debug.go

Documentation: encoding/gob

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Delete the next line to include in the gob package.
     6  //go:build ignore
     7  // +build ignore
     8  
     9  package gob
    10  
    11  // This file is not normally included in the gob package. Used only for debugging the package itself.
    12  // Except for reading uints, it is an implementation of a reader that is independent of
    13  // the one implemented by Decoder.
    14  // To enable the Debug function, delete the +build ignore line above and do
    15  //	go install
    16  
    17  import (
    18  	"bytes"
    19  	"fmt"
    20  	"io"
    21  	"os"
    22  	"strings"
    23  	"sync"
    24  )
    25  
    26  var dumpBytes = false // If true, print the remaining bytes in the input buffer at each item.
    27  
    28  // Init installs the debugging facility. If this file is not compiled in the
    29  // package, the tests in codec_test.go are no-ops.
    30  func init() {
    31  	debugFunc = Debug
    32  }
    33  
    34  var (
    35  	blanks = bytes.Repeat([]byte{' '}, 3*10)
    36  	empty  = []byte(": <empty>\n")
    37  	tabs   = strings.Repeat("\t", 100)
    38  )
    39  
    40  // tab indents itself when printed.
    41  type tab int
    42  
    43  func (t tab) String() string {
    44  	n := int(t)
    45  	if n > len(tabs) {
    46  		n = len(tabs)
    47  	}
    48  	return tabs[0:n]
    49  }
    50  
    51  func (t tab) print() {
    52  	fmt.Fprint(os.Stderr, t)
    53  }
    54  
    55  // A peekReader wraps an io.Reader, allowing one to peek ahead to see
    56  // what's coming without stealing the data from the client of the Reader.
    57  type peekReader struct {
    58  	r    io.Reader
    59  	data []byte // read-ahead data
    60  }
    61  
    62  // newPeekReader returns a peekReader that wraps r.
    63  func newPeekReader(r io.Reader) *peekReader {
    64  	return &peekReader{r: r}
    65  }
    66  
    67  // Read is the usual method. It will first take data that has been read ahead.
    68  func (p *peekReader) Read(b []byte) (n int, err error) {
    69  	if len(p.data) == 0 {
    70  		return p.r.Read(b)
    71  	}
    72  	// Satisfy what's possible from the read-ahead data.
    73  	n = copy(b, p.data)
    74  	// Move data down to beginning of slice, to avoid endless growth
    75  	copy(p.data, p.data[n:])
    76  	p.data = p.data[:len(p.data)-n]
    77  	return
    78  }
    79  
    80  // peek returns as many bytes as possible from the unread
    81  // portion of the stream, up to the length of b.
    82  func (p *peekReader) peek(b []byte) (n int, err error) {
    83  	if len(p.data) > 0 {
    84  		n = copy(b, p.data)
    85  		if n == len(b) {
    86  			return
    87  		}
    88  		b = b[n:]
    89  	}
    90  	if len(b) == 0 {
    91  		return
    92  	}
    93  	m, e := io.ReadFull(p.r, b)
    94  	if m > 0 {
    95  		p.data = append(p.data, b[:m]...)
    96  	}
    97  	n += m
    98  	if e == io.ErrUnexpectedEOF {
    99  		// That means m > 0 but we reached EOF. If we got data
   100  		// we won't complain about not being able to peek enough.
   101  		if n > 0 {
   102  			e = nil
   103  		} else {
   104  			e = io.EOF
   105  		}
   106  	}
   107  	return n, e
   108  }
   109  
   110  type debugger struct {
   111  	mutex          sync.Mutex
   112  	remain         int  // the number of bytes known to remain in the input
   113  	remainingKnown bool // the value of 'remain' is valid
   114  	r              *peekReader
   115  	wireType       map[typeId]*wireType
   116  	tmp            []byte // scratch space for decoding uints.
   117  }
   118  
   119  // dump prints the next nBytes of the input.
   120  // It arranges to print the output aligned from call to
   121  // call, to make it easy to see what has been consumed.
