You'll find me hiding behind a pair of sunglasses.

May 5, 2016

🤖 Building Slack Bots In Swift 🤖

As a remote iOS developer, I love Slack. It’s both my meeting room and my water cooler. As interest in bots exploded, my interest was piqued. Of course I was interested in writing bots for one of my favorite services! The result is SlackKit, a universal Swift framework for building Slack apps.

Do You Want to Build a Slack Bot?

The following is a step-by-step guide to writing a Slack bot in Swift and deploying to Heroku. The focus here is on macOS but this is also doable on Linux — just skip the Xcode steps and use your editor of choice.

[Update 6/4/2017: I’ve updated these instructions to work with Xcode 8.3.2 and the official release of Swift 3.1.1.]

Building the Application

For our example application, we’re going to be making an application that can render judgement on a very specific question: Robot or Not?

First, we need to create the directory for our application and initialize the basic project structure.

mkdir robot-or-not-bot && cd robot-or-not-bot
swift package init --type executable

Next, let’s edit our Package.swift file to add the SlackKit package as a dependency:

and generate our development environment:

swift package generate-xcodeproj

Show Me the Swift Code!

To create our bot, we need to open the robot-or-not-bot.xcodeproj file we just generated, and edit the main.swift file in Sources > robot-or-not-bot to contain our bot logic. The following code uses SlackKit to listen for messages directed at our bot and then respond to them by adding a reaction to the inquiry.

Setting Up Your Slack Bot

Next, we need to create a bot integration in Slack. You’ll need a Slack that you have administrator access to; if you don’t already have one of those to play with, go sign up. Slack is free for small teams.

Go here: https://my.slack.com/services/new/bot
Enter a name for your bot. We’re going to go with “robot-or-not-bot” so there’s no confusion about our bot’s sole purpose in life.
Click “Add Bot Integration”
Copy the API token that Slack generates and replace our placeholder token in main.swift with the real deal.

Testing Locally

With our bot token in place, we’re ready to do some local testing! Back in Xcode, select the robot-or-not-bot application executable target and run your bot (⌘+R).

Then head over to Slack; robot-or-not-bot’s user presence indicator should be filled in. It’s alive!

To test if it’s working, ask it if something is a robot:

@robot-or-not-bot Darth Vader?

robot-or-not-bot should add the 🚫 reaction in response to your question, letting you know that Darth Vader is not a robot.

Deploying to the ☁️

Now that it’s working locally, it’s time to deploy. To the cloud! We’re going to be deploying on Heroku, so if you don’t have an account go and sign up for a free one.

First, we need to add a Procfile for Heroku, and a .swift-version file for swiftenv. Back in the terminal, run:

echo slackbot: .build/release/robot-or-not-bot > Procfile
echo 3.1.1 > .swift-version

Next, let’s check in our code:

git init
git add .
git commit -am'robot-or-not-bot powering up'

Finally, we’ll setup Heroku:

Install the Heroku toolbelt
Log in to Heroku in your terminal:

heroku login

3. Create our application on Heroku and set our buildpack (you’ll need to use a unique name like robot-or-not-bot23 since Heroku app names are unique):

heroku create --buildpack https://github.com/kylef/heroku-buildpack-swift robot-or-not-bot

4. Set up our Heroku remote (use your unique name here, too):

heroku git:remote -a robot-or-not-bot

5. Push to master:

git push heroku master

At this point, you’ll see Heroku go through the build process — exciting!

Run It!

Once the build is complete, run:

heroku run:detached slackbot

Over in Slack, you’ll see robot-or-not-bot’s user presence indicator fill in. It’s alive! (again)

Just to be sure if it’s working, we should ask it an existential question:

@robot-or-not-bot Robot Or Not Bot?

robot-or-not-bot will (sadly, I imagine) add the 🚫 reaction to your question — it knows it is just a computer program, not a robot.

🎊 You’re Done! 🎊

Congratulations, you’ve successfully built and deployed a Slack bot written in Swift on to a Linux server!