Slack app built with Play Framework (Scala)

build.sbt

name := """bolt-play-scala"""
organization := "com.example"
version := "1.0-SNAPSHOT"
lazy val root = (project in file(".")).enablePlugins(PlayScala)
scalaVersion := "2.13.2"
libraryDependencies += guice
libraryDependencies += "com.slack.api" % "bolt-servlet" % "1.0.8"

HomeController.scala

package controllers

import javax.inject._
import play.api.mvc._

@Singleton
class HomeController @Inject()(val controllerComponents: ControllerComponents) extends BaseController {

  def index() = Action { implicit request: Request[AnyContent] =>
    Ok("Hello World!")
  }
}

plugins.sbt

addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.8.2")
addSbtPlugin("org.foundweekends.giter8" % "sbt-giter8-scaffold" % "0.11.0")

routes

# Routes
# This file defines all application routes (Higher priority routes first)
# https://www.playframework.com/documentation/latest/ScalaRouting
# ~~~~
# An example controller showing a sample home page
GET     /                           controllers.HomeController.index
POST    /slack/events               controllers.SlackAppController.index
# Map static resources from the /public folder to the /assets URL path
GET     /assets/*file               controllers.Assets.versioned(path="/public", file: Asset)

SlackAppController.scala

package controllers

import javax.inject._
import play.api.mvc._
import services.SlackAppService

@Singleton
class SlackAppController @Inject()(
  val controllerComponents: ControllerComponents,
  service: SlackAppService) extends BaseController {

  def index() = Action(parse.raw)(service.run(_))
}

SlackAppService.scala

package services

import akka.util.ByteString
import com.slack.api.bolt.handler.builtin.SlashCommandHandler
import com.slack.api.bolt.request.{RequestHeaders, Request => SlackRequest}
import com.slack.api.bolt.response.{Response => SlackResponse}
import com.slack.api.bolt.util.SlackRequestParser
import com.slack.api.bolt.{App => SlackApp}
import javax.inject.Singleton
import play.api.http.HttpEntity
import play.api.mvc._

import scala.jdk.CollectionConverters._

@Singleton
class SlackAppService {

  private[this] lazy val app = new SlackApp()
  private[this] lazy val parser = new SlackRequestParser(app.config)

  val makeRequestHandler: SlashCommandHandler = (req, ctx) => {
    ctx.ack(s"Thanks <@${req.getPayload.getUserId}>!")
  }
  app.command("/make-request", makeRequestHandler)

  def run(implicit request: Request[RawBuffer]): Result = {
    toPlayResponse(app.run(parseRequest(request)))
  }

  def parseRequest(implicit request: Request[RawBuffer]): SlackRequest[_] = {
    parser.parse(SlackRequestParser.HttpRequest.builder()
      .requestUri(request.uri)
      .queryString(request.queryString.map { case (k, vs) => k -> vs.asJava }.asJava)
      .headers(new RequestHeaders(request.headers.toMap.map { case (k, vs) => k -> vs.asJava }.asJava))
      .requestBody(request.body.asBytes().map(_.utf8String).getOrElse(""))
      .remoteAddress(request.remoteAddress)
      .build())
  }

  def toPlayResponse(response: SlackResponse): Result = {
    val headers = response.getHeaders.asScala
      .filter { case (_, v) => v != null && v.size() > 0 }
      .map { case (k, v) => k -> v.get(0) }
      .toMap
    Result(
      header = ResponseHeader(response.getStatusCode, headers),
      body = HttpEntity.Strict(ByteString(response.getBody), Some(response.getContentType))
    )
  }

}

I just tried this with the latest version of Bolt (1.3) and it works fine except it appears that response.getBody can sometimes return null, causing a NullPointerException.

It can be easily fixed with this extra line:

def toPlayResponse(response: SlackResponse): Result = {
  val headers = response.getHeaders.asScala
    .filter { case (_, v) => v != null && v.size() > 0 }
    .map { case (k, v) => k -> v.get(0) }
    .toMap
  // Make sure to handle null case for getBody
  val byteString = Option(response.getBody).map(ByteString(_)).getOrElse(ByteString.empty)
  Result(
      header = ResponseHeader(response.getStatusCode, headers),
      body = HttpEntity.Strict(byteString, Some(response.getContentType))
  )
}

How to set SLACK_BOT_TOKEN and SLACK_SIGNING_SECRET?

Try this:

private val signingSecret = conf.get[String]("com.slack.signingSecret")

private lazy val app = {
  val appConfig = new AppConfig()
  // These need to be set to null, otherwise Slack auto-detects that we're an OAuth app which causes problems
  // This means is that you can't use ctx.client() in the handlers
  appConfig.setClientId(null)
  appConfig.setClientSecret(null)
  appConfig.setSigningSecret(signingSecret)
  new SlackApp(appConfig)
}

The bot token is per workspace, so you want to set that dynamically when you're interacting with Slack.

Can we set Bot User OAuth Token? I am not sure it is setSingleTeamBotToken or not.

Do you know how to create unit test with bolt?