Source File
	binary.go

Belonging Package
	encoding/binary

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package binary implements simple translation between numbers and byte
// sequences and encoding and decoding of varints.
//
// Numbers are translated by reading and writing fixed-size values.
// A fixed-size value is either a fixed-size arithmetic
// type (bool, int8, uint8, int16, float32, complex64, ...)
// or an array or struct containing only fixed-size values.
//
// The varint functions encode and decode single integer values using
// a variable-length encoding; smaller values require fewer bytes.
// For a specification, see
// https://developers.google.com/protocol-buffers/docs/encoding.
//
// This package favors simplicity over efficiency. Clients that require
// high-performance serialization, especially for large data structures,
// should look at more advanced solutions such as the [encoding/gob]
// package or [google.golang.org/protobuf] for protocol buffers.
package binary

import (
	"errors"
	"io"
	"math"
	"reflect"
	"sync"
)

// A ByteOrder specifies how to convert byte slices into
// 16-, 32-, or 64-bit unsigned integers.
//
// It is implemented by [LittleEndian], [BigEndian], and [NativeEndian].
type ByteOrder interface {
	Uint16([]byte) uint16
	Uint32([]byte) uint32
	Uint64([]byte) uint64
	PutUint16([]byte, uint16)
	PutUint32([]byte, uint32)
	PutUint64([]byte, uint64)
	String() string
}

// AppendByteOrder specifies how to append 16-, 32-, or 64-bit unsigned integers
// into a byte slice.
//
// It is implemented by [LittleEndian], [BigEndian], and [NativeEndian].
type AppendByteOrder interface {
	AppendUint16([]byte, uint16) []byte
	AppendUint32([]byte, uint32) []byte
	AppendUint64([]byte, uint64) []byte
	String() string
}

// LittleEndian is the little-endian implementation of [ByteOrder] and [AppendByteOrder].
var LittleEndian littleEndian

// BigEndian is the big-endian implementation of [ByteOrder] and [AppendByteOrder].
var BigEndian bigEndian

type littleEndian struct{}

func (littleEndian) Uint16(b []byte) uint16 {
	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
	return uint16(b[0]) | uint16(b[1])<<8
}

func (littleEndian) PutUint16(b []byte, v uint16) {
	_ = b[1] // early bounds check to guarantee safety of writes below
	b[0] = byte(v)
	b[1] = byte(v >> 8)
}

func (littleEndian) AppendUint16(b []byte, v uint16) []byte {
	return append(b,
		byte(v),
		byte(v>>8),
	)
}

func (littleEndian) Uint32(b []byte) uint32 {
	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
}

func (littleEndian) PutUint32(b []byte, v uint32) {
	_ = b[3] // early bounds check to guarantee safety of writes below
	b[0] = byte(v)
	b[1] = byte(v >> 8)
	b[2] = byte(v >> 16)
	b[3] = byte(v >> 24)
}

func (littleEndian) AppendUint32(b []byte, v uint32) []byte {
	return append(b,
		byte(v),
		byte(v>>8),
		byte(v>>16),
		byte(v>>24),
	)
}

func (littleEndian) Uint64(b []byte) uint64 {
	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
}

func (littleEndian) PutUint64(b []byte, v uint64) {
	_ = b[7] // early bounds check to guarantee safety of writes below
	b[0] = byte(v)
	b[1] = byte(v >> 8)
	b[2] = byte(v >> 16)
	b[3] = byte(v >> 24)
	b[4] = byte(v >> 32)
	b[5] = byte(v >> 40)
	b[6] = byte(v >> 48)
	b[7] = byte(v >> 56)
}

func (littleEndian) AppendUint64(b []byte, v uint64) []byte {
	return append(b,
		byte(v),
		byte(v>>8),
		byte(v>>16),
		byte(v>>24),
		byte(v>>32),
		byte(v>>40),
		byte(v>>48),
		byte(v>>56),
	)
}