   122  func (deb *debugger) dump(format string, args ...interface{}) {
   123  	if !dumpBytes {
   124  		return
   125  	}
   126  	fmt.Fprintf(os.Stderr, format+" ", args...)
   127  	if !deb.remainingKnown {
   128  		return
   129  	}
   130  	if deb.remain < 0 {
   131  		fmt.Fprintf(os.Stderr, "remaining byte count is negative! %d\n", deb.remain)
   132  		return
   133  	}
   134  	data := make([]byte, deb.remain)
   135  	n, _ := deb.r.peek(data)
   136  	if n == 0 {
   137  		os.Stderr.Write(empty)
   138  		return
   139  	}
   140  	b := new(bytes.Buffer)
   141  	fmt.Fprintf(b, "[%d]{\n", deb.remain)
   142  	// Blanks until first byte
   143  	lineLength := 0
   144  	if n := len(data); n%10 != 0 {
   145  		lineLength = 10 - n%10
   146  		fmt.Fprintf(b, "\t%s", blanks[:lineLength*3])
   147  	}
   148  	// 10 bytes per line
   149  	for len(data) > 0 {
   150  		if lineLength == 0 {
   151  			fmt.Fprint(b, "\t")
   152  		}
   153  		m := 10 - lineLength
   154  		lineLength = 0
   155  		if m > len(data) {
   156  			m = len(data)
   157  		}
   158  		fmt.Fprintf(b, "% x\n", data[:m])
   159  		data = data[m:]
   160  	}
   161  	fmt.Fprint(b, "}\n")
   162  	os.Stderr.Write(b.Bytes())
   163  }
   164  
   165  // Debug prints a human-readable representation of the gob data read from r.
   166  // It is a no-op unless debugging was enabled when the package was built.
   167  func Debug(r io.Reader) {
   168  	err := debug(r)
   169  	if err != nil {
   170  		fmt.Fprintf(os.Stderr, "gob debug: %s\n", err)
   171  	}
   172  }
   173  
   174  // debug implements Debug, but catches panics and returns
   175  // them as errors to be printed by Debug.
   176  func debug(r io.Reader) (err error) {
   177  	defer catchError(&err)
   178  	fmt.Fprintln(os.Stderr, "Start of debugging")
   179  	deb := &debugger{
   180  		r:        newPeekReader(r),
   181  		wireType: make(map[typeId]*wireType),
   182  		tmp:      make([]byte, 16),
   183  	}
   184  	if b, ok := r.(*bytes.Buffer); ok {
   185  		deb.remain = b.Len()
   186  		deb.remainingKnown = true
   187  	}
   188  	deb.gobStream()
   189  	return
   190  }
   191  
   192  // note that we've consumed some bytes
   193  func (deb *debugger) consumed(n int) {
   194  	if deb.remainingKnown {
   195  		deb.remain -= n
   196  	}
   197  }
   198  
   199  // int64 decodes and returns the next integer, which must be present.
   200  // Don't call this if you could be at EOF.
   201  func (deb *debugger) int64() int64 {
   202  	return toInt(deb.uint64())
   203  }
   204  
   205  // uint64 returns and decodes the next unsigned integer, which must be present.
   206  // Don't call this if you could be at EOF.
   207  // TODO: handle errors better.
   208  func (deb *debugger) uint64() uint64 {
   209  	n, w, err := decodeUintReader(deb.r, deb.tmp)
   210  	if err != nil {
   211  		errorf("debug: read error: %s", err)
   212  	}
   213  	deb.consumed(w)
   214  	return n
   215  }
   216  
   217  // GobStream:
   218  //	DelimitedMessage* (until EOF)
   219  func (deb *debugger) gobStream() {
   220  	// Make sure we're single-threaded through here.
