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§The Play WS API

Sometimes we would like to call other HTTP services from within a Play application. Play supports this via its WS library, which provides a way to make asynchronous HTTP calls.

There are two important parts to using the WS API: making a request, and processing the response. We’ll discuss how to make both GET and POST HTTP requests first, and then show how to process the response from WS. Finally, we’ll discuss some common use cases.

§Making a Request

To use WS, first add ws to your build.sbt file:

libraryDependencies ++= Seq(
  ws
)

Now any controller or component that wants to use WS will have to declare a dependency on the WSClient:

import javax.inject.Inject
import scala.concurrent.Future
import scala.concurrent.duration._

import play.api.mvc._
import play.api.libs.ws._
import play.api.http.HttpEntity

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import akka.stream.scaladsl._
import akka.util.ByteString

import scala.concurrent.ExecutionContext

class Application @Inject() (ws: WSClient) extends Controller {

}

We’ve called the WSClient instance ws, all the following examples will assume this name.

To build an HTTP request, you start with ws.url() to specify the URL.

val request: WSRequest = ws.url(url)

This returns a WSRequest that you can use to specify various HTTP options, such as setting headers. You can chain calls together to construct complex requests.

val complexRequest: WSRequest =
  request.withHeaders("Accept" -> "application/json")
    .withRequestTimeout(10000.millis)
    .withQueryString("search" -> "play")

You end by calling a method corresponding to the HTTP method you want to use. This ends the chain, and uses all the options defined on the built request in the WSRequest.

val futureResponse: Future[WSResponse] = complexRequest.get()

This returns a Future[WSResponse] where the Response contains the data returned from the server.

§Request with authentication

If you need to use HTTP authentication, you can specify it in the builder, using a username, password, and an AuthScheme. Valid case objects for the AuthScheme are BASIC, DIGEST, KERBEROS, NTLM, and SPNEGO.

ws.url(url).withAuth(user, password, WSAuthScheme.BASIC).get()

§Request with follow redirects

If an HTTP call results in a 302 or a 301 redirect, you can automatically follow the redirect without having to make another call.

ws.url(url).withFollowRedirects(true).get()

§Request with query parameters

Parameters can be specified as a series of key/value tuples.

ws.url(url).withQueryString("paramKey" -> "paramValue").get()

§Request with additional headers

Headers can be specified as a series of key/value tuples.

ws.url(url).withHeaders("headerKey" -> "headerValue").get()

If you are sending plain text in a particular format, you may want to define the content type explicitly.

ws.url(url).withHeaders("Content-Type" -> "application/xml").post(xmlString)

§Request with virtual host

A virtual host can be specified as a string.

ws.url(url).withVirtualHost("192.168.1.1").get()

§Request with timeout

If you wish to specify a request timeout, you can use withRequestTimeout to set a value. An infinite timeout can be set by passing Duration.Inf.

ws.url(url).withRequestTimeout(5000.millis).get()

§Submitting form data

To post url-form-encoded data a Map[String, Seq[String]] needs to be passed into post.

ws.url(url).post(Map("key" -> Seq("value")))

§Submitting multipart/form data

To post multipart-form-encoded data a Source[play.api.mvc.MultipartFormData.Part[Source[ByteString, Any]], Any] needs to be passed into post.

ws.url(url).post(Source.single(DataPart("key", "value")))

To upload a file you need to pass a play.api.mvc.MultipartFormData.FilePart[Source[ByteString, Any]] to the Source:

ws.url(url).post(Source(FilePart("hello", "hello.txt", Option("text/plain"), FileIO.fromFile(tmpFile)) :: DataPart("key", "value") :: List()))

§Submitting JSON data

The easiest way to post JSON data is to use the JSON library.

import play.api.libs.json._
val data = Json.obj(
  "key1" -> "value1",
  "key2" -> "value2"
)
val futureResponse: Future[WSResponse] = ws.url(url).post(data)

§Submitting XML data

The easiest way to post XML data is to use XML literals. XML literals are convenient, but not very fast. For efficiency, consider using an XML view template, or a JAXB library.

val data = <person>
  <name>Steve</name>
  <age>23</age>
</person>
val futureResponse: Future[WSResponse] = ws.url(url).post(data)

§Streaming data

It’s also possible to stream data.

For example, imagine you have executed a database query that is returning a large image, and you would like to forward that data to a different endpoint for further processing. Ideally, if you can send the data as you receive it from the database, you will reduce latency and also avoid problems resulting from loading in memory a large set of data. If your database access library supports Reactive Streams (for instance, Slick does), here is an example showing how you could implement the described behavior:

val wsResponse: Future[WSResponse] = ws.url(url)
  .withBody(StreamedBody(largeImageFromDB)).execute("PUT")

The largeImageFromDB in the code snippet above is an Akka Streams Source[ByteString, _].

§Request Filters

You can do additional processing on a WSRequest by adding a request filter. A request filter is added by extending the play.api.libs.ws.WSRequestFilter trait, and then adding it to the request with request.withRequestFilter(filter).