func (littleEndian) String() string { return "LittleEndian" }

func (littleEndian) GoString() string { return "binary.LittleEndian" }

type bigEndian struct{}

func (bigEndian) Uint16(b []byte) uint16 {
	_ = b[1] // bounds check hint to compiler; see golang.org/issue/14808
	return uint16(b[1]) | uint16(b[0])<<8
}

func (bigEndian) PutUint16(b []byte, v uint16) {
	_ = b[1] // early bounds check to guarantee safety of writes below
	b[0] = byte(v >> 8)
	b[1] = byte(v)
}

func (bigEndian) AppendUint16(b []byte, v uint16) []byte {
	return append(b,
		byte(v>>8),
		byte(v),
	)
}

func (bigEndian) Uint32(b []byte) uint32 {
	_ = b[3] // bounds check hint to compiler; see golang.org/issue/14808
	return uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
}

func (bigEndian) PutUint32(b []byte, v uint32) {
	_ = b[3] // early bounds check to guarantee safety of writes below
	b[0] = byte(v >> 24)
	b[1] = byte(v >> 16)
	b[2] = byte(v >> 8)
	b[3] = byte(v)
}

func (bigEndian) AppendUint32(b []byte, v uint32) []byte {
	return append(b,
		byte(v>>24),
		byte(v>>16),
		byte(v>>8),
		byte(v),
	)
}

func (bigEndian) Uint64(b []byte) uint64 {
	_ = b[7] // bounds check hint to compiler; see golang.org/issue/14808
	return uint64(b[7]) | uint64(b[6])<<8 | uint64(b[5])<<16 | uint64(b[4])<<24 |
		uint64(b[3])<<32 | uint64(b[2])<<40 | uint64(b[1])<<48 | uint64(b[0])<<56
}

func (bigEndian) PutUint64(b []byte, v uint64) {
	_ = b[7] // early bounds check to guarantee safety of writes below
	b[0] = byte(v >> 56)
	b[1] = byte(v >> 48)
	b[2] = byte(v >> 40)
	b[3] = byte(v >> 32)
	b[4] = byte(v >> 24)
	b[5] = byte(v >> 16)
	b[6] = byte(v >> 8)
	b[7] = byte(v)
}

func (bigEndian) AppendUint64(b []byte, v uint64) []byte {
	return append(b,
		byte(v>>56),
		byte(v>>48),
		byte(v>>40),
		byte(v>>32),
		byte(v>>24),
		byte(v>>16),
		byte(v>>8),
		byte(v),
	)
}

