encInstr, state *encoderState, mv reflect.Value) {
+				// We send zero-length (but non-nil) maps because the
+				// receiver might want to use the map.  (Maps don't use append.)
+				if !state.sendZero && mv.IsNil() {
+					return
+				}
+				state.update(i)
+				state.enc.encodeMap(state.b, mv, *keyOp, *elemOp, keyIndir, elemIndir)
+			}
+		case reflect.Struct:
+			// Generate a closure that calls out to the engine for the nested type.
+			getEncEngine(userType(typ))
+			info := mustGetTypeInfo(typ)
+			op = func(i *encInstr, state *encoderState, sv reflect.Value) {
+				state.update(i)
+				// indirect through info to delay evaluation for recursive structs
+				state.enc.encodeStruct(state.b, info.encoder, sv)
+			}
+		case reflect.Interface:
+			op = func(i *encInstr, state *encoderState, iv reflect.Value) {
+				if !state.sendZero && (!iv.IsValid() || iv.IsNil()) {
+					return
+				}
+				state.update(i)
+				state.enc.encodeInterface(state.b, iv)
+			}
+		}
+	}
+	if op == nil {
+		errorf("can't happen: encode type %s", rt)
+	}
+	return &op, indir
+}
+
+// gobEncodeOpFor returns the op for a type that is known to implement GobEncoder.
+func gobEncodeOpFor(ut *userTypeInfo) (*encOp, int) {
+	rt := ut.user
+	if ut.encIndir == -1 {
+		rt = reflect.PtrTo(rt)
+	} else if ut.encIndir > 0 {
+		for i := int8(0); i < ut.encIndir; i++ {
+			rt = rt.Elem()
+		}
+	}
+	var op encOp
+	op = func(i *encInstr, state *encoderState, v reflect.Value) {
+		if ut.encIndir == -1 {
+			// Need to climb up one level to turn value into pointer.
+			if !v.CanAddr() {
+				errorf("unaddressable value of type %s", rt)
+			}
+			v = v.Addr()
+		}
+		if !state.sendZero && isZero(v) {
+			return
+		}
+		state.update(i)
+		state.enc.encodeGobEncoder(state.b, ut, v)
+	}
+	return &op, int(ut.encIndir) // encIndir: op will get called with p == address of receiver.
+}
+
+// compileEnc returns the engine to compile the type.
+func compileEnc(ut *userTypeInfo) *encEngine {
+	srt := ut.base
+	engine := new(encEngine)
+	seen := make(map[reflect.Type]*encOp)
+	rt := ut.base
+	if ut.externalEnc != 0 {
+		rt = ut.user
+	}
+	if ut.externalEnc == 0 && srt.Kind() == reflect.Struct {
+		for fieldNum, wireFieldNum := 0, 0; fieldNum < srt.NumField(); fieldNum++ {
+			f := srt.Field(fieldNum)
+			if !isSent(&f) {
+				continue
+			}
+			op, indir := encOpFor(f.Type, seen)
+			engine.instr = append(engine.instr, encInstr{*op, wireFieldNum, f.Index, indir})
+			wireFieldNum++
+		}
+		if srt.NumField() > 0 && len(engine.instr) == 0 {
+			errorf("type %s has no exported fields", rt)
+		}
+		engine.instr = append(engine.instr, encInstr{encStructTerminator, 0, nil, 0})
+	} else {
+		engine.instr = make([]encInstr, 1)
+		op, indir := encOpFor(rt, seen)
+		engine.instr[0] = encInstr{*op, singletonField, nil, indir}
+	}
+	return engine
+}
+
+// getEncEngine returns the engine to compile the type.
+// typeLock must be held (or we're in initialization and guaranteed single-threaded).
+func getEncEngine(ut *userTypeInfo) *encEngine {
+	info, err1 := getTypeInfo(ut)
+	if err1 != nil {
+		error_(err1)
+	}
+	if info.encoder == nil {
+		// Assign the encEngine now, so recursive types work correctly. But...
+		info.encoder = new(encEngine)
+		// ... if we fail to complete building the engine, don't cache the half-built machine.
+		// Doing this here means we won't cache a type that is itself OK but
+		// that contains a nested type that won't compile. The result is consistent
+		// error behavior when Encode is called multiple times on the top-level type.
+		ok := false
+		defer func() {
+			if !ok {
+				info.encoder = nil
+			}
+		}()
+		info.encoder = compileEnc(ut)
+		ok = true
+	}
+	return info.encoder
+}
+
+// lockAndGetEncEngine is a function that locks and compiles.
+// This lets us hold the lock only while compiling, not when encoding.
+func lockAndGetEncEngine(ut *userTypeInfo) *encEngine {
+	typeLock.Lock()
+	defer typeLock.Unlock()
+	return getEncEngine(ut)
+}
+
+func (enc *Encoder) encode(b *bytes.Buffer, value reflect.Value, ut *userTypeInfo) {
+	defer catchError(&enc.err)
+	engine := lockAndGetEncEngine(ut)
+	indir := ut.indir
+	if ut.externalEnc != 0 {
+		indir = int(ut.encIndir)
+	}
+	for i := 0; i < indir; i++ {
+		value = reflect.Indirect(value)
+	}
+	if ut.externalEnc == 0 && value.Type().Kind() == reflect.Struct {
+		enc.encodeStruct(b, engine, value)
+	} else {
+		enc.encodeSingle(b, engine, value)
+	}
+}
diff --git a/src/encoding/gob/encoder.go b/src/encoding/gob/encoder.go
new file mode 100644
index 0000000000..a3301c3bd3
--- /dev/null
+++ b/src/encoding/gob/encoder.go
@@ -0,0 +1,253 @@
+// 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 (
+	"bytes"
+	"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    bytes.Buffer            // 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(bytes.Buffer))
+	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 *bytes.Buffer) {
+	// 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
+	}
+	typeLock.Lock()
+	info, err := getTypeInfo(ut)
+	typeLock.Unlock()
+	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 {
+			typeLock.Lock()
+			info, err := getTypeInfo(ut)
+			typeLock.Unlock()
+			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
+}
diff --git a/src/encoding/gob/encoder_test.go b/src/encoding/gob/encoder_test.go
new file mode 100644
index 0000000000..376df82f15
--- /dev/null
+++ b/src/encoding/gob/encoder_test.go
@@ -0,0 +1,934 @@
+// 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 (
+	"bytes"
+	"fmt"
+	"io"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+// Test basic operations in a safe manner.
+func TestBasicEncoderDecoder(t *testing.T) {
+	var values = []interface{}{
+		true,
+		int(123),
+		int8(123),
+		int16(-12345),
+		int32(123456),
+		int64(-1234567),
+		uint(123),
+		uint8(123),
+		uint16(12345),
+		uint32(123456),
+		uint64(1234567),
+		uintptr(12345678),
+		float32(1.2345),
+		float64(1.2345678),
+		complex64(1.2345 + 2.3456i),
+		complex128(1.2345678 + 2.3456789i),
+		[]byte("hello"),
+		string("hello"),
+	}
+	for _, value := range values {
+		b := new(bytes.Buffer)
+		enc := NewEncoder(b)
+		err := enc.Encode(value)
+		if err != nil {
+			t.Error("encoder fail:", err)
+		}
+		dec := NewDecoder(b)
+		result := reflect.New(reflect.TypeOf(value))
+		err = dec.Decode(result.Interface())
+		if err != nil {
+			t.Fatalf("error decoding %T: %v:", reflect.TypeOf(value), err)
+		}
+		if !reflect.DeepEqual(value, result.Elem().Interface()) {
+			t.Fatalf("%T: expected %v got %v", value, value, result.Elem().Interface())
+		}
+	}
+}
+
+type ET0 struct {
+	A int
+	B string
+}
+
+type ET2 struct {
+	X string
+}
+
+type ET1 struct {
+	A    int
+	Et2  *ET2
+	Next *ET1
+}
+
+// Like ET1 but with a different name for a field
+type ET3 struct {
+	A             int
+	Et2           *ET2
+	DifferentNext *ET1
+}
+
+// Like ET1 but with a different type for a field
+type ET4 struct {
+	A    int
+	Et2  float64
+	Next int
+}
+
+func TestEncoderDecoder(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	et0 := new(ET0)
+	et0.A = 7
+	et0.B = "gobs of fun"
+	err := enc.Encode(et0)
+	if err != nil {
+		t.Error("encoder fail:", err)
+	}
+	//fmt.Printf("% x %q\n", b, b)
+	//Debug(b)
+	dec := NewDecoder(b)
+	newEt0 := new(ET0)
+	err = dec.Decode(newEt0)
+	if err != nil {
+		t.Fatal("error decoding ET0:", err)
+	}
+
+	if !reflect.DeepEqual(et0, newEt0) {
+		t.Fatalf("invalid data for et0: expected %+v; got %+v", *et0, *newEt0)
+	}
+	if b.Len() != 0 {
+		t.Error("not at eof;", b.Len(), "bytes left")
+	}
+	//	t.FailNow()
+
+	b = new(bytes.Buffer)
+	enc = NewEncoder(b)
+	et1 := new(ET1)
+	et1.A = 7
+	et1.Et2 = new(ET2)
+	err = enc.Encode(et1)
+	if err != nil {
+		t.Error("encoder fail:", err)
+	}
+	dec = NewDecoder(b)
+	newEt1 := new(ET1)
+	err = dec.Decode(newEt1)
+	if err != nil {
+		t.Fatal("error decoding ET1:", err)
+	}
+
+	if !reflect.DeepEqual(et1, newEt1) {
+		t.Fatalf("invalid data for et1: expected %+v; got %+v", *et1, *newEt1)
+	}
+	if b.Len() != 0 {
+		t.Error("not at eof;", b.Len(), "bytes left")
+	}
+
+	enc.Encode(et1)
+	newEt1 = new(ET1)
+	err = dec.Decode(newEt1)
+	if err != nil {
+		t.Fatal("round 2: error decoding ET1:", err)
+	}
+	if !reflect.DeepEqual(et1, newEt1) {
+		t.Fatalf("round 2: invalid data for et1: expected %+v; got %+v", *et1, *newEt1)
+	}
+	if b.Len() != 0 {
+		t.Error("round 2: not at eof;", b.Len(), "bytes left")
+	}
+
+	// Now test with a running encoder/decoder pair that we recognize a type mismatch.
+	err = enc.Encode(et1)
+	if err != nil {
+		t.Error("round 3: encoder fail:", err)
+	}
+	newEt2 := new(ET2)
+	err = dec.Decode(newEt2)
+	if err == nil {
+		t.Fatal("round 3: expected `bad type' error decoding ET2")
+	}
+}
+
+// Run one value through the encoder/decoder, but use the wrong type.
+// Input is always an ET1; we compare it to whatever is under 'e'.
+func badTypeCheck(e interface{}, shouldFail bool, msg string, t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	et1 := new(ET1)
+	et1.A = 7
+	et1.Et2 = new(ET2)
+	err := enc.Encode(et1)
+	if err != nil {
+		t.Error("encoder fail:", err)
+	}
+	dec := NewDecoder(b)
+	err = dec.Decode(e)
+	if shouldFail && err == nil {
+		t.Error("expected error for", msg)
+	}
+	if !shouldFail && err != nil {
+		t.Error("unexpected error for", msg, err)
+	}
+}
+
+// Test that we recognize a bad type the first time.
+func TestWrongTypeDecoder(t *testing.T) {
+	badTypeCheck(new(ET2), true, "no fields in common", t)
+	badTypeCheck(new(ET3), false, "different name of field", t)
+	badTypeCheck(new(ET4), true, "different type of field", t)
+}
+
+func corruptDataCheck(s string, err error, t *testing.T) {
+	b := bytes.NewBufferString(s)
+	dec := NewDecoder(b)
+	err1 := dec.Decode(new(ET2))
+	if err1 != err {
+		t.Errorf("from %q expected error %s; got %s", s, err, err1)
+	}
+}
+
+// Check that we survive bad data.
+func TestBadData(t *testing.T) {
+	corruptDataCheck("", io.EOF, t)
+	corruptDataCheck("\x7Fhi", io.ErrUnexpectedEOF, t)
+	corruptDataCheck("\x03now is the time for all good men", errBadType, t)
+	// issue 6323.
+	corruptDataCheck("\x04\x24foo", errRange, t)
+}
+
+// Types not supported at top level by the Encoder.
