src/encoding/gob/debug.go - go - Git at Google

 // 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)
 }
	// 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)
	}