Routing DSL

In addition to the Core Server API Akka HTTP provides a very flexible “Routing DSL” for elegantly defining RESTful web services. It picks up where the low-level API leaves off and offers much of the higher-level functionality of typical web servers or frameworks, like deconstruction of URIs, content negotiation or static content serving.

Minimal Example

This is a complete, very basic Akka HTTP application relying on the Routing DSL:

Scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.model._
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer
import scala.io.StdIn

object WebServer {
  def main(args: Array[String]) {

    implicit val system = ActorSystem("my-system")
    implicit val materializer = ActorMaterializer()
    // needed for the future flatMap/onComplete in the end
    implicit val executionContext = system.dispatcher

    val route =
      path("hello") {
        get {
          complete(HttpEntity(ContentTypes.`text/html(UTF-8)`, "<h1>Say hello to akka-http</h1>"))
        }
      }

    val bindingFuture = Http().bindAndHandle(route, "localhost", 8080)

    println(s"Server online at http://localhost:8080/\nPress RETURN to stop...")
    StdIn.readLine() // let it run until user presses return
    bindingFuture
      .flatMap(_.unbind()) // trigger unbinding from the port
      .onComplete(_ => system.terminate()) // and shutdown when done
  }
}

Java

import akka.NotUsed;
import akka.actor.ActorSystem;
import akka.http.javadsl.ConnectHttp;
import akka.http.javadsl.Http;
import akka.http.javadsl.ServerBinding;
import akka.http.javadsl.model.HttpRequest;
import akka.http.javadsl.model.HttpResponse;
import akka.http.javadsl.server.AllDirectives;
import akka.http.javadsl.server.Route;
import akka.stream.ActorMaterializer;
import akka.stream.javadsl.Flow;

import java.util.concurrent.CompletionStage;

public class HttpServerMinimalExampleTest extends AllDirectives {

  public static void main(String[] args) throws Exception {
    // boot up server using the route as defined below
    ActorSystem system = ActorSystem.create("routes");

    final Http http = Http.get(system);
    final ActorMaterializer materializer = ActorMaterializer.create(system);

    //In order to access all directives we need an instance where the routes are define.
    HttpServerMinimalExampleTest app = new HttpServerMinimalExampleTest();

    final Flow<HttpRequest, HttpResponse, NotUsed> routeFlow = app.createRoute().flow(system, materializer);
    final CompletionStage<ServerBinding> binding = http.bindAndHandle(routeFlow,
        ConnectHttp.toHost("localhost", 8080), materializer);

    System.out.println("Server online at http://localhost:8080/\nPress RETURN to stop...");
    System.in.read(); // let it run until user presses return

    binding
        .thenCompose(ServerBinding::unbind) // trigger unbinding from the port
        .thenAccept(unbound -> system.terminate()); // and shutdown when done
  }

  private Route createRoute() {
    return route(
        path("hello", () ->
            get(() ->
                complete("<h1>Say hello to akka-http</h1>"))));
  }
}

It starts an HTTP Server on localhost and replies to GET requests to /hello with a simple response.

To help start a server Akka HTTP provides an experimental helper class called HttpAppHttpApp. This is the same example as before rewritten using HttpAppHttpApp:

Scala

import akka.http.scaladsl.model.{ ContentTypes, HttpEntity }
import akka.http.scaladsl.server.HttpApp
import akka.http.scaladsl.server.Route

// Server definition
object WebServer extends HttpApp {
  override def routes: Route =
    path("hello") {
      get {
        complete(HttpEntity(ContentTypes.`text/html(UTF-8)`, "<h1>Say hello to akka-http</h1>"))
      }
    }
}

// Starting the server
WebServer.startServer("localhost", 8080)

Java

// Server definition
class MinimalHttpApp extends HttpApp {
  @Override
  protected Route routes() {
    return path("hello", () ->
      get(() ->
        complete("<h1>Say hello to akka-http</h1>")
      )
    );
  }
}

