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Source file src/encoding/binary/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 (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	)
    30	
    31	// A ByteOrder specifies how to convert byte sequences into
    32	// 16-, 32-, or 64-bit unsigned integers.
    33	type ByteOrder interface {
    34		Uint16([]byte) uint16
    35		Uint32([]byte) uint32
    36		Uint64([]byte) uint64
    37		PutUint16([]byte, uint16)
    38		PutUint32([]byte, uint32)
    39		PutUint64([]byte, uint64)
    40		String() string
    41	}
    42	
    43	// LittleEndian is the little-endian implementation of ByteOrder.
    44	var LittleEndian littleEndian
    45	
    46	// BigEndian is the big-endian implementation of ByteOrder.
    47	var BigEndian bigEndian
    48	
    49	type littleEndian struct{}
    50	
    51	func (littleEndian) Uint16(b []byte) uint16 { return uint16(b[0]) | uint16(b[1])<<8 }
    52	
    53	func (littleEndian) PutUint16(b []byte, v uint16) {
    54		b[0] = byte(v)
    55		b[1] = byte(v >> 8)
    56	}
    57	
    58	func (littleEndian) Uint32(b []byte) uint32 {
    59		return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
    60	}
    61	
    62	func (littleEndian) PutUint32(b []byte, v uint32) {
    63		b[0] = byte(v)
    64		b[1] = byte(v >> 8)
    65		b[2] = byte(v >> 16)
    66		b[3] = byte(v >> 24)
    67	}
    68	
    69	func (littleEndian) Uint64(b []byte) uint64 {
    70		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
    71			uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
    72	}
    73	
    74	func (littleEndian) PutUint64(b []byte, v uint64) {
    75		b[0] = byte(v)
    76		b[1] = byte(v >> 8)
    77		b[2] = byte(v >> 16)
    78		b[3] = byte(v >> 24)
    79		b[4] = byte(v >> 32)
    80		b[5] = byte(v >> 40)
    81		b[6] = byte(v >> 48)
    82		b[7] = byte(v >> 56)
    83	}
    84	
    85	func (littleEndian) String() string { return "LittleEndian" }
    86	
    87	func (littleEndian) GoString() string { return "binary.LittleEndian" }
    88	
    89	type bigEndian struct{}
    90	
    91	func (bigEndian) Uint16(b []byte) uint16 { return uint16(b[1]) | uint16(b[0])<<8 }
    92	
    93	func (bigEndian) PutUint16(b []byte, v uint16) {
    94		b[0] = byte(v >> 8)
    95		b[1] = byte(v)
    96	}
    97	
    98	func (bigEndian) Uint32(b []byte) uint32 {
    99		return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
   100	}
   101	
   102	func (bigEndian) PutUint32(b []byte, v uint32) {
   103		b[0] = byte(v >> 24)
   104		b[1] = byte(v >> 16)
   105		b[2] = byte(v >> 8)
   106		b[3] = byte(v)
   107	}
   108	
   109	func (bigEndian) Uint64(b []byte) uint64 {
   110		return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
   111			uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
   112	}
   113	
   114	func (bigEndian) PutUint64(b []byte, v uint64) {
   115		b[0] = byte(v >> 56)
   116		b[1] = byte(v >> 48)
   117		b[2] = byte(v >> 40)
   118		b[3] = byte(v >> 32)
   119		b[4] = byte(v >> 24)
   120		b[5] = byte(v >> 16)
   121		b[6] = byte(v >> 8)
   122		b[7] = byte(v)
   123	}
   124	
   125	func (bigEndian) String() string { return "BigEndian" }
   126	
   127	func (bigEndian) GoString() string { return "binary.BigEndian" }
   128	
   129	// Read reads structured binary data from r into data.
   130	// Data must be a pointer to a fixed-size value or a slice
   131	// of fixed-size values.
   132	// Bytes read from r are decoded using the specified byte order
   133	// and written to successive fields of the data.
   134	// When reading into structs, the field data for fields with
   135	// blank (_) field names is skipped; i.e., blank field names
   136	// may be used for padding.