   221  	deb.mutex.Lock()
   222  	defer deb.mutex.Unlock()
   223  
   224  	for deb.delimitedMessage(0) {
   225  	}
   226  }
   227  
   228  // DelimitedMessage:
   229  //	uint(lengthOfMessage) Message
   230  func (deb *debugger) delimitedMessage(indent tab) bool {
   231  	for {
   232  		n := deb.loadBlock(true)
   233  		if n < 0 {
   234  			return false
   235  		}
   236  		deb.dump("Delimited message of length %d", n)
   237  		deb.message(indent)
   238  	}
   239  	return true
   240  }
   241  
   242  // loadBlock preps us to read a message
   243  // of the length specified next in the input. It returns
   244  // the length of the block. The argument tells whether
   245  // an EOF is acceptable now. If it is and one is found,
   246  // the return value is negative.
   247  func (deb *debugger) loadBlock(eofOK bool) int {
   248  	n64, w, err := decodeUintReader(deb.r, deb.tmp) // deb.uint64 will error at EOF
   249  	if err != nil {
   250  		if eofOK && err == io.EOF {
   251  			return -1
   252  		}
   253  		errorf("debug: unexpected error: %s", err)
   254  	}
   255  	deb.consumed(w)
   256  	n := int(n64)
   257  	if n < 0 {
   258  		errorf("huge value for message length: %d", n64)
   259  	}
   260  	return int(n)
   261  }
   262  
   263  // Message:
   264  //	TypeSequence TypedValue
   265  // TypeSequence
   266  //	(TypeDefinition DelimitedTypeDefinition*)?
   267  // DelimitedTypeDefinition:
   268  //	uint(lengthOfTypeDefinition) TypeDefinition
   269  // TypedValue:
   270  //	int(typeId) Value
   271  func (deb *debugger) message(indent tab) bool {
   272  	for {
   273  		// Convert the uint64 to a signed integer typeId
   274  		uid := deb.int64()
   275  		id := typeId(uid)
   276  		deb.dump("type id=%d", id)
   277  		if id < 0 {
   278  			deb.typeDefinition(indent, -id)
   279  			n := deb.loadBlock(false)
   280  			deb.dump("Message of length %d", n)
   281  			continue
   282  		} else {
   283  			deb.value(indent, id)
   284  			break
   285  		}
   286  	}
   287  	return true
   288  }
   289  
   290  // Helper methods to make it easy to scan a type descriptor.
   291  
   292  // common returns the CommonType at the input point.
   293  func (deb *debugger) common() CommonType {
   294  	fieldNum := -1
   295  	name := ""
   296  	id := typeId(0)
   297  	for {
   298  		delta := deb.delta(-1)
   299  		if delta == 0 {
   300  			break
   301  		}
   302  		fieldNum += delta
   303  		switch fieldNum {
   304  		case 0:
   305  			name = deb.string()
   306  		case 1:
   307  			// Id typeId
   308  			id = deb.typeId()
   309  		default:
   310  			errorf("corrupted CommonType, delta is %d fieldNum is %d", delta, fieldNum)
   311  		}
   312  	}
   313  	return CommonType{name, id}
   314  }
   315  
   316  // uint returns the unsigned int at the input point, as a uint (not uint64).
   317  func (deb *debugger) uint() uint {
   318  	return uint(deb.uint64())
   319  }
   320  
   321  // int returns the signed int at the input point, as an int (not int64).
   322  func (deb *debugger) int() int {
   323  	return int(deb.int64())
   324  }
   325  
   326  // typeId returns the type id at the input point.
   327  func (deb *debugger) typeId() typeId {
   328  	return typeId(deb.int64())
   329  }
   330  
   331  // string returns the string at the input point.
   332  func (deb *debugger) string() string {
   333  	x := int(deb.uint64())
   334  	b := make([]byte, x)
   335  	nb, _ := deb.r.Read(b)
   336  	if nb != x {
   337  		errorf("corrupted type")
   338  	}
   339  	deb.consumed(nb)
   340  	return string(b)
   341  }
   342  
   343  // delta returns the field delta at the input point. The expect argument,
   344  // if non-negative, identifies what the value should be.
