Go encoding/gob
gob是Go语言自带的一个数据序列化的编码/解码工具。类似于 Java 的 Serialization
。
gob和json,xml之类序列化实现一样,使用Encoder
对数据进行编码,使用Decoder
解码。
类型与值
Gob 文件或流是完全自描述的:里面包含的所有类型都有一个对应的描述。
整数以两种形式传输:有符号的任意精度整数,无符号的任意精度整数。浮点数始终使用IEEE-754 64位精度发送,目标变量必须能够表示足够的精度,否则解码操作将失败。gob
支持struct
,array
和slice
。struct
仅对导出的字段进行编码和解码。字符串和字节数组支持特殊,高效的编解码。切片被解码时,如果现有切片具有容量,则切片将被扩展到适当位置;如果没有,则分配新数组。
源值和目标值类型不需要完全对应:对于struct,源值中存在而目标值中缺少的字段将被忽略(以名称为标识)。目标值中存在,但传输类型或者变量中没有的字段,将被忽略。如果两者都有的字段,类型必须是可兼容的。Encoder
和Decoder
会进行必要的间接操作和解引用,以完成gobs
与Go
类型值之间的转换。
转换与解引用示例
源类型
struct { A, B int }
可编码或者可解码的类型
struct { A, B int } // the same
*struct { A, B int } // extra indirection of the struct
struct { *A, **B int } // extra indirection of the fields
struct { A, B int64 } // different concrete value type; see below
struct { B, A int } // ordering doesn't matter; matching is by name
struct { A, B, C int } // extra field (C) ignored
struct { B int } // missing field (A) ignored; data will be dropped
struct { B, C int } // missing field (A) ignored; extra field (C) ignored.
尝试接收这些类型将返回错误
struct { A int; B uint } // change of signedness for B
struct { A int; B float } // change of type for B
struct { } // no field names in common
struct { C, D int } // no field names in common
主要方法
注册
func Register(value interface{})
func RegisterName(name string, value interface{})
编码
func NewDecoder(r io.Reader) *Decoder
func (dec *Decoder) Decode(e interface{}) error
func (dec *Decoder) DecodeValue(v reflect.Value) error
解码
func NewEncoder(w io.Writer) *Encoder
func (enc *Encoder) Encode(e interface{}) error
func (enc *Encoder) EncodeValue(value reflect.Value) error
基础示例
package main
import (
"bytes"
"encoding/gob"
log "github.com/sirupsen/logrus"
)
func init() {
log.SetFormatter(&log.TextFormatter{
FullTimestamp: true,
})
}
type S struct {
X, Y, Z int
Name string
}
type R struct {
X, Y *int32
Name string
}
func main() {
var err error
buffer := new(bytes.Buffer)
encoder := gob.NewEncoder(buffer)
err = encoder.Encode(S{1, 2, 3, "Sending"})
if err != nil {
log.Error("gob encoding error : ", err)
}
decoder := gob.NewDecoder(buffer)
r := R{}
err = decoder.Decode(&r)
if err != nil {
log.Error("gob decoding error : ", err)
}
log.Infof("receiving data : %d, %d , %s", *(r.X), *(r.Y), r.Name)
}
切片示例
package main
import (
"bytes"
"encoding/gob"
log "github.com/sirupsen/logrus"
)
func init() {
log.SetFormatter(&log.TextFormatter{
FullTimestamp: true,
})
}
func main() {
slist := make([]string, 0, 10)
slist = append(slist, "1", "2", "3")
log.Infof("SEND - LEN : %d CAP : %d VAL : %#v", len(slist), cap(slist), slist)
var err error
buffer := new(bytes.Buffer)
encoder := gob.NewEncoder(buffer)
decoder := gob.NewDecoder(buffer)
err = encoder.Encode(slist)
if err != nil {
log.Error("gob encoding error : ", err)
}
rlist := make([]string, 0)
err = decoder.Decode(&rlist)
if err != nil {
log.Error("gob decoding error : ", err)
}
log.Infof("SEND - LEN : %d CAP : %d VAL : %#v", len(rlist), cap(rlist), rlist)
}
自定义编码解码器
package main
import (
"bytes"
"encoding/gob"
"fmt"
"log"
)
// The Vector type has unexported fields, which the package cannot access.