func (bigEndian) String() string { return "BigEndian" }

func (bigEndian) GoString() string { return "binary.BigEndian" }

func (nativeEndian) String() string { return "NativeEndian" }

func (nativeEndian) GoString() string { return "binary.NativeEndian" }

// Read reads structured binary data from r into data.
// Data must be a pointer to a fixed-size value or a slice
// of fixed-size values.
// Bytes read from r are decoded using the specified byte order
// and written to successive fields of the data.
// When decoding boolean values, a zero byte is decoded as false, and
// any other non-zero byte is decoded as true.
// When reading into structs, the field data for fields with
// blank (_) field names is skipped; i.e., blank field names
// may be used for padding.
// When reading into a struct, all non-blank fields must be exported
// or Read may panic.
//
// The error is [io.EOF] only if no bytes were read.
// If an [io.EOF] happens after reading some but not all the bytes,
// Read returns [io.ErrUnexpectedEOF].
func Read(r io.Reader, order ByteOrder, data any) error {
	// Fast path for basic types and slices.
	if n := intDataSize(data); n != 0 {
		bs := make([]byte, n)
		if _, err := io.ReadFull(r, bs); err != nil {
			return err
		}
		switch data := data.(type) {
		case *bool:
			*data = bs[0] != 0
		case *int8:
			*data = int8(bs[0])
		case *uint8:
			*data = bs[0]
		case *int16:
			*data = int16(order.Uint16(bs))
		case *uint16:
			*data = order.Uint16(bs)
		case *int32:
			*data = int32(order.Uint32(bs))
		case *uint32:
			*data = order.Uint32(bs)
		case *int64:
			*data = int64(order.Uint64(bs))
		case *uint64:
			*data = order.Uint64(bs)
		case *float32:
			*data = math.Float32frombits(order.Uint32(bs))
		case *float64:
			*data = math.Float64frombits(order.Uint64(bs))
		case []bool:
			for i, x := range bs { // Easier to loop over the input for 8-bit values.
				data[i] = x != 0
			}
		case []int8:
			for i, x := range bs {
				data[i] = int8(x)
			}
		case []uint8:
			copy(data, bs)
		case []int16:
			for i := range data {
				data[i] = int16(order.Uint16(bs[2*i:]))
			}
		case []uint16:
			for i := range data {
				data[i] = order.Uint16(bs[2*i:])
			}
		case []int32:
			for i := range data {
				data[i] = int32(order.Uint32(bs[4*i:]))
			}
		case []uint32:
			for i := range data {
				data[i] = order.Uint32(bs[4*i:])
			}
		case []int64:
			for i := range data {
				data[i] = int64(order.Uint64(bs[8*i:]))
			}
		case []uint64:
			for i := range data {
				data[i] = order.Uint64(bs[8*i:])
			}
		case []float32:
			for i := range data {
				data[i] = math.Float32frombits(order.Uint32(bs[4*i:]))
			}
		case []float64:
			for i := range data {
				data[i] = math.Float64frombits(order.Uint64(bs[8*i:]))
			}
		default:
			n = 0 // fast path doesn't apply
		}
		if n != 0 {
			return nil
		}
	}

	// Fallback to reflect-based decoding.
	v := reflect.ValueOf(data)
	size := -1
	switch v.Kind() {
	case reflect.Pointer:
		v = v.Elem()
		size = dataSize(v)
	case reflect.Slice:
		size = dataSize(v)
	}
	if size < 0 {
		return errors.New("binary.Read: invalid type " + reflect.TypeOf(data).String())
	}
	d := &decoder{order: order, buf: make([]byte, size)}
	if _, err := io.ReadFull(r, d.buf); err != nil {
		return err
	}
	d.value(v)
	return nil
}

