Source file src/pkg/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 translation between numbers and byte sequences
     6	// 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	// Varints are a method of encoding integers using one or more bytes;
    14	// numbers with smaller absolute value take a smaller number of bytes.
    15	// For a specification, see http://code.google.com/apis/protocolbuffers/docs/encoding.html.
    16	package binary
    17	
    18	import (
    19		"errors"
    20		"io"
    21		"math"
    22		"reflect"
    23	)
    24	
    25	// A ByteOrder specifies how to convert byte sequences into
    26	// 16-, 32-, or 64-bit unsigned integers.
    27	type ByteOrder interface {
    28		Uint16([]byte) uint16
    29		Uint32([]byte) uint32
    30		Uint64([]byte) uint64
    31		PutUint16([]byte, uint16)
    32		PutUint32([]byte, uint32)
    33		PutUint64([]byte, uint64)
    34		String() string
    35	}
    36	
    37	// LittleEndian is the little-endian implementation of ByteOrder.
    38	var LittleEndian littleEndian
    39	
    40	// BigEndian is the big-endian implementation of ByteOrder.
    41	var BigEndian bigEndian
    42	
    43	type littleEndian struct{}
    44	
    45	func (littleEndian) Uint16(b []byte) uint16 { return uint16(b[0]) | uint16(b[1])<<8 }
    46	
    47	func (littleEndian) PutUint16(b []byte, v uint16) {
    48		b[0] = byte(v)
    49		b[1] = byte(v >> 8)
    50	}
    51	
    52	func (littleEndian) Uint32(b []byte) uint32 {
    53		return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
    54	}
    55	
    56	func (littleEndian) PutUint32(b []byte, v uint32) {
    57		b[0] = byte(v)
    58		b[1] = byte(v >> 8)
    59		b[2] = byte(v >> 16)
    60		b[3] = byte(v >> 24)
    61	}
    62	
    63	func (littleEndian) Uint64(b []byte) uint64 {
    64		return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
    65			uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
    66	}
    67	
    68	func (littleEndian) PutUint64(b []byte, v uint64) {
    69		b[0] = byte(v)
    70		b[1] = byte(v >> 8)
    71		b[2] = byte(v >> 16)
    72		b[3] = byte(v >> 24)
    73		b[4] = byte(v >> 32)
    74		b[5] = byte(v >> 40)
    75		b[6] = byte(v >> 48)
    76		b[7] = byte(v >> 56)
    77	}
    78	
    79	func (littleEndian) String() string { return "LittleEndian" }
    80	
    81	func (littleEndian) GoString() string { return "binary.LittleEndian" }
    82	
    83	type bigEndian struct{}
    84	
    85	func (bigEndian) Uint16(b []byte) uint16 { return uint16(b[1]) | uint16(b[0])<<8 }
    86	
    87	func (bigEndian) PutUint16(b []byte, v uint16) {
    88		b[0] = byte(v >> 8)
    89		b[1] = byte(v)
    90	}
    91	
    92	func (bigEndian) Uint32(b []byte) uint32 {
    93		return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
    94	}
    95	
    96	func (bigEndian) PutUint32(b []byte, v uint32) {
    97		b[0] = byte(v >> 24)
    98		b[1] = byte(v >> 16)
    99		b[2] = byte(v >> 8)
   100		b[3] = byte(v)
   101	}
   102	
   103	func (bigEndian) Uint64(b []byte) uint64 {
   104		return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
   105			uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
   106	}
   107	
   108	func (bigEndian) PutUint64(b []byte, v uint64) {
   109		b[0] = byte(v >> 56)
   110		b[1] = byte(v >> 48)
   111		b[2] = byte(v >> 40)
   112		b[3] = byte(v >> 32)
   113		b[4] = byte(v >> 24)
   114		b[5] = byte(v >> 16)
   115		b[6] = byte(v >> 8)
   116		b[7] = byte(v)
   117	}
   118	
   119	func (bigEndian) String() string { return "BigEndian" }
   120	
   121	func (bigEndian) GoString() string { return "binary.BigEndian" }
   122	
   123	// Read reads structured binary data from r into data.
   124	// Data must be a pointer to a fixed-size value or a slice
   125	// of fixed-size values.
   126	// Bytes read from r are decoded using the specified byte order
   127	// and written to successive fields of the data.
   128	// When reading into structs, the field data for fields with
   129	// blank (_) field names is skipped; i.e., blank field names
   130	// may be used for padding.
   131	func Read(r io.Reader, order ByteOrder, data interface{}) error {
   132		// Fast path for basic types.