A sample request filter that logs the request in cURL format to SLF4J has been added in play.api.libs.ws.ahc.AhcCurlRequestLogger.

ws.url(s"http://localhost:$testServerPort")
  .withRequestFilter(AhcCurlRequestLogger())
  .withBody(Map("param1" -> Seq("value1")))
  .put(Map("key" -> Seq("value")))

will output:

curl \
  --verbose \
  --request PUT \
 --header 'Content-Type: application/x-www-form-urlencoded; charset=utf-8' \
 --data 'key=value' \
 'http://localhost:19001/

§Processing the Response

Working with the Response is easily done by mapping inside the Future.

The examples given below have some common dependencies that will be shown once here for brevity.

Whenever an operation is done on a Future, an implicit execution context must be available - this declares which thread pool the callback to the future should run in. You can inject the default Play execution context in your DI-ed class by declaring an additional dependency to ExecutionContext in the class’ constructor:

class PersonService @Inject()(implicit context: ExecutionContext) {
  // ...
}

If you are not using DI, you can still access the default Play execution context:

implicit val context = play.api.libs.concurrent.Execution.Implicits.defaultContext

The examples also use the following case class for serialization/deserialization:

case class Person(name: String, age: Int)

§Processing a response as JSON

You can process the response as a JSON object by calling response.json.

val futureResult: Future[String] = ws.url(url).get().map {
  response =>
    (response.json \ "person" \ "name").as[String]
}

The JSON library has a useful feature that will map an implicit Reads[T] directly to a class:

import play.api.libs.json._

implicit val personReads = Json.reads[Person]

val futureResult: Future[JsResult[Person]] = ws.url(url).get().map {
  response => (response.json \ "person").validate[Person]
}

§Processing a response as XML

You can process the response as an XML literal by calling response.xml.

val futureResult: Future[scala.xml.NodeSeq] = ws.url(url).get().map {
  response =>
    response.xml \ "message"
}

§Processing large responses

Calling get(), post() or execute() will cause the body of the response to be loaded into memory before the response is made available. When you are downloading a large, multi-gigabyte file, this may result in unwelcomed garbage collection or even out of memory errors.

WS lets you consume the response’s body incrementally by using an Akka Streams Sink. The stream() method on WSRequest returns a Future[StreamedResponse]. A StreamedResponse is a simple container holding together the response’s headers and body.

Here is a trivial example that uses a folding Sink to count the number of bytes returned by the response:

// Make the request
val futureResponse: Future[StreamedResponse] =
  ws.url(url).withMethod("GET").stream()

val bytesReturned: Future[Long] = futureResponse.flatMap {
  res =>
    // Count the number of bytes returned
    res.body.runWith(Sink.fold[Long, ByteString](0L){ (total, bytes) =>
      total + bytes.length
    })
}

Alternatively, you could also stream the body out to another location. For example, a file:

// Make the request
val futureResponse: Future[StreamedResponse] =
  ws.url(url).withMethod("GET").stream()

val downloadedFile: Future[File] = futureResponse.flatMap {
  res =>
    val outputStream = java.nio.file.Files.newOutputStream(file.toPath)

    // The sink that writes to the output stream
    val sink = Sink.foreach[ByteString] { bytes =>
      outputStream.write(bytes.toArray)
    }

    // materialize and run the stream
    res.body.runWith(sink).andThen {
      case result =>
        // Close the output stream whether there was an error or not
        outputStream.close()
        // Get the result or rethrow the error
        result.get
    }.map(_ => file)
}

Another common destination for response bodies is to stream them back from a controller’s Action:

def downloadFile = Action.async {

  // Make the request
  ws.url(url).withMethod("GET").stream().map {
    case StreamedResponse(response, body) =>

      // Check that the response was successful
      if (response.status == 200) {

        // Get the content type
        val contentType = response.headers.get("Content-Type").flatMap(_.headOption)
          .getOrElse("application/octet-stream")

        // If there's a content length, send that, otherwise return the body chunked
        response.headers.get("Content-Length") match {
          case Some(Seq(length)) =>
            Ok.sendEntity(HttpEntity.Streamed(body, Some(length.toLong), Some(contentType)))
          case _ =>
            Ok.chunked(body).as(contentType)
        }
      } else {
        BadGateway
      }
  }
}

As you may have noticed, before calling stream() we need to set the HTTP method to use by calling withMethod on the request. Here follows another example that uses PUT instead of GET:

val futureResponse: Future[StreamedResponse] =
  ws.url(url).withMethod("PUT").withBody("some body").stream()

Of course, you can use any other valid HTTP verb.

