binary.go

Documentation: encoding/binary

     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  // Package binary implements simple translation between numbers and byte
     6  // sequences and encoding and decoding of varints.
     7  //
     8  // Numbers are translated by reading and writing fixed-size values.
     9  // A fixed-size value is either a fixed-size arithmetic
    10  // type (bool, int8, uint8, int16, float32, complex64, ...)
    11  // or an array or struct containing only fixed-size values.
    12  //
    13  // The varint functions encode and decode single integer values using
    14  // a variable-length encoding; smaller values require fewer bytes.
    15  // For a specification, see
    16  // https://developers.google.com/protocol-buffers/docs/encoding.
    17  //
    18  // This package favors simplicity over efficiency. Clients that require
    19  // high-performance serialization, especially for large data structures,
    20  // should look at more advanced solutions such as the encoding/gob
    21  // package or protocol buffers.
    22  package binary
    23  
    24  import (
    25  	"errors"
    26  	"io"
    27  	"math"
    28  	"reflect"
    29  	"sync"
    30  )
    31  
    32  // A ByteOrder specifies how to convert byte slices into
    33  // 16-, 32-, or 64-bit unsigned integers.
    34  type ByteOrder interface {
    35  	Uint16([]byte) uint16
    36  	Uint32([]byte) uint32
    37  	Uint64([]byte) uint64
    38  	PutUint16([]byte, uint16)
    39  	PutUint32([]byte, uint32)
    40  	PutUint64([]byte, uint64)
    41  	String() string
    42  }
    43  
    44  // AppendByteOrder specifies how to append 16-, 32-, or 64-bit unsigned integers
    45  // into a byte slice.
    46  type AppendByteOrder interface {
    47  	AppendUint16([]byte, uint16) []byte
    48  	AppendUint32([]byte, uint32) []byte
    49  	AppendUint64([]byte, uint64) []byte
    50  	String() string
    51  }
    52  
    53  // LittleEndian is the little-endian implementation of ByteOrder and AppendByteOrder.
    54  var LittleEndian littleEndian
    55  
    56  // BigEndian is the big-endian implementation of ByteOrder and AppendByteOrder.
    57  var BigEndian bigEndian
    58  
    59  type littleEndian struct{}
    60  
    61  func (littleEndian) Uint16(b []byte) uint16 {
    62  	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
    63  	return uint16(b[0]) | uint16(b[1])<<8
    64  }
    65  
    66  func (littleEndian) PutUint16(b []byte, v uint16) {
    67  	_ = b[1] // early bounds check to guarantee safety of writes below
    68  	b[0] = byte(v)
    69  	b[1] = byte(v >> 8)
    70  }
    71  
    72  func (littleEndian) AppendUint16(b []byte, v uint16) []byte {
    73  	return append(b,
    74  		byte(v),
    75  		byte(v>>8),
    76  	)
    77  }
    78  
    79  func (littleEndian) Uint32(b []byte) uint32 {
    80  	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
    81  	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
    82  }
    83  
    84  func (littleEndian) PutUint32(b []byte, v uint32) {
    85  	_ = b[3] // early bounds check to guarantee safety of writes below
    86  	b[0] = byte(v)
    87  	b[1] = byte(v >> 8)
    88  	b[2] = byte(v >> 16)
    89  	b[3] = byte(v >> 24)
    90  }
    91  
    92  func (littleEndian) AppendUint32(b []byte, v uint32) []byte {
    93  	return append(b,
    94  		byte(v),
    95  		byte(v>>8),
    96  		byte(v>>16),
    97  		byte(v>>24),
    98  	)
    99  }
   100  
   101  func (littleEndian) Uint64(b []byte) uint64 {
   102  	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
   103  	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
   104  		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
   105  }
   106  
