CODEWITHSUNDEEP
scalaakkaakka-streamakka-http
miguel0afd
miguel0afd

Reputation: 315

Send element to element from a Source in Akka Http

I'm developing a client-server application using Akka Http and Akka Streams. The main idea is that the server must feed the http response with a Source from an Akka streams.

The problem is that the server accumulates some elements before sending the first message to the client. However, I need the server to send element to element as soon as a new element is produced by the source.

Code example:

case class Example(id: Long, txt: String, number: Double)

object MyJsonProtocol extends SprayJsonSupport with DefaultJsonProtocol {
  implicit val exampleFormat = jsonFormat3(Test)
}

class BatchIterator(batchSize: Int, numberOfBatches: Int, pause: FiniteDuration) extends Iterator[Array[Test]]{

  val range = Range(0, batchSize*numberOfBatches).toIterator
  val numberOfBatchesIter = Range(0, numberOfBatches).toIterator

  override def hasNext: Boolean = range.hasNext

  override def next(): Array[Test] = {
    println(s"Sleeping for ${pause.toMillis} ms")
    Thread.sleep(pause.toMillis)
    println(s"Taking $batchSize elements")
    Range(0, batchSize).map{ _ =>
      val count = range.next()
      Test(count, s"Text$count", count*0.5)
    }.toArray
  }
}

object Server extends App {
  import MyJsonProtocol._
  implicit val jsonStreamingSupport: JsonEntityStreamingSupport = EntityStreamingSupport.json()
      .withFramingRenderer(
        Flow[ByteString].intersperse(ByteString(System.lineSeparator))
      )

  implicit val system = ActorSystem("api")
  implicit val materializer = ActorMaterializer()
  implicit val executionContext = system.dispatcher

  def fetchExamples(): Source[Array[Test], NotUsed] = Source.fromIterator(() => new BatchIterator(5, 5, 2 seconds))

  val route =
    path("example") {
      complete(fetchExamples)
    }

  val bindingFuture = Http().bindAndHandle(route, "localhost", 9090)
  println("Server started at localhost:9090")
  StdIn.readLine()
  bindingFuture.flatMap(_.unbind()).onComplete(_ ⇒ system.terminate())
}

Then, if I execute:

curl --no-buffer localhost:9090/example

I get all the elements at the same time instead of receiving an element every 2 seconds.

Any idea about how I can "force" the server to send every element as it comes out from the source?

Upvotes: 0

Views: 153

Answers (1)

miguel0afd
miguel0afd

Reputation: 315

Finally, I've found the solution. The problem was that the source is synchronous... So the solution is just to call to the function async

complete(fetchExamples.async)

Upvotes: 1

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