binary.go

     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  func (nativeEndian) String() string { return "NativeEndian" }
   214  
   215  func (nativeEndian) GoString() string { return "binary.NativeEndian" }
   216  
   217  // Read reads structured binary data from r into data.
   218  // Data must be a pointer to a fixed-size value or a slice
   219  // of fixed-size values.
   220  // Bytes read from r are decoded using the specified byte order
   221  // and written to successive fields of the data.
   222  // When decoding boolean values, a zero byte is decoded as false, and
   223  // any other non-zero byte is decoded as true.
   224  // When reading into structs, the field data for fields with
   225  // blank (_) field names is skipped; i.e., blank field names
   226  // may be used for padding.
   227  // When reading into a struct, all non-blank fields must be exported
   228  // or Read may panic.
   229  //
   230  // The error is EOF only if no bytes were read.
   231  // If an EOF happens after reading some but not all the bytes,
   232  // Read returns ErrUnexpectedEOF.
   233  func Read(r io.Reader, order ByteOrder, data any) error {
   234  	// Fast path for basic types and slices.
   235  	if n := intDataSize(data); n != 0 {
   236  		bs := make([]byte, n)
   237  		if _, err := io.ReadFull(r, bs); err != nil {
   238  			return err
   239  		}
   240  		switch data := data.(type) {
   241  		case *bool:
   242  			*data = bs[0] != 0
   243  		case *int8:
   244  			*data = int8(bs[0])
   245  		case *uint8:
   246  			*data = bs[0]
   247  		case *int16:
   248  			*data = int16(order.Uint16(bs))
   249  		case *uint16:
   250  			*data = order.Uint16(bs)
   251  		case *int32:
   252  			*data = int32(order.Uint32(bs))
   253  		case *uint32:
   254  			*data = order.Uint32(bs)
   255  		case *int64:
   256  			*data = int64(order.Uint64(bs))
   257  		case *uint64:
   258  			*data = order.Uint64(bs)
   259  		case *float32:
   260  			*data = math.Float32frombits(order.Uint32(bs))
   261  		case *float64:
   262  			*data = math.Float64frombits(order.Uint64(bs))
   263  		case []bool:
   264  			for i, x := range bs { // Easier to loop over the input for 8-bit values.
   265  				data[i] = x != 0
   266  			}
   267  		case []int8:
   268  			for i, x := range bs {
   269  				data[i] = int8(x)
   270  			}
   271  		case []uint8:
   272  			copy(data, bs)
   273  		case []int16:
   274  			for i := range data {
   275  				data[i] = int16(order.Uint16(bs[2*i:]))
   276  			}
   277  		case []uint16:
   278  			for i := range data {
   279  				data[i] = order.Uint16(bs[2*i:])
   280  			}
   281  		case []int32:
   282  			for i := range data {
   283  				data[i] = int32(order.Uint32(bs[4*i:]))
   284  			}
   285  		case []uint32:
   286  			for i := range data {
   287  				data[i] = order.Uint32(bs[4*i:])
   288  			}
   289  		case []int64:
   290  			for i := range data {
   291  				data[i] = int64(order.Uint64(bs[8*i:]))
   292  			}
   293  		case []uint64:
   294  			for i := range data {
   295  				data[i] = order.Uint64(bs[8*i:])
   296  			}
   297  		case []float32:
   298  			for i := range data {
   299  				data[i] = math.Float32frombits(order.Uint32(bs[4*i:]))
   300  			}
   301  		case []float64:
   302  			for i := range data {
   303  				data[i] = math.Float64frombits(order.Uint64(bs[8*i:]))
   304  			}
   305  		default:
   306  			n = 0 // fast path doesn't apply
   307  		}
   308  		if n != 0 {
   309  			return nil
   310  		}
   311  	}
   312  
   313  	// Fallback to reflect-based decoding.