   107  func (littleEndian) PutUint64(b []byte, v uint64) {
   108  	_ = b[7] // early bounds check to guarantee safety of writes below
   109  	b[0] = byte(v)
   110  	b[1] = byte(v >> 8)
   111  	b[2] = byte(v >> 16)
   112  	b[3] = byte(v >> 24)
   113  	b[4] = byte(v >> 32)
   114  	b[5] = byte(v >> 40)
   115  	b[6] = byte(v >> 48)
   116  	b[7] = byte(v >> 56)
   117  }
   118  
   119  func (littleEndian) AppendUint64(b []byte, v uint64) []byte {
   120  	return append(b,
   121  		byte(v),
   122  		byte(v>>8),
   123  		byte(v>>16),
   124  		byte(v>>24),
   125  		byte(v>>32),
   126  		byte(v>>40),
   127  		byte(v>>48),
   128  		byte(v>>56),
   129  	)
   130  }
   131  
   132  func (littleEndian) String() string { return "LittleEndian" }
   133  
   134  func (littleEndian) GoString() string { return "binary.LittleEndian" }
   135  
   136  type bigEndian struct{}
   137  
   138  func (bigEndian) Uint16(b []byte) uint16 {
   139  	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
   140  	return uint16(b[1]) | uint16(b[0])<<8
   141  }
   142  
   143  func (bigEndian) PutUint16(b []byte, v uint16) {
   144  	_ = b[1] // early bounds check to guarantee safety of writes below
   145  	b[0] = byte(v >> 8)
   146  	b[1] = byte(v)
   147  }
   148  
   149  func (bigEndian) AppendUint16(b []byte, v uint16) []byte {
   150  	return append(b,
   151  		byte(v>>8),
   152  		byte(v),
   153  	)
   154  }
   155  
   156  func (bigEndian) Uint32(b []byte) uint32 {
   157  	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
   158  	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
   159  }
   160  
   161  func (bigEndian) PutUint32(b []byte, v uint32) {
   162  	_ = b[3] // early bounds check to guarantee safety of writes below
   163  	b[0] = byte(v >> 24)
   164  	b[1] = byte(v >> 16)
   165  	b[2] = byte(v >> 8)
   166  	b[3] = byte(v)
   167  }
   168  
   169  func (bigEndian) AppendUint32(b []byte, v uint32) []byte {
   170  	return append(b,
   171  		byte(v>>24),
   172  		byte(v>>16),
   173  		byte(v>>8),
   174  		byte(v),
   175  	)
   176  }
   177  
   178  func (bigEndian) Uint64(b []byte) uint64 {
   179  	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
   180  	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
   181  		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
   182  }
   183  
   184  func (bigEndian) PutUint64(b []byte, v uint64) {
   185  	_ = b[7] // early bounds check to guarantee safety of writes below
   186  	b[0] = byte(v >> 56)
   187  	b[1] = byte(v >> 48)
   188  	b[2] = byte(v >> 40)
   189  	b[3] = byte(v >> 32)
   190  	b[4] = byte(v >> 24)
   191  	b[5] = byte(v >> 16)
   192  	b[6] = byte(v >> 8)
   193  	b[7] = byte(v)
   194  }
   195  
   196  func (bigEndian) AppendUint64(b []byte, v uint64) []byte {
   197  	return append(b,
   198  		byte(v>>56),
   199  		byte(v>>48),
   200  		byte(v>>40),
   201  		byte(v>>32),
   202  		byte(v>>24),
   203  		byte(v>>16),
   204  		byte(v>>8),
   205  		byte(v),
   206  	)
   207  }
   208  
   209  func (bigEndian) String() string { return "BigEndian" }
   210  
   211  func (bigEndian) GoString() string { return "binary.BigEndian" }
   212  
   213  // Read reads structured binary data from r into data.
   214  // Data must be a pointer to a fixed-size value or a slice
   215  // of fixed-size values.
   216  // Bytes read from r are decoded using the specified byte order
   217  // and written to successive fields of the data.
   218  // When decoding boolean values, a zero byte is decoded as false, and
   219  // any other non-zero byte is decoded as true.
   220  // When reading into structs, the field data for fields with
   221  // blank (_) field names is skipped; i.e., blank field names
   222  // may be used for padding.