// We therefore write a BinaryMarshal/BinaryUnmarshal method pair to allow us
// to send and receive the type with the gob package. These interfaces are
// defined in the "encoding" package.
// We could equivalently use the locally defined GobEncode/GobDecoder
// interfaces.
type Vector struct {
x, y, z int
}
func (v Vector) MarshalBinary() ([]byte, error) {
// A simple encoding: plain text.
var b bytes.Buffer
fmt.Fprintln(&b, v.x, v.y, v.z)
return b.Bytes(), nil
}
// UnmarshalBinary modifies the receiver so it must take a pointer receiver.
func (v *Vector) UnmarshalBinary(data []byte) error {
// A simple encoding: plain text.
b := bytes.NewBuffer(data)
_, err := fmt.Fscanln(b, &v.x, &v.y, &v.z)
return err
}
// This example transmits a value that implements the custom encoding and decoding methods.
func main() {
var network bytes.Buffer // Stand-in for the network.
// Create an encoder and send a value.
enc := gob.NewEncoder(&network)
err := enc.Encode(Vector{3, 4, 5})
if err != nil {
log.Fatal("encode:", err)
}
// Create a decoder and receive a value.
dec := gob.NewDecoder(&network)
var v Vector
err = dec.Decode(&v)
if err != nil {
log.Fatal("decode:", err)
}
fmt.Println(v)
}
上面的示例是godoc的自定义编码解码器示例,Vector实现了
encoding.BinaryMarshaler
和encoding.BinaryUnmarshaler
接口。
以上代码也可以实现GobDecoder
和GobEncoder
接口
当都实现时,优先调用GobDecoder
和GobEncoder
接口的方法
encoding.BinaryMarshaler
type BinaryMarshaler interface {
MarshalBinary() (data []byte, err error)
}
encoding.BinaryUnmarshaler
type BinaryUnmarshaler interface {
UnmarshalBinary(data []byte) error
}
GobEncoder
type GobEncoder interface {
// GobEncode returns a byte slice representing the encoding of the
// receiver for transmission to a GobDecoder, usually of the same
// concrete type.
GobEncode() ([]byte, error)
}
GobDecoder
type GobDecoder interface {
// GobDecode overwrites the receiver, which must be a pointer,
// with the value represented by the byte slice, which was written
// by GobEncode, usually for the same concrete type.
GobDecode([]byte) error
}
接口类型序列化
以下示例展示如何序列化接口值,与常规struct类型的区别在于,使用func Register(value interface{})
函数注册接口实现类型。
package main
import (
"bytes"
"encoding/gob"
"fmt"
"log"
"math"
)
type Point struct {
X, Y int
}
func (p Point) Hypotenuse() float64 {
return math.Hypot(float64(p.X), float64(p.Y))
}
type Pythagoras interface {
Hypotenuse() float64
}
// This example shows how to encode an interface value. The key
// distinction from regular types is to register the concrete type that
// implements the interface.
func main() {
var network bytes.Buffer // Stand-in for the network.
// We must register the concrete type for the encoder and decoder (which would
// normally be on a separate machine from the encoder). On each end, this tells the
// engine which concrete type is being sent that implements the interface.
gob.Register(Point{})
// Create an encoder and send some values.
enc := gob.NewEncoder(&network)
for i := 1; i <= 3; i++ {
interfaceEncode(enc, Point{3 * i, 4 * i})
}
// Create a decoder and receive some values.
dec := gob.NewDecoder(&network)
for i := 1; i <= 3; i++ {
result := interfaceDecode(dec)
fmt.Println(result.Hypotenuse())
}
}
// interfaceEncode encodes the interface value into the encoder.
func interfaceEncode(enc *gob.Encoder, p Pythagoras) {
// The encode will fail unless the concrete type has been
// registered. We registered it in the calling function.
// Pass pointer to interface so Encode sees (and hence sends) a value of
// interface type. If we passed p directly it would see the concrete type instead.
// See the blog post, "The Laws of Reflection" for background.
err := enc.Encode(&p)
if err != nil {
log.Fatal("encode:", err)
}
}
// interfaceDecode decodes the next interface value from the stream and returns it.
func interfaceDecode(dec *gob.Decoder) Pythagoras {
// The decode will fail unless the concrete type on the wire has been
// registered. We registered it in the calling function.
var p Pythagoras
err := dec.Decode(&p)
if err != nil {
log.Fatal("decode:", err)
}
return p
}