   314  	v := reflect.ValueOf(data)
   315  	size := -1
   316  	switch v.Kind() {
   317  	case reflect.Pointer:
   318  		v = v.Elem()
   319  		size = dataSize(v)
   320  	case reflect.Slice:
   321  		size = dataSize(v)
   322  	}
   323  	if size < 0 {
   324  		return errors.New("binary.Read: invalid type " + reflect.TypeOf(data).String())
   325  	}
   326  	d := &decoder{order: order, buf: make([]byte, size)}
   327  	if _, err := io.ReadFull(r, d.buf); err != nil {
   328  		return err
   329  	}
   330  	d.value(v)
   331  	return nil
   332  }
   333  
   334  // Write writes the binary representation of data into w.
   335  // Data must be a fixed-size value or a slice of fixed-size
   336  // values, or a pointer to such data.
   337  // Boolean values encode as one byte: 1 for true, and 0 for false.
   338  // Bytes written to w are encoded using the specified byte order
   339  // and read from successive fields of the data.
   340  // When writing structs, zero values are written for fields
   341  // with blank (_) field names.
   342  func Write(w io.Writer, order ByteOrder, data any) error {
   343  	// Fast path for basic types and slices.
   344  	if n := intDataSize(data); n != 0 {
   345  		bs := make([]byte, n)
   346  		switch v := data.(type) {
   347  		case *bool:
   348  			if *v {
   349  				bs[0] = 1
   350  			} else {
   351  				bs[0] = 0
   352  			}
   353  		case bool:
   354  			if v {
   355  				bs[0] = 1
   356  			} else {
   357  				bs[0] = 0
   358  			}
   359  		case []bool:
   360  			for i, x := range v {
   361  				if x {
   362  					bs[i] = 1
   363  				} else {
   364  					bs[i] = 0
   365  				}
   366  			}
   367  		case *int8:
   368  			bs[0] = byte(*v)
   369  		case int8:
   370  			bs[0] = byte(v)
   371  		case []int8:
   372  			for i, x := range v {
   373  				bs[i] = byte(x)
   374  			}
   375  		case *uint8:
   376  			bs[0] = *v
   377  		case uint8:
   378  			bs[0] = v
   379  		case []uint8:
   380  			bs = v
   381  		case *int16:
   382  			order.PutUint16(bs, uint16(*v))
   383  		case int16:
   384  			order.PutUint16(bs, uint16(v))
   385  		case []int16:
   386  			for i, x := range v {
   387  				order.PutUint16(bs[2*i:], uint16(x))
   388  			}
   389  		case *uint16:
   390  			order.PutUint16(bs, *v)
   391  		case uint16:
   392  			order.PutUint16(bs, v)
   393  		case []uint16:
   394  			for i, x := range v {
   395  				order.PutUint16(bs[2*i:], x)
   396  			}
   397  		case *int32:
   398  			order.PutUint32(bs, uint32(*v))
   399  		case int32:
   400  			order.PutUint32(bs, uint32(v))
   401  		case []int32:
   402  			for i, x := range v {
   403  				order.PutUint32(bs[4*i:], uint32(x))
   404  			}
   405  		case *uint32:
   406  			order.PutUint32(bs, *v)
   407  		case uint32:
   408  			order.PutUint32(bs, v)
   409  		case []uint32:
   410  			for i, x := range v {
   411  				order.PutUint32(bs[4*i:], x)
   412  			}
   413  		case *int64:
   414  			order.PutUint64(bs, uint64(*v))
   415  		case int64:
   416  			order.PutUint64(bs, uint64(v))
   417  		case []int64:
   418  			for i, x := range v {
   419  				order.PutUint64(bs[8*i:], uint64(x))
   420  			}
   421  		case *uint64:
   422  			order.PutUint64(bs, *v)
   423  		case uint64:
   424  			order.PutUint64(bs, v)
   425  		case []uint64:
   426  			for i, x := range v {
   427  				order.PutUint64(bs[8*i:], x)
   428  			}
   429  		case *float32:
   430  			order.PutUint32(bs, math.Float32bits(*v))
   431  		case float32:
   432  			order.PutUint32(bs, math.Float32bits(v))
   433  		case []float32:
   434  			for i, x := range v {
   435  				order.PutUint32(bs[4*i:], math.Float32bits(x))
   436  			}
   437  		case *float64:
   438  			order.PutUint64(bs, math.Float64bits(*v))
   439  		case float64:
   440  			order.PutUint64(bs, math.Float64bits(v))
   441  		case []float64:
   442  			for i, x := range v {
   443  				order.PutUint64(bs[8*i:], math.Float64bits(x))
   444  			}
   445  		}
   446  		_, err := w.Write(bs)
   447  		return err
   448  	}
   449  
   450  	// Fallback to reflect-based encoding.