   137	// When reading into a struct, all non-blank fields must be exported.
   138	//
   139	// The error is EOF only if no bytes were read.
   140	// If an EOF happens after reading some but not all the bytes,
   141	// Read returns ErrUnexpectedEOF.
   142	func Read(r io.Reader, order ByteOrder, data interface{}) error {
   143		// Fast path for basic types and slices.
   144		if n := intDataSize(data); n != 0 {
   145			var b [8]byte
   146			var bs []byte
   147			if n > len(b) {
   148				bs = make([]byte, n)
   149			} else {
   150				bs = b[:n]
   151			}
   152			if _, err := io.ReadFull(r, bs); err != nil {
   153				return err
   154			}
   155			switch data := data.(type) {
   156			case *int8:
   157				*data = int8(b[0])
   158			case *uint8:
   159				*data = b[0]
   160			case *int16:
   161				*data = int16(order.Uint16(bs))
   162			case *uint16:
   163				*data = order.Uint16(bs)
   164			case *int32:
   165				*data = int32(order.Uint32(bs))
   166			case *uint32:
   167				*data = order.Uint32(bs)
   168			case *int64:
   169				*data = int64(order.Uint64(bs))
   170			case *uint64:
   171				*data = order.Uint64(bs)
   172			case []int8:
   173				for i, x := range bs { // Easier to loop over the input for 8-bit values.
   174					data[i] = int8(x)
   175				}
   176			case []uint8:
   177				copy(data, bs)
   178			case []int16:
   179				for i := range data {
   180					data[i] = int16(order.Uint16(bs[2*i:]))
   181				}
   182			case []uint16:
   183				for i := range data {
   184					data[i] = order.Uint16(bs[2*i:])
   185				}
   186			case []int32:
   187				for i := range data {
   188					data[i] = int32(order.Uint32(bs[4*i:]))
   189				}
   190			case []uint32:
   191				for i := range data {
   192					data[i] = order.Uint32(bs[4*i:])
   193				}
   194			case []int64:
   195				for i := range data {
   196					data[i] = int64(order.Uint64(bs[8*i:]))
   197				}
   198			case []uint64:
   199				for i := range data {
   200					data[i] = order.Uint64(bs[8*i:])
   201				}
   202			}
   203			return nil
   204		}
   205	
   206		// Fallback to reflect-based decoding.
   207		v := reflect.ValueOf(data)
   208		size := -1
   209		switch v.Kind() {
   210		case reflect.Ptr:
   211			v = v.Elem()
   212			size = dataSize(v)
   213		case reflect.Slice:
   214			size = dataSize(v)
   215		}
   216		if size < 0 {
   217			return errors.New("binary.Read: invalid type " + reflect.TypeOf(data).String())
   218		}
   219		d := &decoder{order: order, buf: make([]byte, size)}
   220		if _, err := io.ReadFull(r, d.buf); err != nil {
   221			return err
   222		}
   223		d.value(v)
   224		return nil
   225	}
   226	
   227	// Write writes the binary representation of data into w.
   228	// Data must be a fixed-size value or a slice of fixed-size
   229	// values, or a pointer to such data.
   230	// Bytes written to w are encoded using the specified byte order
   231	// and read from successive fields of the data.
   232	// When writing structs, zero values are written for fields
   233	// with blank (_) field names.
   234	func Write(w io.Writer, order ByteOrder, data interface{}) error {
   235		// Fast path for basic types and slices.