+var unsupportedValues = []interface{}{
+	make(chan int),
+	func(a int) bool { return true },
+}
+
+func TestUnsupported(t *testing.T) {
+	var b bytes.Buffer
+	enc := NewEncoder(&b)
+	for _, v := range unsupportedValues {
+		err := enc.Encode(v)
+		if err == nil {
+			t.Errorf("expected error for %T; got none", v)
+		}
+	}
+}
+
+func encAndDec(in, out interface{}) error {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err := enc.Encode(in)
+	if err != nil {
+		return err
+	}
+	dec := NewDecoder(b)
+	err = dec.Decode(out)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func TestTypeToPtrType(t *testing.T) {
+	// Encode a T, decode a *T
+	type Type0 struct {
+		A int
+	}
+	t0 := Type0{7}
+	t0p := new(Type0)
+	if err := encAndDec(t0, t0p); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestPtrTypeToType(t *testing.T) {
+	// Encode a *T, decode a T
+	type Type1 struct {
+		A uint
+	}
+	t1p := &Type1{17}
+	var t1 Type1
+	if err := encAndDec(t1, t1p); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestTypeToPtrPtrPtrPtrType(t *testing.T) {
+	type Type2 struct {
+		A ****float64
+	}
+	t2 := Type2{}
+	t2.A = new(***float64)
+	*t2.A = new(**float64)
+	**t2.A = new(*float64)
+	***t2.A = new(float64)
+	****t2.A = 27.4
+	t2pppp := new(***Type2)
+	if err := encAndDec(t2, t2pppp); err != nil {
+		t.Fatal(err)
+	}
+	if ****(****t2pppp).A != ****t2.A {
+		t.Errorf("wrong value after decode: %g not %g", ****(****t2pppp).A, ****t2.A)
+	}
+}
+
+func TestSlice(t *testing.T) {
+	type Type3 struct {
+		A []string
+	}
+	t3p := &Type3{[]string{"hello", "world"}}
+	var t3 Type3
+	if err := encAndDec(t3, t3p); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestValueError(t *testing.T) {
+	// Encode a *T, decode a T
+	type Type4 struct {
+		A int
+	}
+	t4p := &Type4{3}
+	var t4 Type4 // note: not a pointer.
+	if err := encAndDec(t4p, t4); err == nil || strings.Index(err.Error(), "pointer") < 0 {
+		t.Error("expected error about pointer; got", err)
+	}
+}
+
+func TestArray(t *testing.T) {
+	type Type5 struct {
+		A [3]string
+		B [3]byte
+	}
+	type Type6 struct {
+		A [2]string // can't hold t5.a
+	}
+	t5 := Type5{[3]string{"hello", ",", "world"}, [3]byte{1, 2, 3}}
+	var t5p Type5
+	if err := encAndDec(t5, &t5p); err != nil {
+		t.Error(err)
+	}
+	var t6 Type6
+	if err := encAndDec(t5, &t6); err == nil {
+		t.Error("should fail with mismatched array sizes")
+	}
+}
+
+func TestRecursiveMapType(t *testing.T) {
+	type recursiveMap map[string]recursiveMap
+	r1 := recursiveMap{"A": recursiveMap{"B": nil, "C": nil}, "D": nil}
+	r2 := make(recursiveMap)
+	if err := encAndDec(r1, &r2); err != nil {
+		t.Error(err)
+	}
+}
+
+func TestRecursiveSliceType(t *testing.T) {
+	type recursiveSlice []recursiveSlice
+	r1 := recursiveSlice{0: recursiveSlice{0: nil}, 1: nil}
+	r2 := make(recursiveSlice, 0)
+	if err := encAndDec(r1, &r2); err != nil {
+		t.Error(err)
+	}
+}
+
+// Regression test for bug: must send zero values inside arrays
+func TestDefaultsInArray(t *testing.T) {
+	type Type7 struct {
+		B []bool
+		I []int
+		S []string
+		F []float64
+	}
+	t7 := Type7{
+		[]bool{false, false, true},
+		[]int{0, 0, 1},
+		[]string{"hi", "", "there"},
+		[]float64{0, 0, 1},
+	}
+	var t7p Type7
+	if err := encAndDec(t7, &t7p); err != nil {
+		t.Error(err)
+	}
+}
+
+var testInt int
+var testFloat32 float32
+var testString string
+var testSlice []string
+var testMap map[string]int
+var testArray [7]int
+
+type SingleTest struct {
+	in  interface{}
+	out interface{}
+	err string
+}
+
+var singleTests = []SingleTest{
+	{17, &testInt, ""},
+	{float32(17.5), &testFloat32, ""},
+	{"bike shed", &testString, ""},
+	{[]string{"bike", "shed", "paint", "color"}, &testSlice, ""},
+	{map[string]int{"seven": 7, "twelve": 12}, &testMap, ""},
+	{[7]int{4, 55, 0, 0, 0, 0, 0}, &testArray, ""}, // case that once triggered a bug
+	{[7]int{4, 55, 1, 44, 22, 66, 1234}, &testArray, ""},
+
+	// Decode errors
+	{172, &testFloat32, "type"},
+}
+
+func TestSingletons(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	dec := NewDecoder(b)
+	for _, test := range singleTests {
+		b.Reset()
+		err := enc.Encode(test.in)
+		if err != nil {
+			t.Errorf("error encoding %v: %s", test.in, err)
+			continue
+		}
+		err = dec.Decode(test.out)
+		switch {
+		case err != nil && test.err == "":
+			t.Errorf("error decoding %v: %s", test.in, err)
+			continue
+		case err == nil && test.err != "":
+			t.Errorf("expected error decoding %v: %s", test.in, test.err)
+			continue
+		case err != nil && test.err != "":
+			if strings.Index(err.Error(), test.err) < 0 {
+				t.Errorf("wrong error decoding %v: wanted %s, got %v", test.in, test.err, err)
+			}
+			continue
+		}
+		// Get rid of the pointer in the rhs
+		val := reflect.ValueOf(test.out).Elem().Interface()
+		if !reflect.DeepEqual(test.in, val) {
+			t.Errorf("decoding singleton: expected %v got %v", test.in, val)
+		}
+	}
+}
+
+func TestStructNonStruct(t *testing.T) {
+	type Struct struct {
+		A string
+	}
+	type NonStruct string
+	s := Struct{"hello"}
+	var sp Struct
+	if err := encAndDec(s, &sp); err != nil {
+		t.Error(err)
+	}
+	var ns NonStruct
+	if err := encAndDec(s, &ns); err == nil {
+		t.Error("should get error for struct/non-struct")
+	} else if strings.Index(err.Error(), "type") < 0 {
+		t.Error("for struct/non-struct expected type error; got", err)
+	}
+	// Now try the other way
+	var nsp NonStruct
+	if err := encAndDec(ns, &nsp); err != nil {
+		t.Error(err)
+	}
+	if err := encAndDec(ns, &s); err == nil {
+		t.Error("should get error for non-struct/struct")
+	} else if strings.Index(err.Error(), "type") < 0 {
+		t.Error("for non-struct/struct expected type error; got", err)
+	}
+}
+
+type interfaceIndirectTestI interface {
+	F() bool
+}
+
+type interfaceIndirectTestT struct{}
+
+func (this *interfaceIndirectTestT) F() bool {
+	return true
+}
+
+// A version of a bug reported on golang-nuts.  Also tests top-level
+// slice of interfaces.  The issue was registering *T caused T to be
+// stored as the concrete type.
+func TestInterfaceIndirect(t *testing.T) {
+	Register(&interfaceIndirectTestT{})
+	b := new(bytes.Buffer)
+	w := []interfaceIndirectTestI{&interfaceIndirectTestT{}}
+	err := NewEncoder(b).Encode(w)
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+
+	var r []interfaceIndirectTestI
+	err = NewDecoder(b).Decode(&r)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+}
+
+// Now follow various tests that decode into things that can't represent the
+// encoded value, all of which should be legal.
+
+// Also, when the ignored object contains an interface value, it may define
+// types. Make sure that skipping the value still defines the types by using
+// the encoder/decoder pair to send a value afterwards.  If an interface
+// is sent, its type in the test is always NewType0, so this checks that the
+// encoder and decoder don't skew with respect to type definitions.
+
+type Struct0 struct {
+	I interface{}
+}
+
+type NewType0 struct {
+	S string
+}
+
+type ignoreTest struct {
+	in, out interface{}
+}
+
+var ignoreTests = []ignoreTest{
+	// Decode normal struct into an empty struct
+	{&struct{ A int }{23}, &struct{}{}},
+	// Decode normal struct into a nil.
+	{&struct{ A int }{23}, nil},
+	// Decode singleton string into a nil.
+	{"hello, world", nil},
+	// Decode singleton slice into a nil.
+	{[]int{1, 2, 3, 4}, nil},
+	// Decode struct containing an interface into a nil.
+	{&Struct0{&NewType0{"value0"}}, nil},
+	// Decode singleton slice of interfaces into a nil.
+	{[]interface{}{"hi", &NewType0{"value1"}, 23}, nil},
+}
+
+func TestDecodeIntoNothing(t *testing.T) {
+	Register(new(NewType0))
+	for i, test := range ignoreTests {
+		b := new(bytes.Buffer)
+		enc := NewEncoder(b)
+		err := enc.Encode(test.in)
+		if err != nil {
+			t.Errorf("%d: encode error %s:", i, err)
+			continue
+		}
+		dec := NewDecoder(b)
+		err = dec.Decode(test.out)
+		if err != nil {
+			t.Errorf("%d: decode error: %s", i, err)
+			continue
+		}
+		// Now see if the encoder and decoder are in a consistent state.
+		str := fmt.Sprintf("Value %d", i)
+		err = enc.Encode(&NewType0{str})
+		if err != nil {
+			t.Fatalf("%d: NewType0 encode error: %s", i, err)
+		}
+		ns := new(NewType0)
+		err = dec.Decode(ns)
+		if err != nil {
+			t.Fatalf("%d: NewType0 decode error: %s", i, err)
+		}
+		if ns.S != str {
+			t.Fatalf("%d: expected %q got %q", i, str, ns.S)
+		}
+	}
+}
+
+// Another bug from golang-nuts, involving nested interfaces.
+type Bug0Outer struct {
+	Bug0Field interface{}
+}
+
+type Bug0Inner struct {
+	A int
+}
+
+func TestNestedInterfaces(t *testing.T) {
+	var buf bytes.Buffer
+	e := NewEncoder(&buf)
+	d := NewDecoder(&buf)
+	Register(new(Bug0Outer))
+	Register(new(Bug0Inner))
+	f := &Bug0Outer{&Bug0Outer{&Bug0Inner{7}}}
+	var v interface{} = f
+	err := e.Encode(&v)
+	if err != nil {
+		t.Fatal("Encode:", err)
+	}
+	err = d.Decode(&v)
+	if err != nil {
+		t.Fatal("Decode:", err)
+	}
+	// Make sure it decoded correctly.
+	outer1, ok := v.(*Bug0Outer)
+	if !ok {
+		t.Fatalf("v not Bug0Outer: %T", v)
+	}
+	outer2, ok := outer1.Bug0Field.(*Bug0Outer)
+	if !ok {
+		t.Fatalf("v.Bug0Field not Bug0Outer: %T", outer1.Bug0Field)
+	}
+	inner, ok := outer2.Bug0Field.(*Bug0Inner)
+	if !ok {
+		t.Fatalf("v.Bug0Field.Bug0Field not Bug0Inner: %T", outer2.Bug0Field)
+	}
+	if inner.A != 7 {
+		t.Fatalf("final value %d; expected %d", inner.A, 7)
+	}
+}
+
+// The bugs keep coming. We forgot to send map subtypes before the map.
+
+type Bug1Elem struct {
+	Name string
+	Id   int
+}
+
+type Bug1StructMap map[string]Bug1Elem
+
+func bug1EncDec(in Bug1StructMap, out *Bug1StructMap) error {
+	return nil
+}
+
+func TestMapBug1(t *testing.T) {
+	in := make(Bug1StructMap)
+	in["val1"] = Bug1Elem{"elem1", 1}
+	in["val2"] = Bug1Elem{"elem2", 2}
+
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err := enc.Encode(in)
+	if err != nil {
+		t.Fatal("encode:", err)
+	}
+	dec := NewDecoder(b)
+	out := make(Bug1StructMap)
+	err = dec.Decode(&out)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if !reflect.DeepEqual(in, out) {
+		t.Errorf("mismatch: %v %v", in, out)
+	}
+}
+
+func TestGobMapInterfaceEncode(t *testing.T) {
+	m := map[string]interface{}{
+		"up": uintptr(0),
+		"i0": []int{-1},
+		"i1": []int8{-1},
+		"i2": []int16{-1},
+		"i3": []int32{-1},
+		"i4": []int64{-1},
+		"u0": []uint{1},
+		"u1": []uint8{1},
+		"u2": []uint16{1},
+		"u3": []uint32{1},
+		"u4": []uint64{1},
+		"f0": []float32{1},
+		"f1": []float64{1},
+		"c0": []complex64{complex(2, -2)},
+		"c1": []complex128{complex(2, float64(-2))},
+		"us": []uintptr{0},
+		"bo": []bool{false},
+		"st": []string{"s"},
+	}
+	enc := NewEncoder(new(bytes.Buffer))
+	err := enc.Encode(m)
+	if err != nil {
+		t.Errorf("encode map: %s", err)
+	}
+}
+
+func TestSliceReusesMemory(t *testing.T) {
+	buf := new(bytes.Buffer)
+	// Bytes
+	{
+		x := []byte("abcd")
+		enc := NewEncoder(buf)
+		err := enc.Encode(x)
+		if err != nil {
+			t.Errorf("bytes: encode: %s", err)
+		}
+		// Decode into y, which is big enough.