   133		if n := intDestSize(data); n != 0 {
   134			var b [8]byte
   135			bs := b[:n]
   136			if _, err := io.ReadFull(r, bs); err != nil {
   137				return err
   138			}
   139			switch v := data.(type) {
   140			case *int8:
   141				*v = int8(b[0])
   142			case *uint8:
   143				*v = b[0]
   144			case *int16:
   145				*v = int16(order.Uint16(bs))
   146			case *uint16:
   147				*v = order.Uint16(bs)
   148			case *int32:
   149				*v = int32(order.Uint32(bs))
   150			case *uint32:
   151				*v = order.Uint32(bs)
   152			case *int64:
   153				*v = int64(order.Uint64(bs))
   154			case *uint64:
   155				*v = order.Uint64(bs)
   156			}
   157			return nil
   158		}
   159	
   160		// Fallback to reflect-based decoding.
   161		var v reflect.Value
   162		switch d := reflect.ValueOf(data); d.Kind() {
   163		case reflect.Ptr:
   164			v = d.Elem()
   165		case reflect.Slice:
   166			v = d
   167		default:
   168			return errors.New("binary.Read: invalid type " + d.Type().String())
   169		}
   170		size, err := dataSize(v)
   171		if err != nil {
   172			return errors.New("binary.Read: " + err.Error())
   173		}
   174		d := &decoder{order: order, buf: make([]byte, size)}
   175		if _, err := io.ReadFull(r, d.buf); err != nil {
   176			return err
   177		}
   178		d.value(v)
   179		return nil
   180	}
   181	
   182	// Write writes the binary representation of data into w.
   183	// Data must be a fixed-size value or a slice of fixed-size
   184	// values, or a pointer to such data.
   185	// Bytes written to w are encoded using the specified byte order
   186	// and read from successive fields of the data.
   187	// When writing structs, zero values are written for fields
   188	// with blank (_) field names.
   189	func Write(w io.Writer, order ByteOrder, data interface{}) error {
   190		// Fast path for basic types.
   191		var b [8]byte
   192		var bs []byte
   193		switch v := data.(type) {
   194		case *int8:
   195			bs = b[:1]
   196			b[0] = byte(*v)
   197		case int8:
   198			bs = b[:1]
   199			b[0] = byte(v)
   200		case *uint8:
   201			bs = b[:1]
   202			b[0] = *v
   203		case uint8:
   204			bs = b[:1]
   205			b[0] = byte(v)
   206		case *int16:
   207			bs = b[:2]
   208			order.PutUint16(bs, uint16(*v))
   209		case int16:
   210			bs = b[:2]
   211			order.PutUint16(bs, uint16(v))
   212		case *uint16:
   213			bs = b[:2]
   214			order.PutUint16(bs, *v)
   215		case uint16:
   216			bs = b[:2]
   217			order.PutUint16(bs, v)
   218		case *int32:
   219			bs = b[:4]
   220			order.PutUint32(bs, uint32(*v))
   221		case int32:
   222			bs = b[:4]
   223			order.PutUint32(bs, uint32(v))
   224		case *uint32:
   225			bs = b[:4]
   226			order.PutUint32(bs, *v)
   227		case uint32:
   228			bs = b[:4]
   229			order.PutUint32(bs, v)
   230		case *int64:
   231			bs = b[:8]
   232			order.PutUint64(bs, uint64(*v))
   233		case int64:
   234			bs = b[:8]
   235			order.PutUint64(bs, uint64(v))
   236		case *uint64:
   237			bs = b[:8]
   238			order.PutUint64(bs, *v)
   239		case uint64:
   240			bs = b[:8]
   241			order.PutUint64(bs, v)
   242		}
   243		if bs != nil {
   244			_, err := w.Write(bs)
   245			return err
   246		}
   247	
   248		// Fallback to reflect-based encoding.
   249		v := reflect.Indirect(reflect.ValueOf(data))
   250		size, err := dataSize(v)
   251		if err != nil {
   252			return errors.New("binary.Write: " + err.Error())
   253		}
   254		buf := make([]byte, size)
   255		e := &encoder{order: order, buf: buf}
   256		e.value(v)
   257		_, err = w.Write(buf)
   258		return err
   259	}
   260	
   261	// Size returns how many bytes Write would generate to encode the value v, which
   262	// must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
   263	func Size(v interface{}) int {
   264		n, err := dataSize(reflect.Indirect(reflect.ValueOf(v)))
   265		if err != nil {
   266			return -1
   267		}
   268		return n
   269	}
   270	
   271	// dataSize returns the number of bytes the actual data represented by v occupies in memory.