   345  func (deb *debugger) delta(expect int) int {
   346  	delta := int(deb.uint64())
   347  	if delta < 0 || (expect >= 0 && delta != expect) {
   348  		errorf("decode: corrupted type: delta %d expected %d", delta, expect)
   349  	}
   350  	return delta
   351  }
   352  
   353  // TypeDefinition:
   354  //	[int(-typeId) (already read)] encodingOfWireType
   355  func (deb *debugger) typeDefinition(indent tab, id typeId) {
   356  	deb.dump("type definition for id %d", id)
   357  	// Encoding is of a wireType. Decode the structure as usual
   358  	fieldNum := -1
   359  	wire := new(wireType)
   360  	// A wireType defines a single field.
   361  	delta := deb.delta(-1)
   362  	fieldNum += delta
   363  	switch fieldNum {
   364  	case 0: // array type, one field of {{Common}, elem, length}
   365  		// Field number 0 is CommonType
   366  		deb.delta(1)
   367  		com := deb.common()
   368  		// Field number 1 is type Id of elem
   369  		deb.delta(1)
   370  		id := deb.typeId()
   371  		// Field number 3 is length
   372  		deb.delta(1)
   373  		length := deb.int()
   374  		wire.ArrayT = &arrayType{com, id, length}
   375  
   376  	case 1: // slice type, one field of {{Common}, elem}
   377  		// Field number 0 is CommonType
   378  		deb.delta(1)
   379  		com := deb.common()
   380  		// Field number 1 is type Id of elem
   381  		deb.delta(1)
   382  		id := deb.typeId()
   383  		wire.SliceT = &sliceType{com, id}
   384  
   385  	case 2: // struct type, one field of {{Common}, []fieldType}
   386  		// Field number 0 is CommonType
   387  		deb.delta(1)
   388  		com := deb.common()
   389  		// Field number 1 is slice of FieldType
   390  		deb.delta(1)
   391  		numField := int(deb.uint())
   392  		field := make([]*fieldType, numField)
   393  		for i := 0; i < numField; i++ {
   394  			field[i] = new(fieldType)
   395  			deb.delta(1) // field 0 of fieldType: name
   396  			field[i].Name = deb.string()
   397  			deb.delta(1) // field 1 of fieldType: id
   398  			field[i].Id = deb.typeId()
   399  			deb.delta(0) // end of fieldType
   400  		}
   401  		wire.StructT = &structType{com, field}
   402  
   403  	case 3: // map type, one field of {{Common}, key, elem}
   404  		// Field number 0 is CommonType
   405  		deb.delta(1)
   406  		com := deb.common()
   407  		// Field number 1 is type Id of key
   408  		deb.delta(1)
   409  		keyId := deb.typeId()
   410  		// Field number 2 is type Id of elem
   411  		deb.delta(1)
   412  		elemId := deb.typeId()
   413  		wire.MapT = &mapType{com, keyId, elemId}
   414  	case 4: // GobEncoder type, one field of {{Common}}
   415  		// Field number 0 is CommonType
   416  		deb.delta(1)
   417  		com := deb.common()
   418  		wire.GobEncoderT = &gobEncoderType{com}
   419  	case 5: // BinaryMarshaler type, one field of {{Common}}
   420  		// Field number 0 is CommonType
   421  		deb.delta(1)
   422  		com := deb.common()
   423  		wire.BinaryMarshalerT = &gobEncoderType{com}
   424  	case 6: // TextMarshaler type, one field of {{Common}}
   425  		// Field number 0 is CommonType
   426  		deb.delta(1)
   427  		com := deb.common()
   428  		wire.TextMarshalerT = &gobEncoderType{com}
   429  	default:
   430  		errorf("bad field in type %d", fieldNum)
   431  	}
   432  	deb.printWireType(indent, wire)
   433  	deb.delta(0) // end inner type (arrayType, etc.)
   434  	deb.delta(0) // end wireType
   435  	// Remember we've seen this type.