+		y := []byte("ABCDE")
+		addr := &y[0]
+		dec := NewDecoder(buf)
+		err = dec.Decode(&y)
+		if err != nil {
+			t.Fatal("bytes: decode:", err)
+		}
+		if !bytes.Equal(x, y) {
+			t.Errorf("bytes: expected %q got %q\n", x, y)
+		}
+		if addr != &y[0] {
+			t.Errorf("bytes: unnecessary reallocation")
+		}
+	}
+	// general slice
+	{
+		x := []rune("abcd")
+		enc := NewEncoder(buf)
+		err := enc.Encode(x)
+		if err != nil {
+			t.Errorf("ints: encode: %s", err)
+		}
+		// Decode into y, which is big enough.
+		y := []rune("ABCDE")
+		addr := &y[0]
+		dec := NewDecoder(buf)
+		err = dec.Decode(&y)
+		if err != nil {
+			t.Fatal("ints: decode:", err)
+		}
+		if !reflect.DeepEqual(x, y) {
+			t.Errorf("ints: expected %q got %q\n", x, y)
+		}
+		if addr != &y[0] {
+			t.Errorf("ints: unnecessary reallocation")
+		}
+	}
+}
+
+// Used to crash: negative count in recvMessage.
+func TestBadCount(t *testing.T) {
+	b := []byte{0xfb, 0xa5, 0x82, 0x2f, 0xca, 0x1}
+	if err := NewDecoder(bytes.NewReader(b)).Decode(nil); err == nil {
+		t.Error("expected error from bad count")
+	} else if err.Error() != errBadCount.Error() {
+		t.Error("expected bad count error; got", err)
+	}
+}
+
+// Verify that sequential Decoders built on a single input will
+// succeed if the input implements ReadByte and there is no
+// type information in the stream.
+func TestSequentialDecoder(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	const count = 10
+	for i := 0; i < count; i++ {
+		s := fmt.Sprintf("%d", i)
+		if err := enc.Encode(s); err != nil {
+			t.Error("encoder fail:", err)
+		}
+	}
+	for i := 0; i < count; i++ {
+		dec := NewDecoder(b)
+		var s string
+		if err := dec.Decode(&s); err != nil {
+			t.Fatal("decoder fail:", err)
+		}
+		if s != fmt.Sprintf("%d", i) {
+			t.Fatalf("decode expected %d got %s", i, s)
+		}
+	}
+}
+
+// Should be able to have unrepresentable fields (chan, func, *chan etc.); we just ignore them.
+type Bug2 struct {
+	A   int
+	C   chan int
+	CP  *chan int
+	F   func()
+	FPP **func()
+}
+
+func TestChanFuncIgnored(t *testing.T) {
+	c := make(chan int)
+	f := func() {}
+	fp := &f
+	b0 := Bug2{23, c, &c, f, &fp}
+	var buf bytes.Buffer
+	enc := NewEncoder(&buf)
+	if err := enc.Encode(b0); err != nil {
+		t.Fatal("error encoding:", err)
+	}
+	var b1 Bug2
+	err := NewDecoder(&buf).Decode(&b1)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if b1.A != b0.A {
+		t.Fatalf("got %d want %d", b1.A, b0.A)
+	}
+	if b1.C != nil || b1.CP != nil || b1.F != nil || b1.FPP != nil {
+		t.Fatal("unexpected value for chan or func")
+	}
+}
+
+func TestSliceIncompatibility(t *testing.T) {
+	var in = []byte{1, 2, 3}
+	var out []int
+	if err := encAndDec(in, &out); err == nil {
+		t.Error("expected compatibility error")
+	}
+}
+
+// Mutually recursive slices of structs caused problems.
+type Bug3 struct {
+	Num      int
+	Children []*Bug3
+}
+
+func TestGobPtrSlices(t *testing.T) {
+	in := []*Bug3{
+		{1, nil},
+		{2, nil},
+	}
+	b := new(bytes.Buffer)
+	err := NewEncoder(b).Encode(&in)
+	if err != nil {
+		t.Fatal("encode:", err)
+	}
+
+	var out []*Bug3
+	err = NewDecoder(b).Decode(&out)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if !reflect.DeepEqual(in, out) {
+		t.Fatalf("got %v; wanted %v", out, in)
+	}
+}
+
+// getDecEnginePtr cached engine for ut.base instead of ut.user so we passed
+// a *map and then tried to reuse its engine to decode the inner map.
+func TestPtrToMapOfMap(t *testing.T) {
+	Register(make(map[string]interface{}))
+	subdata := make(map[string]interface{})
+	subdata["bar"] = "baz"
+	data := make(map[string]interface{})
+	data["foo"] = subdata
+
+	b := new(bytes.Buffer)
+	err := NewEncoder(b).Encode(data)
+	if err != nil {
+		t.Fatal("encode:", err)
+	}
+	var newData map[string]interface{}
+	err = NewDecoder(b).Decode(&newData)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if !reflect.DeepEqual(data, newData) {
+		t.Fatalf("expected %v got %v", data, newData)
+	}
+}
+
+// A top-level nil pointer generates a panic with a helpful string-valued message.
+func TestTopLevelNilPointer(t *testing.T) {
+	errMsg := topLevelNilPanic(t)
+	if errMsg == "" {
+		t.Fatal("top-level nil pointer did not panic")
+	}
+	if !strings.Contains(errMsg, "nil pointer") {
+		t.Fatal("expected nil pointer error, got:", errMsg)
+	}
+}
+
+func topLevelNilPanic(t *testing.T) (panicErr string) {
+	defer func() {
+		e := recover()
+		if err, ok := e.(string); ok {
+			panicErr = err
+		}
+	}()
+	var ip *int
+	buf := new(bytes.Buffer)
+	if err := NewEncoder(buf).Encode(ip); err != nil {
+		t.Fatal("error in encode:", err)
+	}
+	return
+}
+
+func TestNilPointerInsideInterface(t *testing.T) {
+	var ip *int
+	si := struct {
+		I interface{}
+	}{
+		I: ip,
+	}
+	buf := new(bytes.Buffer)
+	err := NewEncoder(buf).Encode(si)
+	if err == nil {
+		t.Fatal("expected error, got none")
+	}
+	errMsg := err.Error()
+	if !strings.Contains(errMsg, "nil pointer") || !strings.Contains(errMsg, "interface") {
+		t.Fatal("expected error about nil pointer and interface, got:", errMsg)
+	}
+}
+
+type Bug4Public struct {
+	Name   string
+	Secret Bug4Secret
+}
+
+type Bug4Secret struct {
+	a int // error: no exported fields.
+}
+
+// Test that a failed compilation doesn't leave around an executable encoder.
+// Issue 3273.
+func TestMutipleEncodingsOfBadType(t *testing.T) {
+	x := Bug4Public{
+		Name:   "name",
+		Secret: Bug4Secret{1},
+	}
+	buf := new(bytes.Buffer)
+	enc := NewEncoder(buf)
+	err := enc.Encode(x)
+	if err == nil {
+		t.Fatal("first encoding: expected error")
+	}
+	buf.Reset()
+	enc = NewEncoder(buf)
+	err = enc.Encode(x)
+	if err == nil {
+		t.Fatal("second encoding: expected error")
+	}
+	if !strings.Contains(err.Error(), "no exported fields") {
+		t.Errorf("expected error about no exported fields; got %v", err)
+	}
+}
+
+// There was an error check comparing the length of the input with the
+// length of the slice being decoded. It was wrong because the next
+// thing in the input might be a type definition, which would lead to
+// an incorrect length check.  This test reproduces the corner case.
+
+type Z struct {
+}
+
+func Test29ElementSlice(t *testing.T) {
+	Register(Z{})
+	src := make([]interface{}, 100) // Size needs to be bigger than size of type definition.
+	for i := range src {
+		src[i] = Z{}
+	}
+	buf := new(bytes.Buffer)
+	err := NewEncoder(buf).Encode(src)
+	if err != nil {
+		t.Fatalf("encode: %v", err)
+		return
+	}
+
+	var dst []interface{}
+	err = NewDecoder(buf).Decode(&dst)
+	if err != nil {
+		t.Errorf("decode: %v", err)
+		return
+	}
+}
diff --git a/src/encoding/gob/error.go b/src/encoding/gob/error.go
new file mode 100644
index 0000000000..92cc0c615e
--- /dev/null
+++ b/src/encoding/gob/error.go
@@ -0,0 +1,43 @@
+// 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 "fmt"
+
+// Errors in decoding and encoding are handled using panic and recover.
+// Panics caused by user error (that is, everything except run-time panics
+// such as "index out of bounds" errors) do not leave the file that caused
+// them, but are instead turned into plain error returns.  Encoding and
+// decoding functions and methods that do not return an error either use
+// panic to report an error or are guaranteed error-free.
+
+// A gobError is used to distinguish errors (panics) generated in this package.
+type gobError struct {
+	err error
+}
+
+// errorf is like error_ but takes Printf-style arguments to construct an error.
+// It always prefixes the message with "gob: ".
+func errorf(format string, args ...interface{}) {
+	error_(fmt.Errorf("gob: "+format, args...))
+}
+
+// error wraps the argument error and uses it as the argument to panic.
+func error_(err error) {
+	panic(gobError{err})
+}
+
+// catchError is meant to be used as a deferred function to turn a panic(gobError) into a
+// plain error.  It overwrites the error return of the function that deferred its call.
+func catchError(err *error) {
+	if e := recover(); e != nil {
+		ge, ok := e.(gobError)
+		if !ok {
+			panic(e)
+		}
+		*err = ge.err
+	}
+	return
+}
diff --git a/src/encoding/gob/example_encdec_test.go b/src/encoding/gob/example_encdec_test.go
new file mode 100644
index 0000000000..e45ad4ccfb
--- /dev/null
+++ b/src/encoding/gob/example_encdec_test.go
@@ -0,0 +1,61 @@
+// Copyright 2013 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_test
+
+import (
+	"bytes"
+	"encoding/gob"
+	"fmt"
+	"log"
+)
+
+// The Vector type has unexported fields, which the package cannot access.
+// We therefore write a BinaryMarshal/BinaryUnmarshal method pair to allow us
+// to send and receive the type with the gob package. These interfaces are
+// defined in the "encoding" package.
+// We could equivalently use the locally defined GobEncode/GobDecoder
+// interfaces.
+type Vector struct {
+	x, y, z int
+}
+
+func (v Vector) MarshalBinary() ([]byte, error) {
+	// A simple encoding: plain text.
+	var b bytes.Buffer
+	fmt.Fprintln(&b, v.x, v.y, v.z)
+	return b.Bytes(), nil
+}
+
+// UnmarshalBinary modifies the receiver so it must take a pointer receiver.
+func (v *Vector) UnmarshalBinary(data []byte) error {
+	// A simple encoding: plain text.
+	b := bytes.NewBuffer(data)
+	_, err := fmt.Fscanln(b, &v.x, &v.y, &v.z)
+	return err
+}
+
+// This example transmits a value that implements the custom encoding and decoding methods.
+func Example_encodeDecode() {
+	var network bytes.Buffer // Stand-in for the network.
+
+	// Create an encoder and send a value.
+	enc := gob.NewEncoder(&network)
+	err := enc.Encode(Vector{3, 4, 5})
+	if err != nil {
+		log.Fatal("encode:", err)
+	}
+
+	// Create a decoder and receive a value.
+	dec := gob.NewDecoder(&network)
+	var v Vector
+	err = dec.Decode(&v)
+	if err != nil {
+		log.Fatal("decode:", err)
+	}
+	fmt.Println(v)
+
+	// Output:
+	// {3 4 5}
+}
diff --git a/src/encoding/gob/example_interface_test.go b/src/encoding/gob/example_interface_test.go
new file mode 100644
index 0000000000..4681e6307b
--- /dev/null
+++ b/src/encoding/gob/example_interface_test.go
@@ -0,0 +1,81 @@
+// Copyright 2013 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_test
+
+import (
+	"bytes"
+	"encoding/gob"
+	"fmt"
+	"log"
+	"math"
+)
+
+type Point struct {
+	X, Y int
+}
+
+func (p Point) Hypotenuse() float64 {
+	return math.Hypot(float64(p.X), float64(p.Y))
+}
+
+type Pythagoras interface {
+	Hypotenuse() float64
+}
+
+// This example shows how to encode an interface value. The key
+// distinction from regular types is to register the concrete type that
+// implements the interface.
+func Example_interface() {
+	var network bytes.Buffer // Stand-in for the network.
+
+	// We must register the concrete type for the encoder and decoder (which would
+	// normally be on a separate machine from the encoder). On each end, this tells the
+	// engine which concrete type is being sent that implements the interface.
+	gob.Register(Point{})
+
+	// Create an encoder and send some values.
+	enc := gob.NewEncoder(&network)
+	for i := 1; i <= 3; i++ {
+		interfaceEncode(enc, Point{3 * i, 4 * i})
+	}
+
+	// Create a decoder and receive some values.
+	dec := gob.NewDecoder(&network)
+	for i := 1; i <= 3; i++ {
+		result := interfaceDecode(dec)
+		fmt.Println(result.Hypotenuse())
+	}
+
+	// Output:
+	// 5
+	// 10
+	// 15
+}
+
+// interfaceEncode encodes the interface value into the encoder.
+func interfaceEncode(enc *gob.Encoder, p Pythagoras) {
+	// The encode will fail unless the concrete type has been
+	// registered. We registered it in the calling function.