   236		if n := intDataSize(data); n != 0 {
   237			var b [8]byte
   238			var bs []byte
   239			if n > len(b) {
   240				bs = make([]byte, n)
   241			} else {
   242				bs = b[:n]
   243			}
   244			switch v := data.(type) {
   245			case *int8:
   246				b[0] = byte(*v)
   247			case int8:
   248				b[0] = byte(v)
   249			case []int8:
   250				for i, x := range v {
   251					bs[i] = byte(x)
   252				}
   253			case *uint8:
   254				b[0] = *v
   255			case uint8:
   256				b[0] = byte(v)
   257			case []uint8:
   258				bs = v
   259			case *int16:
   260				order.PutUint16(bs, uint16(*v))
   261			case int16:
   262				order.PutUint16(bs, uint16(v))
   263			case []int16:
   264				for i, x := range v {
   265					order.PutUint16(bs[2*i:], uint16(x))
   266				}
   267			case *uint16:
   268				order.PutUint16(bs, *v)
   269			case uint16:
   270				order.PutUint16(bs, v)
   271			case []uint16:
   272				for i, x := range v {
   273					order.PutUint16(bs[2*i:], x)
   274				}
   275			case *int32:
   276				order.PutUint32(bs, uint32(*v))
   277			case int32:
   278				order.PutUint32(bs, uint32(v))
   279			case []int32:
   280				for i, x := range v {
   281					order.PutUint32(bs[4*i:], uint32(x))
   282				}
   283			case *uint32:
   284				order.PutUint32(bs, *v)
   285			case uint32:
   286				order.PutUint32(bs, v)
   287			case []uint32:
   288				for i, x := range v {
   289					order.PutUint32(bs[4*i:], x)
   290				}
   291			case *int64:
   292				order.PutUint64(bs, uint64(*v))
   293			case int64:
   294				order.PutUint64(bs, uint64(v))
   295			case []int64:
   296				for i, x := range v {
   297					order.PutUint64(bs[8*i:], uint64(x))
   298				}
   299			case *uint64:
   300				order.PutUint64(bs, *v)
   301			case uint64:
   302				order.PutUint64(bs, v)
   303			case []uint64:
   304				for i, x := range v {
   305					order.PutUint64(bs[8*i:], x)
   306				}
   307			}
   308			_, err := w.Write(bs)
   309			return err
   310		}
   311	
   312		// Fallback to reflect-based encoding.
   313		v := reflect.Indirect(reflect.ValueOf(data))
   314		size := dataSize(v)
   315		if size < 0 {
   316			return errors.New("binary.Write: invalid type " + reflect.TypeOf(data).String())
   317		}
   318		buf := make([]byte, size)
   319		e := &encoder{order: order, buf: buf}
   320		e.value(v)
   321		_, err := w.Write(buf)
   322		return err
   323	}
   324	
   325	// Size returns how many bytes Write would generate to encode the value v, which
   326	// must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
   327	// If v is neither of these, Size returns -1.
   328	func Size(v interface{}) int {
   329		return dataSize(reflect.Indirect(reflect.ValueOf(v)))
   330	}
   331	
   332	// dataSize returns the number of bytes the actual data represented by v occupies in memory.
   333	// For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
   334	// it returns the length of the slice times the element size and does not count the memory
   335	// occupied by the header. If the type of v is not acceptable, dataSize returns -1.
   336	func dataSize(v reflect.Value) int {
   337		if v.Kind() == reflect.Slice {
   338			if s := sizeof(v.Type().Elem()); s >= 0 {
   339				return s * v.Len()
   340			}
   341			return -1
   342		}
   343		return sizeof(v.Type())
   344	}
   345	
   346	// sizeof returns the size >= 0 of variables for the given type or -1 if the type is not acceptable.
