Spray route get response from child actor - scala

I am trying to figure out how I can setup a Master Actor that calls the appropriate children, in support of some spray routes where I am trying to emulate db calls. I am new to akka / spray, so just trying to gain a better understanding of how you would properly setup spray -> actors -> db calls (etc.). I can get the response back from the top level actor, but when I try to get it back from one actor level below the parent I can't seem to get anything to work.
When looking at the paths of the actors, it appears that from the way I am making the call from my spray route that I am passing from a temp actor. Below is what I have so far for stubbing this out. This has to be just user error / ignorance, just not sure how to proceed. Any suggestions would be appreciated.
The Demo Spray Service and Redis Actor code snippets below show where I am calling the actor from my route and the multiple actors where I am having the issue (want my route to get response from SummaryActor). Thanks!
Boot:
object Boot extends App {
// we need an ActorSystem to host our application in
implicit val system = ActorSystem("on-spray-can")
// create and start our service actor
val service = system.actorOf(Props[DemoServiceActor], "demo-service")
implicit val timeout = Timeout(5.seconds)
// start a new HTTP server on port 8080 with our service actor as the handler
IO(Http) ? Http.Bind(service, interface = "localhost", port = 8080)
}
Demo Service Actor (For Spray)
class DemoServiceActor extends Actor with Api {
// the HttpService trait defines only one abstract member, which
// connects the services environment to the enclosing actor or test
def actorRefFactory = context
// this actor only runs our route, but you could add
// other things here, like request stream processing
// or timeout handling
def receive = handleTimeouts orElse runRoute(route)
//Used to watch for request timeouts
//http://spray.io/documentation/1.1.2/spray-routing/key-concepts/timeout-handling/
def handleTimeouts: Receive = {
case Timedout(x: HttpRequest) =>
sender ! HttpResponse(StatusCodes.InternalServerError, "Too late")
}
}
//Master trait for handling large APIs
//http://stackoverflow.com/questions/14653526/can-spray-io-routes-be-split-into-multiple-controllers
trait Api extends DemoService {
val route = {
messageApiRouting
}
}
Demo Spray Service (Route):
trait DemoService extends HttpService with Actor {
implicit val timeout = Timeout(5 seconds) // needed for `?` below
val redisActor = context.actorOf(Props[RedisActor], "redisactor")
val messageApiRouting =
path("summary" / Segment / Segment) { (dataset, timeslice) =>
onComplete(getSummary(redisActor, dataset, timeslice)) {
case Success(value) => complete(s"The result was $value")
case Failure(ex) => complete(s"An error occurred: ${ex.getMessage}")
}
}
def getSummary(redisActor: ActorRef, dataset: String, timeslice: String): Future[String] = Future {
val dbMessage = DbMessage("summary", dataset + timeslice)
val future = redisActor ? dbMessage
val result = Await.result(future, timeout.duration).asInstanceOf[String]
result
}
}
Redis Actor (Mock no actual redis client yet)
class RedisActor extends Actor with ActorLogging {
// val pool = REDIS
implicit val timeout = Timeout(5 seconds) // needed for `?` below
val summaryActor = context.actorOf(Props[SummaryActor], "summaryactor")
def receive = {
case msg: DbMessage => {
msg.query match {
case "summary" => {
log.debug("Summary Query Request")
log.debug(sender.path.toString)
summaryActor ! msg
}
}
}
//If not match log an error
case _ => log.error("Received unknown message: {} ")
}
}
class SummaryActor extends Actor with ActorLogging{
def receive = {
case msg: DbMessage =>{
log.debug("Summary Actor Received Message")
//Send back to Spray Route
}
}
}

The first problem with your code is that you need to forward from the master actor to the child so that the sender is properly propagated and available for the child to respond to. So change this (in RedisActor):
summaryActor ! msg
To:
summaryActor forward msg
That's the primary issue. Fix that and your code should start working. There is something else that needs attention though. Your getSummary method is currently defined as:
def getSummary(redisActor: ActorRef, dataset: String, timeslice: String): Future[String] =
Future {
val dbMessage = DbMessage("summary", dataset + timeslice)
val future = redisActor ? dbMessage
val result = Await.result(future, timeout.duration).asInstanceOf[String]
result
}
The issue here is that the ask operation (?) already returns a Future, so there and you are blocking on it to get the result, wrapping that in another Future so that you can return a Future for onComplete to work with. You should be able to simplify things by using the Future returned from ask directly like so:
def getSummary(redisActor: ActorRef, dataset: String, timeslice: String): Future[String] = {
val dbMessage = DbMessage("summary", dataset + timeslice)
(redisActor ? dbMessage).mapTo[String]
}

Just an important comment on the above approaches.
Since the getSummary(...) function returns a Future[String] object and you call it in onComplete(...) function you need to import:
import ExecutionContext.Implicits.global
That way you will have ExecutionContext in scope by letting Future
declare an implicit ExecutionContext parameter.
** If you don't, you will end up getting a mismatching error
since onComplete(...) expects an onComplete Future
magnet Object but you gave a Future[String] Object.