§Common Patterns and Use Cases

§Chaining WS calls

Using for comprehensions is a good way to chain WS calls in a trusted environment. You should use for comprehensions together with Future.recover to handle possible failure.

val futureResponse: Future[WSResponse] = for {
  responseOne <- ws.url(urlOne).get()
  responseTwo <- ws.url(responseOne.body).get()
  responseThree <- ws.url(responseTwo.body).get()
} yield responseThree

futureResponse.recover {
  case e: Exception =>
    val exceptionData = Map("error" -> Seq(e.getMessage))
    ws.url(exceptionUrl).post(exceptionData)
}

§Using in a controller

When making a request from a controller, you can map the response to a Future[Result]. This can be used in combination with Play’s Action.async action builder, as described in Handling Asynchronous Results.

def wsAction = Action.async {
  ws.url(url).get().map { response =>
    Ok(response.body)
  }
}
status(wsAction(FakeRequest())) must_== OK

§Using WSClient with Future Timeout

If a chain of WS calls does not complete in time, it may be useful to wrap the result in a timeout block, which will return a failed Future if the chain does not complete in time. The best way to do this is with Play’s non-blocking Timeout feature, using play.api.libs.concurrent.Timeout.

§Directly creating WSClient

We recommend that you get your WSClient instances using dependency injection as described above. WSClient instances created through dependency injection are simpler to use because they are automatically created when the application starts and cleaned up when the application stops.

However, if you choose, you can instantiate a WSClient directly from code and use this for making requests or for configuring underlying AsyncHttpClient options. If you create a WSClient manually then you must call client.close() to clean it up when you’ve finished with it. Each client creates its own thread pool. If you fail to close the client or if you create too many clients then you will run out of threads or file handles -— you’ll get errors like “Unable to create new native thread” or “too many open files” as the underlying resources are consumed.

import com.typesafe.config.ConfigFactory
import play.api._
import play.api.libs.ws._

val configuration = Configuration.reference ++ Configuration(ConfigFactory.parseString(
  """
    |ws.followRedirects = true
  """.stripMargin))

// If running in Play, environment should be injected
val environment = Environment(new File("."), this.getClass.getClassLoader, Mode.Prod)

val parser = new WSConfigParser(configuration, environment)
val config = new AhcWSClientConfig(wsClientConfig = parser.parse())
val builder = new AhcConfigBuilder(config)
val logging = new AsyncHttpClientConfig.AdditionalChannelInitializer() {
  override def initChannel(channel: io.netty.channel.Channel): Unit = {
    channel.pipeline.addFirst("log", new io.netty.handler.logging.LoggingHandler("debug"))
  }
}
val ahcBuilder = builder.configure()
ahcBuilder.setHttpAdditionalChannelInitializer(logging)
val ahcConfig = ahcBuilder.build()
val wsClient = AhcWSClient(ahcConfig)

You can also use play.api.test.WsTestClient.withTestClient to create an instance of WSClient in a functional test. See ScalaTestingWebServiceClients for more details.

Or, you can run the WSClient completely standalone without involving a running Play application at all:

import akka.actor.ActorSystem
import akka.stream.ActorMaterializer
import play.api.libs.ws._
import play.api.libs.ws.ahc.AhcWSClient

import scala.concurrent.Future

object Main {
  import scala.concurrent.ExecutionContext.Implicits._

  def main(args: Array[String]): Unit = {
    implicit val system = ActorSystem()
    implicit val materializer = ActorMaterializer()
    val wsClient = AhcWSClient()

    call(wsClient)
      .andThen { case _ => wsClient.close() }
      .andThen { case _ => system.terminate() }
  }

  def call(wsClient: WSClient): Future[Unit] = {
    wsClient.url("http://www.google.com").get().map { response =>
      val statusText: String = response.statusText
      println(s"Got a response $statusText")
    }
  }
}

Again, once you are done with your custom client work, you must close the client:

wsClient.close()

Ideally, you should close a client after you know all requests have been completed. Be careful of using an automatic resource management pattern to close the client, because WSClient logic is asynchronous and many ARM solutions may be designed for a single threaded synchronous solution.

§Accessing AsyncHttpClient

You can get access to the underlying AsyncHttpClient from a WSClient.

import org.asynchttpclient.AsyncHttpClient

val client: AsyncHttpClient = ws.underlying

This is important in a couple of cases. WS has a couple of limitations that require access to the underlying client:

§Configuring WS

Use the following properties in application.conf to configure the WS client:

§Configuring WS with SSL

To configure WS for use with HTTP over SSL/TLS (HTTPS), please see Configuring WS SSL.

§Configuring Timeouts

There are 3 different timeouts in WS. Reaching a timeout causes the WS request to interrupt.

The request timeout can be overridden for a specific connection with withRequestTimeout() (see “Making a Request” section).

§Configuring AsyncHttpClientConfig

The following advanced settings can be configured on the underlying AsyncHttpClientConfig.

Please refer to the AsyncHttpClientConfig Documentation for more information.

Note: allowPoolingConnection and allowSslConnectionPool are combined in AsyncHttpClient 2.0 into a single keepAlive variable. As such, play.ws.ning.allowPoolingConnection and play.ws.ning.allowSslConnectionPool are not valid and will throw an exception if configured.

Next: Connecting to OpenID services

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