Ready for the bot uprising?

Building Slack Bots In Swift

Peter Zignego
May 5, 2016 4 min read

As a remote iOS developer, I love Slack. Its 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 11/14/2019: Ive updated these instructions to work with Xcode 11.2 and the official release of Swift 5.1.1.]

Building the Application

For our example application, were 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, lets edit our Package.swift file to add the SlackKit package as a dependency:

Show Me the Swift Code!

To create our bot, first double click on the Package.swift file. This will open Xcode and create our development environment by resolving our project dependencies. Next, we need to 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. Youll need a Slack that you have administrator access to; if you dont already have one of those to play with, go sign up. Slack is free for small teams.

  1. Go here:
  2. Enter a name for your bot. Were going to go with robot-or-not-bot so theres no confusion about our bots sole purpose in life.
  3. Click Add Bot Integration
  4. 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, were 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-bots user presence indicator should be filled in. Its alive!

To test if its 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 儭

Now that its working locally, its time to deploy. To the cloud! Were going to be deploying on Heroku, so if you dont 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: robot-or-not-bot > Procfile
echo 5.1.1 > .swift-version

Next, lets check in our code:

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

Finally, well setup Heroku:

  1. Install the Heroku toolbelt
  2. Log in to Heroku in your terminal:
heroku login

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

heroku create --buildpack vapor/vapor robot-or-not-bot

4. Set our configuration environment variable to release:

heroku config:set -a robot-or-not-bot SWIFT_BUILD_CONFIGURATION=release

5. Set up our Heroku remote:

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

6. Push to master:

git push heroku master

At this point, youll see Heroku go through the build process exciting!

Run It!

Once the build is complete, run:

heroku run:detached slackbot

Over in Slack, youll see robot-or-not-bots user presence indicator fill in. Its alive! (again)

All systems operational

Just to be sure if its 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.

Youre Done!

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

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