UDP

The UDP connector provides Akka Stream flows that allow for sending and receiving UDP datagrams.

Artifacts

The Akka dependencies are available from Akka’s library repository. To access them there, you need to configure the URL for this repository.

sbt

resolvers += "Akka library repository".at("https://repo.akka.io/maven")

Maven

<project>
  ...
  <repositories>
    <repository>
      <id>akka-repository</id>
      <name>Akka library repository</name>
      <url>https://repo.akka.io/maven</url>
    </repository>
  </repositories>
</project>

Gradle

repositories {
    mavenCentral()
    maven {
        url "https://repo.akka.io/maven"
    }
}

Additionally, add the dependencies as below.

sbt

val AkkaVersion = "2.10.0"
libraryDependencies ++= Seq(
  "com.lightbend.akka" %% "akka-stream-alpakka-udp" % "9.0.1",
  "com.typesafe.akka" %% "akka-stream" % AkkaVersion
)

Maven

<properties>
  <akka.version>2.10.0</akka.version>
  <scala.binary.version>2.13</scala.binary.version>
</properties>
<dependencies>
  <dependency>
    <groupId>com.lightbend.akka</groupId>
    <artifactId>akka-stream-alpakka-udp_${scala.binary.version}</artifactId>
    <version>9.0.1</version>
  </dependency>
  <dependency>
    <groupId>com.typesafe.akka</groupId>
    <artifactId>akka-stream_${scala.binary.version}</artifactId>
    <version>${akka.version}</version>
  </dependency>
</dependencies>

Gradle

def versions = [
  AkkaVersion: "2.10.0",
  ScalaBinary: "2.13"
]
dependencies {
  implementation "com.lightbend.akka:akka-stream-alpakka-udp_${versions.ScalaBinary}:9.0.1"
  implementation "com.typesafe.akka:akka-stream_${versions.ScalaBinary}:${versions.AkkaVersion}"
}

The table below shows direct dependencies of this module and the second tab shows all libraries it depends on transitively.

Direct dependencies

Organization	Artifact	Version
com.typesafe.akka	akka-stream_2.13	2.10.0
org.scala-lang	scala-library	2.13.12

Dependency tree

com.typesafe.akka    akka-stream_2.13    2.10.0    BUSL-1.1
    com.typesafe.akka    akka-actor_2.13    2.10.0    BUSL-1.1
        com.typesafe    config    1.4.3    Apache-2.0
        org.scala-lang    scala-library    2.13.12    Apache-2.0
    com.typesafe.akka    akka-protobuf-v3_2.13    2.10.0    BUSL-1.1
    org.reactivestreams    reactive-streams    1.0.4    MIT-0
    org.scala-lang    scala-library    2.13.12    Apache-2.0
org.scala-lang    scala-library    2.13.12    Apache-2.0

Sending

Datagrams can be sent to remote destinations by using a Udp.sendFlow or Udp.sendSink which can be found in the UdpUdp factory object.

Scala

copysource  val destination = new InetSocketAddress("my.server", 27015)
val messagesToSend = 100

Source(1 to messagesToSend)
  .map(i => ByteString(s"Message $i"))
  .map(Datagram(_, destination))
  .runWith(Udp.sendSink())

Java

copysource  final InetSocketAddress destination = new InetSocketAddress("my.server", 27015);
final Integer messagesToSend = 100;

Source.range(1, messagesToSend)
    .map(i -> ByteString.fromString("Message " + i))
    .map(bs -> Datagram.create(bs, destination))
    .runWith(Udp.sendSink(system), system);

Receiving

First create an address which will be used to bind and listen for incoming datagrams.

Scala

copysourceval bindToLocal = new InetSocketAddress("localhost", 0)

Java

copysourcefinal InetSocketAddress bindToLocal = new InetSocketAddress("localhost", 0);

A Flow created from Udp.bindFlow will bind to the given address. All datagrams coming from the network to the bound address will be sent downstream. Datagrams received from the upstream will be sent to their corresponding destination addresses.

The flow materializes to the Future[InetSocketAddress]CompletionStage<InetSocketAddress> which will eventually hold the address the flow was finally bound to.

Scala

copysourceval bindFlow: Flow[Datagram, Datagram, Future[InetSocketAddress]] =
  Udp.bindFlow(bindToLocal)

Java

copysourcefinal Flow<Datagram, Datagram, CompletionStage<InetSocketAddress>> bindFlow =
    Udp.bindFlow(bindToLocal, system);

Running the example code

The code in this guide is part of runnable tests of this project. You are welcome to browse the code, edit and run it in sbt.

Scala

sbt
> udp/testOnly *.UdpSpec

Java

sbt
> udp/testOnly *.UdpTest