// Write writes the binary representation of data into w.
// Data must be a fixed-size value or a slice of fixed-size
// values, or a pointer to such data.
// Boolean values encode as one byte: 1 for true, and 0 for false.
// Bytes written to w are encoded using the specified byte order
// and read from successive fields of the data.
// When writing structs, zero values are written for fields
// with blank (_) field names.
func Write(w io.Writer, order ByteOrder, data any) error {
	// Fast path for basic types and slices.
	if n := intDataSize(data); n != 0 {
		bs := make([]byte, n)
		switch v := data.(type) {
		case *bool:
			if *v {
				bs[0] = 1
			} else {
				bs[0] = 0
			}
		case bool:
			if v {
				bs[0] = 1
			} else {
				bs[0] = 0
			}
		case []bool:
			for i, x := range v {
				if x {
					bs[i] = 1
				} else {
					bs[i] = 0
				}
			}
		case *int8:
			bs[0] = byte(*v)
		case int8:
			bs[0] = byte(v)
		case []int8:
			for i, x := range v {
				bs[i] = byte(x)
			}
		case *uint8:
			bs[0] = *v
		case uint8:
			bs[0] = v
		case []uint8:
			bs = v
		case *int16:
			order.PutUint16(bs, uint16(*v))
		case int16:
			order.PutUint16(bs, uint16(v))
		case []int16:
			for i, x := range v {
				order.PutUint16(bs[2*i:], uint16(x))
			}
		case *uint16:
			order.PutUint16(bs, *v)
		case uint16:
			order.PutUint16(bs, v)
		case []uint16:
			for i, x := range v {
				order.PutUint16(bs[2*i:], x)
			}
		case *int32:
			order.PutUint32(bs, uint32(*v))
		case int32:
			order.PutUint32(bs, uint32(v))
		case []int32:
			for i, x := range v {
				order.PutUint32(bs[4*i:], uint32(x))
			}
		case *uint32:
			order.PutUint32(bs, *v)
		case uint32:
			order.PutUint32(bs, v)
		case []uint32:
			for i, x := range v {
				order.PutUint32(bs[4*i:], x)
			}
		case *int64:
			order.PutUint64(bs, uint64(*v))
		case int64:
			order.PutUint64(bs, uint64(v))
		case []int64:
			for i, x := range v {
				order.PutUint64(bs[8*i:], uint64(x))
			}
		case *uint64:
			order.PutUint64(bs, *v)
		case uint64:
			order.PutUint64(bs, v)
		case []uint64:
			for i, x := range v {
				order.PutUint64(bs[8*i:], x)
			}
		case *float32:
			order.PutUint32(bs, math.Float32bits(*v))
		case float32:
			order.PutUint32(bs, math.Float32bits(v))
		case []float32:
			for i, x := range v {
				order.PutUint32(bs[4*i:], math.Float32bits(x))
			}
		case *float64:
			order.PutUint64(bs, math.Float64bits(*v))
		case float64:
			order.PutUint64(bs, math.Float64bits(v))
		case []float64:
			for i, x := range v {
				order.PutUint64(bs[8*i:], math.Float64bits(x))
			}
		}
		_, err := w.Write(bs)
		return err
	}

	// Fallback to reflect-based encoding.
	v := reflect.Indirect(reflect.ValueOf(data))
	size := dataSize(v)
	if size < 0 {
		return errors.New("binary.Write: some values are not fixed-sized in type " + reflect.TypeOf(data).String())
	}
	buf := make([]byte, size)
	e := &encoder{order: order, buf: buf}
	e.value(v)
	_, err := w.Write(buf)
	return err
}

// Size returns how many bytes [Write] would generate to encode the value v, which
// must be a fixed-size value or a slice of fixed-size values, or a pointer to such data.
// If v is neither of these, Size returns -1.
func Size(v any) int {
	return dataSize(reflect.Indirect(reflect.ValueOf(v)))
}

var structSize sync.Map // map[reflect.Type]int

// dataSize returns the number of bytes the actual data represented by v occupies in memory.
// For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
// it returns the length of the slice times the element size and does not count the memory
// occupied by the header. If the type of v is not acceptable, dataSize returns -1.
func dataSize(v reflect.Value) int {
	switch v.Kind() {
	case reflect.Slice:
		if s := sizeof(v.Type().Elem()); s >= 0 {
			return s * v.Len()
		}

	case reflect.Struct:
		t := v.Type()
		if size, ok := structSize.Load(t); ok {
			return size.(int)
		}
		size := sizeof(t)
		structSize.Store(t, size)
		return size

	default:
		if v.IsValid() {
			return sizeof(v.Type())
		}
	}

	return -1
}

// sizeof returns the size >= 0 of variables for the given type or -1 if the type is not acceptable.
func sizeof(t reflect.Type) int {
	switch t.Kind() {
	case reflect.Array:
		if s := sizeof(t.Elem()); s >= 0 {
			return s * t.Len()
		}

	case reflect.Struct:
		sum := 0
		for i, n := 0, t.NumField(); i < n; i++ {
			s := sizeof(t.Field(i).Type)
			if s < 0 {
				return -1
			}
			sum += s
		}
		return sum

	case reflect.Bool,
		reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
		reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
		reflect.Float32, reflect.Float64, reflect.Complex64, reflect.Complex128:
		return int(t.Size())
	}

