timercb.md

The Timer Callback

Timer Callbacks let you arrange for Lazlo to wake your module up every so often. There are many different reasons you might want to implement a timer. I often use them to periodically query an external service like an RSS feed. They also make it easy to create bot's that appear to "randomly" say things in channel.

cb := broker.TimerCallback(`0 */1 * * * * *`)

The formal definition is here in callbacks.go

As you can see, TimerCallback() is a method on the lazlo.Broker type. Whenever you write a lazlo module, you'll always be passed a pointer to the broker (more about that here)

TimerCallback() requires one argument: the schedule, which is a string that specifies a cron-syntax schedule.

Lazlo will give you back an object of type lazlo.TimerCallback. It looks like this:

type TimerCallback struct {
   ID       string
   Schedule string
   State    string
   Next     time.Time
   Chan     chan time.Time
}

ID uniquely identifies this callback with the broker. It's set automatically when you register the module and you can use it to deregister the module later if you want.

Schedule is the cron schedule you specified

State is a human-readable string that describes the current state of the timer (it will have an error if something went wrong with the schedule you specified)

Next is a time.Time value that specifies the next time this timer will fire.

Chan is a Channel of type time.Time. When the "alarm" goes off so to speak, Lazlo notifies you using this channel.

Waiting for something to happen

A common pattern is to block on the callback's Chan attribute, waiting for the timer to fire.

alarm := broker.TimerCallback(`0 0 14 * * * *`) //wake me up at 2pm every day
for{
	alarm := <-timer.Chan
	broker.Say(`welp it's 2pm, time to update the DB`)
	update_db_from_RSS_feed()

You can combine timers with other callbacks to achieve more advanced patterns, like verifying dangerous chatops commands

shieldsUp := broker.MessageCallback(`(?i)shields up$`, true)

for{
	// block waiting for a shields up command
	scb := <-shieldsUp.Chan 

	// register new verify and timeout callbacks
	scb.Reply(`Verify shields up by pasting this verification code: 234567`)
	verify := broker.MessageCallback(`234567`)
	timeout := broker.TimerCallback(`30 * * * * * *`)

	// Give the user 30 seconds to verify it wants the shields up
	select{
	case v := <- verify.Chan:
		go putTheShieldsUP()
	case v := <-timeout.Chan:
		go nevermind()
	}
	broker.DeRegister(verify)
	broker.DeRegister(timeout)
}