   451  	v := reflect.Indirect(reflect.ValueOf(data))
   452  	size := dataSize(v)
   453  	if size < 0 {
   454  		return errors.New("binary.Write: some values are not fixed-sized in type " + reflect.TypeOf(data).String())
   455  	}
   456  	buf := make([]byte, size)
   457  	e := &encoder{order: order, buf: buf}
   458  	e.value(v)
   459  	_, err := w.Write(buf)
   460  	return err
   461  }
   462  
   463  // Size returns how many bytes Write would generate to encode the value v, which
   464  // must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
   465  // If v is neither of these, Size returns -1.
   466  func Size(v any) int {
   467  	return dataSize(reflect.Indirect(reflect.ValueOf(v)))
   468  }
   469  
   470  var structSize sync.Map // map[reflect.Type]int
   471  
   472  // dataSize returns the number of bytes the actual data represented by v occupies in memory.
   473  // For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
   474  // it returns the length of the slice times the element size and does not count the memory
   475  // occupied by the header. If the type of v is not acceptable, dataSize returns -1.
   476  func dataSize(v reflect.Value) int {
   477  	switch v.Kind() {
   478  	case reflect.Slice:
   479  		if s := sizeof(v.Type().Elem()); s >= 0 {
   480  			return s * v.Len()
   481  		}
   482  
   483  	case reflect.Struct:
   484  		t := v.Type()
   485  		if size, ok := structSize.Load(t); ok {
   486  			return size.(int)
   487  		}
   488  		size := sizeof(t)
   489  		structSize.Store(t, size)
   490  		return size
   491  
   492  	default:
   493  		if v.IsValid() {
   494  			return sizeof(v.Type())
   495  		}
   496  	}
   497  
   498  	return -1
   499  }
   500  
   501  // sizeof returns the size >= 0 of variables for the given type or -1 if the type is not acceptable.
   502  func sizeof(t reflect.Type) int {
   503  	switch t.Kind() {
   504  	case reflect.Array:
   505  		if s := sizeof(t.Elem()); s >= 0 {
   506  			return s * t.Len()
   507  		}
   508  
   509  	case reflect.Struct:
   510  		sum := 0
   511  		for i, n := 0, t.NumField(); i < n; i++ {
   512  			s := sizeof(t.Field(i).Type)
   513  			if s < 0 {
   514  				return -1
   515  			}
   516  			sum += s
   517  		}
   518  		return sum
   519  
   520  	case reflect.Bool,
   521  		reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
   522  		reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   523  		reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
   524  		return int(t.Size())
   525  	}
   526  
   527  	return -1
   528  }
   529  
   530  type coder struct {
   531  	order  ByteOrder
   532  	buf    []byte
   533  	offset int
   534  }
   535  
   536  type decoder coder
   537  type encoder coder
   538  
   539  func (d *decoder) bool() bool {
   540  	x := d.buf[d.offset]
   541  	d.offset++
   542  	return x != 0
   543  }
   544  
   545  func (e *encoder) bool(x bool) {
   546  	if x {
   547  		e.buf[e.offset] = 1
   548  	} else {
   549  		e.buf[e.offset] = 0
   550  	}
   551  	e.offset++
   552  }
   553  
   554  func (d *decoder) uint8() uint8 {
   555  	x := d.buf[d.offset]
   556  	d.offset++
   557  	return x
   558  }
   559  
   560  func (e *encoder) uint8(x uint8) {
   561  	e.buf[e.offset] = x
   562  	e.offset++
   563  }
   564  
   565  func (d *decoder) uint16() uint16 {
   566  	x := d.order.Uint16(d.buf[d.offset : d.offset+2])
   567  	d.offset += 2
   568  	return x
   569  }
   570  
   571  func (e *encoder) uint16(x uint16) {
   572  	e.order.PutUint16(e.buf[e.offset:e.offset+2], x)
   573  	e.offset += 2