+
+	// Pass pointer to interface so Encode sees (and hence sends) a value of
+	// interface type.  If we passed p directly it would see the concrete type instead.
+	// See the blog post, "The Laws of Reflection" for background.
+	err := enc.Encode(&p)
+	if err != nil {
+		log.Fatal("encode:", err)
+	}
+}
+
+// interfaceDecode decodes the next interface value from the stream and returns it.
+func interfaceDecode(dec *gob.Decoder) Pythagoras {
+	// The decode will fail unless the concrete type on the wire has been
+	// registered. We registered it in the calling function.
+	var p Pythagoras
+	err := dec.Decode(&p)
+	if err != nil {
+		log.Fatal("decode:", err)
+	}
+	return p
+}
diff --git a/src/encoding/gob/example_test.go b/src/encoding/gob/example_test.go
new file mode 100644
index 0000000000..020352ceee
--- /dev/null
+++ b/src/encoding/gob/example_test.go
@@ -0,0 +1,60 @@
+// Copyright 2013 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_test
+
+import (
+	"bytes"
+	"encoding/gob"
+	"fmt"
+	"log"
+)
+
+type P struct {
+	X, Y, Z int
+	Name    string
+}
+
+type Q struct {
+	X, Y *int32
+	Name string
+}
+
+// This example shows the basic usage of the package: Create an encoder,
+// transmit some values, receive them with a decoder.
+func Example_basic() {
+	// Initialize the encoder and decoder.  Normally enc and dec would be
+	// bound to network connections and the encoder and decoder would
+	// run in different processes.
+	var network bytes.Buffer        // Stand-in for a network connection
+	enc := gob.NewEncoder(&network) // Will write to network.
+	dec := gob.NewDecoder(&network) // Will read from network.
+
+	// Encode (send) some values.
+	err := enc.Encode(P{3, 4, 5, "Pythagoras"})
+	if err != nil {
+		log.Fatal("encode error:", err)
+	}
+	err = enc.Encode(P{1782, 1841, 1922, "Treehouse"})
+	if err != nil {
+		log.Fatal("encode error:", err)
+	}
+
+	// Decode (receive) and print the values.
+	var q Q
+	err = dec.Decode(&q)
+	if err != nil {
+		log.Fatal("decode error 1:", err)
+	}
+	fmt.Printf("%q: {%d, %d}\n", q.Name, *q.X, *q.Y)
+	err = dec.Decode(&q)
+	if err != nil {
+		log.Fatal("decode error 2:", err)
+	}
+	fmt.Printf("%q: {%d, %d}\n", q.Name, *q.X, *q.Y)
+
+	// Output:
+	// "Pythagoras": {3, 4}
+	// "Treehouse": {1782, 1841}
+}
diff --git a/src/encoding/gob/gobencdec_test.go b/src/encoding/gob/gobencdec_test.go
new file mode 100644
index 0000000000..eb76b481d1
--- /dev/null
+++ b/src/encoding/gob/gobencdec_test.go
@@ -0,0 +1,798 @@
+// Copyright 2011 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.
+
+// This file contains tests of the GobEncoder/GobDecoder support.
+
+package gob
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"strings"
+	"testing"
+	"time"
+)
+
+// Types that implement the GobEncoder/Decoder interfaces.
+
+type ByteStruct struct {
+	a byte // not an exported field
+}
+
+type StringStruct struct {
+	s string // not an exported field
+}
+
+type ArrayStruct struct {
+	a [8192]byte // not an exported field
+}
+
+type Gobber int
+
+type ValueGobber string // encodes with a value, decodes with a pointer.
+
+type BinaryGobber int
+
+type BinaryValueGobber string
+
+type TextGobber int
+
+type TextValueGobber string
+
+// The relevant methods
+
+func (g *ByteStruct) GobEncode() ([]byte, error) {
+	b := make([]byte, 3)
+	b[0] = g.a
+	b[1] = g.a + 1
+	b[2] = g.a + 2
+	return b, nil
+}
+
+func (g *ByteStruct) GobDecode(data []byte) error {
+	if g == nil {
+		return errors.New("NIL RECEIVER")
+	}
+	// Expect N sequential-valued bytes.
+	if len(data) == 0 {
+		return io.EOF
+	}
+	g.a = data[0]
+	for i, c := range data {
+		if c != g.a+byte(i) {
+			return errors.New("invalid data sequence")
+		}
+	}
+	return nil
+}
+
+func (g *StringStruct) GobEncode() ([]byte, error) {
+	return []byte(g.s), nil
+}
+
+func (g *StringStruct) GobDecode(data []byte) error {
+	// Expect N sequential-valued bytes.
+	if len(data) == 0 {
+		return io.EOF
+	}
+	a := data[0]
+	for i, c := range data {
+		if c != a+byte(i) {
+			return errors.New("invalid data sequence")
+		}
+	}
+	g.s = string(data)
+	return nil
+}
+
+func (a *ArrayStruct) GobEncode() ([]byte, error) {
+	return a.a[:], nil
+}
+
+func (a *ArrayStruct) GobDecode(data []byte) error {
+	if len(data) != len(a.a) {
+		return errors.New("wrong length in array decode")
+	}
+	copy(a.a[:], data)
+	return nil
+}
+
+func (g *Gobber) GobEncode() ([]byte, error) {
+	return []byte(fmt.Sprintf("VALUE=%d", *g)), nil
+}
+
+func (g *Gobber) GobDecode(data []byte) error {
+	_, err := fmt.Sscanf(string(data), "VALUE=%d", (*int)(g))
+	return err
+}
+
+func (g *BinaryGobber) MarshalBinary() ([]byte, error) {
+	return []byte(fmt.Sprintf("VALUE=%d", *g)), nil
+}
+
+func (g *BinaryGobber) UnmarshalBinary(data []byte) error {
+	_, err := fmt.Sscanf(string(data), "VALUE=%d", (*int)(g))
+	return err
+}
+
+func (g *TextGobber) MarshalText() ([]byte, error) {
+	return []byte(fmt.Sprintf("VALUE=%d", *g)), nil
+}
+
+func (g *TextGobber) UnmarshalText(data []byte) error {
+	_, err := fmt.Sscanf(string(data), "VALUE=%d", (*int)(g))
+	return err
+}
+
+func (v ValueGobber) GobEncode() ([]byte, error) {
+	return []byte(fmt.Sprintf("VALUE=%s", v)), nil
+}
+
+func (v *ValueGobber) GobDecode(data []byte) error {
+	_, err := fmt.Sscanf(string(data), "VALUE=%s", (*string)(v))
+	return err
+}
+
+func (v BinaryValueGobber) MarshalBinary() ([]byte, error) {
+	return []byte(fmt.Sprintf("VALUE=%s", v)), nil
+}
+
+func (v *BinaryValueGobber) UnmarshalBinary(data []byte) error {
+	_, err := fmt.Sscanf(string(data), "VALUE=%s", (*string)(v))
+	return err
+}
+
+func (v TextValueGobber) MarshalText() ([]byte, error) {
+	return []byte(fmt.Sprintf("VALUE=%s", v)), nil
+}
+
+func (v *TextValueGobber) UnmarshalText(data []byte) error {
+	_, err := fmt.Sscanf(string(data), "VALUE=%s", (*string)(v))
+	return err
+}
+
+// Structs that include GobEncodable fields.
+
+type GobTest0 struct {
+	X int // guarantee we have  something in common with GobTest*
+	G *ByteStruct
+}
+
+type GobTest1 struct {
+	X int // guarantee we have  something in common with GobTest*
+	G *StringStruct
+}
+
+type GobTest2 struct {
+	X int    // guarantee we have  something in common with GobTest*
+	G string // not a GobEncoder - should give us errors
+}
+
+type GobTest3 struct {
+	X int // guarantee we have  something in common with GobTest*
+	G *Gobber
+	B *BinaryGobber
+	T *TextGobber
+}
+
+type GobTest4 struct {
+	X  int // guarantee we have  something in common with GobTest*
+	V  ValueGobber
+	BV BinaryValueGobber
+	TV TextValueGobber
+}
+
+type GobTest5 struct {
+	X  int // guarantee we have  something in common with GobTest*
+	V  *ValueGobber
+	BV *BinaryValueGobber
+	TV *TextValueGobber
+}
+
+type GobTest6 struct {
+	X  int // guarantee we have  something in common with GobTest*
+	V  ValueGobber
+	W  *ValueGobber
+	BV BinaryValueGobber
+	BW *BinaryValueGobber
+	TV TextValueGobber
+	TW *TextValueGobber
+}
+
+type GobTest7 struct {
+	X  int // guarantee we have  something in common with GobTest*
+	V  *ValueGobber
+	W  ValueGobber
+	BV *BinaryValueGobber
+	BW BinaryValueGobber
+	TV *TextValueGobber
+	TW TextValueGobber
+}
+
+type GobTestIgnoreEncoder struct {
+	X int // guarantee we have  something in common with GobTest*
+}
+
+type GobTestValueEncDec struct {
+	X int          // guarantee we have  something in common with GobTest*
+	G StringStruct // not a pointer.
+}
+
+type GobTestIndirectEncDec struct {
+	X int             // guarantee we have  something in common with GobTest*
+	G ***StringStruct // indirections to the receiver.
+}
+
+type GobTestArrayEncDec struct {
+	X int         // guarantee we have  something in common with GobTest*
+	A ArrayStruct // not a pointer.
+}
+
+type GobTestIndirectArrayEncDec struct {
+	X int            // guarantee we have  something in common with GobTest*
+	A ***ArrayStruct // indirections to a large receiver.
+}
+
+func TestGobEncoderField(t *testing.T) {
+	b := new(bytes.Buffer)
+	// First a field that's a structure.
+	enc := NewEncoder(b)
+	err := enc.Encode(GobTest0{17, &ByteStruct{'A'}})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTest0)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x.G.a != 'A' {
+		t.Errorf("expected 'A' got %c", x.G.a)
+	}
+	// Now a field that's not a structure.
+	b.Reset()
+	gobber := Gobber(23)
+	bgobber := BinaryGobber(24)
+	tgobber := TextGobber(25)
+	err = enc.Encode(GobTest3{17, &gobber, &bgobber, &tgobber})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	y := new(GobTest3)
+	err = dec.Decode(y)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if *y.G != 23 || *y.B != 24 || *y.T != 25 {
+		t.Errorf("expected '23 got %d", *y.G)
+	}
+}
+
+// Even though the field is a value, we can still take its address
+// and should be able to call the methods.
+func TestGobEncoderValueField(t *testing.T) {
+	b := new(bytes.Buffer)
+	// First a field that's a structure.
+	enc := NewEncoder(b)
+	err := enc.Encode(&GobTestValueEncDec{17, StringStruct{"HIJKL"}})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTestValueEncDec)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x.G.s != "HIJKL" {
+		t.Errorf("expected `HIJKL` got %s", x.G.s)
+	}
+}
+
+// GobEncode/Decode should work even if the value is
+// more indirect than the receiver.
+func TestGobEncoderIndirectField(t *testing.T) {
+	b := new(bytes.Buffer)
+	// First a field that's a structure.
+	enc := NewEncoder(b)
+	s := &StringStruct{"HIJKL"}
+	sp := &s
+	err := enc.Encode(GobTestIndirectEncDec{17, &sp})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTestIndirectEncDec)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if (***x.G).s != "HIJKL" {
+		t.Errorf("expected `HIJKL` got %s", (***x.G).s)
+	}
+}
+
+// Test with a large field with methods.
+func TestGobEncoderArrayField(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	var a GobTestArrayEncDec
+	a.X = 17
+	for i := range a.A.a {
+		a.A.a[i] = byte(i)
+	}
+	err := enc.Encode(&a)
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTestArrayEncDec)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	for i, v := range x.A.a {
+		if v != byte(i) {
+			t.Errorf("expected %x got %x", byte(i), v)
+			break
+		}
+	}
+}
+
+// Test an indirection to a large field with methods.
+func TestGobEncoderIndirectArrayField(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	var a GobTestIndirectArrayEncDec
+	a.X = 17
+	var array ArrayStruct
+	ap := &array
+	app := &ap
+	a.A = &app
+	for i := range array.a {
+		array.a[i] = byte(i)
+	}
+	err := enc.Encode(a)
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTestIndirectArrayEncDec)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	for i, v := range (***x.A).a {
+		if v != byte(i) {
+			t.Errorf("expected %x got %x", byte(i), v)
+			break
+		}
+	}
+}
+
+// As long as the fields have the same name and implement the
+// interface, we can cross-connect them.  Not sure it's useful
+// and may even be bad but it works and it's hard to prevent
+// without exposing the contents of the object, which would
+// defeat the purpose.
+func TestGobEncoderFieldsOfDifferentType(t *testing.T) {
+	// first, string in field to byte in field
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err := enc.Encode(GobTest1{17, &StringStruct{"ABC"}})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTest0)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x.G.a != 'A' {
+		t.Errorf("expected 'A' got %c", x.G.a)
+	}
+	// now the other direction, byte in field to string in field
+	b.Reset()
+	err = enc.Encode(GobTest0{17, &ByteStruct{'X'}})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	y := new(GobTest1)
+	err = dec.Decode(y)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if y.G.s != "XYZ" {
+		t.Fatalf("expected `XYZ` got %q", y.G.s)
+	}
+}
+
+// Test that we can encode a value and decode into a pointer.
