Play controller for serving a React App out of /public - including front-end routes

FrontEndServingController.scala

package controllers

import play.api.mvc.{Action, Controller}
import play.api.Logger
import javax.inject.Inject
import java.io.File
import play.api.libs.json.Json


class FrontEndServingController @Inject() (val assets:Assets) extends Controller {

  val logger = Logger("FrontEndServingController")

  val publicDirectory = "/public"
  val indexFile = "index.html"

  val physicalPublicDirectory="./public/"

  lazy val physicalAssets:Set[String] = {
    val startingDirectory = new File(physicalPublicDirectory)
    deepList(startingDirectory)
  }

  private def deepList(f: File): Set[String] = {
    val these = f.listFiles.toSet
    val inHere = these.filter(_.isFile).map { f =>
      f.getPath.replace(physicalPublicDirectory, "")
    }
    val belowHere = these.filter(_.isDirectory).flatMap(deepList)
    inHere ++ belowHere
  }

  val index = serve(indexFile)

  def frontEndPath(path: String) = serve(path)

  private def serve(path: String) = {
    if (physicalAssets.contains(path)) {
      logger.debug(s"Serving physical resource: '$path'")
      assets.at(publicDirectory, path, true)
    } else {
      logger.debug(s"Serving virtual resource: '$path'")
      // It's some kind of "virtual resource" -
      // a front-end "route" most likely
      assets.at(publicDirectory, indexFile, true)
    }
  }

  val listPhysicalAssets = Action {
    Ok(Json.toJson(physicalAssets))
  }
}

More info: http://blog.themillhousegroup.com/2017/07/the-crap-stack-part-3-front-end-routes.html

Example of corresponding routes file:

...
# Last of all, fall through to the React app
GET         /list-assets               controllers.FrontEndServingController.listPhysicalAssets
GET         /                          controllers.FrontEndServingController.index
GET         /*file                     controllers.FrontEndServingController.frontEndPath(file)