Slack

This is for creating Slack applications or bots in Elixir.

Why?

The existing libraries I was looking at use the deprecated RTM API, and no longer work with new apps or bots.

What?

To listen for subscribed events, it uses Socket Mode to connect to Slack. It has some pros and cons, so please read up on it (and pay attention to the info blocks).

It's a relatively thin wrapper, which keeps it flexible and easy to maintain.

How

• connects to Slack using a websocket connection to listen for your event subscriptions.
• uses the Web API to send messages, etc.
• uses dynamically supervised gen servers to handle each channel's message rate-limiting with a message queue per channel.

Installation

Add slack_elixir to your list of dependencies in mix.exs:

def deps do
  [
    {:slack_elixir, "~> 1.2.0"}
  ]
end

Setup

You will need to:

• Create a Slack app for your workspace
• Add permissions (scopes)
• Connect it to your workspace
• Get an OAuth Bot Token (will have the scopes you defined)
• Enable Socket Mode
• Get an app-level token with connections:write scope
• Add Event Subscriptions

See below for some minimum required scopes and event subscriptions. You will need to add more scopes and subscriptions depending on what you want to do.

Required Bot Token scopes:

• channels:history
• channels:read
• groups:read
• im:read
• mpim:read

Required Bot Event Subscriptions

• message.channels
• member_joined_channel
• channel_left

Usage

Write the Bot module:

defmodule MyApp.Slackbot do
  use Slack.Bot

  require Logger

  @impl true
  # A silly example of old-school style bot commands.
  def handle_event("message", %{"text" => "!" <> cmd, "channel" => channel, "user" => user}, _bot) do
    case cmd do
      "roll" ->
        send_message(channel, "<@#{user}> rolled a #{Enum.random(1..6)}")

      "echo " <> text ->
        send_message(channel, text)

      _ ->
        send_message(channel, "Unknown command: #{cmd}")
    end
  end

  def handle_event("message", %{"channel" => channel, "text" => text, "user" => user}, _bot) do
    if String.match?(text, ~r/hello/i) do
      send_message(channel, "Hello! <@#{user}>")
    end
  end

  def handle_event(type, payload, _bot) do
    Logger.debug("Unhandled #{type} event: #{inspect(payload)}")
    :ok
  end
end

Then you start the Slack Supervisor in your application's supervision tree.

For example:

  def start(_type, _args) do
    children = [
      # ...
      {Slack.Supervisor, Application.fetch_env!(:my_app, MyApp.SlackBot)}
    ]

    opts = [strategy: :one_for_one, name: MyApp.Supervisor]
    Supervisor.start_link(children, opts)
  end

# config/runtime.exs

config :my_app, MyApp.SlackBot,
  app_token: "MY_SLACK_APP_TOKEN",
  bot_token: "MY_SLACK_BOT_TOKEN",
  bot: MyApp.SlackBot,
  # Add this if you want to customize the channel types to join.
  # By default we join all channel types: public_channel, private_channel, im, mpim.
  channels: [
    types: ["public_channel", "im", "private_channel"]
  ]

Journey to v1.0 (Things that may or may not be added)

PRs welcome!

• Socket Mode for events
• Web API POST requests
• Web API GET requests
• Message Server per channel (rate-limited to 1 message per second per channel).