// Starting the server
final MinimalHttpApp myServer = new MinimalHttpApp();
myServer.startServer("localhost", 8080);

See HttpApp Bootstrap for more details about setting up a server using this approach.

import akka.actor.{ActorRef, ActorSystem}
import akka.http.scaladsl.coding.Deflate
import akka.http.scaladsl.marshalling.ToResponseMarshaller
import akka.http.scaladsl.model.StatusCodes.MovedPermanently
import akka.http.scaladsl.server.Directives._
import akka.http.scaladsl.unmarshalling.FromRequestUnmarshaller
import akka.pattern.ask
import akka.stream.ActorMaterializer
import akka.util.Timeout

// types used by the API routes
type Money = Double // only for demo purposes, don't try this at home!
type TransactionResult = String
case class User(name: String)
case class Order(email: String, amount: Money)
case class Update(order: Order)
case class OrderItem(i: Int, os: Option[String], s: String)

// marshalling would usually be derived automatically using libraries
implicit val orderUM: FromRequestUnmarshaller[Order] = ???
implicit val orderM: ToResponseMarshaller[Order] = ???
implicit val orderSeqM: ToResponseMarshaller[Seq[Order]] = ???
implicit val timeout: Timeout = ??? // for actor asks
implicit val ec: ExecutionContext = ???
implicit val mat: ActorMaterializer = ???
implicit val sys: ActorSystem = ???

// backend entry points
def myAuthenticator: Authenticator[User] = ???
def retrieveOrdersFromDB: Seq[Order] = ???
def myDbActor: ActorRef = ???
def processOrderRequest(id: Int, complete: Order => Unit): Unit = ???

val route = {
  path("orders") {
    authenticateBasic(realm = "admin area", myAuthenticator) { user =>
      get {
        encodeResponseWith(Deflate) {
          complete {
            // marshal custom object with in-scope marshaller
            retrieveOrdersFromDB
          }
        }
      } ~
      post {
        // decompress gzipped or deflated requests if required
        decodeRequest {
          // unmarshal with in-scope unmarshaller
          entity(as[Order]) { order =>
            complete {
              // ... write order to DB
              "Order received"
            }
          }
        }
      }
    }
  } ~
  // extract URI path element as Int
  pathPrefix("order" / IntNumber) { orderId =>
    pathEnd {
      (put | parameter('method ! "put")) {
        // form extraction from multipart or www-url-encoded forms
        formFields(('email, 'total.as[Money])).as(Order) { order =>
          complete {
            // complete with serialized Future result
            (myDbActor ? Update(order)).mapTo[TransactionResult]
          }
        }
      } ~
      get {
        // debugging helper
        logRequest("GET-ORDER") {
          // use in-scope marshaller to create completer function
          completeWith(instanceOf[Order]) { completer =>
            // custom
            processOrderRequest(orderId, completer)
          }
        }
      }
    } ~
    path("items") {
      get {
        // parameters to case class extraction
        parameters(('size.as[Int], 'color ?, 'dangerous ? "no"))
          .as(OrderItem) { orderItem =>
            // ... route using case class instance created from
            // required and optional query parameters
          }
      }
    }
  } ~
  pathPrefix("documentation") {
    // optionally compresses the response with Gzip or Deflate
    // if the client accepts compressed responses
    encodeResponse {
      // serve up static content from a JAR resource
      getFromResourceDirectory("docs")
    }
  } ~
  path("oldApi" / Remaining) { pathRest =>
    redirect("http://oldapi.example.com/" + pathRest, MovedPermanently)
  }
}

Handling HTTP Server failures in the High-Level API

There are various situations when failure may occur while initialising or running an Akka HTTP server. Akka by default will log all these failures, however sometimes one may want to react to failures in addition to them just being logged, for example by shutting down the actor system, or notifying some external monitoring end-point explicitly.

