do - Dependency Injection

⚙️ A dependency injection toolkit based on Go 1.18+ Generics.

This library implements the Dependency Injection design pattern. It may replace the uber/dig fantastic package in simple Go projects. samber/do uses Go 1.18+ generics instead of reflection and therefore is typesafe.

See also:

• samber/lo: A Lodash-style Go library based on Go 1.18+ Generics
• samber/mo: Monads based on Go 1.18+ Generics (Option, Result, Either...)

Why this name?

I love short name for such utility library. This name is the sum of DI and Go and no Go package currently uses this name.

💡 Features

• Service registration
• Service invocation
• Service health check
• Service shutdown
• Service lifecycle hooks
• Named or anonymous services
• Eagerly or lazily loaded services
• Dependency graph resolution
• Default injector
• Injector cloning
• Service override

🚀 Services are loaded in invocation order.

🕵️ Service health can be checked individually or globally. Services implementing do.Healthcheckable interface will be called via do.HealthCheck[type]() or injector.HealthCheck().

🛑 Services can be shutdowned properly, in back-initialization order. Services implementing do.Shutdownable interface will be called via do.Shutdown[type]() or injector.Shutdown().

🚀 Install

go get github.com/samber/do@v1

This library is v1 and follows SemVer strictly.

No breaking changes will be made to exported APIs before v2.0.0.

💡 Quick start

You can import do using:

import (
    "github.com/samber/do"
)

Then instanciate services:

func main() {
    injector := do.New()

    // provides CarService
    do.Provide(injector, NewCarService)

    // provides EngineService
    do.Provide(injector, NewEngineService)

    car := do.MustInvoke[*CarService](injector)
    car.Start()
    // prints "car starting"

    do.HealthCheck[EngineService](injector)
    // returns "engine broken"

    // injector.ShutdownOnSIGTERM()    // will block until receiving sigterm signal
    injector.Shutdown()
    // prints "car stopped"
}

Services:

type EngineService interface{}

func NewEngineService(i *do.Injector) (EngineService, error) {
    return &engineServiceImplem{}, nil
}

type engineServiceImplem struct {}

// [Optional] Implements do.Healthcheckable.
func (c *engineServiceImplem) HealthCheck() error {
	return fmt.Errorf("engine broken")
}

func NewCarService(i *do.Injector) (*CarService, error) {
    engine := do.MustInvoke[EngineService](i)
    car := CarService{Engine: engine}
    return &car, nil
}

type CarService struct {
	Engine EngineService
}

func (c *CarService) Start() {
	println("car starting")
}

// [Optional] Implements do.Shutdownable.
func (c *CarService) Shutdown() error {
	println("car stopped")
	return nil
}

🤠 Spec

GoDoc: https://godoc.org/github.com/samber/do

Injector:

• do.New
• do.NewWithOpts
  • injector.Clone
  • injector.CloneWithOpts
  • injector.HealthCheck
  • injector.Shutdown
  • injector.ShutdownOnSIGTERM
  • injector.ListProvidedServices
  • injector.ListInvokedServices
• do.HealthCheck
• do.HealthCheckNamed
• do.Shutdown
• do.ShutdownNamed
• do.MustShutdown
• do.MustShutdownNamed

Service registration:

• do.Provide
• do.ProvideNamed
• do.ProvideNamedValue
• do.ProvideValue

Service invocation:

• do.Invoke
• do.MustInvoke
• do.InvokeNamed
• do.MustInvokeNamed

Service override:

• do.Override
• do.OverrideNamed
• do.OverrideNamedValue
• do.OverrideValue

Injector (DI container)

Build a container for your components. Injector is responsible for building services in the right order, and managing service lifecycle.

injector := do.New()

Or use nil as the default injector:

do.Provide(nil, func (i *Injector) (int, error) {
    return 42, nil
})

service := do.MustInvoke[int](nil)

You can check health of services implementing func HealthCheck() error.

type DBService struct {
    db *sql.DB
}

func (s *DBService) HealthCheck() error {
    return s.db.Ping()
}

injector := do.New()
do.Provide(injector, ...)
do.Invoke(injector, ...)

statuses := injector.HealthCheck()
// map[string]error{
//   "*DBService": nil,
// }

De-initialize all compoments properly. Services implementing func Shutdown() error will be called synchronously in back-initialization order.

type DBService struct {
    db *sql.DB
}

func (s *DBService) Shutdown() error {
    return s.db.Close()
}

injector := do.New()
do.Provide(injector, ...)
do.Invoke(injector, ...)