+func TestGobEncoderValueEncoder(t *testing.T) {
+	// first, string in field to byte in field
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err := enc.Encode(GobTest4{17, ValueGobber("hello"), BinaryValueGobber("Καλημέρα"), TextValueGobber("こんにちは")})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTest5)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if *x.V != "hello" || *x.BV != "Καλημέρα" || *x.TV != "こんにちは" {
+		t.Errorf("expected `hello` got %s", *x.V)
+	}
+}
+
+// Test that we can use a value then a pointer type of a GobEncoder
+// in the same encoded value.  Bug 4647.
+func TestGobEncoderValueThenPointer(t *testing.T) {
+	v := ValueGobber("forty-two")
+	w := ValueGobber("six-by-nine")
+	bv := BinaryValueGobber("1nanocentury")
+	bw := BinaryValueGobber("πseconds")
+	tv := TextValueGobber("gravitationalacceleration")
+	tw := TextValueGobber("π²ft/s²")
+
+	// this was a bug: encoding a GobEncoder by value before a GobEncoder
+	// pointer would cause duplicate type definitions to be sent.
+
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	if err := enc.Encode(GobTest6{42, v, &w, bv, &bw, tv, &tw}); err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTest6)
+	if err := dec.Decode(x); err != nil {
+		t.Fatal("decode error:", err)
+	}
+
+	if got, want := x.V, v; got != want {
+		t.Errorf("v = %q, want %q", got, want)
+	}
+	if got, want := x.W, w; got == nil {
+		t.Errorf("w = nil, want %q", want)
+	} else if *got != want {
+		t.Errorf("w = %q, want %q", *got, want)
+	}
+
+	if got, want := x.BV, bv; got != want {
+		t.Errorf("bv = %q, want %q", got, want)
+	}
+	if got, want := x.BW, bw; got == nil {
+		t.Errorf("bw = nil, want %q", want)
+	} else if *got != want {
+		t.Errorf("bw = %q, want %q", *got, want)
+	}
+
+	if got, want := x.TV, tv; got != want {
+		t.Errorf("tv = %q, want %q", got, want)
+	}
+	if got, want := x.TW, tw; got == nil {
+		t.Errorf("tw = nil, want %q", want)
+	} else if *got != want {
+		t.Errorf("tw = %q, want %q", *got, want)
+	}
+}
+
+// Test that we can use a pointer then a value type of a GobEncoder
+// in the same encoded value.
+func TestGobEncoderPointerThenValue(t *testing.T) {
+	v := ValueGobber("forty-two")
+	w := ValueGobber("six-by-nine")
+	bv := BinaryValueGobber("1nanocentury")
+	bw := BinaryValueGobber("πseconds")
+	tv := TextValueGobber("gravitationalacceleration")
+	tw := TextValueGobber("π²ft/s²")
+
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	if err := enc.Encode(GobTest7{42, &v, w, &bv, bw, &tv, tw}); err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTest7)
+	if err := dec.Decode(x); err != nil {
+		t.Fatal("decode error:", err)
+	}
+
+	if got, want := x.V, v; got == nil {
+		t.Errorf("v = nil, want %q", want)
+	} else if *got != want {
+		t.Errorf("v = %q, want %q", *got, want)
+	}
+	if got, want := x.W, w; got != want {
+		t.Errorf("w = %q, want %q", got, want)
+	}
+
+	if got, want := x.BV, bv; got == nil {
+		t.Errorf("bv = nil, want %q", want)
+	} else if *got != want {
+		t.Errorf("bv = %q, want %q", *got, want)
+	}
+	if got, want := x.BW, bw; got != want {
+		t.Errorf("bw = %q, want %q", got, want)
+	}
+
+	if got, want := x.TV, tv; got == nil {
+		t.Errorf("tv = nil, want %q", want)
+	} else if *got != want {
+		t.Errorf("tv = %q, want %q", *got, want)
+	}
+	if got, want := x.TW, tw; got != want {
+		t.Errorf("tw = %q, want %q", got, want)
+	}
+}
+
+func TestGobEncoderFieldTypeError(t *testing.T) {
+	// GobEncoder to non-decoder: error
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err := enc.Encode(GobTest1{17, &StringStruct{"ABC"}})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := &GobTest2{}
+	err = dec.Decode(x)
+	if err == nil {
+		t.Fatal("expected decode error for mismatched fields (encoder to non-decoder)")
+	}
+	if strings.Index(err.Error(), "type") < 0 {
+		t.Fatal("expected type error; got", err)
+	}
+	// Non-encoder to GobDecoder: error
+	b.Reset()
+	err = enc.Encode(GobTest2{17, "ABC"})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	y := &GobTest1{}
+	err = dec.Decode(y)
+	if err == nil {
+		t.Fatal("expected decode error for mismatched fields (non-encoder to decoder)")
+	}
+	if strings.Index(err.Error(), "type") < 0 {
+		t.Fatal("expected type error; got", err)
+	}
+}
+
+// Even though ByteStruct is a struct, it's treated as a singleton at the top level.
+func TestGobEncoderStructSingleton(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err := enc.Encode(&ByteStruct{'A'})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(ByteStruct)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x.a != 'A' {
+		t.Errorf("expected 'A' got %c", x.a)
+	}
+}
+
+func TestGobEncoderNonStructSingleton(t *testing.T) {
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	var g Gobber = 1234
+	err := enc.Encode(&g)
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	var x Gobber
+	err = dec.Decode(&x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x != 1234 {
+		t.Errorf("expected 1234 got %d", x)
+	}
+}
+
+func TestGobEncoderIgnoreStructField(t *testing.T) {
+	b := new(bytes.Buffer)
+	// First a field that's a structure.
+	enc := NewEncoder(b)
+	err := enc.Encode(GobTest0{17, &ByteStruct{'A'}})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTestIgnoreEncoder)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x.X != 17 {
+		t.Errorf("expected 17 got %c", x.X)
+	}
+}
+
+func TestGobEncoderIgnoreNonStructField(t *testing.T) {
+	b := new(bytes.Buffer)
+	// First a field that's a structure.
+	enc := NewEncoder(b)
+	gobber := Gobber(23)
+	bgobber := BinaryGobber(24)
+	tgobber := TextGobber(25)
+	err := enc.Encode(GobTest3{17, &gobber, &bgobber, &tgobber})
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTestIgnoreEncoder)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x.X != 17 {
+		t.Errorf("expected 17 got %c", x.X)
+	}
+}
+
+func TestGobEncoderIgnoreNilEncoder(t *testing.T) {
+	b := new(bytes.Buffer)
+	// First a field that's a structure.
+	enc := NewEncoder(b)
+	err := enc.Encode(GobTest0{X: 18}) // G is nil
+	if err != nil {
+		t.Fatal("encode error:", err)
+	}
+	dec := NewDecoder(b)
+	x := new(GobTest0)
+	err = dec.Decode(x)
+	if err != nil {
+		t.Fatal("decode error:", err)
+	}
+	if x.X != 18 {
+		t.Errorf("expected x.X = 18, got %v", x.X)
+	}
+	if x.G != nil {
+		t.Errorf("expected x.G = nil, got %v", x.G)
+	}
+}
+
+type gobDecoderBug0 struct {
+	foo, bar string
+}
+
+func (br *gobDecoderBug0) String() string {
+	return br.foo + "-" + br.bar
+}
+
+func (br *gobDecoderBug0) GobEncode() ([]byte, error) {
+	return []byte(br.String()), nil
+}
+
+func (br *gobDecoderBug0) GobDecode(b []byte) error {
+	br.foo = "foo"
+	br.bar = "bar"
+	return nil
+}
+
+// This was a bug: the receiver has a different indirection level
+// than the variable.
+func TestGobEncoderExtraIndirect(t *testing.T) {
+	gdb := &gobDecoderBug0{"foo", "bar"}
+	buf := new(bytes.Buffer)
+	e := NewEncoder(buf)
+	if err := e.Encode(gdb); err != nil {
+		t.Fatalf("encode: %v", err)
+	}
+	d := NewDecoder(buf)
+	var got *gobDecoderBug0
+	if err := d.Decode(&got); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if got.foo != gdb.foo || got.bar != gdb.bar {
+		t.Errorf("got = %q, want %q", got, gdb)
+	}
+}
+
+// Another bug: this caused a crash with the new Go1 Time type.
+// We throw in a gob-encoding array, to test another case of isZero,
+// and a struct containing an nil interface, to test a third.
+type isZeroBug struct {
+	T time.Time
+	S string
+	I int
+	A isZeroBugArray
+	F isZeroBugInterface
+}
+
+type isZeroBugArray [2]uint8
+
+// Receiver is value, not pointer, to test isZero of array.
+func (a isZeroBugArray) GobEncode() (b []byte, e error) {
+	b = append(b, a[:]...)
+	return b, nil
+}
+
+func (a *isZeroBugArray) GobDecode(data []byte) error {
+	if len(data) != len(a) {
+		return io.EOF
+	}
+	a[0] = data[0]
+	a[1] = data[1]
+	return nil
+}
+
+type isZeroBugInterface struct {
+	I interface{}
+}
+
+func (i isZeroBugInterface) GobEncode() (b []byte, e error) {
+	return []byte{}, nil
+}
+
+func (i *isZeroBugInterface) GobDecode(data []byte) error {
+	return nil
+}
+
+func TestGobEncodeIsZero(t *testing.T) {
+	x := isZeroBug{time.Now(), "hello", -55, isZeroBugArray{1, 2}, isZeroBugInterface{}}
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err := enc.Encode(x)
+	if err != nil {
+		t.Fatal("encode:", err)
+	}
+	var y isZeroBug
+	dec := NewDecoder(b)
+	err = dec.Decode(&y)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if x != y {
+		t.Fatalf("%v != %v", x, y)
+	}
+}
+
+func TestGobEncodePtrError(t *testing.T) {
+	var err error
+	b := new(bytes.Buffer)
+	enc := NewEncoder(b)
+	err = enc.Encode(&err)
+	if err != nil {
+		t.Fatal("encode:", err)
+	}
+	dec := NewDecoder(b)
+	err2 := fmt.Errorf("foo")
+	err = dec.Decode(&err2)
+	if err != nil {
+		t.Fatal("decode:", err)
+	}
+	if err2 != nil {
+		t.Fatalf("expected nil, got %v", err2)
+	}
+}
+
+func TestNetIP(t *testing.T) {
+	// Encoding of net.IP{1,2,3,4} in Go 1.1.