Related

How to continually call a REST service using non blocking code with Akka

I'm accessing data from a REST endpoint :
"https://api-public.sandbox.pro.coinbase.com/products/BTC-EUR/ticker"
To access the data once per second I use an infinite loop while(true) { to invoke a message send to the actor once per second which begins the process of invoking the REST request:
The actor to access the data is:
object ProductTickerRestActor {
case class StringData(data: String)
}
class ProductTickerRestActor extends Actor {
override def receive: PartialFunction[Any, Unit] = {
case ProductTickerRestActor.StringData(data) =>
try {
println("in ProductTickerRestActor")
val rData = scala.io.Source.fromURL("https://api-public.sandbox.pro.coinbase.com/products/BTC-EUR/ticker").mkString
println("rData : "+rData)
}
catch {
case e: Exception =>
println("Exception thrown in ProductTickerRestActor: " + e.getMessage)
}
case msg => println(s"I cannot understand ${msg.toString}")
}
}
I start the application using:
object ExchangeModelDataApplication {
def main(args: Array[String]): Unit = {
val actorSystem = ActorSystemConfig.getActorSystem
val priceDataActor = actorSystem.actorOf(Props[ProductTickerRestActor], "ProductTickerRestActor")
val throttler = Throttlers.getThrottler(priceDataActor)
while(true) {
throttler ! ProductTickerRestActor.StringData("test")
Thread.sleep(1000)
}
}
Throttler:
object Throttlers {
implicit val materializer = ActorMaterializer.create(ActorSystemConfig.getActorSystem)
def getThrottler(priceDataActor: ActorRef) = Source.actorRef(bufferSize = 1000, OverflowStrategy.dropNew)
.throttle(1, 1.second)
.to(Sink.actorRef(priceDataActor, NotUsed))
.run()
}
How to run the following code asynchronously instead of blocking using an infinite loop? :
throttler ! ProductTickerRestActor.StringData("test")
Thread.sleep(1000)
Also, the throttler, in this case, maybe redundant as I'm throttling requests within the loop regardless.
I would just use Akka Streams for this along with Akka HTTP. Using Akka 2.6.x, something along these lines would be sufficient for 1 request/second
import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.stream.scaladsl._
import scala.concurrent.duration._
object HTTPRepeatedly {
implicit val system = ActorSystem()
import system.dispatcher
val sourceFromHttp: Source[String, NotUsed] =
Source.repeated("test") // Not sure what "test" is actually used for here...
.throttle(1, 1.second)
.map { str =>
HttpRequest(uri = "https://api-public.sandbox.pro.coinbase.com/products/BTC-EUR/ticker")
}.mapAsync(1) { req =>
Http().singleRequest(req)
}.mapAsync(1)(_.entity.toStrict(1.minute))
.map(_.data.decodeString(java.nio.charset.StandardCharsets.UTF_8))
}
Then you could, for instance (for simplicity, put this in a main within HTTPRepeatedly so the implicits are in scope etc.)
val done: Future[Done] =
sourceFromHttp
.take(10) // stop after 10 requests
.runWith(Sink.foreach { rData => println(s"rData: $rData") })
scala.concurrent.Await.result(done, 11.minute)
system.terminate()
Sending a request every second is not a good idea. If, for some reason, the request is delayed, you are going to get a lot of requests piled up. Instead, send the next request one second after the previous requests completes.
Because this code uses a synchronous GET request, you can just send the next request one second after mkString returns.
But using synchronous requests is not a good way to consume a RESTful API in Akka. It blocks the actor receive method until the request is complete, which can eventually block the whole ActorSystem.
Instead, use Akka Http and singleRequest to perform an asynchronous request.
Http().singleRequest(HttpRequest(uri = "https://api-public.sandbox.pro.coinbase.com/products/BTC-EUR/ticker"))
This returns a Future. Make the new request one second after the request completes (e.g. using onComplete on the Future).
Not only is this safer and more asynchronous, it also provides much more control over the REST API call than fromUrl

when an actor contains an async method, this will lead to dead letter error with the Ask time out exception

