golang Protobuf学习

   protobuf是一种高效的数据传输格式（Google's data interchange format），且与语言无关，protobuf和json是基于http服务中最多见的两种数据格式。今天来学习基于golang的protobuf相关内容。

google protocol buffer: https://developers.google.com/protocol-buffers/
golang 官方提供的protobuf支持插件:https://github.com/golang/protobuf

要想使用protobuf，须要4步：

1. 下载安装google protocol buffer 编译器:https://github.com/google/protobuf/releases/tag/v3.5.1
2. 下载安装golang protobuf plugin:https://github.com/golang/protobuf
   使用go tools安装:go get -u github.com/golang/protobuf/protoc-gen-go
3. 按照protobuf 语法规则编写.proto文件
4. 将proto文件编译成golang代码模型
   protoc -I=$SRC_DIR --go_out=$DST_DIR $SRC_DIR/addressbook.proto
   -IPATH, --proto_path=PATH 指定import路径
   --go_out 指定生成go代码路径（同理--java_out是指定java生成路径）
     

---

下面以一个实际例子来讲明：
addressbook.proto

syntax = "proto3";
package test.protobuf.tutorial;
message Person{
    string name  = 1;//姓名
    int32  id    = 2;//id编号
    string email = 3;//邮箱
    enum PhoneType { //枚举类型（电话类型）
        MOBILE = 0;
        HOME = 1;
        WORK = 2;
    }
    message PhoneNumber{
        string    number = 1;
        PhoneType type   = 2;
    }
    repeated PhoneNumber phones = 4; //repeated可理解为动态数组
}

// Our address book file is just one of these.
message AddressBook {
    repeated Person people = 1;
}

编译生成go文件。protoc会调用protoc-go-gen来生成go文件
.
├── addressbook.proto
└── src
└── addressbook.pb.go
protoc --go_out=./src addressbook.proto

addressbook.pb.go

// Code generated by protoc-gen-go. DO NOT EDIT.
// source: addressbook.proto

/*
Package test_protobuf_tutorial is a generated protocol buffer package.

It is generated from these files:
    addressbook.proto

It has these top-level messages:
    Person
    AddressBook
*/
package test_protobuf_tutorial

import proto "github.com/golang/protobuf/proto"
import fmt "fmt"
import math "math"

// Reference imports to suppress errors if they are not otherwise used.
var _ = proto.Marshal
var _ = fmt.Errorf
var _ = math.Inf

// This is a compile-time assertion to ensure that this generated file
// is compatible with the proto package it is being compiled against.
// A compilation error at this line likely means your copy of the
// proto package needs to be updated.
const _ = proto.ProtoPackageIsVersion2 // please upgrade the proto package

type Person_PhoneType int32

const (
    Person_MOBILE Person_PhoneType = 0
    Person_HOME   Person_PhoneType = 1
    Person_WORK   Person_PhoneType = 2
)

var Person_PhoneType_name = map[int32]string{
    0: "MOBILE",
    1: "HOME",
    2: "WORK",
}
var Person_PhoneType_value = map[string]int32{
    "MOBILE": 0,
    "HOME":   1,
    "WORK":   2,
}

func (x Person_PhoneType) String() string {
    return proto.EnumName(Person_PhoneType_name, int32(x))
}
func (Person_PhoneType) EnumDescriptor() ([]byte, []int) { return fileDescriptor0, []int{0, 0} }

type Person struct {
    Name   string                `protobuf:"bytes,1,opt,name=name" json:"name,omitempty"`
    Id     int32                 `protobuf:"varint,2,opt,name=id" json:"id,omitempty"`
    Email  string                `protobuf:"bytes,3,opt,name=email" json:"email,omitempty"`
    Phones []*Person_PhoneNumber `protobuf:"bytes,4,rep,name=phones" json:"phones,omitempty"`
}

func (m *Person) Reset()                    { *m = Person{} }
func (m *Person) String() string            { return proto.CompactTextString(m) }
func (*Person) ProtoMessage()               {}
func (*Person) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{0} }

func (m *Person) GetName() string {
    if m != nil {
        return m.Name
    }
    return ""
}

func (m *Person) GetId() int32 {
    if m != nil {
        return m.Id
    }
    return 0
}

func (m *Person) GetEmail() string {
    if m != nil {
        return m.Email
    }
    return ""
}

func (m *Person) GetPhones() []*Person_PhoneNumber {
    if m != nil {
        return m.Phones
    }
    return nil
}

type Person_PhoneNumber struct {
    Number string           `protobuf:"bytes,1,opt,name=number" json:"number,omitempty"`
    Type   Person_PhoneType `protobuf:"varint,2,opt,name=type,enum=test.protobuf.tutorial.Person_PhoneType" json:"type,omitempty"`
}

func (m *Person_PhoneNumber) Reset()                    { *m = Person_PhoneNumber{} }
func (m *Person_PhoneNumber) String() string            { return proto.CompactTextString(m) }
func (*Person_PhoneNumber) ProtoMessage()               {}
func (*Person_PhoneNumber) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{0, 0} }

func (m *Person_PhoneNumber) GetNumber() string {
    if m != nil {
        return m.Number
    }
    return ""
}

func (m *Person_PhoneNumber) GetType() Person_PhoneType {
    if m != nil {
        return m.Type
    }
    return Person_MOBILE
}