   223  // When reading into a struct, all non-blank fields must be exported
   224  // or Read may panic.
   225  //
   226  // The error is EOF only if no bytes were read.
   227  // If an EOF happens after reading some but not all the bytes,
   228  // Read returns ErrUnexpectedEOF.
   229  func Read(r io.Reader, order ByteOrder, data any) error {
   230  	// Fast path for basic types and slices.
   231  	if n := intDataSize(data); n != 0 {
   232  		bs := make([]byte, n)
   233  		if _, err := io.ReadFull(r, bs); err != nil {
   234  			return err
   235  		}
   236  		switch data := data.(type) {
   237  		case *bool:
   238  			*data = bs[0] != 0
   239  		case *int8:
   240  			*data = int8(bs[0])
   241  		case *uint8:
   242  			*data = bs[0]
   243  		case *int16:
   244  			*data = int16(order.Uint16(bs))
   245  		case *uint16:
   246  			*data = order.Uint16(bs)
   247  		case *int32:
   248  			*data = int32(order.Uint32(bs))
   249  		case *uint32:
   250  			*data = order.Uint32(bs)
   251  		case *int64:
   252  			*data = int64(order.Uint64(bs))
   253  		case *uint64:
   254  			*data = order.Uint64(bs)
   255  		case *float32:
   256  			*data = math.Float32frombits(order.Uint32(bs))
   257  		case *float64:
   258  			*data = math.Float64frombits(order.Uint64(bs))
   259  		case []bool:
   260  			for i, x := range bs { // Easier to loop over the input for 8-bit values.
   261  				data[i] = x != 0
   262  			}
   263  		case []int8:
   264  			for i, x := range bs {
   265  				data[i] = int8(x)
   266  			}
   267  		case []uint8:
   268  			copy(data, bs)
   269  		case []int16:
   270  			for i := range data {
   271  				data[i] = int16(order.Uint16(bs[2*i:]))
   272  			}
   273  		case []uint16:
   274  			for i := range data {
   275  				data[i] = order.Uint16(bs[2*i:])
   276  			}
   277  		case []int32:
   278  			for i := range data {
   279  				data[i] = int32(order.Uint32(bs[4*i:]))
   280  			}
   281  		case []uint32:
   282  			for i := range data {
   283  				data[i] = order.Uint32(bs[4*i:])
   284  			}
   285  		case []int64:
   286  			for i := range data {
   287  				data[i] = int64(order.Uint64(bs[8*i:]))
   288  			}
   289  		case []uint64:
   290  			for i := range data {
   291  				data[i] = order.Uint64(bs[8*i:])
   292  			}
   293  		case []float32:
   294  			for i := range data {
   295  				data[i] = math.Float32frombits(order.Uint32(bs[4*i:]))
   296  			}
   297  		case []float64:
   298  			for i := range data {
   299  				data[i] = math.Float64frombits(order.Uint64(bs[8*i:]))
   300  			}
   301  		default:
   302  			n = 0 // fast path doesn't apply
   303  		}
   304  		if n != 0 {
   305  			return nil
   306  		}
   307  	}
   308  
   309  	// Fallback to reflect-based decoding.
   310  	v := reflect.ValueOf(data)
   311  	size := -1
   312  	switch v.Kind() {
   313  	case reflect.Pointer:
   314  		v = v.Elem()
   315  		size = dataSize(v)
   316  	case reflect.Slice:
   317  		size = dataSize(v)
   318  	}
   319  	if size < 0 {
   320  		return errors.New("binary.Read: invalid type " + reflect.TypeOf(data).String())
   321  	}
   322  	d := &decoder{order: order, buf: make([]byte, size)}
   323  	if _, err := io.ReadFull(r, d.buf); err != nil {
   324  		return err
   325  	}
   326  	d.value(v)
   327  	return nil
   328  }
   329  
   330  // Write writes the binary representation of data into w.
   331  // Data must be a fixed-size value or a slice of fixed-size
   332  // values, or a pointer to such data.
   333  // Boolean values encode as one byte: 1 for true, and 0 for false.