   436  	deb.wireType[id] = wire
   437  }
   438  
   439  // Value:
   440  //	SingletonValue | StructValue
   441  func (deb *debugger) value(indent tab, id typeId) {
   442  	wire, ok := deb.wireType[id]
   443  	if ok && wire.StructT != nil {
   444  		deb.structValue(indent, id)
   445  	} else {
   446  		deb.singletonValue(indent, id)
   447  	}
   448  }
   449  
   450  // SingletonValue:
   451  //	uint(0) FieldValue
   452  func (deb *debugger) singletonValue(indent tab, id typeId) {
   453  	deb.dump("Singleton value")
   454  	// is it a builtin type?
   455  	wire := deb.wireType[id]
   456  	_, ok := builtinIdToType[id]
   457  	if !ok && wire == nil {
   458  		errorf("type id %d not defined", id)
   459  	}
   460  	m := deb.uint64()
   461  	if m != 0 {
   462  		errorf("expected zero; got %d", m)
   463  	}
   464  	deb.fieldValue(indent, id)
   465  }
   466  
   467  // InterfaceValue:
   468  //	NilInterfaceValue | NonNilInterfaceValue
   469  func (deb *debugger) interfaceValue(indent tab) {
   470  	deb.dump("Start of interface value")
   471  	if nameLen := deb.uint64(); nameLen == 0 {
   472  		deb.nilInterfaceValue(indent)
   473  	} else {
   474  		deb.nonNilInterfaceValue(indent, int(nameLen))
   475  	}
   476  }
   477  
   478  // NilInterfaceValue:
   479  //	uint(0) [already read]
   480  func (deb *debugger) nilInterfaceValue(indent tab) int {
   481  	fmt.Fprintf(os.Stderr, "%snil interface\n", indent)
   482  	return 0
   483  }
   484  
   485  // NonNilInterfaceValue:
   486  //	ConcreteTypeName TypeSequence InterfaceContents
   487  // ConcreteTypeName:
   488  //	uint(lengthOfName) [already read=n] name
   489  // InterfaceContents:
   490  //	int(concreteTypeId) DelimitedValue
   491  // DelimitedValue:
   492  //	uint(length) Value
   493  func (deb *debugger) nonNilInterfaceValue(indent tab, nameLen int) {
   494  	// ConcreteTypeName
   495  	b := make([]byte, nameLen)
   496  	deb.r.Read(b) // TODO: CHECK THESE READS!!
   497  	deb.consumed(nameLen)
   498  	name := string(b)
   499  
   500  	for {
   501  		id := deb.typeId()
   502  		if id < 0 {
   503  			deb.typeDefinition(indent, -id)
   504  			n := deb.loadBlock(false)
   505  			deb.dump("Nested message of length %d", n)
   506  		} else {
   507  			// DelimitedValue
   508  			x := deb.uint64() // in case we want to ignore the value; we don't.
   509  			fmt.Fprintf(os.Stderr, "%sinterface value, type %q id=%d; valueLength %d\n", indent, name, id, x)
   510  			deb.value(indent, id)
   511  			break
   512  		}
   513  	}
   514  }
   515  
   516  // printCommonType prints a common type; used by printWireType.
   517  func (deb *debugger) printCommonType(indent tab, kind string, common *CommonType) {
   518  	indent.print()
   519  	fmt.Fprintf(os.Stderr, "%s %q id=%d\n", kind, common.Name, common.Id)
   520  }
   521  
   522  // printWireType prints the contents of a wireType.