I use ask mode send a request to an actor called actor-A in a function called fun-F. The actor will get an ID generated by another system in an async way, when this is completed, I will forward a message contains this ID to another actor called actor-B, the actor-B will do some DB operations and then send back the DB operation result in a message to the sender, since in my case I use forward mode, so the actor-B recognize the sender as fun-F, the akka will give the fun-F a temporary actor name, so the returned value should be delivered to the temp actor.
My question is:
If I use sync-method to get the ID from another system, then forward this message to the actor-B, after actor-B's DB operation, the result can be delivered to the value of fun-F, and the fun-F is defined as temporary actor Actor[akka://ai-feedback-service/temp/$b] by the akka framework runtime.
If I use async-method to get the ID from another system, when it completed, I will forward the message in the oncompleted {} code block in another call back thread, the DB operation in actor-B is handled successfully, but the returned value cannot be delivered to the value defined in the fun-F, and in this case the fun-F is defined as Actor[akka://ai-feedback-service/deadLetters] by the akka framwork runtime. So the actor-B lose its way and do not know how to get back or where should this message be delivered, and this will cause an Ask time out exception throws in my log.
How can I handled this issue? or how can I avoid this dead letter ask time out exception?
Below is my code:
// this is the so-called fun-F [createFeedback]
def createFeedback(query: String,
response: String,
userId: Long,
userAgent: String,
requestId: Long,
errType: Short,
memo: String): Future[java.lang.Long] = {
val ticket = Ticket(userId,
requestId,
query,
response,
errType,
userAgent,
memo)
val issueId = (jiraActor ? CreateJiraTicketSignal(ticket))
.mapTo[CreateFeedbackResponseSignal].map{ r =>
r.issueId.asInstanceOf[java.lang.Long]
}
issueId
}
//this is the so-called actor-A [jiraActor]
//receive method are run in its parent actor for some authorization
//in this actor only override the handleActorMsg method to deal msg
override def handleActorMsg(msg: ActorMsgSignal): Unit = {
msg match {
case s:CreateJiraTicketSignal =>
val issueId = createIssue(cookieCache.cookieContext.flag,
cookieCache.cookieContext.cookie,
s.ticket)
println(s">> ${sender()} before map $issueId")
issueId.map{
case(id:Long) =>
println(s">> again++issueId = $id ${id.getClass}")
println(s">>> $self / ${sender()}")
println("again ++ jira action finished")
dbActor.forward(CreateFeedbackSignal(id,s.ticket))
case(message:String) if(!s.retry) =>
self ! CreateJiraTicketSignal(s.ticket,true)
case(message:String) if(s.retry) =>
log.error("cannot create ticket :" + message)
}
println(s">> after map $issueId")
}
//this is the so-called actor-B [dbActor]
override def receive: Receive = {
case CreateFeedbackSignal(issueId:Long, ticket:Ticket) =>
val timestampTicks = System.currentTimeMillis()
val description: String = Json.obj("question" -> ticket.query,
"answer" -> ticket.response)
.toString()
dao.createFeedback(issueId,
ticket.usrId.toString,
description,
FeedbackStatus.Open.getValue
.asInstanceOf[Byte],
new Timestamp(timestampTicks),
new Timestamp(timestampTicks),
ticket.usrAgent,
ticket.errType,
ticket.memo)
println(s">> sender = ${sender()}")
sender() ! (CreateFeedbackResponseSignal(issueId))
println("db issue id is " + issueId)
println("db action finished")
}
To avoid the dead letters issue, do the following:
For every request, use an identifier (probably the requestId) that you can associate with the ultimate target for the request. That is, tie the requestId that you're passing to the createFeedback method to the caller (ActorRef) of that method, then pass this id through your messaging chain. You can use a map to hold these associations.
Change CreateFeedbackResponseSignal(issueId) to include the requestId from the Ticket class: CreateFeedbackResponseSignal(requestId, issueId).
When dealing with the asynchronous result of a Future from inside an actor, pipe the result of the Future to self instead of using a callback.
With this approach, the result of createIssue will be sent to jiraActor when the result is available. jiraActor then sends that result to dbActor.
jiraActor will be the sender in dbActor. When jiraActor receives the result from dbActor, jiraActor can look up the reference to the target in its internal map.
Below is a simple example that mimics your use case and is runnable in ScalaFiddle:
import akka.actor._
import akka.pattern.{ask, pipe}
import akka.util.Timeout
import language.postfixOps
import scala.concurrent._
import scala.concurrent.duration._
case class Signal(requestId: Long)
case class ResponseSignal(requestId: Long, issueId: Long)
object ActorA {
def props(actorB: ActorRef) = Props(new ActorA(actorB))
}
class ActorA(dbActor: ActorRef) extends Actor {
import context.dispatcher
var targets: Map[Long, ActorRef] = Map.empty
def receive = {
case Signal(requestId) =>
val s = sender
targets = targets + (requestId -> s)
createIssue(requestId).mapTo[Tuple2[Long, Long]].pipeTo(self) // <-- use pipeTo
case ids: Tuple2[Long, Long] =>
println(s"Sending $ids to dbActor")
dbActor ! ids
case r: ResponseSignal =>
println(s"Received from dbActor: $r")
val target = targets.get(r.requestId)
println(s"In actorA, sending to: $target")
target.foreach(_ ! r)
targets = targets - r.requestId
}
}
class DbActor extends Actor {
def receive = {
case (requestId: Long, issueId: Long) =>
val response = ResponseSignal(requestId, issueId)
println(s"In dbActor, sending $response to $sender")
sender ! response
}
}
val system = ActorSystem("jiratest")
implicit val ec = system.dispatcher
val dbActor = system.actorOf(Props[DbActor])
val jiraActor = system.actorOf(Props(new ActorA(dbActor)))
val requestId = 2L
def createIssue(requestId: Long): Future[(Long, Long)] = {
println(s"Creating an issue ID for requestId[$requestId]")
Future((requestId, 99L))
}
def createFeedback(): Future[Long] = {
implicit val timeout = Timeout(5.seconds)
val res = (jiraActor ? Signal(requestId)).mapTo[ResponseSignal]
res.map(_.issueId)
}
createFeedback().onComplete { x =>
println(s"Done: $x")
}
Running the above code in ScalaFiddle results in the following output:
Creating an issue ID for requestId[2]
Sending (2,99) to dbActor
In dbActor, sending ResponseSignal(2,99) to Actor[akka://jiratest/user/$b#-710097339]
Received from dbActor: ResponseSignal(2,99)
In actorA, sending to: Some(Actor[akka://jiratest/temp/$a])
Done: Success(99)

