Golang依赖注入框架wire使用详解

What is wire?

wire是google开源的依赖注入框架。或者引用官方的话来说：“Wire is a code generation tool that automates connecting components using dependency injection.”。

Why wire?

runtime dependency injectioncompile-time dependency injection

Provider & Injector

providerinjectorwire

provider: a function that can produce a value. These functions are ordinary Go code.
injector: a function that calls providers in dependency order. With Wire, you write the injector’s signature, then Wire generates the function’s body.

providerwirewireinjectorinjectorinjectorprovider

provider

providerproviderwire

// NewUserStore是*UserStore的provider，表明*UserStore依赖于*Config和 *mysql.DB.
func NewUserStore(cfg *Config, db *mysql.DB) (*UserStore, error) {...}

// NewDefaultConfig是*Config的provider，没有依赖
func NewDefaultConfig() *Config {...}

// NewDB是*mysql.DB的provider，依赖于ConnectionInfo
func NewDB(info ConnectionInfo) (*mysql.DB, error) {...}

// UserStoreSet 可选项，可以使用wire.NewSet将通常会一起使用的依赖组合起来。
var UserStoreSet = wire.NewSet(NewUserStore, NewDefaultConfig)

injector

injectorwireinjectorprovider

// File: wire_gen.go
// Code generated by Wire. DO NOT EDIT.
//go:generate wire
//+build !wireinject

// initUserStore是由wire生成的injector
func initUserStore(info ConnectionInfo) (*UserStore, error) {
    // *Config的provider函数
    defaultConfig := NewDefaultConfig()
    // *mysql.DB的provider函数
    db, err := NewDB(info)
    if err != nil {
        return nil, err
    }
    // *UserStore的provider函数
    userStore, err := NewUserStore(defaultConfig, db)
    if err != nil {
        return nil, err
    }
    return userStore, nil
}

injectormain.goinitUserStore

wireinjector

injectorwire.Buildinjectorprovider

例如：
// initUserStore用于声明injector的函数签名
func initUserStore(info ConnectionInfo) (*UserStore, error) {  
    // wire.Build声明要获取一个UserStore需要调用到哪些provider函数
    wire.Build(UserStoreSet, NewDB)
    return nil, nil  // 这些返回值wire并不关心。
}

wireinjectorwireinjector

injectorfunc initUserStore(info ConnectionInfo) (*UserStore, error)*UserStorewire.Build*UserStoreprovider：NewUserStorefunc NewUserStore(cfg *Config, db *mysql.DB)NewUserStore*Config*mysql.DBwire.Build*Config*mysql.DBprovider：NewDefaultConfigNewDBfunc NewDefaultConfig() *Config*Configfunc NewDB(info *ConnectionInfo) (*mysql.DB, error)*mysql.DBConnectionInfowire.BuildConnectionInfoproviderNewDBerrorproviderinjector

最佳实践

Installing

$ go get github.com/google/wire/cmd/wire

Quick Start

wire

$ ls
main.go  wire.go

main.go

package main

import "fmt"

type Message struct {
	msg string
}
type Greeter struct {
	Message Message
}
type Event struct {
	Greeter Greeter
}
// NewMessage Message的构造函数
func NewMessage(msg string) Message {
	return Message{
		msg:msg,
	}
}
// NewGreeter Greeter构造函数
func NewGreeter(m Message) Greeter {
	return Greeter{Message: m}
}
// NewEvent Event构造函数
func NewEvent(g Greeter) Event {
	return Event{Greeter: g}
}
func (e Event) Start() {
	msg := e.Greeter.Greet()
	fmt.Println(msg)
}
func (g Greeter) Greet() Message {
	return g.Message
}

// 使用wire前
func main() {
	message := NewMessage("hello world")
	greeter := NewGreeter(message)
	event := NewEvent(greeter)

	event.Start()
}
/*
// 使用wire后
func main() {
	event := InitializeEvent("hello_world")

	event.Start()
}*/

wire.go

// +build wireinject
// The build tag makes sure the stub is not built in the final build.

package main

import "github.com/google/wire"

// InitializeEvent 声明injector的函数签名
func InitializeEvent(msg string) Event{
	wire.Build(NewEvent, NewGreeter, NewMessage)
	return Event{}  //返回值没有实际意义，只需符合函数签名即可
}

wire

$ wire
wire: github.com/DrmagicE/wire-examples/quickstart: wrote XXXX\github.com\DrmagicE\wire-examples\quickstart\wire_gen.go
$ ls
main.go  wire.go  wire_gen.go

wire生成的文件: wire_gen.go

// Code generated by Wire. DO NOT EDIT.