   334  // Bytes written to w are encoded using the specified byte order
   335  // and read from successive fields of the data.
   336  // When writing structs, zero values are written for fields
   337  // with blank (_) field names.
   338  func Write(w io.Writer, order ByteOrder, data any) error {
   339  	// Fast path for basic types and slices.
   340  	if n := intDataSize(data); n != 0 {
   341  		bs := make([]byte, n)
   342  		switch v := data.(type) {
   343  		case *bool:
   344  			if *v {
   345  				bs[0] = 1
   346  			} else {
   347  				bs[0] = 0
   348  			}
   349  		case bool:
   350  			if v {
   351  				bs[0] = 1
   352  			} else {
   353  				bs[0] = 0
   354  			}
   355  		case []bool:
   356  			for i, x := range v {
   357  				if x {
   358  					bs[i] = 1
   359  				} else {
   360  					bs[i] = 0
   361  				}
   362  			}
   363  		case *int8:
   364  			bs[0] = byte(*v)
   365  		case int8:
   366  			bs[0] = byte(v)
   367  		case []int8:
   368  			for i, x := range v {
   369  				bs[i] = byte(x)
   370  			}
   371  		case *uint8:
   372  			bs[0] = *v
   373  		case uint8:
   374  			bs[0] = v
   375  		case []uint8:
   376  			bs = v
   377  		case *int16:
   378  			order.PutUint16(bs, uint16(*v))
   379  		case int16:
   380  			order.PutUint16(bs, uint16(v))
   381  		case []int16:
   382  			for i, x := range v {
   383  				order.PutUint16(bs[2*i:], uint16(x))
   384  			}
   385  		case *uint16:
   386  			order.PutUint16(bs, *v)
   387  		case uint16:
   388  			order.PutUint16(bs, v)
   389  		case []uint16:
   390  			for i, x := range v {
   391  				order.PutUint16(bs[2*i:], x)
   392  			}
   393  		case *int32:
   394  			order.PutUint32(bs, uint32(*v))
   395  		case int32:
   396  			order.PutUint32(bs, uint32(v))
   397  		case []int32:
   398  			for i, x := range v {
   399  				order.PutUint32(bs[4*i:], uint32(x))
   400  			}
   401  		case *uint32:
   402  			order.PutUint32(bs, *v)
   403  		case uint32:
   404  			order.PutUint32(bs, v)
   405  		case []uint32:
   406  			for i, x := range v {
   407  				order.PutUint32(bs[4*i:], x)
   408  			}
   409  		case *int64:
   410  			order.PutUint64(bs, uint64(*v))
   411  		case int64:
   412  			order.PutUint64(bs, uint64(v))
   413  		case []int64:
   414  			for i, x := range v {
   415  				order.PutUint64(bs[8*i:], uint64(x))
   416  			}
   417  		case *uint64:
   418  			order.PutUint64(bs, *v)
   419  		case uint64:
   420  			order.PutUint64(bs, v)
   421  		case []uint64:
   422  			for i, x := range v {
   423  				order.PutUint64(bs[8*i:], x)
   424  			}
   425  		case *float32:
   426  			order.PutUint32(bs, math.Float32bits(*v))
   427  		case float32:
   428  			order.PutUint32(bs, math.Float32bits(v))
   429  		case []float32:
   430  			for i, x := range v {
   431  				order.PutUint32(bs[4*i:], math.Float32bits(x))
   432  			}
   433  		case *float64:
   434  			order.PutUint64(bs, math.Float64bits(*v))
   435  		case float64:
   436  			order.PutUint64(bs, math.Float64bits(v))
   437  		case []float64:
   438  			for i, x := range v {
   439  				order.PutUint64(bs[8*i:], math.Float64bits(x))
   440  			}
   441  		}
   442  		_, err := w.Write(bs)
   443  		return err
   444  	}
   445  
   446  	// Fallback to reflect-based encoding.