// Our address book file is just one of these.
type AddressBook struct {
    People []*Person `protobuf:"bytes,1,rep,name=people" json:"people,omitempty"`
}

func (m *AddressBook) Reset()                    { *m = AddressBook{} }
func (m *AddressBook) String() string            { return proto.CompactTextString(m) }
func (*AddressBook) ProtoMessage()               {}
func (*AddressBook) Descriptor() ([]byte, []int) { return fileDescriptor0, []int{1} }

func (m *AddressBook) GetPeople() []*Person {
    if m != nil {
        return m.People
    }
    return nil
}

func init() {
    proto.RegisterType((*Person)(nil), "test.protobuf.tutorial.Person")
    proto.RegisterType((*Person_PhoneNumber)(nil), "test.protobuf.tutorial.Person.PhoneNumber")
    proto.RegisterType((*AddressBook)(nil), "test.protobuf.tutorial.AddressBook")
    proto.RegisterEnum("test.protobuf.tutorial.Person_PhoneType", Person_PhoneType_name, Person_PhoneType_value)
}

func init() { proto.RegisterFile("addressbook.proto", fileDescriptor0) }

var fileDescriptor0 = []byte{
    // 265 bytes of a gzipped FileDescriptorProto
    0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0x8c, 0x90, 0xc1, 0x4b, 0xbc, 0x50,
    0x10, 0xc7, 0x7f, 0xba, 0xee, 0xe3, 0xb7, 0x23, 0x2c, 0x36, 0xc4, 0x22, 0x1d, 0x42, 0x3c, 0x49,
    0x81, 0x87, 0x0d, 0x3a, 0x75, 0x49, 0x10, 0x8a, 0xda, 0x5c, 0x1e, 0x41, 0x67, 0xcd, 0x89, 0x64,
    0xd5, 0x79, 0xe8, 0xf3, 0xb0, 0xff, 0x49, 0x7f, 0x6e, 0xf8, 0x94, 0xe8, 0x10, 0xd1, 0xed, 0x3b,
    0xc3, 0x67, 0xf8, 0xcc, 0x0c, 0x9c, 0xe4, 0x65, 0xd9, 0x51, 0xdf, 0x17, 0xcc, 0x87, 0x58, 0x75,
    0xac, 0x19, 0x37, 0x9a, 0x7a, 0x3d, 0xe5, 0x62, 0x78, 0x8b, 0xf5, 0xa0, 0xb9, 0xab, 0xf2, 0x3a,
    0xfc, 0xb0, 0x41, 0xec, 0xa9, 0xeb, 0xb9, 0x45, 0x04, 0xa7, 0xcd, 0x1b, 0xf2, 0xad, 0xc0, 0x8a,
    0x56, 0xd2, 0x64, 0x5c, 0x83, 0x5d, 0x95, 0xbe, 0x1d, 0x58, 0xd1, 0x52, 0xda, 0x55, 0x89, 0xa7,
    0xb0, 0xa4, 0x26, 0xaf, 0x6a, 0x7f, 0x61, 0xa0, 0xa9, 0xc0, 0x04, 0x84, 0x7a, 0xe7, 0x96, 0x7a,
    0xdf, 0x09, 0x16, 0x91, 0xbb, 0xbd, 0x88, 0x7f, 0xb6, 0xc5, 0x93, 0x29, 0xde, 0x8f, 0xf0, 0xd3,
    0xd0, 0x14, 0xd4, 0xc9, 0x79, 0xf2, 0xec, 0x15, 0xdc, 0x6f, 0x6d, 0xdc, 0x80, 0x68, 0x4d, 0x9a,
    0xd7, 0x99, 0x2b, 0xbc, 0x01, 0x47, 0x1f, 0x15, 0x99, 0x95, 0xd6, 0xdb, 0xe8, 0x2f, 0xa2, 0xe7,
    0xa3, 0x22, 0x69, 0xa6, 0xc2, 0x4b, 0x58, 0x7d, 0xb5, 0x10, 0x40, 0xec, 0xb2, 0xe4, 0xfe, 0x31,
    0xf5, 0xfe, 0xe1, 0x7f, 0x70, 0xee, 0xb2, 0x5d, 0xea, 0x59, 0x63, 0x7a, 0xc9, 0xe4, 0x83, 0x67,
    0x87, 0x29, 0xb8, 0xb7, 0xd3, 0x1f, 0x13, 0xe6, 0x03, 0x5e, 0x83, 0x50, 0xc4, 0xaa, 0x1e, 0x1f,
    0x34, 0x1e, 0x79, 0xfe, 0xbb, 0x5b, 0xce, 0x74, 0x21, 0x0c, 0x71, 0xf5, 0x19, 0x00, 0x00, 0xff,
    0xff, 0x38, 0xba, 0x26, 0x8c, 0x95, 0x01, 0x00, 0x00,
}

ok,生成模型代码后，咱们就可使用protobuf协议来对数据进行编解码了

//将数据编码成protobuf 二进制格式--Writing a Message
 func EncodeAddressBook (book *pb.AddressBook)(out []byte, err error) {
    // Write the new address book back to disk.
    out, err = proto.Marshal(book)
    if err != nil {
        log.Println("Failed to encode address book:", err)
        return nil,err
    }
    if err := ioutil.WriteFile("addressbook_proto.data", out, 0644); err != nil {
        log.Fatalln("Failed to write address book:", err)
        return nil,err
    }
    fmt.Println("[Debug]: ", out)
    return
}

//将二进制数据解码为golang 数据结构 --Reading a Message
 func DecodeAddressBook(in []byte) (book *pb.AddressBook, err error){
    // Read the existing address book.
    book = &pb.AddressBook{}
    if err := proto.Unmarshal(in, book); err != nil {
        log.Println("Failed to parse address book:", err)
        return nil,err
    }
    return
}

proto buffer 3 指南:https://developers.google.com/protocol-buffers/docs/proto3
Go Generated Code Guide:https://developers.google.com/protocol-buffers/docs/reference/go-generated