//go:generate wire
//+build !wireinject

package main

// Injectors from wire.go:

func InitializeEvent(msg string) Event {
	message := NewMessage(msg)
	greeter := NewGreeter(message)
	event := NewEvent(greeter)
	return event
}

使用前 V.S 使用后

/*
// 使用wire前
func main() {
	message := NewMessage("hello world")
	greeter := NewGreeter(message)
	event := NewEvent(greeter)

	event.Start()
}*/

// 使用wire后
func main() {
	event := InitializeEvent("hello_world")

	event.Start()
}

示例代码： quickstart

quickstartNewMessageNewGreeterNewEventproviderwire_gen.goInitializeEventinjectorinjectorprovider

wire.goinjector

// +build wireinject
...

injectorwire.Buildprovider

// InitializeEvent 声明injector的函数签名
func InitializeEvent(msg string) Event{
	wire.Build(NewEvent, NewGreeter, NewMessage) // <--- 传入provider函数
	return Event{}  //返回值没有实际意义，只需符合函数签名即可
}

该方法的返回值没有实际意义，只需要符合函数签名的要求即可。

高级特性

接口绑定

根据依赖倒置原则（Dependence Inversion Principle），对象应当依赖于接口，而不是直接依赖于具体实现。

quickstartwire

// UserService 
type UserService struct {
	userRepo UserRepository // <-- UserService依赖UserRepository接口
}

// UserRepository 存放User对象的数据仓库接口,比如可以是mysql,restful api ....
type UserRepository interface {
	// GetUserByID 根据ID获取User, 如果找不到User返回对应错误信息
	GetUserByID(id int) (*User, error)
}
// NewUserService *UserService构造函数
func NewUserService(userRepo UserRepository) *UserService {
	return &UserService{
		userRepo:userRepo,
	}
}

// mockUserRepo 模拟一个UserRepository实现
type mockUserRepo struct {
	foo string
	bar int
}
// GetUserByID UserRepository接口实现
func (u *mockUserRepo) GetUserByID(id int) (*User,error){
	return &User{}, nil
}
// NewMockUserRepo *mockUserRepo构造函数
func NewMockUserRepo(foo string,bar int) *mockUserRepo {
	return &mockUserRepo{
		foo:foo,
		bar:bar,
	}
}
// MockUserRepoSet 将 *mockUserRepo与UserRepository绑定
var MockUserRepoSet = wire.NewSet(NewMockUserRepo,wire.Bind(new(UserRepository), new(*mockUserRepo)))

UserServiceUserRepositorymockUserRepoUserRepositorymockUserRepoprovider*mockUserRepowirewire.NewSetwire.Bind*mockUserRepoUserRepository

/ MockUserRepoSet 将 *mockUserRepo与UserRepository绑定
var MockUserRepoSet = wire.NewSet(NewMockUserRepo,wire.Bind(new(UserRepository), new(*mockUserRepo)))

定义injector函数签名：

func InitializeUserService(foo string, bar int) *UserService{
	wire.Build(NewUserService,MockUserRepoSet) // 使用MockUserRepoSet
	return nil
}

组合Provider

providerprovider setquickstart

// NewMessage Message的构造函数
func NewMessage(msg string) Message {
	return Message{
		msg:msg,
	}
}
// NewGreeter Greeter构造函数
func NewGreeter(m Message) Greeter {
	return Greeter{Message: m}
}
// NewEvent Event构造函数
func NewEvent(g Greeter) Event {
	return Event{Greeter: g}
}
func (e Event) Start() {
	msg := e.Greeter.Greet()
	fmt.Println(msg)
}
// EventSet Event通常是一起使用的一个集合，使用wire.NewSet进行组合
var EventSet  = wire.NewSet(NewEvent, NewMessage, NewGreeter)

Eventwire.NewSetinjector

func InitializeEvent(msg string) Event{
	//wire.Build(NewEvent, NewGreeter, NewMessage)
	wire.Build(EventSet) 
	return Event{}
}

