HomeController.scala

package controllers

import akka.stream.scaladsl.Source
import akka.util.ByteString
import com.google.inject.{Inject, Singleton}
import play.api.mvc._
import play.api.http.HttpEntity

@Singleton
class HomeController @Inject()(cc: ControllerComponents) extends AbstractController(cc) {
  private val length = 100000000
  private val payload = ByteString.fromArray(Array.fill(length)('1'))

  // doesn't work for slow clients
  def large1(): Action[AnyContent] = Action { implicit req =>
    val entity = HttpEntity.Streamed(Source.single(payload), Some(length.toLong), Some("text/plain"))
    Result(ResponseHeader(OK), entity)
  }
  
  // doesn't work for slow clients
  def large2(): Action[AnyContent] = Action { implicit req =>
    val entity = HttpEntity.Strict(payload, Some("text/plain"))
    Result(ResponseHeader(OK), entity)
  }

  // works for both regualr and slow clients
  def large3(): Action[AnyContent] = Action { implicit req =>
    val one = ByteString("1")
    val iteratorSource = Source.fromIterator(() => Iterator.range(0, length).map(_ => one))
    val entity = HttpEntity.Streamed(iteratorSource, Some(length.toLong), Some("text/plain"))
    Result(ResponseHeader(OK), entity)
  }
}