   447  	v := reflect.Indirect(reflect.ValueOf(data))
   448  	size := dataSize(v)
   449  	if size < 0 {
   450  		return errors.New("binary.Write: invalid type " + reflect.TypeOf(data).String())
   451  	}
   452  	buf := make([]byte, size)
   453  	e := &encoder{order: order, buf: buf}
   454  	e.value(v)
   455  	_, err := w.Write(buf)
   456  	return err
   457  }
   458  
   459  // Size returns how many bytes Write would generate to encode the value v, which
   460  // must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
   461  // If v is neither of these, Size returns -1.
   462  func Size(v any) int {
   463  	return dataSize(reflect.Indirect(reflect.ValueOf(v)))
   464  }
   465  
   466  var structSize sync.Map // map[reflect.Type]int
   467  
   468  // dataSize returns the number of bytes the actual data represented by v occupies in memory.
   469  // For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
   470  // it returns the length of the slice times the element size and does not count the memory
   471  // occupied by the header. If the type of v is not acceptable, dataSize returns -1.
   472  func dataSize(v reflect.Value) int {
   473  	switch v.Kind() {
   474  	case reflect.Slice:
   475  		if s := sizeof(v.Type().Elem()); s >= 0 {
   476  			return s * v.Len()
   477  		}
   478  		return -1
   479  
   480  	case reflect.Struct:
   481  		t := v.Type()
   482  		if size, ok := structSize.Load(t); ok {
   483  			return size.(int)
   484  		}
   485  		size := sizeof(t)
   486  		structSize.Store(t, size)
   487  		return size
   488  
   489  	default:
   490  		return sizeof(v.Type())
   491  	}
   492  }
   493  
   494  // sizeof returns the size >= 0 of variables for the given type or -1 if the type is not acceptable.
   495  func sizeof(t reflect.Type) int {
   496  	switch t.Kind() {
   497  	case reflect.Array:
   498  		if s := sizeof(t.Elem()); s >= 0 {
   499  			return s * t.Len()
   500  		}
   501  
   502  	case reflect.Struct:
   503  		sum := 0
   504  		for i, n := 0, t.NumField(); i < n; i++ {
   505  			s := sizeof(t.Field(i).Type)
   506  			if s < 0 {
   507  				return -1
   508  			}
   509  			sum += s
   510  		}
   511  		return sum
   512  
   513  	case reflect.Bool,
   514  		reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
   515  		reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   516  		reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
   517  		return int(t.Size())
   518  	}
   519  
   520  	return -1
   521  }
   522  
   523  type coder struct {
   524  	order  ByteOrder
   525  	buf    []byte
   526  	offset int
   527  }
   528  
   529  type decoder coder
   530  type encoder coder
   531  
   532  func (d *decoder) bool() bool {
   533  	x := d.buf[d.offset]
   534  	d.offset++
   535  	return x != 0
   536  }
   537  
   538  func (e *encoder) bool(x bool) {
   539  	if x {
   540  		e.buf[e.offset] = 1
   541  	} else {
   542  		e.buf[e.offset] = 0
   543  	}
   544  	e.offset++
   545  }
   546  
   547  func (d *decoder) uint8() uint8 {
   548  	x := d.buf[d.offset]
   549  	d.offset++
   550  	return x
   551  }
   552  
   553  func (e *encoder) uint8(x uint8) {
   554  	e.buf[e.offset] = x
   555  	e.offset++
   556  }
   557  
   558  func (d *decoder) uint16() uint16 {
   559  	x := d.order.Uint16(d.buf[d.offset : d.offset+2])
   560  	d.offset += 2
   561  	return x
   562  }
   563  
   564  func (e *encoder) uint16(x uint16) {
   565  	e.order.PutUint16(e.buf[e.offset:e.offset+2], x)
   566  	e.offset += 2
   567  }
   568  
   569  func (d *decoder) uint32() uint32 {
