events

github.com/gobuffalo/events

Note: This package was first introduced to Buffalo in this PR. Assuming the PR is merged Buffalo will not start emitting events until v0.13.0-beta.2 or greater.

A list of known emitted events can be found at https://godoc.org/github.com/gobuffalo/events#pkg-constants

Installation

$ go get -u -v github.com/gobuffalo/events

Listening For Events

To listen for events you need to register an events#Listener function first.

func init() {
  // if you want to give your listener a nice name to identify itself
  events.NamedListen("my-listener", func(e events.Event) {
    fmt.Println("### e ->", e)
  })

  // if you don't care about identifying your listener
  events.Listen(func(e events.Event) {
    fmt.Println("### e ->", e)
  })
}

Emitting Events

events.Emit(events.Event{
  Kind:    "my-event",
  Message: // optional message,
  Payload: // optional payload,
  Error:   // optional error,
})

There is only one required field when emitting an event, Kind.

The Kind field is key to how people will interpret your messages, and should be constructed as such: <namespace>:<event-kind>:<err-optional>.

In the examples below from Buffalo you can see it is using the buffalo: name space for its events.

// EvtAppStart is emitted when buffalo.App#Serve is called
EvtAppStart = "buffalo:app:start"
// EvtAppStartErr is emitted when an error occurs calling buffalo.App#Serve
EvtAppStartErr = "buffalo:app:start:err"
// EvtAppStop is emitted when buffalo.App#Stop is called
EvtAppStop = "buffalo:app:stop"
// EvtAppStopErr is emitted when an error occurs calling buffalo.App#Stop
EvtAppStopErr = "buffalo:app:stop:err"

Implementing a Manager

By default events implements a basic manager for you. Should you want to replace that with your own implementation, perhaps that's backed by a proper message queue, you can implement the events#Manager interface.

var _ events.Manager = MyManager{}
events.SetManager(MyManager{})

Listening via Buffalo Plugins

Once Buffalo is actively emitting events, plugins, will be able to listen those events via their CLIs.

To do so you can set the BuffaloCommand to events when telling Buffalo which plugin in commands are available. Buffalo will create a new listener that says the JSON version of the event to that command in question.

var availableCmd = &cobra.Command{
	Use:   "available",
	Short: "a list of available buffalo plugins",
	RunE: func(cmd *cobra.Command, args []string) error {
		plugs := plugins.Commands{
			{Name: "echo", UseCommand: "echo", BuffaloCommand: "events", Description: echoCmd.Short, Aliases: echoCmd.Aliases},
		}
		return json.NewEncoder(os.Stdout).Encode(plugs)
	},
}


events.Emit(events.Event{
  Kind:    "my-event",
})

// buffalo-foo echo "{\"kind\": \"my-event\"}"