Get a message out of an Akka Actor

I've built an Akka actor that queries an API at regular intervals, like this:
val cancellable =
system.scheduler.schedule(0 milliseconds,
5 seconds,
actor,
QueryController(1))
The Actor, in essence is:
object UpdateStatistics {
/**
* Query the controller for the given switch Id
*
* #param dpId Switch's Id
*/
case class QueryController(dpId: Int)
case object Stop
def props: Props = Props[UpdateStatistics]
}
class UpdateStatistics extends Actor with akka.actor.ActorLogging {
import UpdateStatistics._
def receive = {
case QueryController(id) =>
import context.dispatcher
log.info(s"Receiving request to query controller")
Future { FlowCollector.getSwitchFlows(1) } onComplete {
f => self ! f.get
}
case Stop =>
log.info(s"Shuting down")
context stop self
case json: JValue =>
log.info("Getting json response, computing features...")
val features = FeatureExtractor.getFeatures(json)
log.debug(s"Features: $features")
sender ! features
case x =>
log.warning("Received unknown message: {}", x)
}
}
What I am trying to do is get the json:Jvalue message out of UpdateStatistics actor. Reading the Akka docs I thought this may be useful:
implicit val i = inbox()
i.select() {
case x => println(s"Valor Devuelto $x")
}
println(i receive(2.second))
But I do not know how to modify UpdateStatistics actor in order to send the result to the inbox above.
Another option I've read in the docs are event streams.
But I do not think this is the correct way.
Is there a way of achieving what I want to do? Or do I need to use a second Actor to which I send the JSON response?
You probably are looking for the ask pattern in AKKA. This will allow you to return a value to the sender.
import akka.pattern.ask
import akka.util.duration._
implicit val timeout = Timeout(5 seconds)
val future = actor ? QueryController(1)
val result = Await.result(future, timeout.duration).asInstanceOf[JValue]
println(result)
To make this work, you need to send the response to the original sender, rather than self. Also, you should beware the dangers of closing over sender in a future when handling messages.