EventSetwire.Build

示例代码： provider-set

结构体provider

provider

ype Foo int
type Bar int

func ProvideFoo() Foo {
	return 1
}
func ProvideBar() Bar {
	return 2
}
type FooBar struct {
	MyFoo Foo
	MyBar Bar
}
var Set = wire.NewSet(
	ProvideFoo,
	ProvideBar,
	wire.Struct(new(FooBar), "MyFoo", "MyBar"))

wire.Struct

var Set = wire.NewSet(
	ProvideFoo,
	ProvideBar,
	wire.Struct(new(FooBar), "*")) // * 表示注入全部字段

生成的injector函数：

func InitializeFooBar() FooBar {
	foo := ProvideFoo()
	bar := ProvideBar()
	fooBar := FooBar{
		MyFoo: foo,
		MyBar: bar,
	}
	return fooBar
}

示例代码： struct-provider

区分类型

injectorwire

type FooBar struct {
	foo string
	bar string
}

func NewFooBar(foo string, bar string) FooBar {
	return FooBar{
	    foo: foo,  
	    bar: bar,
	}
}

injector函数签名定义:

// wire无法得知入参a,b跟FooBar.foo,FooBar.bar的对应关系
func InitializeFooBar(a string, b string) FooBar {
	wire.Build(NewFooBar)
	return FooBar{}
}

providerinjectorwire

provider has multiple parameters of type string

wireFooBar.fooFooBar.bar

type Foo string
type Bar string
type FooBar struct {
	foo Foo
	bar Bar
}

func NewFooBar(foo Foo, bar Bar) FooBar {
	return FooBar{
	    foo: foo,
	    bar: bar,
	}
}

injector函数签名定义：

func InitializeFooBar(a Foo, b Bar) FooBar {
	wire.Build(NewFooBar)
	return FooBar{}
}

provider

type MySQLConnectionString string
type FileReader io.Reader

Options 结构体

provideroptions

type Message string

// Options
type Options struct {
	Messages []Message
	Writer   io.Writer
	Reader   io.Reader
}
type Greeter struct {
}

// NewGreeter Greeter的provider方法使用Options以避免构造函数过长
func NewGreeter(ctx context.Context, opts *Options) (*Greeter, error) {
	return nil, nil
}
// GreeterSet 使用wire.Struct设置Options为provider
var GreeterSet = wire.NewSet(wire.Struct(new(Options), "*"), NewGreeter)

injector

func InitializeGreeter(ctx context.Context, msg []Message, w io.Writer, r io.Reader) (*Greeter, error) {
	wire.Build(GreeterSet)
	return nil, nil
}

示例代码： options-structs

error返回

providererrorwireprovidererror

// Config 配置
type Config struct {
    // RemoteAddr 连接的远程地址
	RemoteAddr string
	
}
// APIClient API客户端
type APIClient struct {
	c Config
}
// NewAPIClient  APIClient构造函数，如果入参校验失败，返回错误原因
func NewAPIClient(c Config) (*APIClient,error) { // <-- 第二个参数设置成error
	if c.RemoteAddr == "" {
		return nil, errors.New("没有设置远程地址")
	}
	return &APIClient{
		c:c,
	},nil
}
// Service
type Service struct {
	client *APIClient
}
// NewService Service构造函数
func NewService(client *APIClient) *Service{
	return &Service{
		client:client,
	}
}

injectorerror

...
func InitializeClient(config Config) (*Service, error) { // <-- 第二个参数设置成error
	wire.Build(NewService,NewAPIClient)
	return nil,nil
}
...

wireinjector

func InitializeClient(config Config) (*Service, error) {
	apiClient, err := NewAPIClient(config)
	if err != nil { // <-- 在构造依赖的顺序中如果发生错误，则会返回对应的"零值"和相应错误
		return nil, err
	}
	service := NewService(apiClient)
	return service, nil
}

在构造依赖的顺序中如果发生错误，则会返回对应的"零值"和相应错误。

示例代码： return-error

Cleanup 处理

providercleanupprovider

// FileReader
type FileReader struct {
	f *os.File
}
// NewFileReader *FileReader 构造函数，第二个参数是cleanup function
func NewFileReader(filePath string) (*FileReader, func(), error){
	f, err := os.Open(filePath)
	if err != nil {
	    return nil,nil,err
	}
	fr := &FileReader{
	    f:f,
	}
	fn := func() {
	    log.Println("cleanup") 
	    fr.f.Close()
	}
	return fr,fn,nil
}

providerfunc()cleanup functionerror

wireprovider

func()errorfunc()error