   272	// For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
   273	// it returns the length of the slice times the element size and does not count the memory
   274	// occupied by the header.
   275	func dataSize(v reflect.Value) (int, error) {
   276		if v.Kind() == reflect.Slice {
   277			elem, err := sizeof(v.Type().Elem())
   278			if err != nil {
   279				return 0, err
   280			}
   281			return v.Len() * elem, nil
   282		}
   283		return sizeof(v.Type())
   284	}
   285	
   286	func sizeof(t reflect.Type) (int, error) {
   287		switch t.Kind() {
   288		case reflect.Array:
   289			n, err := sizeof(t.Elem())
   290			if err != nil {
   291				return 0, err
   292			}
   293			return t.Len() * n, nil
   294	
   295		case reflect.Struct:
   296			sum := 0
   297			for i, n := 0, t.NumField(); i < n; i++ {
   298				s, err := sizeof(t.Field(i).Type)
   299				if err != nil {
   300					return 0, err
   301				}
   302				sum += s
   303			}
   304			return sum, nil
   305	
   306		case reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
   307			reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   308			reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
   309			return int(t.Size()), nil
   310		}
   311		return 0, errors.New("invalid type " + t.String())
   312	}
   313	
   314	type coder struct {
   315		order ByteOrder
   316		buf   []byte
   317	}
   318	
   319	type decoder coder
   320	type encoder coder
   321	
   322	func (d *decoder) uint8() uint8 {
   323		x := d.buf[0]
   324		d.buf = d.buf[1:]
   325		return x
   326	}
   327	
   328	func (e *encoder) uint8(x uint8) {
   329		e.buf[0] = x
   330		e.buf = e.buf[1:]
   331	}
   332	
   333	func (d *decoder) uint16() uint16 {
   334		x := d.order.Uint16(d.buf[0:2])
   335		d.buf = d.buf[2:]
   336		return x
   337	}
   338	
   339	func (e *encoder) uint16(x uint16) {
   340		e.order.PutUint16(e.buf[0:2], x)
   341		e.buf = e.buf[2:]
   342	}
   343	
   344	func (d *decoder) uint32() uint32 {
   345		x := d.order.Uint32(d.buf[0:4])
   346		d.buf = d.buf[4:]
   347		return x
   348	}
   349	
   350	func (e *encoder) uint32(x uint32) {
   351		e.order.PutUint32(e.buf[0:4], x)
   352		e.buf = e.buf[4:]
   353	}
   354	
   355	func (d *decoder) uint64() uint64 {
   356		x := d.order.Uint64(d.buf[0:8])
   357		d.buf = d.buf[8:]
   358		return x
   359	}
   360	
   361	func (e *encoder) uint64(x uint64) {
   362		e.order.PutUint64(e.buf[0:8], x)
   363		e.buf = e.buf[8:]
   364	}
   365	
   366	func (d *decoder) int8() int8 { return int8(d.uint8()) }
   367	
   368	func (e *encoder) int8(x int8) { e.uint8(uint8(x)) }
   369	
   370	func (d *decoder) int16() int16 { return int16(d.uint16()) }
   371	
   372	func (e *encoder) int16(x int16) { e.uint16(uint16(x)) }
   373	
   374	func (d *decoder) int32() int32 { return int32(d.uint32()) }
   375	
   376	func (e *encoder) int32(x int32) { e.uint32(uint32(x)) }
   377	
   378	func (d *decoder) int64() int64 { return int64(d.uint64()) }
   379	
   380	func (e *encoder) int64(x int64) { e.uint64(uint64(x)) }
   381	
   382	func (d *decoder) value(v reflect.Value) {
   383		switch v.Kind() {
   384		case reflect.Array:
   385			l := v.Len()
   386			for i := 0; i < l; i++ {
   387				d.value(v.Index(i))
   388			}
   389	
   390		case reflect.Struct:
   391			t := v.Type()
   392			l := v.NumField()
   393			for i := 0; i < l; i++ {
   394				// Note: Calling v.CanSet() below is an optimization.
   395				// It would be sufficient to check the field name,
   396				// but creating the StructField info for each field is
   397				// costly (run "go test -bench=ReadStruct" and compare
   398				// results when making changes to this code).