   570  	x := d.order.Uint32(d.buf[d.offset : d.offset+4])
   571  	d.offset += 4
   572  	return x
   573  }
   574  
   575  func (e *encoder) uint32(x uint32) {
   576  	e.order.PutUint32(e.buf[e.offset:e.offset+4], x)
   577  	e.offset += 4
   578  }
   579  
   580  func (d *decoder) uint64() uint64 {
   581  	x := d.order.Uint64(d.buf[d.offset : d.offset+8])
   582  	d.offset += 8
   583  	return x
   584  }
   585  
   586  func (e *encoder) uint64(x uint64) {
   587  	e.order.PutUint64(e.buf[e.offset:e.offset+8], x)
   588  	e.offset += 8
   589  }
   590  
   591  func (d *decoder) int8() int8 { return int8(d.uint8()) }
   592  
   593  func (e *encoder) int8(x int8) { e.uint8(uint8(x)) }
   594  
   595  func (d *decoder) int16() int16 { return int16(d.uint16()) }
   596  
   597  func (e *encoder) int16(x int16) { e.uint16(uint16(x)) }
   598  
   599  func (d *decoder) int32() int32 { return int32(d.uint32()) }
   600  
   601  func (e *encoder) int32(x int32) { e.uint32(uint32(x)) }
   602  
   603  func (d *decoder) int64() int64 { return int64(d.uint64()) }
   604  
   605  func (e *encoder) int64(x int64) { e.uint64(uint64(x)) }
   606  
   607  func (d *decoder) value(v reflect.Value) {
   608  	switch v.Kind() {
   609  	case reflect.Array:
   610  		l := v.Len()
   611  		for i := 0; i < l; i++ {
   612  			d.value(v.Index(i))
   613  		}
   614  
   615  	case reflect.Struct:
   616  		t := v.Type()
   617  		l := v.NumField()
   618  		for i := 0; i < l; i++ {
   619  			// Note: Calling v.CanSet() below is an optimization.
   620  			// It would be sufficient to check the field name,
   621  			// but creating the StructField info for each field is
   622  			// costly (run "go test -bench=ReadStruct" and compare
   623  			// results when making changes to this code).
   624  			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   625  				d.value(v)
   626  			} else {
   627  				d.skip(v)
   628  			}
   629  		}
   630  
   631  	case reflect.Slice:
   632  		l := v.Len()
   633  		for i := 0; i < l; i++ {
   634  			d.value(v.Index(i))
   635  		}
   636  
   637  	case reflect.Bool:
   638  		v.SetBool(d.bool())
   639  
   640  	case reflect.Int8:
   641  		v.SetInt(int64(d.int8()))
   642  	case reflect.Int16:
   643  		v.SetInt(int64(d.int16()))
   644  	case reflect.Int32:
   645  		v.SetInt(int64(d.int32()))
   646  	case reflect.Int64:
   647  		v.SetInt(d.int64())
   648  
   649  	case reflect.Uint8:
   650  		v.SetUint(uint64(d.uint8()))
   651  	case reflect.Uint16:
   652  		v.SetUint(uint64(d.uint16()))
   653  	case reflect.Uint32:
   654  		v.SetUint(uint64(d.uint32()))
   655  	case reflect.Uint64:
   656  		v.SetUint(d.uint64())
   657  
   658  	case reflect.Float32:
   659  		v.SetFloat(float64(math.Float32frombits(d.uint32())))
   660  	case reflect.Float64:
   661  		v.SetFloat(math.Float64frombits(d.uint64()))
   662  
   663  	case reflect.Complex64:
   664  		v.SetComplex(complex(
   665  			float64(math.Float32frombits(d.uint32())),
   666  			float64(math.Float32frombits(d.uint32())),
   667  		))
   668  	case reflect.Complex128:
   669  		v.SetComplex(complex(
   670  			math.Float64frombits(d.uint64()),
   671  			math.Float64frombits(d.uint64()),
   672  		))
   673  	}
   674  }
   675  
   676  func (e *encoder) value(v reflect.Value) {
   677  	switch v.Kind() {
   678  	case reflect.Array:
   679  		l := v.Len()
   680  		for i := 0; i < l; i++ {
   681  			e.value(v.Index(i))
   682  		}
   683  
   684  	case reflect.Struct:
   685  		t := v.Type()
   686  		l := v.NumField()