	return -1
}

type coder struct {
	order  ByteOrder
	buf    []byte
	offset int
}

type decoder coder
type encoder coder

func (d *decoder) bool() bool {
	x := d.buf[d.offset]
	d.offset++
	return x != 0
}

func (e *encoder) bool(x bool) {
	if x {
		e.buf[e.offset] = 1
	} else {
		e.buf[e.offset] = 0
	}
	e.offset++
}

func (d *decoder) uint8() uint8 {
	x := d.buf[d.offset]
	d.offset++
	return x
}

func (e *encoder) uint8(x uint8) {
	e.buf[e.offset] = x
	e.offset++
}

func (d *decoder) uint16() uint16 {
	x := d.order.Uint16(d.buf[d.offset : d.offset+2])
	d.offset += 2
	return x
}

func (e *encoder) uint16(x uint16) {
	e.order.PutUint16(e.buf[e.offset:e.offset+2], x)
	e.offset += 2
}

func (d *decoder) uint32() uint32 {
	x := d.order.Uint32(d.buf[d.offset : d.offset+4])
	d.offset += 4
	return x
}

func (e *encoder) uint32(x uint32) {
	e.order.PutUint32(e.buf[e.offset:e.offset+4], x)
	e.offset += 4
}

func (d *decoder) uint64() uint64 {
	x := d.order.Uint64(d.buf[d.offset : d.offset+8])
	d.offset += 8
	return x
}

func (e *encoder) uint64(x uint64) {
	e.order.PutUint64(e.buf[e.offset:e.offset+8], x)
	e.offset += 8
}

func (d *decoder) int8() int8 { return int8(d.uint8()) }

func (e *encoder) int8(x int8) { e.uint8(uint8(x)) }

func (d *decoder) int16() int16 { return int16(d.uint16()) }

func (e *encoder) int16(x int16) { e.uint16(uint16(x)) }

func (d *decoder) int32() int32 { return int32(d.uint32()) }

func (e *encoder) int32(x int32) { e.uint32(uint32(x)) }

func (d *decoder) int64() int64 { return int64(d.uint64()) }

func (e *encoder) int64(x int64) { e.uint64(uint64(x)) }

func (d *decoder) value(v reflect.Value) {
	switch v.Kind() {
	case reflect.Array:
		l := v.Len()
		for i := 0; i < l; i++ {
			d.value(v.Index(i))
		}

	case reflect.Struct:
		t := v.Type()
		l := v.NumField()
		for i := 0; i < l; i++ {
			// Note: Calling v.CanSet() below is an optimization.
			// It would be sufficient to check the field name,
			// but creating the StructField info for each field is
			// costly (run "go test -bench=ReadStruct" and compare
			// results when making changes to this code).
			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
				d.value(v)
			} else {
				d.skip(v)
			}
		}

	case reflect.Slice:
		l := v.Len()
		for i := 0; i < l; i++ {
			d.value(v.Index(i))
		}

	case reflect.Bool:
		v.SetBool(d.bool())

	case reflect.Int8:
		v.SetInt(int64(d.int8()))
	case reflect.Int16:
		v.SetInt(int64(d.int16()))
	case reflect.Int32:
		v.SetInt(int64(d.int32()))
	case reflect.Int64:
		v.SetInt(d.int64())

	case reflect.Uint8:
		v.SetUint(uint64(d.uint8()))
	case reflect.Uint16:
		v.SetUint(uint64(d.uint16()))
	case reflect.Uint32:
		v.SetUint(uint64(d.uint32()))
	case reflect.Uint64:
		v.SetUint(d.uint64())

	case reflect.Float32:
		v.SetFloat(float64(math.Float32frombits(d.uint32())))
	case reflect.Float64:
		v.SetFloat(math.Float64frombits(d.uint64()))