Bind failures

For example the server might be unable to bind to the given port. For example when the port is already taken by another application, or if the port is privileged (i.e. only usable by root). In this case the “binding future” will fail immediately, and we can react to it by listening on the FutureCompletionStage’s completion:

Scala

import akka.actor.ActorSystem
import akka.http.scaladsl.Http
import akka.http.scaladsl.Http.ServerBinding
import akka.http.scaladsl.server.Directives._
import akka.stream.ActorMaterializer

import scala.concurrent.Future

object WebServer {
  def main(args: Array[String]) {
    implicit val system = ActorSystem()
    implicit val materializer = ActorMaterializer()
    // needed for the future foreach in the end
    implicit val executionContext = system.dispatcher

    val handler = get {
      complete("Hello world!")
    }

    // let's say the OS won't allow us to bind to 80.
    val (host, port) = ("localhost", 80)
    val bindingFuture: Future[ServerBinding] =
      Http().bindAndHandle(handler, host, port)

    bindingFuture.failed.foreach { ex =>
      log.error(ex, "Failed to bind to {}:{}!", host, port)
    }
  }
}

Java

import akka.NotUsed;
import akka.actor.ActorSystem;
import akka.http.javadsl.ConnectHttp;
import akka.http.javadsl.ServerBinding;
import akka.http.javadsl.model.HttpRequest;
import akka.http.javadsl.model.HttpResponse;
import akka.http.javadsl.server.Route;
import akka.http.javadsl.Http;
import akka.stream.ActorMaterializer;
import akka.stream.javadsl.Flow;

import java.io.IOException;
import java.util.concurrent.CompletionStage;

public class HighLevelServerBindFailureExample {
  public static void main(String[] args) throws IOException {
    // boot up server using the route as defined below
    final ActorSystem system = ActorSystem.create();
    final ActorMaterializer materializer = ActorMaterializer.create(system);

    final HighLevelServerExample app = new HighLevelServerExample();
    final Route route = app.createRoute();

    final Flow<HttpRequest, HttpResponse, NotUsed> handler = route.flow(system, materializer);
    final CompletionStage<ServerBinding> binding = Http.get(system).bindAndHandle(handler, ConnectHttp.toHost("127.0.0.1", 8080), materializer);

    binding.exceptionally(failure -> {
      System.err.println("Something very bad happened! " + failure.getMessage());
      system.terminate();
      return null;
    });

    system.terminate();
  }
}

Failures and exceptions inside the Routing DSL

Exception handling within the Routing DSL is done by providing ExceptionHandlerExceptionHandler s which are documented in-depth in the Exception Handling section of the documentation. You can use them to transform exceptions into HttpResponseHttpResponse s with appropriate error codes and human-readable failure descriptions.

File uploads

For high level directives to handle uploads see the FileUploadDirectives.

Handling a simple file upload from for example a browser form with a file input can be done by accepting a Multipart.FormData entity, note that the body parts are Source rather than all available right away, and so is the individual body part payload so you will need to consume those streams both for the file and for the form fields.

Here is a simple example which just dumps the uploaded file into a temporary file on disk, collects some form fields and saves an entry to a fictive database:

Scala

val uploadVideo =
  path("video") {
    entity(as[Multipart.FormData]) { formData =>

      // collect all parts of the multipart as it arrives into a map
      val allPartsF: Future[Map[String, Any]] = formData.parts.mapAsync[(String, Any)](1) {

        case b: BodyPart if b.name == "file" =>
          // stream into a file as the chunks of it arrives and return a future
          // file to where it got stored
          val file = File.createTempFile("upload", "tmp")
          b.entity.dataBytes.runWith(FileIO.toPath(file.toPath)).map(_ =>
            (b.name -> file))

        case b: BodyPart =>
          // collect form field values
          b.toStrict(2.seconds).map(strict =>
            (b.name -> strict.entity.data.utf8String))

      }.runFold(Map.empty[String, Any])((map, tuple) => map + tuple)

      val done = allPartsF.map { allParts =>
        // You would have some better validation/unmarshalling here
        db.create(Video(
          file = allParts("file").asInstanceOf[File],
          title = allParts("title").asInstanceOf[String],
          author = allParts("author").asInstanceOf[String]))
      }

