Server-side Swift: Building a Slack Bot, Part 1

As a remote iOS developer, I love Slack. It’s my meeting room and my water cooler over the course of a work day. If you’re not familiar with Slack, it is a group communication tool popular in Silicon Valley and beyond. What makes Slack valuable beyond replacing email as the go-to communication method for buisnesses is that it is more than chat; it is a platform. Thanks to Slack’s open attitude toward developers with its API, hundreds of developers have been building what have become known as Slack bots.

There are many different libraries available to help you start writing your Slack bot, covering a wide range of programming languages. I wrote a library in Apple’s new programming language (Swift) for this very purpose, called SlackKit. SlackKit wasn’t very practical initially—it only ran on iOS and OS X. On the modern web, you need to support Linux to deploy on Amazon Web Servies, Heroku, or hosted server companies such as Linode and Digital Ocean.

But last June, Apple open sourced Swift, including official support for Linux (Ubuntu 14 and 15 specifically). This made it possible to deploy Swift code on Linux servers, and developers hit the ground running to build out the infrastructure needed to make Swift a viable language for server applications.

Even with this huge developer effort, it is still early days for server-side Swift. Apple’s Linux Foundation port is a huge undertaking, as is the work to get libdispatch, a concurrency framework that provides much of the underpinning for Foundation. In addition to rough official tooling, writing code for server-side Swift can be a bit like hitting a moving target, with biweekly snapshot releases and multiple, ABI-incompatible versions to target.

Zewo to Sixty on Linux

Fortunately, there are some good options for deploying Swift code on servers right now, even with Apple’s libraries in flux. I’m going to focus in on one in particular: Zewo. Zewo is modular by design, allowing us to use the Swift Package Manager to pull in only what we need instead of a monolithic framework. It’s open source and is a great community of developers that spans the globe. If you’re interested in the world of server-side Swift, you should get involved! Oh, and of course they have a Slack. Using Zewo and a few other open source libraries, I was able to build a version of SlackKit that runs on Linux.

A Swift Tutorial

In this two-part post series I have detailed a step-by-step guide to writing a Slack bot in Swift and deploying it to Heroku. I’m going to be using OS X but this is also achievable on Linux using the editor of your choice.

Prerequisites

1. Install Homebrew:

 	/usr/bin/ruby -e “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

2. Install swiftenv:

brew install kylef/formulae/swiftenv

3. Configure your shell:

 	echo ‘if which swiftenv > /dev/null; then eval “$(swiftenv init -)”; fi’ >> ~/.bash_profile

4. Download and install the latest Zewo-compatible snapshot:

 	swiftenv install DEVELOPMENT-SNAPSHOT-2016-05-09-a
        swiftenv local DEVELOPMENT-SNAPSHOT-2016-05-09-a

5. Install and Link OpenSSL:

 	brew install openssl
        brew link openssl --force

Let’s Keep Score

The sample application we’ll be building is a leaderboard for Slack, like PlusPlus++ by Betaworks. It works like this: add a point for every @thing++, subtract a point for every @thing--, and show a leaderboard when asked @botname leaderboard.

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

mkdir leaderbot && cd leaderbot
swift build --init

Next, we need to edit Package.swift to add our dependency, SlackKit:

importPackageDescription

let package = Package(
name: "Leaderbot",
targets: [],
dependencies: [
        .Package(url: "https://github.com/pvzig/SlackKit.git", majorVersion: 0, minor: 0),
    ]
)

SlackKit is dependent on several Zewo libraries, but thanks to the Swift Package Manager, we don’t have to worry about importing them explicitly.

Then we need to build our dependencies:

swift build

And our development environment (we need to pass in some linker flags so that swift build knows where to find the version of OpenSSL we installed via Homebrew and the C modules that some of our Zewo libraries depend on):

swift build -Xlinker -L$(pwd)/.build/debug/ -Xswiftc -I/usr/local/include -Xlinker -L/usr/local/lib -X

In Part 2, I will show all of the Swift code, how to get an API token, how to test the app and deploy it on Heroku, and finally how to launch it.

Disclaimer

The linux version of SlackKit should be considered an alpha release. It’s a fun tech demo to show what’s possible with Swift on the server, not something to be relied upon. Feel free to report issues you come across.

About the author

Peter Zignego is an iOS developer in Durham, North Carolina. He writes at bytesized.co, tweets @pvzig, and freelances at Launch Software.fto help you start writing your Slack bot, covering a wide range of programming languages. I wrote a library in Apple’s new programming language (Swift) for this very purpose, called SlackKit. SlackKit wasn’t very practical initially—it only ran on iOS and OS X. On the modern web, you need to support Linux to deploy on Amazon Web Servies, Heroku, or hosted server