// shutdown all services in reverse order
injector.Shutdown()

List services:

type DBService struct {
    db *sql.DB
}

injector := do.New()

do.Provide(injector, ...)
println(do.ListProvidedServices())
// output: []string{"*DBService"}

do.Invoke(injector, ...)
println(do.ListInvokedServices())
// output: []string{"*DBService"}

Service registration

Services can be registered in multiple way:

• with implicit name (struct or interface name)
• with explicit name
• eagerly
• lazily

Anonymous service, loaded lazily:

type DBService struct {
    db *sql.DB
}

do.Provide[DBService](injector, func(i *Injector) (*DBService, error) {
    db, err := sql.Open(...)
    if err != nil {
        return nil, err
    }

    return &DBService{db: db}, nil
})

Named service, loaded lazily:

type DBService struct {
    db *sql.DB
}

do.ProvideNamed(injector, "dbconn", func(i *Injector) (*DBService, error) {
    db, err := sql.Open(...)
    if err != nil {
        return nil, err
    }

    return &DBService{db: db}, nil
})

Anonymous service, loaded eagerly:

type Config struct {
    uri string
}

do.ProvideValue[Config](injector, Config{uri: "postgres://user:pass@host:5432/db"})

Named service, loaded eagerly:

type Config struct {
    uri string
}

do.ProvideNamedValue(injector, "configuration", Config{uri: "postgres://user:pass@host:5432/db"})

Service invocation

Loads anonymous service:

type DBService struct {
    db *sql.DB
}

dbService, err := do.Invoke[DBService](injector)

Loads anonymous service or panics if service was not registered:

type DBService struct {
    db *sql.DB
}

dbService := do.MustInvoke[DBService](injector)

Loads named service:

config, err := do.InvokeNamed[Config](injector, "configuration")

Loads named service or panics if service was not registered:

config := do.MustInvokeNamed[Config](injector, "configuration")

Individual service healthcheck

Check health of anonymous service:

type DBService struct {
    db *sql.DB
}

dbService, err := do.Invoke[DBService](injector)
err = do.HealthCheck[DBService](injector)

Check health of named service:

config, err := do.InvokeNamed[Config](injector, "configuration")
err = do.HealthCheckNamed(injector, "configuration")

Individual service shutdown

Unloads anonymous service:

type DBService struct {
    db *sql.DB
}

dbService, err := do.Invoke[DBService](injector)
err = do.Shutdown[DBService](injector)

Unloads anonymous service or panics if service was not registered:

type DBService struct {
    db *sql.DB
}

dbService := do.MustInvoke[DBService](injector)
do.MustShutdown[DBService](injector)

Unloads named service:

config, err := do.InvokeNamed[Config](injector, "configuration")
err = do.ShutdownNamed(injector, "configuration")

Unloads named service or panics if service was not registered:

config := do.MustInvokeNamed[Config](injector, "configuration")
do.MustShutdownNamed(injector, "configuration")

Service override

By default, providing a service twice will panic. Service can be replaced at runtime using do.Override helper.

do.Provide[Vehicle](injector, func (i *do.Injector) (Vehicle, error) {
    return &CarImplem{}, nil
})

do.Override[Vehicle](injector, func (i *do.Injector) (Vehicle, error) {
    return &BusImplem{}, nil
})

Hooks

2 lifecycle hooks are available in Injectors:

• After registration
• After shutdown

injector := do.NewWithOpts(&do.InjectorOpts{
    HookAfterRegistration: func(injector *do.Injector, serviceName string) {
        fmt.Printf("Service registered: %s\n", serviceName)
    },
    HookAfterShutdown: func(injector *do.Injector, serviceName string) {
        fmt.Printf("Service stopped: %s\n", serviceName)
    },

    Logf: func(format string, args ...any) {
        log.Printf(format, args...)
    },
})

Cloning injector

Cloned injector have same service registrations as it's parent, but it doesn't share invoked service state.

Clones are useful for unit testing by replacing some services to mocks.

var injector *do.Injector;

func init() {
    do.Provide[Service](injector, func (i *do.Injector) (Service, error) {
        return &RealService{}, nil
    })
    do.Provide[*App](injector, func (i *do.Injector) (*App, error) {
        return &App{i.MustInvoke[Service](i)}, nil
    })
}

func TestService(t *testing.T) {
    i := injector.Clone()
    defer i.Shutdown()

    // replace Service to MockService
    do.Override[Service](i, func (i *do.Injector) (Service, error) {
        return &MockService{}, nil
    }))

    app := do.Invoke[*App](i)
    // do unit testing with mocked service
}

🛩 Benchmark

// @TODO

This library does not use reflect package. We don't expect overhead.

🤝 Contributing

• Ping me on twitter @samuelberthe (DMs, mentions, whatever :))
• Fork the project
• Fix open issues or request new features

Don't hesitate ;)

With Docker

docker-compose run --rm dev

Without Docker

# Install some dev dependencies
make tools

# Run tests
make test
# or
make watch-test

👤 Contributors

💫 Show your support

Give a ⭐️ if this project helped you!

📝 License

Copyright © 2022 Samuel Berthe.

This project is MIT licensed.