      // when processing have finished create a response for the user
      onSuccess(allPartsF) { allParts =>
        complete {
          "ok!"
        }
      }
    }
  }

Java

  path("video", () ->
  entity(Unmarshaller.entityToMultipartFormData(), formData -> {
    // collect all parts of the multipart as it arrives into a map
    final CompletionStage<Map<String, Object>> allParts =
      formData.getParts().mapAsync(1, bodyPart -> {
        if ("file".equals(bodyPart.getName())) {
          // stream into a file as the chunks of it arrives and return a CompletionStage
          // file to where it got stored
          final File file = File.createTempFile("upload", "tmp");
          return bodyPart.getEntity().getDataBytes()
            .runWith(FileIO.toPath(file.toPath()), materializer)
            .thenApply(ignore ->
              new Pair<String, Object>(bodyPart.getName(), file)
            );
        } else {
          // collect form field values
          return bodyPart.toStrict(2 * 1000, materializer)
            .thenApply(strict ->
              new Pair<String, Object>(bodyPart.getName(),
                strict.getEntity().getData().utf8String())
            );
        }
      }).runFold(new HashMap<String, Object>(), (acc, pair) -> {
        acc.put(pair.first(), pair.second());
        return acc;
      }, materializer);

    // simulate a DB call
    final CompletionStage<Void> done = allParts.thenCompose(map ->
      // You would have some better validation/unmarshalling here
      DB.create((File) map.get("file"),
        (String) map.get("title"),
        (String) map.get("author")
      ));

    // when processing have finished create a response for the user
    return onSuccess(allParts, x -> complete("ok!"));
  })
);

You can transform the uploaded files as they arrive rather than storing them in a temporary file as in the previous example. In this example we accept any number of .csv files, parse those into lines and split each line before we send it to an actor for further processing:

Scala

val splitLines = Framing.delimiter(ByteString("\n"), 256)

val csvUploads =
  path("metadata" / LongNumber) { id =>
    entity(as[Multipart.FormData]) { formData =>
      val done: Future[Done] = formData.parts.mapAsync(1) {
        case b: BodyPart if b.filename.exists(_.endsWith(".csv")) =>
          b.entity.dataBytes
            .via(splitLines)
            .map(_.utf8String.split(",").toVector)
            .runForeach(csv =>
              metadataActor ! MetadataActor.Entry(id, csv))
        case _ => Future.successful(Done)
      }.runWith(Sink.ignore)

      // when processing have finished create a response for the user
      onSuccess(done) { _ =>
        complete {
          "ok!"
        }
      }
    }
  }

Java

Route csvUploads() {
  final Flow<ByteString, ByteString, NotUsed> splitLines =
    Framing.delimiter(ByteString.fromString("\n"), 256);

  return path(segment("metadata").slash(longSegment()), id ->
    entity(Unmarshaller.entityToMultipartFormData(), formData -> {

      final CompletionStage<Done> done = formData.getParts().mapAsync(1, bodyPart ->
        bodyPart.getFilename().filter(name -> name.endsWith(".csv")).map(ignored ->
          bodyPart.getEntity().getDataBytes()
            .via(splitLines)
            .map(bs -> bs.utf8String().split(","))
            .runForeach(csv ->
                metadataActor.tell(new Entry(id, csv), ActorRef.noSender()),
              materializer)
        ).orElseGet(() ->
          // in case the uploaded file is not a CSV
          CompletableFuture.completedFuture(Done.getInstance()))
      ).runWith(Sink.ignore(), materializer);

      // when processing have finished create a response for the user
      return onComplete(() -> done, ignored -> complete("ok!"));
    })
  );
}

Configuring Server-side HTTPS

For detailed documentation about configuring and using HTTPS on the server-side refer to Server-Side HTTPS Support.