   347	func sizeof(t reflect.Type) int {
   348		switch t.Kind() {
   349		case reflect.Array:
   350			if s := sizeof(t.Elem()); s >= 0 {
   351				return s * t.Len()
   352			}
   353	
   354		case reflect.Struct:
   355			sum := 0
   356			for i, n := 0, t.NumField(); i < n; i++ {
   357				s := sizeof(t.Field(i).Type)
   358				if s < 0 {
   359					return -1
   360				}
   361				sum += s
   362			}
   363			return sum
   364	
   365		case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
   366			reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   367			reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
   368			return int(t.Size())
   369		}
   370	
   371		return -1
   372	}
   373	
   374	type coder struct {
   375		order ByteOrder
   376		buf   []byte
   377	}
   378	
   379	type decoder coder
   380	type encoder coder
   381	
   382	func (d *decoder) uint8() uint8 {
   383		x := d.buf[0]
   384		d.buf = d.buf[1:]
   385		return x
   386	}
   387	
   388	func (e *encoder) uint8(x uint8) {
   389		e.buf[0] = x
   390		e.buf = e.buf[1:]
   391	}
   392	
   393	func (d *decoder) uint16() uint16 {
   394		x := d.order.Uint16(d.buf[0:2])
   395		d.buf = d.buf[2:]
   396		return x
   397	}
   398	
   399	func (e *encoder) uint16(x uint16) {
   400		e.order.PutUint16(e.buf[0:2], x)
   401		e.buf = e.buf[2:]
   402	}
   403	
   404	func (d *decoder) uint32() uint32 {
   405		x := d.order.Uint32(d.buf[0:4])
   406		d.buf = d.buf[4:]
   407		return x
   408	}
   409	
   410	func (e *encoder) uint32(x uint32) {
   411		e.order.PutUint32(e.buf[0:4], x)
   412		e.buf = e.buf[4:]
   413	}
   414	
   415	func (d *decoder) uint64() uint64 {
   416		x := d.order.Uint64(d.buf[0:8])
   417		d.buf = d.buf[8:]
   418		return x
   419	}
   420	
   421	func (e *encoder) uint64(x uint64) {
   422		e.order.PutUint64(e.buf[0:8], x)
   423		e.buf = e.buf[8:]
   424	}
   425	
   426	func (d *decoder) int8() int8 { return int8(d.uint8()) }
   427	
   428	func (e *encoder) int8(x int8) { e.uint8(uint8(x)) }
   429	
   430	func (d *decoder) int16() int16 { return int16(d.uint16()) }
   431	
   432	func (e *encoder) int16(x int16) { e.uint16(uint16(x)) }
   433	
   434	func (d *decoder) int32() int32 { return int32(d.uint32()) }
   435	
   436	func (e *encoder) int32(x int32) { e.uint32(uint32(x)) }
   437	
   438	func (d *decoder) int64() int64 { return int64(d.uint64()) }
   439	
   440	func (e *encoder) int64(x int64) { e.uint64(uint64(x)) }
   441	
   442	func (d *decoder) value(v reflect.Value) {
   443		switch v.Kind() {
   444		case reflect.Array:
   445			l := v.Len()
   446			for i := 0; i < l; i++ {
   447				d.value(v.Index(i))
   448			}
   449	
   450		case reflect.Struct:
   451			t := v.Type()
   452			l := v.NumField()
   453			for i := 0; i < l; i++ {
   454				// Note: Calling v.CanSet() below is an optimization.
   455				// It would be sufficient to check the field name,
   456				// but creating the StructField info for each field is
   457				// costly (run "go test -bench=ReadStruct" and compare
   458				// results when making changes to this code).
   459				if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   460					d.value(v)
   461				} else {
   462					d.skip(v)
   463				}
   464			}
   465	
   466		case reflect.Slice:
   467			l := v.Len()
   468			for i := 0; i < l; i++ {
   469				d.value(v.Index(i))
   470			}
   471	
   472		case reflect.Int8:
   473			v.SetInt(int64(d.int8()))
   474		case reflect.Int16:
   475			v.SetInt(int64(d.int16()))
   476		case reflect.Int32:
   477			v.SetInt(int64(d.int32()))
   478		case reflect.Int64:
   479			v.SetInt(d.int64())
   480	
   481		case reflect.Uint8:
   482			v.SetUint(uint64(d.uint8()))
   483		case reflect.Uint16:
   484			v.SetUint(uint64(d.uint16()))
   485		case reflect.Uint32:
   486			v.SetUint(uint64(d.uint32()))
   487		case reflect.Uint64:
   488			v.SetUint(d.uint64())
   489	
   490		case reflect.Float32:
   491			v.SetFloat(float64(math.Float32frombits(d.uint32())))
   492		case reflect.Float64:
   493			v.SetFloat(math.Float64frombits(d.uint64()))
   494	
   495		case reflect.Complex64:
   496			v.SetComplex(complex(
   497				float64(math.Float32frombits(d.uint32())),
   498				float64(math.Float32frombits(d.uint32())),
   499			))
   500		case reflect.Complex128:
   501			v.SetComplex(complex(
   502				math.Float64frombits(d.uint64()),
   503				math.Float64frombits(d.uint64()),
   504			))
   505		}
   506	}
   507	
   508	func (e *encoder) value(v reflect.Value) {
   509		switch v.Kind() {
   510		case reflect.Array:
   511			l := v.Len()
   512			for i := 0; i < l; i++ {
   513				e.value(v.Index(i))
   514			}
   515	
   516		case reflect.Struct:
   517			t := v.Type()
   518			l := v.NumField()
   519			for i := 0; i < l; i++ {
   520				// see comment for corresponding code in decoder.value()
   521				if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   522					e.value(v)
   523				} else {
   524					e.skip(v)
   525				}
   526			}
   527	
   528		case reflect.Slice:
   529			l := v.Len()
   530			for i := 0; i < l; i++ {
   531				e.value(v.Index(i))
   532			}
   533	
   534		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   535			switch v.Type().Kind() {
   536			case reflect.Int8:
   537				e.int8(int8(v.Int()))
   538			case reflect.Int16:
   539				e.int16(int16(v.Int()))
   540			case reflect.Int32:
   541				e.int32(int32(v.Int()))
   542			case reflect.Int64:
   543				e.int64(v.Int())
   544			}
   545	
   546		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   547			switch v.Type().Kind() {
   548			case reflect.Uint8:
   549				e.uint8(uint8(v.Uint()))
   550			case reflect.Uint16:
   551				e.uint16(uint16(v.Uint()))
   552			case reflect.Uint32:
   553				e.uint32(uint32(v.Uint()))
   554			case reflect.Uint64:
   555				e.uint64(v.Uint())
   556			}
   557	
   558		case reflect.Float32, reflect.Float64:
   559			switch v.Type().Kind() {
   560			case reflect.Float32:
   561				e.uint32(math.Float32bits(float32(v.Float())))
   562			case reflect.Float64:
   563				e.uint64(math.Float64bits(v.Float()))
   564			}
   565	
   566		case reflect.Complex64, reflect.Complex128:
   567			switch v.Type().Kind() {
   568			case reflect.Complex64:
   569				x := v.Complex()
   570				e.uint32(math.Float32bits(float32(real(x))))
   571				e.uint32(math.Float32bits(float32(imag(x))))
   572			case reflect.Complex128:
   573				x := v.Complex()
   574				e.uint64(math.Float64bits(real(x)))
   575				e.uint64(math.Float64bits(imag(x)))
   576			}
   577		}
   578	}
   579	
   580	func (d *decoder) skip(v reflect.Value) {
   581		d.buf = d.buf[dataSize(v):]
   582	}
   583	
   584	func (e *encoder) skip(v reflect.Value) {
   585		n := dataSize(v)
   586		for i := range e.buf[0:n] {
   587			e.buf[i] = 0
   588		}
   589		e.buf = e.buf[n:]
   590	}
   591	
   592	// intDataSize returns the size of the data required to represent the data when encoded.
   593	// It returns zero if the type cannot be implemented by the fast path in Read or Write.
   594	func intDataSize(data interface{}) int {
   595		switch data := data.(type) {
   596		case int8, uint8, *int8, *uint8:
   597			return 1
   598		case []int8:
   599			return len(data)
   600		case []uint8:
   601			return len(data)
   602		case int16, uint16, *int16, *uint16:
   603			return 2
   604		case []int16:
   605			return 2 * len(data)
   606		case []uint16:
   607			return 2 * len(data)
   608		case int32, uint32, *int32, *uint32:
   609			return 4
   610		case []int32:
   611			return 4 * len(data)
   612		case []uint32:
   613			return 4 * len(data)
   614		case int64, uint64, *int64, *uint64:
   615			return 8
   616		case []int64:
   617			return 8 * len(data)
   618		case []uint64:
   619			return 8 * len(data)
   620		}
   621		return 0
   622	}
   623	

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