   399				if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   400					d.value(v)
   401				} else {
   402					d.skip(v)
   403				}
   404			}
   405	
   406		case reflect.Slice:
   407			l := v.Len()
   408			for i := 0; i < l; i++ {
   409				d.value(v.Index(i))
   410			}
   411	
   412		case reflect.Int8:
   413			v.SetInt(int64(d.int8()))
   414		case reflect.Int16:
   415			v.SetInt(int64(d.int16()))
   416		case reflect.Int32:
   417			v.SetInt(int64(d.int32()))
   418		case reflect.Int64:
   419			v.SetInt(d.int64())
   420	
   421		case reflect.Uint8:
   422			v.SetUint(uint64(d.uint8()))
   423		case reflect.Uint16:
   424			v.SetUint(uint64(d.uint16()))
   425		case reflect.Uint32:
   426			v.SetUint(uint64(d.uint32()))
   427		case reflect.Uint64:
   428			v.SetUint(d.uint64())
   429	
   430		case reflect.Float32:
   431			v.SetFloat(float64(math.Float32frombits(d.uint32())))
   432		case reflect.Float64:
   433			v.SetFloat(math.Float64frombits(d.uint64()))
   434	
   435		case reflect.Complex64:
   436			v.SetComplex(complex(
   437				float64(math.Float32frombits(d.uint32())),
   438				float64(math.Float32frombits(d.uint32())),
   439			))
   440		case reflect.Complex128:
   441			v.SetComplex(complex(
   442				math.Float64frombits(d.uint64()),
   443				math.Float64frombits(d.uint64()),
   444			))
   445		}
   446	}
   447	
   448	func (e *encoder) value(v reflect.Value) {
   449		switch v.Kind() {
   450		case reflect.Array:
   451			l := v.Len()
   452			for i := 0; i < l; i++ {
   453				e.value(v.Index(i))
   454			}
   455	
   456		case reflect.Struct:
   457			t := v.Type()
   458			l := v.NumField()
   459			for i := 0; i < l; i++ {
   460				// see comment for corresponding code in decoder.value()
   461				if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
   462					e.value(v)
   463				} else {
   464					e.skip(v)
   465				}
   466			}
   467	
   468		case reflect.Slice:
   469			l := v.Len()
   470			for i := 0; i < l; i++ {
   471				e.value(v.Index(i))
   472			}
   473	
   474		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   475			switch v.Type().Kind() {
   476			case reflect.Int8:
   477				e.int8(int8(v.Int()))
   478			case reflect.Int16:
   479				e.int16(int16(v.Int()))
   480			case reflect.Int32:
   481				e.int32(int32(v.Int()))
   482			case reflect.Int64:
   483				e.int64(v.Int())
   484			}
   485	
   486		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   487			switch v.Type().Kind() {
   488			case reflect.Uint8:
   489				e.uint8(uint8(v.Uint()))
   490			case reflect.Uint16:
   491				e.uint16(uint16(v.Uint()))
   492			case reflect.Uint32:
   493				e.uint32(uint32(v.Uint()))
   494			case reflect.Uint64:
   495				e.uint64(v.Uint())
   496			}
   497	
   498		case reflect.Float32, reflect.Float64:
   499			switch v.Type().Kind() {
   500			case reflect.Float32:
   501				e.uint32(math.Float32bits(float32(v.Float())))
   502			case reflect.Float64:
   503				e.uint64(math.Float64bits(v.Float()))
   504			}
   505	
   506		case reflect.Complex64, reflect.Complex128:
   507			switch v.Type().Kind() {
   508			case reflect.Complex64:
   509				x := v.Complex()
   510				e.uint32(math.Float32bits(float32(real(x))))
   511				e.uint32(math.Float32bits(float32(imag(x))))
   512			case reflect.Complex128:
   513				x := v.Complex()
   514				e.uint64(math.Float64bits(real(x)))
   515				e.uint64(math.Float64bits(imag(x)))
   516			}
   517		}
   518	}
   519	
   520	func (d *decoder) skip(v reflect.Value) {
   521		n, _ := dataSize(v)
   522		d.buf = d.buf[n:]
   523	}
   524	
   525	func (e *encoder) skip(v reflect.Value) {
   526		n, _ := dataSize(v)
   527		for i := range e.buf[0:n] {
   528			e.buf[i] = 0
   529		}
   530		e.buf = e.buf[n:]
   531	}
   532	
   533	// intDestSize returns the size of the integer that ptrType points to,
   534	// or 0 if the type is not supported.
   535	func intDestSize(ptrType interface{}) int {
   536		switch ptrType.(type) {
   537		case *int8, *uint8:
   538			return 1
   539		case *int16, *uint16:
   540			return 2
   541		case *int32, *uint32:
   542			return 4
   543		case *int64, *uint64:
   544			return 8
   545		}
   546		return 0
   547	}

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