+	enc := []byte{0x07, 0x0a, 0x00, 0x04, 0x01, 0x02, 0x03, 0x04}
+
+	var ip net.IP
+	err := NewDecoder(bytes.NewReader(enc)).Decode(&ip)
+	if err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if ip.String() != "1.2.3.4" {
+		t.Errorf("decoded to %v, want 1.2.3.4", ip.String())
+	}
+}
diff --git a/src/encoding/gob/timing_test.go b/src/encoding/gob/timing_test.go
new file mode 100644
index 0000000000..ec55c4d63d
--- /dev/null
+++ b/src/encoding/gob/timing_test.go
@@ -0,0 +1,133 @@
+// Copyright 2011 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 (
+	"bytes"
+	"io"
+	"os"
+	"runtime"
+	"testing"
+)
+
+type Bench struct {
+	A int
+	B float64
+	C string
+	D []byte
+}
+
+func benchmarkEndToEnd(b *testing.B, ctor func() interface{}, pipe func() (r io.Reader, w io.Writer, err error)) {
+	b.RunParallel(func(pb *testing.PB) {
+		r, w, err := pipe()
+		if err != nil {
+			b.Fatal("can't get pipe:", err)
+		}
+		v := ctor()
+		enc := NewEncoder(w)
+		dec := NewDecoder(r)
+		for pb.Next() {
+			if err := enc.Encode(v); err != nil {
+				b.Fatal("encode error:", err)
+			}
+			if err := dec.Decode(v); err != nil {
+				b.Fatal("decode error:", err)
+			}
+		}
+	})
+}
+
+func BenchmarkEndToEndPipe(b *testing.B) {
+	benchmarkEndToEnd(b, func() interface{} {
+		return &Bench{7, 3.2, "now is the time", bytes.Repeat([]byte("for all good men"), 100)}
+	}, func() (r io.Reader, w io.Writer, err error) {
+		r, w, err = os.Pipe()
+		return
+	})
+}
+
+func BenchmarkEndToEndByteBuffer(b *testing.B) {
+	benchmarkEndToEnd(b, func() interface{} {
+		return &Bench{7, 3.2, "now is the time", bytes.Repeat([]byte("for all good men"), 100)}
+	}, func() (r io.Reader, w io.Writer, err error) {
+		var buf bytes.Buffer
+		return &buf, &buf, nil
+	})
+}
+
+func BenchmarkEndToEndSliceByteBuffer(b *testing.B) {
+	benchmarkEndToEnd(b, func() interface{} {
+		v := &Bench{7, 3.2, "now is the time", nil}
+		Register(v)
+		arr := make([]interface{}, 100)
+		for i := range arr {
+			arr[i] = v
+		}
+		return &arr
+	}, func() (r io.Reader, w io.Writer, err error) {
+		var buf bytes.Buffer
+		return &buf, &buf, nil
+	})
+}
+
+func TestCountEncodeMallocs(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping malloc count in short mode")
+	}
+	if runtime.GOMAXPROCS(0) > 1 {
+		t.Skip("skipping; GOMAXPROCS>1")
+	}
+
+	const N = 1000
+
+	var buf bytes.Buffer
+	enc := NewEncoder(&buf)
+	bench := &Bench{7, 3.2, "now is the time", []byte("for all good men")}
+
+	allocs := testing.AllocsPerRun(N, func() {
+		err := enc.Encode(bench)
+		if err != nil {
+			t.Fatal("encode:", err)
+		}
+	})
+	if allocs != 0 {
+		t.Fatalf("mallocs per encode of type Bench: %v; wanted 0\n", allocs)
+	}
+}
+
+func TestCountDecodeMallocs(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping malloc count in short mode")
+	}
+	if runtime.GOMAXPROCS(0) > 1 {
+		t.Skip("skipping; GOMAXPROCS>1")
+	}
+
+	const N = 1000
+
+	var buf bytes.Buffer
+	enc := NewEncoder(&buf)
+	bench := &Bench{7, 3.2, "now is the time", []byte("for all good men")}
+
+	// Fill the buffer with enough to decode
+	testing.AllocsPerRun(N, func() {
+		err := enc.Encode(bench)
+		if err != nil {
+			t.Fatal("encode:", err)
+		}
+	})
+
+	dec := NewDecoder(&buf)
+	allocs := testing.AllocsPerRun(N, func() {
+		*bench = Bench{}
+		err := dec.Decode(&bench)
+		if err != nil {
+			t.Fatal("decode:", err)
+		}
+	})
+	if allocs != 4 {
+		t.Fatalf("mallocs per decode of type Bench: %v; wanted 4\n", allocs)
+	}
+}
diff --git a/src/encoding/gob/type.go b/src/encoding/gob/type.go
new file mode 100644
index 0000000000..cad1452795
--- /dev/null
+++ b/src/encoding/gob/type.go
@@ -0,0 +1,893 @@
+// 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 (
+	"encoding"
+	"errors"
+	"fmt"
+	"os"
+	"reflect"
+	"sync"
+	"unicode"
+	"unicode/utf8"
+)
+
+// userTypeInfo stores the information associated with a type the user has handed
+// to the package.  It's computed once and stored in a map keyed by reflection
+// type.
+type userTypeInfo struct {
+	user        reflect.Type // the type the user handed us
+	base        reflect.Type // the base type after all indirections
+	indir       int          // number of indirections to reach the base type
+	externalEnc int          // xGob, xBinary, or xText
+	externalDec int          // xGob, xBinary or xText
+	encIndir    int8         // number of indirections to reach the receiver type; may be negative
+	decIndir    int8         // number of indirections to reach the receiver type; may be negative
+}
+
+// externalEncoding bits
+const (
+	xGob    = 1 + iota // GobEncoder or GobDecoder
+	xBinary            // encoding.BinaryMarshaler or encoding.BinaryUnmarshaler
+	xText              // encoding.TextMarshaler or encoding.TextUnmarshaler
+)
+
+var (
+	// Protected by an RWMutex because we read it a lot and write
+	// it only when we see a new type, typically when compiling.
+	userTypeLock  sync.RWMutex
+	userTypeCache = make(map[reflect.Type]*userTypeInfo)
+)
+
+// validType returns, and saves, the information associated with user-provided type rt.
+// If the user type is not valid, err will be non-nil.  To be used when the error handler
+// is not set up.
+func validUserType(rt reflect.Type) (ut *userTypeInfo, err error) {
+	userTypeLock.RLock()
+	ut = userTypeCache[rt]
+	userTypeLock.RUnlock()
+	if ut != nil {
+		return
+	}
+	// Now set the value under the write lock.
+	userTypeLock.Lock()
+	defer userTypeLock.Unlock()
+	if ut = userTypeCache[rt]; ut != nil {
+		// Lost the race; not a problem.
+		return
+	}
+	ut = new(userTypeInfo)
+	ut.base = rt
+	ut.user = rt
+	// A type that is just a cycle of pointers (such as type T *T) cannot
+	// be represented in gobs, which need some concrete data.  We use a
+	// cycle detection algorithm from Knuth, Vol 2, Section 3.1, Ex 6,
+	// pp 539-540.  As we step through indirections, run another type at
+	// half speed. If they meet up, there's a cycle.
+	slowpoke := ut.base // walks half as fast as ut.base
+	for {
+		pt := ut.base
+		if pt.Kind() != reflect.Ptr {
+			break
+		}
+		ut.base = pt.Elem()
+		if ut.base == slowpoke { // ut.base lapped slowpoke
+			// recursive pointer type.
+			return nil, errors.New("can't represent recursive pointer type " + ut.base.String())
+		}
+		if ut.indir%2 == 0 {
+			slowpoke = slowpoke.Elem()
+		}
+		ut.indir++
+	}
+
+	if ok, indir := implementsInterface(ut.user, gobEncoderInterfaceType); ok {
+		ut.externalEnc, ut.encIndir = xGob, indir
+	} else if ok, indir := implementsInterface(ut.user, binaryMarshalerInterfaceType); ok {
+		ut.externalEnc, ut.encIndir = xBinary, indir
+	}
+
+	// NOTE(rsc): Would like to allow MarshalText here, but results in incompatibility
+	// with older encodings for net.IP. See golang.org/issue/6760.
+	// } else if ok, indir := implementsInterface(ut.user, textMarshalerInterfaceType); ok {
+	// 	ut.externalEnc, ut.encIndir = xText, indir
+	// }
+
+	if ok, indir := implementsInterface(ut.user, gobDecoderInterfaceType); ok {
+		ut.externalDec, ut.decIndir = xGob, indir
+	} else if ok, indir := implementsInterface(ut.user, binaryUnmarshalerInterfaceType); ok {
+		ut.externalDec, ut.decIndir = xBinary, indir
+	}
+
+	// See note above.
+	// } else if ok, indir := implementsInterface(ut.user, textUnmarshalerInterfaceType); ok {
+	// 	ut.externalDec, ut.decIndir = xText, indir
+	// }
+
+	userTypeCache[rt] = ut
+	return
+}
+
+var (
+	gobEncoderInterfaceType        = reflect.TypeOf((*GobEncoder)(nil)).Elem()
+	gobDecoderInterfaceType        = reflect.TypeOf((*GobDecoder)(nil)).Elem()
+	binaryMarshalerInterfaceType   = reflect.TypeOf((*encoding.BinaryMarshaler)(nil)).Elem()
+	binaryUnmarshalerInterfaceType = reflect.TypeOf((*encoding.BinaryUnmarshaler)(nil)).Elem()
+	textMarshalerInterfaceType     = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
+	textUnmarshalerInterfaceType   = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
+)
+
+// implementsInterface reports whether the type implements the
+// gobEncoder/gobDecoder interface.
+// It also returns the number of indirections required to get to the
+// implementation.
+func implementsInterface(typ, gobEncDecType reflect.Type) (success bool, indir int8) {
+	if typ == nil {
+		return
+	}
+	rt := typ
+	// The type might be a pointer and we need to keep
+	// dereferencing to the base type until we find an implementation.
+	for {
+		if rt.Implements(gobEncDecType) {
+			return true, indir
+		}
+		if p := rt; p.Kind() == reflect.Ptr {
+			indir++
+			if indir > 100 { // insane number of indirections
+				return false, 0
+			}
+			rt = p.Elem()
+			continue
+		}
+		break
+	}
+	// No luck yet, but if this is a base type (non-pointer), the pointer might satisfy.
+	if typ.Kind() != reflect.Ptr {
+		// Not a pointer, but does the pointer work?
+		if reflect.PtrTo(typ).Implements(gobEncDecType) {
+			return true, -1
+		}
+	}
+	return false, 0
+}
+
+// userType returns, and saves, the information associated with user-provided type rt.
+// If the user type is not valid, it calls error.
+func userType(rt reflect.Type) *userTypeInfo {
+	ut, err := validUserType(rt)
+	if err != nil {
+		error_(err)
+	}
+	return ut
+}
+
+// A typeId represents a gob Type as an integer that can be passed on the wire.
+// Internally, typeIds are used as keys to a map to recover the underlying type info.
+type typeId int32
+
+var nextId typeId       // incremented for each new type we build
+var typeLock sync.Mutex // set while building a type
+const firstUserId = 64  // lowest id number granted to user
+
+type gobType interface {
+	id() typeId
+	setId(id typeId)
+	name() string
+	string() string // not public; only for debugging
+	safeString(seen map[typeId]bool) string
+}
+
+var types = make(map[reflect.Type]gobType)
+var idToType = make(map[typeId]gobType)
+var builtinIdToType map[typeId]gobType // set in init() after builtins are established
+
+func setTypeId(typ gobType) {
+	// When building recursive types, someone may get there before us.
+	if typ.id() != 0 {
+		return
+	}
+	nextId++
+	typ.setId(nextId)
+	idToType[nextId] = typ
+}
+
+func (t typeId) gobType() gobType {
+	if t == 0 {
+		return nil
+	}
+	return idToType[t]
+}
+
+// string returns the string representation of the type associated with the typeId.
+func (t typeId) string() string {
+	if t.gobType() == nil {
+		return "<nil>"
+	}
+	return t.gobType().string()
+}
+
+// Name returns the name of the type associated with the typeId.
+func (t typeId) name() string {
+	if t.gobType() == nil {
+		return "<nil>"
+	}
+	return t.gobType().name()
+}
+
+// CommonType holds elements of all types.
+// It is a historical artifact, kept for binary compatibility and exported
+// only for the benefit of the package's encoding of type descriptors. It is
+// not intended for direct use by clients.
+type CommonType struct {
+	Name string
+	Id   typeId
+}
+
+func (t *CommonType) id() typeId { return t.Id }
+
+func (t *CommonType) setId(id typeId) { t.Id = id }
+
+func (t *CommonType) string() string { return t.Name }
+
+func (t *CommonType) safeString(seen map[typeId]bool) string {
+	return t.Name
+}
+
+func (t *CommonType) name() string { return t.Name }
+
+// Create and check predefined types
+// The string for tBytes is "bytes" not "[]byte" to signify its specialness.
+
+var (
+	// Primordial types, needed during initialization.
+	// Always passed as pointers so the interface{} type
+	// goes through without losing its interfaceness.
+	tBool      = bootstrapType("bool", (*bool)(nil), 1)
+	tInt       = bootstrapType("int", (*int)(nil), 2)
+	tUint      = bootstrapType("uint", (*uint)(nil), 3)
+	tFloat     = bootstrapType("float", (*float64)(nil), 4)
+	tBytes     = bootstrapType("bytes", (*[]byte)(nil), 5)
+	tString    = bootstrapType("string", (*string)(nil), 6)
+	tComplex   = bootstrapType("complex", (*complex128)(nil), 7)
+	tInterface = bootstrapType("interface", (*interface{})(nil), 8)
+	// Reserve some Ids for compatible expansion
+	tReserved7 = bootstrapType("_reserved1", (*struct{ r7 int })(nil), 9)
+	tReserved6 = bootstrapType("_reserved1", (*struct{ r6 int })(nil), 10)
+	tReserved5 = bootstrapType("_reserved1", (*struct{ r5 int })(nil), 11)
+	tReserved4 = bootstrapType("_reserved1", (*struct{ r4 int })(nil), 12)
+	tReserved3 = bootstrapType("_reserved1", (*struct{ r3 int })(nil), 13)
+	tReserved2 = bootstrapType("_reserved1", (*struct{ r2 int })(nil), 14)
+	tReserved1 = bootstrapType("_reserved1", (*struct{ r1 int })(nil), 15)
+)
+
+// Predefined because it's needed by the Decoder
+var tWireType = mustGetTypeInfo(reflect.TypeOf(wireType{})).id
+var wireTypeUserInfo *userTypeInfo // userTypeInfo of (*wireType)
+
+func init() {
+	// Some magic numbers to make sure there are no surprises.
+	checkId(16, tWireType)
+	checkId(17, mustGetTypeInfo(reflect.TypeOf(arrayType{})).id)
+	checkId(18, mustGetTypeInfo(reflect.TypeOf(CommonType{})).id)
+	checkId(19, mustGetTypeInfo(reflect.TypeOf(sliceType{})).id)
+	checkId(20, mustGetTypeInfo(reflect.TypeOf(structType{})).id)
+	checkId(21, mustGetTypeInfo(reflect.TypeOf(fieldType{})).id)
+	checkId(23, mustGetTypeInfo(reflect.TypeOf(mapType{})).id)
+
+	builtinIdToType = make(map[typeId]gobType)
+	for k, v := range idToType {
+		builtinIdToType[k] = v
+	}
+
+	// Move the id space upwards to allow for growth in the predefined world
+	// without breaking existing files.