   523  func (deb *debugger) printWireType(indent tab, wire *wireType) {
   524  	fmt.Fprintf(os.Stderr, "%stype definition {\n", indent)
   525  	indent++
   526  	switch {
   527  	case wire.ArrayT != nil:
   528  		deb.printCommonType(indent, "array", &wire.ArrayT.CommonType)
   529  		fmt.Fprintf(os.Stderr, "%slen %d\n", indent+1, wire.ArrayT.Len)
   530  		fmt.Fprintf(os.Stderr, "%selemid %d\n", indent+1, wire.ArrayT.Elem)
   531  	case wire.MapT != nil:
   532  		deb.printCommonType(indent, "map", &wire.MapT.CommonType)
   533  		fmt.Fprintf(os.Stderr, "%skey id=%d\n", indent+1, wire.MapT.Key)
   534  		fmt.Fprintf(os.Stderr, "%selem id=%d\n", indent+1, wire.MapT.Elem)
   535  	case wire.SliceT != nil:
   536  		deb.printCommonType(indent, "slice", &wire.SliceT.CommonType)
   537  		fmt.Fprintf(os.Stderr, "%selem id=%d\n", indent+1, wire.SliceT.Elem)
   538  	case wire.StructT != nil:
   539  		deb.printCommonType(indent, "struct", &wire.StructT.CommonType)
   540  		for i, field := range wire.StructT.Field {
   541  			fmt.Fprintf(os.Stderr, "%sfield %d:\t%s\tid=%d\n", indent+1, i, field.Name, field.Id)
   542  		}
   543  	case wire.GobEncoderT != nil:
   544  		deb.printCommonType(indent, "GobEncoder", &wire.GobEncoderT.CommonType)
   545  	}
   546  	indent--
   547  	fmt.Fprintf(os.Stderr, "%s}\n", indent)
   548  }
   549  
   550  // fieldValue prints a value of any type, such as a struct field.
   551  // FieldValue:
   552  //	builtinValue | ArrayValue | MapValue | SliceValue | StructValue | InterfaceValue
   553  func (deb *debugger) fieldValue(indent tab, id typeId) {
   554  	_, ok := builtinIdToType[id]
   555  	if ok {
   556  		if id == tInterface {
   557  			deb.interfaceValue(indent)
   558  		} else {
   559  			deb.printBuiltin(indent, id)
   560  		}
   561  		return
   562  	}
   563  	wire, ok := deb.wireType[id]
   564  	if !ok {
   565  		errorf("type id %d not defined", id)
   566  	}
   567  	switch {
   568  	case wire.ArrayT != nil:
   569  		deb.arrayValue(indent, wire)
   570  	case wire.MapT != nil:
   571  		deb.mapValue(indent, wire)
   572  	case wire.SliceT != nil:
   573  		deb.sliceValue(indent, wire)
   574  	case wire.StructT != nil:
   575  		deb.structValue(indent, id)
   576  	case wire.GobEncoderT != nil:
   577  		deb.gobEncoderValue(indent, id)
   578  	default:
   579  		panic("bad wire type for field")
   580  	}
   581  }
   582  
   583  // printBuiltin prints a value not of a fundamental type, that is,
   584  // one whose type is known to gobs at bootstrap time.
   585  func (deb *debugger) printBuiltin(indent tab, id typeId) {
   586  	switch id {
   587  	case tBool:
   588  		x := deb.int64()
   589  		if x == 0 {
   590  			fmt.Fprintf(os.Stderr, "%sfalse\n", indent)
   591  		} else {
   592  			fmt.Fprintf(os.Stderr, "%strue\n", indent)
   593  		}
   594  	case tInt:
   595  		x := deb.int64()
   596  		fmt.Fprintf(os.Stderr, "%s%d\n", indent, x)
   597  	case tUint:
   598  		x := deb.uint64()
   599  		fmt.Fprintf(os.Stderr, "%s%d\n", indent, x)
   600  	case tFloat:
   601  		x := deb.uint64()
   602  		fmt.Fprintf(os.Stderr, "%s%g\n", indent, float64FromBits(x))
   603  	case tComplex:
   604  		r := deb.uint64()
   605  		i := deb.uint64()
   606  		fmt.Fprintf(os.Stderr, "%s%g+%gi\n", indent, float64FromBits(r), float64FromBits(i))
   607  	case tBytes:
   608  		x := int(deb.uint64())
   609  		b := make([]byte, x)
   610  		deb.r.Read(b)
