Golang标准库binary详解

Golang标准库binary

binary包实现了数字和字节序列之间的简单转换。

1、ByteOrder

ByteOrder指定了如何将一个字节序列转换为16、32或64位的无符号整数：

type ByteOrder interface {
Uint16([]byte) uint16
Uint32([]byte) uint32
Uint64([]byte) uint64
PutUint16([]byte, uint16)
PutUint32([]byte, uint32)
PutUint64([]byte, uint64)
String() string
}

ByteOrder是一个接口，在binary中有两个实现了该接口的结构体，分别是littleEndian和bigEndian，也就是小端和大端。大端小端指的是数据如何存储在内存中，比如：将低位字节存储在低地址空间中、高位字节存储在高地址空间中就是小端字节序；相反，将低位字节存储在高地址空间中、高位字节存储在低地址空间中就是大端字节序。

例如：十六进制数0X12345678以小端和大端字节序分别在内存中的存储方式如下：

littleEndian：

littleEndian在其它包中是无法创建的，但是在binary中已经创建了一个名为LittleEndian的该结构体，我们可以直接使用。

var LittleEndian littleEndian
type littleEndian struct{}
func (littleEndian) Uint16(b []byte) uint16 {
_ = b[1] // 编译器的边界检测提示
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) 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) 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) String() string { return "LittleEndian" }
func (littleEndian) GoString() string { return "binary.LittleEndian" }

在上面定义的方法也比较简单，就是字节序列与无符号数之间的转换。例如Uint16这个方法，在这里是小端字节序，因此低字节存储在低地址空间中，随着切片的索引的增大，地址空间也是增大的，所以b[1]所在空间是高地址，因此将b[1]左移八位后与b[0]位与就可以得到uint16类型的数据了。

bigEndian：

大端与小端相反：

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

2、binary.Read

Read方法从一个reader中读取数据到data中，data必须是一个指针或一个固定大小的值或切片：

该方法也可以将reader中读取的数据赋值给结构体的各个字段中。

func Read(r io.Reader, order ByteOrder, data interface{}) 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.Ptr:
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
}

3、binary.Write

Write方法将数据的二进制写入一个Writer中，data必须为一个固定值的值或者切片或指向该类数据的一个指针：

func Write(w io.Writer, order ByteOrder, data interface{}) 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: invalid type " + reflect.TypeOf(data).String())
}
buf := make([]byte, size)
e := &encoder{order: order, buf: buf}
e.value(v)
_, err := w.Write(buf)
return err
}

4、binary.Read和binary.Write的应用

当我们使用tcp传输数据时，常常会遇到粘包的现象，因此为了解决粘包我们需要告诉对方我们发送的数据包的大小。一般是使用TLV类型的数据协议，分别是Type、Len、Value，Type和Len为数据头，可以将这个两个字段都固定为四个字节。读取数据时，先将Type和Len读取出来，然后再根据Len来读取剩余的数据：

例如我们使用客户端向一个服务端发送数据：

client：

package main
import (
"bytes"
"encoding/binary"
"fmt"
"net"
)
// 对数据进行编码
func Encode(id uint32, msg []byte) []byte {
var dataLen uint32 = uint32(len(msg))
// *Buffer实现了Writer
buffer := bytes.NewBuffer([]byte{})
   // 将id写入字节切片
if err := binary.Write(buffer, binary.LittleEndian, &id); err != nil {
fmt.Println("Write to buffer error:", err)
}
// 将数据长度写入字节切片
if err := binary.Write(buffer, binary.LittleEndian, &dataLen); err != nil {
fmt.Println("Write to buffer error:", err)
}
   // 最后将数据添加到后面
msg = append(buffer.Bytes(), msg...)
return msg
}
func main() {
dial, err := net.Dial("tcp4", "127.0.0.1:6666")
if err != nil {
fmt.Println("Dial tcp error:", err)
}
   // 向服务端发送hello,world!
msg := []byte("hello,world!")
var id uint32 = 1
data := Encode(id, msg)
dial.Write(data)
dial.Close()
}
// 运行结果：
Receive Data, Type:1, Len:12, Message:hello,world!
Connection has been closed by client

server：

package main
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"net"
)
// 解码，从字节切片中获取id和len
func Decode(encoded []byte) (id uint32, l uint32) {
buffer := bytes.NewBuffer(encoded)
if err := binary.Read(buffer, binary.LittleEndian, &id); err != nil {
fmt.Println("Read from buffer error:", err)
}
if err := binary.Read(buffer, binary.LittleEndian, &l); err != nil {
fmt.Println("Read from buffer error:", err)
}
return id, l
}
const MAX_PACKAGE = 4096
func DealConn(conn net.Conn) {
defer conn.Close()
head := make([]byte, 8)
for {
       // 先读取8个字节的头部，也就是id和dataLen
_, err := io.ReadFull(conn, head)
if err != nil {
if err == io.EOF {
fmt.Println("Connection has been closed by client")
} else {
fmt.Println("Read error:", err)
}
return
}
id, l := Decode(head)
if l > MAX_PACKAGE {
fmt.Println("Received data grater than MAX_PACKAGE")
return
}
       // 然后读取剩余数据
data := make([]byte, l)
_, err = io.ReadFull(conn, data)
if err != nil {
if err == io.EOF {
fmt.Println("Connection has been closed by client")
} else {
fmt.Println("Read error:", err)
}
return
}
       // 打印收到的数据
fmt.Printf("Receive Data, Type:％d, Len:％d, Message:％s\n",
id, l, string(data))
}
}
func main() {
listener, err := net.Listen("tcp", "127.0.0.1:6666")
if err != nil {
fmt.Println("Listen tcp error:", err)
return
}
for {
conn, err := listener.Accept()
if err != nil {
fmt.Println("Accept error:", err)
           break
}
// 启动一个协程处理客户端
go DealConn(conn)
}
}

运行结果：
Receive Data, Type:1, Len:12, Message:hello,world!
Connection has been closed by client

来源：https://blog.csdn.net/Peerless__/article/details/121443159