go-event

Go simple (zero deps) library for event handling. The main goal of this library is to provide a simple and easy to use event handling system with a minimal footprint within a Go application. This library is inspired by Node.js EventEmitter.

Usage

go-event is compatible with modern Go releases. This pkg use Go generics, so you need to use Go 1.18 or later.

Take into account that each event listener is executed in a goroutine, so you need to take care with race conditions.

package main

import (
 "context"
 "log"
 "os"
 "time"

 "github.com/jferrl/go-event"
)

const (
 // UserCreated .
 UserCreated event.Event = "user.created"
 // UserDeleted .
 UserDeleted event.Event = "user.deleted"
 // UserUpdated .
 UserUpdated event.Event = "user.updated"
)

// UserEvent .
type UserEvent struct {
 ID string
}

func main() {
 logger := log.New(os.Stdout, "go-event: ", log.LstdFlags)

 ctx := context.Background()

 emitter := event.NewEmitter[UserEvent]()

 emitter.
  On(UserCreated, func(ctx context.Context, data UserEvent) {
   // handle user created event
   logger.Printf("user created: %s", data.ID)
  }).
  On(UserDeleted, func(ctx context.Context, data UserEvent) {
   // handle user deleted event
   logger.Printf("user deleted: %s", data.ID)
  }).
  On(UserUpdated,
   func(ctx context.Context, data UserEvent) {
    // handle user updated event
    logger.Printf("user updated: %s", data.ID)
   },
   func(ctx context.Context, data UserEvent) {
    // other event listener for the same event.
    logger.Printf("making some actions with user: %s", data.ID)
   },
  )

 emitter.Emit(ctx, UserCreated, UserEvent{ID: "1"})
 emitter.Emit(ctx, UserDeleted, UserEvent{ID: "2"})
 emitter.Emit(ctx, UserUpdated, UserEvent{ID: "3"})

 time.Sleep(1 * time.Second)
}

If you need to execute the event listeners synchronously, you can set SyncEmitter option.

package main

import "github.com/jferrl/go-event"

// UserEvent .
type UserEvent struct {
 ID string
}

func main() {
 emitter := event.NewEmitter[UserEvent](event.SyncEmitter[UserEvent])
}

Bootstrap complex event listeners

In some scenarios, you may need to bootstrap complex event listeners. For example, the listerner has several dependencies, like a logger, a database connection, etc. In this case, you can use a function to bootstrap the event listener and pass the dependencies to it.

package main

import (
 "context"
 "log"
 "os"
 "time"

 "github.com/jferrl/go-event"
)

// UserCreated .
const UserCreated event.Event = "user.created"

// UserEvent .
type UserEvent struct {
 ID string
}

// EmailClient handles the email scheduling.
type EmailClient struct{}

// Schedule schedules an email to be sent to the user.
func (e *EmailClient) Schedule(_ context.Context, _ string) error {
 return nil
}

// EmailScheduler handles the email scheduling.
type EmailScheduler interface {
 Schedule(ctx context.Context, userID string) error
}

// Logger handles the logging.
type Logger interface {
 Printf(format string, v ...interface{})
}

// BootstrapEmailSheduleHandler bootstraps the email scheduler handler
// Handler will be called when user created event is emitted.
// It will schedule an email to be sent to the user.
func BootstrapEmailSheduleHandler(logger Logger, s EmailScheduler) event.Listerner[UserEvent] {
 return func(ctx context.Context, data UserEvent) {
  // handle user created event
  logger.Printf("user created: %s", data.ID)

  // schedule email
  if err := s.Schedule(ctx, data.ID); err != nil {
   logger.Printf("failed to schedule email: %v", err)
  }
 }
}

func main() {
 logger := log.New(os.Stdout, "go-event: ", log.LstdFlags)
 e := &EmailClient{}

 ctx := context.Background()

 emitter := event.NewEmitter[UserEvent]()

 emitter.On(UserCreated, BootstrapEmailSheduleHandler(logger, e))

 emitter.Emit(ctx, UserCreated, UserEvent{ID: "1"})

 time.Sleep(1 * time.Second)
}

License

This library is distributed under the MIT license found in the LICENSE