+	if nextId > firstUserId {
+		panic(fmt.Sprintln("nextId too large:", nextId))
+	}
+	nextId = firstUserId
+	registerBasics()
+	wireTypeUserInfo = userType(reflect.TypeOf((*wireType)(nil)))
+}
+
+// Array type
+type arrayType struct {
+	CommonType
+	Elem typeId
+	Len  int
+}
+
+func newArrayType(name string) *arrayType {
+	a := &arrayType{CommonType{Name: name}, 0, 0}
+	return a
+}
+
+func (a *arrayType) init(elem gobType, len int) {
+	// Set our type id before evaluating the element's, in case it's our own.
+	setTypeId(a)
+	a.Elem = elem.id()
+	a.Len = len
+}
+
+func (a *arrayType) safeString(seen map[typeId]bool) string {
+	if seen[a.Id] {
+		return a.Name
+	}
+	seen[a.Id] = true
+	return fmt.Sprintf("[%d]%s", a.Len, a.Elem.gobType().safeString(seen))
+}
+
+func (a *arrayType) string() string { return a.safeString(make(map[typeId]bool)) }
+
+// GobEncoder type (something that implements the GobEncoder interface)
+type gobEncoderType struct {
+	CommonType
+}
+
+func newGobEncoderType(name string) *gobEncoderType {
+	g := &gobEncoderType{CommonType{Name: name}}
+	setTypeId(g)
+	return g
+}
+
+func (g *gobEncoderType) safeString(seen map[typeId]bool) string {
+	return g.Name
+}
+
+func (g *gobEncoderType) string() string { return g.Name }
+
+// Map type
+type mapType struct {
+	CommonType
+	Key  typeId
+	Elem typeId
+}
+
+func newMapType(name string) *mapType {
+	m := &mapType{CommonType{Name: name}, 0, 0}
+	return m
+}
+
+func (m *mapType) init(key, elem gobType) {
+	// Set our type id before evaluating the element's, in case it's our own.
+	setTypeId(m)
+	m.Key = key.id()
+	m.Elem = elem.id()
+}
+
+func (m *mapType) safeString(seen map[typeId]bool) string {
+	if seen[m.Id] {
+		return m.Name
+	}
+	seen[m.Id] = true
+	key := m.Key.gobType().safeString(seen)
+	elem := m.Elem.gobType().safeString(seen)
+	return fmt.Sprintf("map[%s]%s", key, elem)
+}
+
+func (m *mapType) string() string { return m.safeString(make(map[typeId]bool)) }
+
+// Slice type
+type sliceType struct {
+	CommonType
+	Elem typeId
+}
+
+func newSliceType(name string) *sliceType {
+	s := &sliceType{CommonType{Name: name}, 0}
+	return s
+}
+
+func (s *sliceType) init(elem gobType) {
+	// Set our type id before evaluating the element's, in case it's our own.
+	setTypeId(s)
+	// See the comments about ids in newTypeObject. Only slices and
+	// structs have mutual recursion.
+	if elem.id() == 0 {
+		setTypeId(elem)
+	}
+	s.Elem = elem.id()
+}
+
+func (s *sliceType) safeString(seen map[typeId]bool) string {
+	if seen[s.Id] {
+		return s.Name
+	}
+	seen[s.Id] = true
+	return fmt.Sprintf("[]%s", s.Elem.gobType().safeString(seen))
+}
+
+func (s *sliceType) string() string { return s.safeString(make(map[typeId]bool)) }
+
+// Struct type
+type fieldType struct {
+	Name string
+	Id   typeId
+}
+
+type structType struct {
+	CommonType
+	Field []*fieldType
+}
+
+func (s *structType) safeString(seen map[typeId]bool) string {
+	if s == nil {
+		return "<nil>"
+	}
+	if _, ok := seen[s.Id]; ok {
+		return s.Name
+	}
+	seen[s.Id] = true
+	str := s.Name + " = struct { "
+	for _, f := range s.Field {
+		str += fmt.Sprintf("%s %s; ", f.Name, f.Id.gobType().safeString(seen))
+	}
+	str += "}"
+	return str
+}
+
+func (s *structType) string() string { return s.safeString(make(map[typeId]bool)) }
+
+func newStructType(name string) *structType {
+	s := &structType{CommonType{Name: name}, nil}
+	// For historical reasons we set the id here rather than init.
+	// See the comment in newTypeObject for details.
+	setTypeId(s)
+	return s
+}
+
+// newTypeObject allocates a gobType for the reflection type rt.
+// Unless ut represents a GobEncoder, rt should be the base type
+// of ut.
+// This is only called from the encoding side. The decoding side
+// works through typeIds and userTypeInfos alone.
+func newTypeObject(name string, ut *userTypeInfo, rt reflect.Type) (gobType, error) {
+	// Does this type implement GobEncoder?
+	if ut.externalEnc != 0 {
+		return newGobEncoderType(name), nil
+	}
+	var err error
+	var type0, type1 gobType
+	defer func() {
+		if err != nil {
+			delete(types, rt)
+		}
+	}()
+	// Install the top-level type before the subtypes (e.g. struct before
+	// fields) so recursive types can be constructed safely.
+	switch t := rt; t.Kind() {
+	// All basic types are easy: they are predefined.
+	case reflect.Bool:
+		return tBool.gobType(), nil
+
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		return tInt.gobType(), nil
+
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		return tUint.gobType(), nil
+
+	case reflect.Float32, reflect.Float64:
+		return tFloat.gobType(), nil
+
+	case reflect.Complex64, reflect.Complex128:
+		return tComplex.gobType(), nil
+
+	case reflect.String:
+		return tString.gobType(), nil
+
+	case reflect.Interface:
+		return tInterface.gobType(), nil
+
+	case reflect.Array:
+		at := newArrayType(name)
+		types[rt] = at
+		type0, err = getBaseType("", t.Elem())
+		if err != nil {
+			return nil, err
+		}
+		// Historical aside:
+		// For arrays, maps, and slices, we set the type id after the elements
+		// are constructed. This is to retain the order of type id allocation after
+		// a fix made to handle recursive types, which changed the order in
+		// which types are built.  Delaying the setting in this way preserves
+		// type ids while allowing recursive types to be described. Structs,
+		// done below, were already handling recursion correctly so they
+		// assign the top-level id before those of the field.
+		at.init(type0, t.Len())
+		return at, nil
+
+	case reflect.Map:
+		mt := newMapType(name)
+		types[rt] = mt
+		type0, err = getBaseType("", t.Key())
+		if err != nil {
+			return nil, err
+		}
+		type1, err = getBaseType("", t.Elem())
+		if err != nil {
+			return nil, err
+		}
+		mt.init(type0, type1)
+		return mt, nil
+
+	case reflect.Slice:
+		// []byte == []uint8 is a special case
+		if t.Elem().Kind() == reflect.Uint8 {
+			return tBytes.gobType(), nil
+		}
+		st := newSliceType(name)
+		types[rt] = st
+		type0, err = getBaseType(t.Elem().Name(), t.Elem())
+		if err != nil {
+			return nil, err
+		}
+		st.init(type0)
+		return st, nil
+
+	case reflect.Struct:
+		st := newStructType(name)
+		types[rt] = st
+		idToType[st.id()] = st
+		for i := 0; i < t.NumField(); i++ {
+			f := t.Field(i)
+			if !isSent(&f) {
+				continue
+			}
+			typ := userType(f.Type).base
+			tname := typ.Name()
+			if tname == "" {
+				t := userType(f.Type).base
+				tname = t.String()
+			}
+			gt, err := getBaseType(tname, f.Type)
+			if err != nil {
+				return nil, err
+			}
+			// Some mutually recursive types can cause us to be here while
+			// still defining the element. Fix the element type id here.
+			// We could do this more neatly by setting the id at the start of
+			// building every type, but that would break binary compatibility.
+			if gt.id() == 0 {
+				setTypeId(gt)
+			}
+			st.Field = append(st.Field, &fieldType{f.Name, gt.id()})
+		}
+		return st, nil
+
+	default:
+		return nil, errors.New("gob NewTypeObject can't handle type: " + rt.String())
+	}
+}
+
+// isExported reports whether this is an exported - upper case - name.
+func isExported(name string) bool {
+	rune, _ := utf8.DecodeRuneInString(name)
+	return unicode.IsUpper(rune)
+}
+
+// isSent reports whether this struct field is to be transmitted.
+// It will be transmitted only if it is exported and not a chan or func field
+// or pointer to chan or func.
+func isSent(field *reflect.StructField) bool {
+	if !isExported(field.Name) {
+		return false
+	}
+	// If the field is a chan or func or pointer thereto, don't send it.
+	// That is, treat it like an unexported field.
+	typ := field.Type
+	for typ.Kind() == reflect.Ptr {
+		typ = typ.Elem()
+	}
+	if typ.Kind() == reflect.Chan || typ.Kind() == reflect.Func {
+		return false
+	}
+	return true
+}
+
+// getBaseType returns the Gob type describing the given reflect.Type's base type.
+// typeLock must be held.
+func getBaseType(name string, rt reflect.Type) (gobType, error) {
+	ut := userType(rt)
+	return getType(name, ut, ut.base)
+}
+
+// getType returns the Gob type describing the given reflect.Type.
+// Should be called only when handling GobEncoders/Decoders,
+// which may be pointers.  All other types are handled through the
+// base type, never a pointer.
+// typeLock must be held.
+func getType(name string, ut *userTypeInfo, rt reflect.Type) (gobType, error) {
+	typ, present := types[rt]
+	if present {
+		return typ, nil
+	}
+	typ, err := newTypeObject(name, ut, rt)
+	if err == nil {
+		types[rt] = typ
+	}
+	return typ, err
+}
+
+func checkId(want, got typeId) {
+	if want != got {
+		fmt.Fprintf(os.Stderr, "checkId: %d should be %d\n", int(got), int(want))
+		panic("bootstrap type wrong id: " + got.name() + " " + got.string() + " not " + want.string())
+	}
+}
+
+// used for building the basic types; called only from init().  the incoming
+// interface always refers to a pointer.
+func bootstrapType(name string, e interface{}, expect typeId) typeId {
+	rt := reflect.TypeOf(e).Elem()
+	_, present := types[rt]
+	if present {
+		panic("bootstrap type already present: " + name + ", " + rt.String())
+	}
+	typ := &CommonType{Name: name}
+	types[rt] = typ
+	setTypeId(typ)
+	checkId(expect, nextId)
+	userType(rt) // might as well cache it now
+	return nextId
+}
+
+// Representation of the information we send and receive about this type.
+// Each value we send is preceded by its type definition: an encoded int.
+// However, the very first time we send the value, we first send the pair
+// (-id, wireType).
+// For bootstrapping purposes, we assume that the recipient knows how
+// to decode a wireType; it is exactly the wireType struct here, interpreted
+// using the gob rules for sending a structure, except that we assume the
+// ids for wireType and structType etc. are known.  The relevant pieces
+// are built in encode.go's init() function.
+// To maintain binary compatibility, if you extend this type, always put
+// the new fields last.
+type wireType struct {
+	ArrayT           *arrayType
+	SliceT           *sliceType
+	StructT          *structType
+	MapT             *mapType
+	GobEncoderT      *gobEncoderType
+	BinaryMarshalerT *gobEncoderType
+	TextMarshalerT   *gobEncoderType
+}
+
+func (w *wireType) string() string {
+	const unknown = "unknown type"
+	if w == nil {
+		return unknown
+	}
+	switch {
+	case w.ArrayT != nil:
+		return w.ArrayT.Name
+	case w.SliceT != nil:
+		return w.SliceT.Name
+	case w.StructT != nil:
+		return w.StructT.Name
+	case w.MapT != nil:
+		return w.MapT.Name
+	case w.GobEncoderT != nil:
+		return w.GobEncoderT.Name
+	case w.BinaryMarshalerT != nil:
+		return w.BinaryMarshalerT.Name
+	case w.TextMarshalerT != nil:
+		return w.TextMarshalerT.Name
+	}
+	return unknown
+}
+
+type typeInfo struct {
+	id      typeId
+	encoder *encEngine
+	wire    *wireType
+}
+
+var typeInfoMap = make(map[reflect.Type]*typeInfo) // protected by typeLock
+
+// typeLock must be held.
+func getTypeInfo(ut *userTypeInfo) (*typeInfo, error) {
+	rt := ut.base
+	if ut.externalEnc != 0 {
+		// We want the user type, not the base type.
+		rt = ut.user
+	}
+	info, ok := typeInfoMap[rt]
+	if ok {
+		return info, nil
+	}
+	info = new(typeInfo)
+	gt, err := getBaseType(rt.Name(), rt)
+	if err != nil {
+		return nil, err
+	}
+	info.id = gt.id()
+
+	if ut.externalEnc != 0 {
+		userType, err := getType(rt.Name(), ut, rt)
+		if err != nil {
+			return nil, err
+		}
+		gt := userType.id().gobType().(*gobEncoderType)
+		switch ut.externalEnc {
+		case xGob:
+			info.wire = &wireType{GobEncoderT: gt}
+		case xBinary:
+			info.wire = &wireType{BinaryMarshalerT: gt}
+		case xText:
+			info.wire = &wireType{TextMarshalerT: gt}
+		}
+		typeInfoMap[ut.user] = info
+		return info, nil
+	}
+
+	t := info.id.gobType()
+	switch typ := rt; typ.Kind() {
+	case reflect.Array:
+		info.wire = &wireType{ArrayT: t.(*arrayType)}
+	case reflect.Map:
+		info.wire = &wireType{MapT: t.(*mapType)}
+	case reflect.Slice:
+		// []byte == []uint8 is a special case handled separately
+		if typ.Elem().Kind() != reflect.Uint8 {
+			info.wire = &wireType{SliceT: t.(*sliceType)}
+		}
+	case reflect.Struct:
+		info.wire = &wireType{StructT: t.(*structType)}
+	}
+	typeInfoMap[rt] = info
+	return info, nil
+}
+
+// Called only when a panic is acceptable and unexpected.