   611  		deb.consumed(x)
   612  		fmt.Fprintf(os.Stderr, "%s{% x}=%q\n", indent, b, b)
   613  	case tString:
   614  		x := int(deb.uint64())
   615  		b := make([]byte, x)
   616  		deb.r.Read(b)
   617  		deb.consumed(x)
   618  		fmt.Fprintf(os.Stderr, "%s%q\n", indent, b)
   619  	default:
   620  		panic("unknown builtin")
   621  	}
   622  }
   623  
   624  // ArrayValue:
   625  //	uint(n) FieldValue*n
   626  func (deb *debugger) arrayValue(indent tab, wire *wireType) {
   627  	elemId := wire.ArrayT.Elem
   628  	u := deb.uint64()
   629  	length := int(u)
   630  	for i := 0; i < length; i++ {
   631  		deb.fieldValue(indent, elemId)
   632  	}
   633  	if length != wire.ArrayT.Len {
   634  		fmt.Fprintf(os.Stderr, "%s(wrong length for array: %d should be %d)\n", indent, length, wire.ArrayT.Len)
   635  	}
   636  }
   637  
   638  // MapValue:
   639  //	uint(n) (FieldValue FieldValue)*n  [n (key, value) pairs]
   640  func (deb *debugger) mapValue(indent tab, wire *wireType) {
   641  	keyId := wire.MapT.Key
   642  	elemId := wire.MapT.Elem
   643  	u := deb.uint64()
   644  	length := int(u)
   645  	for i := 0; i < length; i++ {
   646  		deb.fieldValue(indent+1, keyId)
   647  		deb.fieldValue(indent+1, elemId)
   648  	}
   649  }
   650  
   651  // SliceValue:
   652  //	uint(n) (n FieldValue)
   653  func (deb *debugger) sliceValue(indent tab, wire *wireType) {
   654  	elemId := wire.SliceT.Elem
   655  	u := deb.uint64()
   656  	length := int(u)
   657  	deb.dump("Start of slice of length %d", length)
   658  
   659  	for i := 0; i < length; i++ {
   660  		deb.fieldValue(indent, elemId)
   661  	}
   662  }
   663  
   664  // StructValue:
   665  //	(uint(fieldDelta) FieldValue)*
   666  func (deb *debugger) structValue(indent tab, id typeId) {
   667  	deb.dump("Start of struct value of %q id=%d\n<<\n", id.name(), id)
   668  	fmt.Fprintf(os.Stderr, "%s%s struct {\n", indent, id.name())
   669  	wire, ok := deb.wireType[id]
   670  	if !ok {
   671  		errorf("type id %d not defined", id)
   672  	}
   673  	strct := wire.StructT
   674  	fieldNum := -1
   675  	indent++
   676  	for {
   677  		delta := deb.uint64()
   678  		if delta == 0 { // struct terminator is zero delta fieldnum
   679  			break
   680  		}
   681  		fieldNum += int(delta)
   682  		if fieldNum < 0 || fieldNum >= len(strct.Field) {
   683  			deb.dump("field number out of range: prevField=%d delta=%d", fieldNum-int(delta), delta)
   684  			break
   685  		}
   686  		fmt.Fprintf(os.Stderr, "%sfield %d:\t%s\n", indent, fieldNum, wire.StructT.Field[fieldNum].Name)
   687  		deb.fieldValue(indent+1, strct.Field[fieldNum].Id)
   688  	}
   689  	indent--
   690  	fmt.Fprintf(os.Stderr, "%s} // end %s struct\n", indent, id.name())
   691  	deb.dump(">> End of struct value of type %d %q", id, id.name())
   692  }
   693  
   694  // GobEncoderValue:
   695  //	uint(n) byte*n
   696  func (deb *debugger) gobEncoderValue(indent tab, id typeId) {
   697  	len := deb.uint64()
   698  	deb.dump("GobEncoder value of %q id=%d, length %d\n", id.name(), id, len)
   699  	fmt.Fprintf(os.Stderr, "%s%s (implements GobEncoder)\n", indent, id.name())
   700  	data := make([]byte, len)
   701  	_, err := deb.r.Read(data)
   702  	if err != nil {
   703  		errorf("gobEncoder data read: %s", err)
   704  	}
   705  	fmt.Fprintf(os.Stderr, "%s[% .2x]\n", indent+1, data)
   706  }
   707
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