   574  }
   575  
   576  func (d *decoder) uint32() uint32 {
   577  	x := d.order.Uint32(d.buf[d.offset : d.offset+4])
   578  	d.offset += 4
   579  	return x
   580  }
   581  
   582  func (e *encoder) uint32(x uint32) {
   583  	e.order.PutUint32(e.buf[e.offset:e.offset+4], x)
   584  	e.offset += 4
   585  }
   586  
   587  func (d *decoder) uint64() uint64 {
   588  	x := d.order.Uint64(d.buf[d.offset : d.offset+8])
   589  	d.offset += 8
   590  	return x
   591  }
   592  
   593  func (e *encoder) uint64(x uint64) {
   594  	e.order.PutUint64(e.buf[e.offset:e.offset+8], x)
   595  	e.offset += 8
   596  }
   597  
   598  func (d *decoder) int8() int8 { return int8(d.uint8()) }
   599  
   600  func (e *encoder) int8(x int8) { e.uint8(uint8(x)) }
   601  
   602  func (d *decoder) int16() int16 { return int16(d.uint16()) }
   603  
   604  func (e *encoder) int16(x int16) { e.uint16(uint16(x)) }
   605  
   606  func (d *decoder) int32() int32 { return int32(d.uint32()) }
   607  
   608  func (e *encoder) int32(x int32) { e.uint32(uint32(x)) }
   609  
   610  func (d *decoder) int64() int64 { return int64(d.uint64()) }
   611  
   612  func (e *encoder) int64(x int64) { e.uint64(uint64(x)) }
   613  
   614  func (d *decoder) value(v reflect.Value) {
   615  	switch v.Kind() {
   616  	case reflect.Array:
   617  		l := v.Len()
   618  		for i := 0; i < l; i++ {
   619  			d.value(v.Index(i))
   620  		}
   621  
   622  	case reflect.Struct:
   623  		t := v.Type()
   624  		l := v.NumField()
   625  		for i := 0; i < l; i++ {
   626  			// Note: Calling v.CanSet() below is an optimization.
   627  			// It would be sufficient to check the field name,
   628  			// but creating the StructField info for each field is
   629  			// costly (run "go test -bench=ReadStruct" and compare
   630  			// results when making changes to this code).
   631  			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   632  				d.value(v)
   633  			} else {
   634  				d.skip(v)
   635  			}
   636  		}
   637  
   638  	case reflect.Slice:
   639  		l := v.Len()
   640  		for i := 0; i < l; i++ {
   641  			d.value(v.Index(i))
   642  		}
   643  
   644  	case reflect.Bool:
   645  		v.SetBool(d.bool())
   646  
   647  	case reflect.Int8:
   648  		v.SetInt(int64(d.int8()))
   649  	case reflect.Int16:
   650  		v.SetInt(int64(d.int16()))
   651  	case reflect.Int32:
   652  		v.SetInt(int64(d.int32()))
   653  	case reflect.Int64:
   654  		v.SetInt(d.int64())
   655  
   656  	case reflect.Uint8:
   657  		v.SetUint(uint64(d.uint8()))
   658  	case reflect.Uint16:
   659  		v.SetUint(uint64(d.uint16()))
   660  	case reflect.Uint32:
   661  		v.SetUint(uint64(d.uint32()))
   662  	case reflect.Uint64:
   663  		v.SetUint(d.uint64())
   664  
   665  	case reflect.Float32:
   666  		v.SetFloat(float64(math.Float32frombits(d.uint32())))
   667  	case reflect.Float64:
   668  		v.SetFloat(math.Float64frombits(d.uint64()))
   669  
   670  	case reflect.Complex64:
   671  		v.SetComplex(complex(
   672  			float64(math.Float32frombits(d.uint32())),
   673  			float64(math.Float32frombits(d.uint32())),
   674  		))
   675  	case reflect.Complex128:
   676  		v.SetComplex(complex(
   677  			math.Float64frombits(d.uint64()),
   678  			math.Float64frombits(d.uint64()),
   679  		))
   680  	}
   681  }
   682  
   683  func (e *encoder) value(v reflect.Value) {
   684  	switch v.Kind() {
   685  	case reflect.Array:
   686  		l := v.Len()
   687  		for i := 0; i < l; i++ {
   688  			e.value(v.Index(i))
   689  		}
   690  
   691  	case reflect.Struct:
   692  		t := v.Type()