+func mustGetTypeInfo(rt reflect.Type) *typeInfo {
+	t, err := getTypeInfo(userType(rt))
+	if err != nil {
+		panic("getTypeInfo: " + err.Error())
+	}
+	return t
+}
+
+// GobEncoder is the interface describing data that provides its own
+// representation for encoding values for transmission to a GobDecoder.
+// A type that implements GobEncoder and GobDecoder has complete
+// control over the representation of its data and may therefore
+// contain things such as private fields, channels, and functions,
+// which are not usually transmissible in gob streams.
+//
+// Note: Since gobs can be stored permanently, It is good design
+// to guarantee the encoding used by a GobEncoder is stable as the
+// software evolves.  For instance, it might make sense for GobEncode
+// to include a version number in the encoding.
+type GobEncoder interface {
+	// GobEncode returns a byte slice representing the encoding of the
+	// receiver for transmission to a GobDecoder, usually of the same
+	// concrete type.
+	GobEncode() ([]byte, error)
+}
+
+// GobDecoder is the interface describing data that provides its own
+// routine for decoding transmitted values sent by a GobEncoder.
+type GobDecoder interface {
+	// GobDecode overwrites the receiver, which must be a pointer,
+	// with the value represented by the byte slice, which was written
+	// by GobEncode, usually for the same concrete type.
+	GobDecode([]byte) error
+}
+
+var (
+	registerLock       sync.RWMutex
+	nameToConcreteType = make(map[string]reflect.Type)
+	concreteTypeToName = make(map[reflect.Type]string)
+)
+
+// RegisterName is like Register but uses the provided name rather than the
+// type's default.
+func RegisterName(name string, value interface{}) {
+	if name == "" {
+		// reserved for nil
+		panic("attempt to register empty name")
+	}
+	registerLock.Lock()
+	defer registerLock.Unlock()
+	ut := userType(reflect.TypeOf(value))
+	// Check for incompatible duplicates. The name must refer to the
+	// same user type, and vice versa.
+	if t, ok := nameToConcreteType[name]; ok && t != ut.user {
+		panic(fmt.Sprintf("gob: registering duplicate types for %q: %s != %s", name, t, ut.user))
+	}
+	if n, ok := concreteTypeToName[ut.base]; ok && n != name {
+		panic(fmt.Sprintf("gob: registering duplicate names for %s: %q != %q", ut.user, n, name))
+	}
+	// Store the name and type provided by the user....
+	nameToConcreteType[name] = reflect.TypeOf(value)
+	// but the flattened type in the type table, since that's what decode needs.
+	concreteTypeToName[ut.base] = name
+}
+
+// Register records a type, identified by a value for that type, under its
+// internal type name.  That name will identify the concrete type of a value
+// sent or received as an interface variable.  Only types that will be
+// transferred as implementations of interface values need to be registered.
+// Expecting to be used only during initialization, it panics if the mapping
+// between types and names is not a bijection.
+func Register(value interface{}) {
+	// Default to printed representation for unnamed types
+	rt := reflect.TypeOf(value)
+	name := rt.String()
+
+	// But for named types (or pointers to them), qualify with import path (but see inner comment).
+	// Dereference one pointer looking for a named type.
+	star := ""
+	if rt.Name() == "" {
+		if pt := rt; pt.Kind() == reflect.Ptr {
+			star = "*"
+			// NOTE: The following line should be rt = pt.Elem() to implement
+			// what the comment above claims, but fixing it would break compatibility
+			// with existing gobs.
+			//
+			// Given package p imported as "full/p" with these definitions:
+			//     package p
+			//     type T1 struct { ... }
+			// this table shows the intended and actual strings used by gob to
+			// name the types:
+			//
+			// Type      Correct string     Actual string
+			//
+			// T1        full/p.T1          full/p.T1
+			// *T1       *full/p.T1         *p.T1
+			//
+			// The missing full path cannot be fixed without breaking existing gob decoders.
+			rt = pt
+		}
+	}
+	if rt.Name() != "" {
+		if rt.PkgPath() == "" {
+			name = star + rt.Name()
+		} else {
+			name = star + rt.PkgPath() + "." + rt.Name()
+		}
+	}
+
+	RegisterName(name, value)
+}
+
+func registerBasics() {
+	Register(int(0))
+	Register(int8(0))
+	Register(int16(0))
+	Register(int32(0))
+	Register(int64(0))
+	Register(uint(0))
+	Register(uint8(0))
+	Register(uint16(0))
+	Register(uint32(0))
+	Register(uint64(0))
+	Register(float32(0))
+	Register(float64(0))
+	Register(complex64(0i))
+	Register(complex128(0i))
+	Register(uintptr(0))
+	Register(false)
+	Register("")
+	Register([]byte(nil))
+	Register([]int(nil))
+	Register([]int8(nil))
+	Register([]int16(nil))
+	Register([]int32(nil))
+	Register([]int64(nil))
+	Register([]uint(nil))
+	Register([]uint8(nil))
+	Register([]uint16(nil))
+	Register([]uint32(nil))
+	Register([]uint64(nil))
+	Register([]float32(nil))
+	Register([]float64(nil))
+	Register([]complex64(nil))
+	Register([]complex128(nil))
+	Register([]uintptr(nil))
+	Register([]bool(nil))
+	Register([]string(nil))
+}
diff --git a/src/encoding/gob/type_test.go b/src/encoding/gob/type_test.go
new file mode 100644
index 0000000000..e230d22d43
--- /dev/null
+++ b/src/encoding/gob/type_test.go
@@ -0,0 +1,222 @@
+// 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 (
+	"bytes"
+	"reflect"
+	"testing"
+)
+
+type typeT struct {
+	id  typeId
+	str string
+}
+
+var basicTypes = []typeT{
+	{tBool, "bool"},
+	{tInt, "int"},
+	{tUint, "uint"},
+	{tFloat, "float"},
+	{tBytes, "bytes"},
+	{tString, "string"},
+}
+
+func getTypeUnlocked(name string, rt reflect.Type) gobType {
+	typeLock.Lock()
+	defer typeLock.Unlock()
+	t, err := getBaseType(name, rt)
+	if err != nil {
+		panic("getTypeUnlocked: " + err.Error())
+	}
+	return t
+}
+
+// Sanity checks
+func TestBasic(t *testing.T) {
+	for _, tt := range basicTypes {
+		if tt.id.string() != tt.str {
+			t.Errorf("checkType: expected %q got %s", tt.str, tt.id.string())
+		}
+		if tt.id == 0 {
+			t.Errorf("id for %q is zero", tt.str)
+		}
+	}
+}
+
+// Reregister some basic types to check registration is idempotent.
+func TestReregistration(t *testing.T) {
+	newtyp := getTypeUnlocked("int", reflect.TypeOf(int(0)))
+	if newtyp != tInt.gobType() {
+		t.Errorf("reregistration of %s got new type", newtyp.string())
+	}
+	newtyp = getTypeUnlocked("uint", reflect.TypeOf(uint(0)))
+	if newtyp != tUint.gobType() {
+		t.Errorf("reregistration of %s got new type", newtyp.string())
+	}
+	newtyp = getTypeUnlocked("string", reflect.TypeOf("hello"))
+	if newtyp != tString.gobType() {
+		t.Errorf("reregistration of %s got new type", newtyp.string())
+	}
+}
+
+func TestArrayType(t *testing.T) {
+	var a3 [3]int
+	a3int := getTypeUnlocked("foo", reflect.TypeOf(a3))
+	newa3int := getTypeUnlocked("bar", reflect.TypeOf(a3))
+	if a3int != newa3int {
+		t.Errorf("second registration of [3]int creates new type")
+	}
+	var a4 [4]int
+	a4int := getTypeUnlocked("goo", reflect.TypeOf(a4))
+	if a3int == a4int {
+		t.Errorf("registration of [3]int creates same type as [4]int")
+	}
+	var b3 [3]bool
+	a3bool := getTypeUnlocked("", reflect.TypeOf(b3))
+	if a3int == a3bool {
+		t.Errorf("registration of [3]bool creates same type as [3]int")
+	}
+	str := a3bool.string()
+	expected := "[3]bool"
+	if str != expected {
+		t.Errorf("array printed as %q; expected %q", str, expected)
+	}
+}
+
+func TestSliceType(t *testing.T) {
+	var s []int
+	sint := getTypeUnlocked("slice", reflect.TypeOf(s))
+	var news []int
+	newsint := getTypeUnlocked("slice1", reflect.TypeOf(news))
+	if sint != newsint {
+		t.Errorf("second registration of []int creates new type")
+	}
+	var b []bool
+	sbool := getTypeUnlocked("", reflect.TypeOf(b))
+	if sbool == sint {
+		t.Errorf("registration of []bool creates same type as []int")
+	}
+	str := sbool.string()
+	expected := "[]bool"
+	if str != expected {
+		t.Errorf("slice printed as %q; expected %q", str, expected)
+	}
+}
+
+func TestMapType(t *testing.T) {
+	var m map[string]int
+	mapStringInt := getTypeUnlocked("map", reflect.TypeOf(m))
+	var newm map[string]int
+	newMapStringInt := getTypeUnlocked("map1", reflect.TypeOf(newm))
+	if mapStringInt != newMapStringInt {
+		t.Errorf("second registration of map[string]int creates new type")
+	}
+	var b map[string]bool
+	mapStringBool := getTypeUnlocked("", reflect.TypeOf(b))
+	if mapStringBool == mapStringInt {
+		t.Errorf("registration of map[string]bool creates same type as map[string]int")
+	}
+	str := mapStringBool.string()
+	expected := "map[string]bool"
+	if str != expected {
+		t.Errorf("map printed as %q; expected %q", str, expected)
+	}
+}
+
+type Bar struct {
+	X string
+}
+
+// This structure has pointers and refers to itself, making it a good test case.
+type Foo struct {
+	A int
+	B int32 // will become int
+	C string
+	D []byte
+	E *float64    // will become float64
+	F ****float64 // will become float64
+	G *Bar
+	H *Bar // should not interpolate the definition of Bar again
+	I *Foo // will not explode
+}
+
+func TestStructType(t *testing.T) {
+	sstruct := getTypeUnlocked("Foo", reflect.TypeOf(Foo{}))
+	str := sstruct.string()
+	// If we can print it correctly, we built it correctly.
+	expected := "Foo = struct { A int; B int; C string; D bytes; E float; F float; G Bar = struct { X string; }; H Bar; I Foo; }"
+	if str != expected {
+		t.Errorf("struct printed as %q; expected %q", str, expected)
+	}
+}
+
+// Should be OK to register the same type multiple times, as long as they're
+// at the same level of indirection.
+func TestRegistration(t *testing.T) {
+	type T struct{ a int }
+	Register(new(T))
+	Register(new(T))
+}
+
+type N1 struct{}
+type N2 struct{}
+
+// See comment in type.go/Register.
+func TestRegistrationNaming(t *testing.T) {
+	testCases := []struct {
+		t    interface{}
+		name string
+	}{
+		{&N1{}, "*gob.N1"},
+		{N2{}, "encoding/gob.N2"},
+	}
+
+	for _, tc := range testCases {
+		Register(tc.t)
+
+		tct := reflect.TypeOf(tc.t)
+		registerLock.RLock()
+		ct := nameToConcreteType[tc.name]
+		registerLock.RUnlock()
+		if ct != tct {
+			t.Errorf("nameToConcreteType[%q] = %v, want %v", tc.name, ct, tct)
+		}
+		// concreteTypeToName is keyed off the base type.
+		if tct.Kind() == reflect.Ptr {
+			tct = tct.Elem()
+		}
+		if n := concreteTypeToName[tct]; n != tc.name {
+			t.Errorf("concreteTypeToName[%v] got %v, want %v", tct, n, tc.name)
+		}
+	}
+}
+
+func TestStressParallel(t *testing.T) {
+	type T2 struct{ A int }
+	c := make(chan bool)
+	const N = 10
+	for i := 0; i < N; i++ {
+		go func() {
+			p := new(T2)
+			Register(p)
+			b := new(bytes.Buffer)
+			enc := NewEncoder(b)
+			err := enc.Encode(p)
+			if err != nil {
+				t.Error("encoder fail:", err)
+			}
+			dec := NewDecoder(b)
+			err = dec.Decode(p)
+			if err != nil {
+				t.Error("decoder fail:", err)
+			}
+			c <- true
+		}()
+	}
+	for i := 0; i < N; i++ {
+		<-c
+	}
+}