akka-http-streaming.scala

path("test") {
  extract(ctx => ctx.request.entity.dataBytes) { body =>
    complete {
      val processing = body
        .map { chunk =>
          //println(s"Received ${chunk.length} bytes")
          chunk
        }
        .map { chunk =>
          // simulate slow processing speed
          //Thread.sleep(100L)
          chunk
        }

      HttpEntity.Chunked.fromData(ContentTypes.`application/octet-stream`, processing)
    }
  }
}