   687  		for i := 0; i < l; i++ {
   688  			// see comment for corresponding code in decoder.value()
   689  			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   690  				e.value(v)
   691  			} else {
   692  				e.skip(v)
   693  			}
   694  		}
   695  
   696  	case reflect.Slice:
   697  		l := v.Len()
   698  		for i := 0; i < l; i++ {
   699  			e.value(v.Index(i))
   700  		}
   701  
   702  	case reflect.Bool:
   703  		e.bool(v.Bool())
   704  
   705  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   706  		switch v.Type().Kind() {
   707  		case reflect.Int8:
   708  			e.int8(int8(v.Int()))
   709  		case reflect.Int16:
   710  			e.int16(int16(v.Int()))
   711  		case reflect.Int32:
   712  			e.int32(int32(v.Int()))
   713  		case reflect.Int64:
   714  			e.int64(v.Int())
   715  		}
   716  
   717  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   718  		switch v.Type().Kind() {
   719  		case reflect.Uint8:
   720  			e.uint8(uint8(v.Uint()))
   721  		case reflect.Uint16:
   722  			e.uint16(uint16(v.Uint()))
   723  		case reflect.Uint32:
   724  			e.uint32(uint32(v.Uint()))
   725  		case reflect.Uint64:
   726  			e.uint64(v.Uint())
   727  		}
   728  
   729  	case reflect.Float32, reflect.Float64:
   730  		switch v.Type().Kind() {
   731  		case reflect.Float32:
   732  			e.uint32(math.Float32bits(float32(v.Float())))
   733  		case reflect.Float64:
   734  			e.uint64(math.Float64bits(v.Float()))
   735  		}
   736  
   737  	case reflect.Complex64, reflect.Complex128:
   738  		switch v.Type().Kind() {
   739  		case reflect.Complex64:
   740  			x := v.Complex()
   741  			e.uint32(math.Float32bits(float32(real(x))))
   742  			e.uint32(math.Float32bits(float32(imag(x))))
   743  		case reflect.Complex128:
   744  			x := v.Complex()
   745  			e.uint64(math.Float64bits(real(x)))
   746  			e.uint64(math.Float64bits(imag(x)))
   747  		}
   748  	}
   749  }
   750  
   751  func (d *decoder) skip(v reflect.Value) {
   752  	d.offset += dataSize(v)
   753  }
   754  
   755  func (e *encoder) skip(v reflect.Value) {
   756  	n := dataSize(v)
   757  	zero := e.buf[e.offset : e.offset+n]
   758  	for i := range zero {
   759  		zero[i] = 0
   760  	}
   761  	e.offset += n
   762  }
   763  
   764  // intDataSize returns the size of the data required to represent the data when encoded.
   765  // It returns zero if the type cannot be implemented by the fast path in Read or Write.
   766  func intDataSize(data any) int {
   767  	switch data := data.(type) {
   768  	case bool, int8, uint8, *bool, *int8, *uint8:
   769  		return 1
   770  	case []bool:
   771  		return len(data)
   772  	case []int8:
   773  		return len(data)
   774  	case []uint8:
   775  		return len(data)
   776  	case int16, uint16, *int16, *uint16:
   777  		return 2
   778  	case []int16:
   779  		return 2 * len(data)
   780  	case []uint16:
   781  		return 2 * len(data)
   782  	case int32, uint32, *int32, *uint32:
   783  		return 4
   784  	case []int32:
   785  		return 4 * len(data)
   786  	case []uint32:
   787  		return 4 * len(data)
   788  	case int64, uint64, *int64, *uint64:
   789  		return 8
   790  	case []int64:
   791  		return 8 * len(data)
   792  	case []uint64:
   793  		return 8 * len(data)
   794  	case float32, *float32:
   795  		return 4
   796  	case float64, *float64:
   797  		return 8
   798  	case []float32:
   799  		return 4 * len(data)
   800  	case []float64:
   801  		return 8 * len(data)
   802  	}
   803  	return 0
   804  }
   805
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