   693  		l := v.NumField()
   694  		for i := 0; i < l; i++ {
   695  			// see comment for corresponding code in decoder.value()
   696  			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   697  				e.value(v)
   698  			} else {
   699  				e.skip(v)
   700  			}
   701  		}
   702  
   703  	case reflect.Slice:
   704  		l := v.Len()
   705  		for i := 0; i < l; i++ {
   706  			e.value(v.Index(i))
   707  		}
   708  
   709  	case reflect.Bool:
   710  		e.bool(v.Bool())
   711  
   712  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   713  		switch v.Type().Kind() {
   714  		case reflect.Int8:
   715  			e.int8(int8(v.Int()))
   716  		case reflect.Int16:
   717  			e.int16(int16(v.Int()))
   718  		case reflect.Int32:
   719  			e.int32(int32(v.Int()))
   720  		case reflect.Int64:
   721  			e.int64(v.Int())
   722  		}
   723  
   724  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   725  		switch v.Type().Kind() {
   726  		case reflect.Uint8:
   727  			e.uint8(uint8(v.Uint()))
   728  		case reflect.Uint16:
   729  			e.uint16(uint16(v.Uint()))
   730  		case reflect.Uint32:
   731  			e.uint32(uint32(v.Uint()))
   732  		case reflect.Uint64:
   733  			e.uint64(v.Uint())
   734  		}
   735  
   736  	case reflect.Float32, reflect.Float64:
   737  		switch v.Type().Kind() {
   738  		case reflect.Float32:
   739  			e.uint32(math.Float32bits(float32(v.Float())))
   740  		case reflect.Float64:
   741  			e.uint64(math.Float64bits(v.Float()))
   742  		}
   743  
   744  	case reflect.Complex64, reflect.Complex128:
   745  		switch v.Type().Kind() {
   746  		case reflect.Complex64:
   747  			x := v.Complex()
   748  			e.uint32(math.Float32bits(float32(real(x))))
   749  			e.uint32(math.Float32bits(float32(imag(x))))
   750  		case reflect.Complex128:
   751  			x := v.Complex()
   752  			e.uint64(math.Float64bits(real(x)))
   753  			e.uint64(math.Float64bits(imag(x)))
   754  		}
   755  	}
   756  }
   757  
   758  func (d *decoder) skip(v reflect.Value) {
   759  	d.offset += dataSize(v)
   760  }
   761  
   762  func (e *encoder) skip(v reflect.Value) {
   763  	n := dataSize(v)
   764  	zero := e.buf[e.offset : e.offset+n]
   765  	for i := range zero {
   766  		zero[i] = 0
   767  	}
   768  	e.offset += n
   769  }
   770  
   771  // intDataSize returns the size of the data required to represent the data when encoded.
   772  // It returns zero if the type cannot be implemented by the fast path in Read or Write.
   773  func intDataSize(data any) int {
   774  	switch data := data.(type) {
   775  	case bool, int8, uint8, *bool, *int8, *uint8:
   776  		return 1
   777  	case []bool:
   778  		return len(data)
   779  	case []int8:
   780  		return len(data)
   781  	case []uint8:
   782  		return len(data)
   783  	case int16, uint16, *int16, *uint16:
   784  		return 2
   785  	case []int16:
   786  		return 2 * len(data)
   787  	case []uint16:
   788  		return 2 * len(data)
   789  	case int32, uint32, *int32, *uint32:
   790  		return 4
   791  	case []int32:
   792  		return 4 * len(data)
   793  	case []uint32:
   794  		return 4 * len(data)
   795  	case int64, uint64, *int64, *uint64:
   796  		return 8
   797  	case []int64:
   798  		return 8 * len(data)
   799  	case []uint64:
   800  		return 8 * len(data)
   801  	case float32, *float32:
   802  		return 4
   803  	case float64, *float64:
   804  		return 8
   805  	case []float32:
   806  		return 4 * len(data)
   807  	case []float64:
   808  		return 8 * len(data)
   809  	}
   810  	return 0
   811  }
   812
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