Akka round-robin: Sending response from remote routees to sender

I am using Akka Cluster (version 2.4.10) with few nodes designated for "front-end" role and few others as "workers". The workers are on remote machines. The incoming work is distributed by the front-end actor to workers by round-robin routing. The issue is sending back the response from the "workers" back to the front-end actor. I can see that the work is getting completed by the workers. But the message sent by the workers to front-end does not reach and ends up as dead-letters. I see the below error in the log.
[Cluster-akka.actor.default-dispatcher-21] [akka://Cluster/deadLetters] Message [scala.collection.immutable.$colon$colon] from Actor[akka://Cluster/user] to Actor[akka://Cluster/deadLetters] was not delivered. [6] dead letters encountered.
I have seen this and I am following the same in my code. I have also seen this, but the solution suggested does not apply in this case, because I do not know the routees up-front. It comes through the configuration and it can change. The round-robin router configuration is as below.
akka.actor.deployment {
/frontEnd/hm = {
router = round-robin-group
nr-of-instances = 5
routees.paths = ["/user/hmWorker"]
cluster {
enabled = on
use-role = backend
allow-local-routees = on
}
}
}
The router is instantiated in front-end actor like below.
val router = context.actorOf(FromConfig.props(), name = "hm")
val controller = context.actorOf(Props(classOf[Controller], router))
The controller and the worker codes are below.
// Node 1 : Controller routes requests using round-robin
class Controller(router: ActorRef) extends Actor {
val list = List("a", "b") // Assume this is a big list
val groups = list.grouped(500)
override def receive: Actor.Receive = {
val futures = groups.map(grp => (router ? Message(grp)).mapTo[List[String]]))
val future = Future.sequence(futures).map(_.flatten)
val result = Await.result(future, 50 seconds)
println(s"Result is $result")
}
}
// Node 2
class Worker extends Actor {
override def receive: Actor.Receive = {
case Message(lst) =>
val future: Future[List[String]] = // Do Something asynchronous
future onComplete {
case Success(r) => sender.!(r)(context.parent) // This message is not delivered to Controller actor.
case Failure(th) => // Error handling
}
}
}
Please let me know what I am doing wrong here. Appreciate your help.
You shouldn't use sender() in the callback on a Future. By the time the callback is processed, the sender() is likely referring to something different than it was when you received the message.
Consider either saving the reference outside of the callback first like:
override def receive: Actor.Receive = {
case Message(lst) =>
val future: Future[List[String]] = // Do Something asynchronous
val replyTo: ActorRef = sender()
future onComplete {
case Success(r) => replyTo.!(r)(context.parent) // This message is not delivered to Controller actor.
case Failure(th) => // Error handling
}
}
Or even better, use the pipe pattern:
import akka.pattern.pipe
override def receive: Actor.Receive = {
case Message(lst) =>
val future: Future[List[String]] = // Do Something asynchronous
future.pipeTo(sender())
}

How to send iterables between actors or from an actor to a Future?

A future from the main method of a program sends a msg to its actor asking for an iterable object. The actor then creates another future that asks for the iterable object (say an ArrayBuffer) from a remote actor. After receiving the ArrayBuffer from the remote actor, how would the actor send it back to the first future in the main method? It seems creating a local alias of sender and creating a separate case class to represent the iterable does not prevent dead letters from being encountered.
Here is a sample code:
case class SequenceObject(sqnce:Seq[someArrayBuffer])
//...
implicit val timeout = Timeout(10 seconds)
val fut1: Future[Any] = myActor ? iNeedAnArrayBufferObject
fut1.onSuccess {
case listOfItems: SequenceObject => {
//do sth with listofItems.sqnce
}
class myActor extends Actor {
implicit val timeout = Timeout(1 seconds)
def receive = {
case a: iNeedAnArrayBufferObject => {
val originalSender = sender
val fut: Future[Any] = (remoteActor ? a)
fut.onSuccess {
case list: SequenceObject => {
originalSender ! SequenceObject(list.sqnce)
}
}
The remote actor code is:
class ServerActorClass extends Actor {
def receive = {
case a: iNeedAnArrayBufferObject => {
val closer = sender()
closer ! SequenceObject(ArrayBufferObject[information])
}
}
The above does not seem to work. The remote actor and the local actor can communicate and messages are received correctly. However, the iterable object is never send back to fut1. Why is that? Thanks in advance.
Check pipeTo pattern in Ask: Send-And-Receive-Future section