	case reflect.Complex64:
		v.SetComplex(complex(
			float64(math.Float32frombits(d.uint32())),
			float64(math.Float32frombits(d.uint32())),
		))
	case reflect.Complex128:
		v.SetComplex(complex(
			math.Float64frombits(d.uint64()),
			math.Float64frombits(d.uint64()),
		))
	}
}

func (e *encoder) value(v reflect.Value) {
	switch v.Kind() {
	case reflect.Array:
		l := v.Len()
		for i := 0; i < l; i++ {
			e.value(v.Index(i))
		}

	case reflect.Struct:
		t := v.Type()
		l := v.NumField()
		for i := 0; i < l; i++ {
			// see comment for corresponding code in decoder.value()
			if v := v.Field(i); v.CanSet() || t.Field(i).Name != "_" {
				e.value(v)
			} else {
				e.skip(v)
			}
		}

	case reflect.Slice:
		l := v.Len()
		for i := 0; i < l; i++ {
			e.value(v.Index(i))
		}

	case reflect.Bool:
		e.bool(v.Bool())

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		switch v.Type().Kind() {
		case reflect.Int8:
			e.int8(int8(v.Int()))
		case reflect.Int16:
			e.int16(int16(v.Int()))
		case reflect.Int32:
			e.int32(int32(v.Int()))
		case reflect.Int64:
			e.int64(v.Int())
		}

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		switch v.Type().Kind() {
		case reflect.Uint8:
			e.uint8(uint8(v.Uint()))
		case reflect.Uint16:
			e.uint16(uint16(v.Uint()))
		case reflect.Uint32:
			e.uint32(uint32(v.Uint()))
		case reflect.Uint64:
			e.uint64(v.Uint())
		}

	case reflect.Float32, reflect.Float64:
		switch v.Type().Kind() {
		case reflect.Float32:
			e.uint32(math.Float32bits(float32(v.Float())))
		case reflect.Float64:
			e.uint64(math.Float64bits(v.Float()))
		}

	case reflect.Complex64, reflect.Complex128:
		switch v.Type().Kind() {
		case reflect.Complex64:
			x := v.Complex()
			e.uint32(math.Float32bits(float32(real(x))))
			e.uint32(math.Float32bits(float32(imag(x))))
		case reflect.Complex128:
			x := v.Complex()
			e.uint64(math.Float64bits(real(x)))
			e.uint64(math.Float64bits(imag(x)))
		}
	}
}

func (d *decoder) skip(v reflect.Value) {
	d.offset += dataSize(v)
}

func (e *encoder) skip(v reflect.Value) {
	n := dataSize(v)
	zero := e.buf[e.offset : e.offset+n]
	for i := range zero {
		zero[i] = 0
	}
	e.offset += n
}

// intDataSize returns the size of the data required to represent the data when encoded.
// It returns zero if the type cannot be implemented by the fast path in Read or Write.
func intDataSize(data any) int {
	switch data := data.(type) {
	case bool, int8, uint8, *bool, *int8, *uint8:
		return 1
	case []bool:
		return len(data)
	case []int8:
		return len(data)
	case []uint8:
		return len(data)
	case int16, uint16, *int16, *uint16:
		return 2
	case []int16:
		return 2 * len(data)
	case []uint16:
		return 2 * len(data)
	case int32, uint32, *int32, *uint32:
		return 4
	case []int32:
		return 4 * len(data)
	case []uint32:
		return 4 * len(data)
	case int64, uint64, *int64, *uint64:
		return 8
	case []int64:
		return 8 * len(data)
	case []uint64:
		return 8 * len(data)
	case float32, *float32:
		return 4
	case float64, *float64:
		return 8
	case []float32:
		return 4 * len(data)
	case []float64:
		return 8 * len(data)
	}
	return 0
}

The pages are generated with Golds v0.6.9-preview. (GOOS=linux GOARCH=amd64)
Golds is a Go 101 project developed by Tapir Liu.
PR and bug reports are welcome and can be submitted to the issue list.
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