akka-docs/src/main/paradox/io-udp.md
@@@note The Akka dependencies are available from Akka’s secure library repository. To access them you need to use a secure, tokenized URL as specified at https://account.akka.io/token. @@@
To use UDP, you must add the following dependency in your project:
@@dependency[sbt,Maven,Gradle] { bomGroup=com.typesafe.akka bomArtifact=akka-bom_$scala.binary.version$ bomVersionSymbols=AkkaVersion symbol1=AkkaVersion value1="$akka.version$" group="com.typesafe.akka" artifact="akka-actor_$scala.binary.version$" version=AkkaVersion }
UDP is a connectionless datagram protocol which offers two different ways of communication on the JDK level:
In the low-level API the distinction is made—confusingly—by whether or not
connect has been called on the socket (even when connect has been
called the protocol is still connectionless). These two forms of UDP usage are
offered using distinct IO extensions described below.
Scala : @@snip UdpDocSpec.scala { #sender }
Java : @@snip UdpDocTest.java { #sender }
The simplest form of UDP usage is to just send datagrams without the need of
getting a reply. To this end a “simple sender” facility is provided as
demonstrated above. The UDP extension is queried using the
@scala[SimpleSender]@java[UdpMessage.simpleSender] message, which is answered by a SimpleSenderReady
notification. The sender of this message is the newly created sender actor
which from this point onward can be used to send datagrams to arbitrary
destinations; in this example it will send any UTF-8 encoded
String it receives to a predefined remote address.
@@@ note
The simple sender will not shut itself down because it cannot know when you are done with it. You will need to send it a @apidoc[akka.actor.PoisonPill] when you want to close the ephemeral port the sender is bound to.
@@@
Scala : @@snip UdpDocSpec.scala { #listener }
Java : @@snip UdpDocTest.java { #listener }
If you want to implement a UDP server which listens on a socket for incoming
datagrams then you need to use the @scala[@scaladocBind]@java[@javadocUdpMessage.bind] message as shown above. The
local address specified may have a zero port in which case the operating system
will automatically choose a free port and assign it to the new socket. Which
port was actually bound can be found out by inspecting the Bound
message.
The sender of the @apidoc[akka.io.Udp.Bound] message is the actor which manages the new socket. Sending datagrams is achieved by using the @scala[@scaladocSend]@java[@javadocUdpMessage.send] message and the socket can be closed by sending a @scala[@scaladocUnbind]@java[@javadocUdpMessage.unbind] message, in which case the socket actor will reply with a @apidoc[akka.io.Udp.Unbound] notification.
Received datagrams are sent to the actor designated in the Bind
message, whereas the Bound message will be sent to the sender of the
@scala[@scaladocBind]@java[@javadocUdpMessage.bind].
The service provided by the connection based UDP API is similar to the
bind-and-send service we saw earlier, but the main difference is that a
connection is only able to send to the remoteAddress it was connected to,
and will receive datagrams only from that address.
Scala : @@snip UdpDocSpec.scala { #connected }
Java : @@snip UdpDocTest.java { #connected }
Consequently the example shown here looks quite similar to the previous one,
the biggest difference is the absence of remote address information in
@scala[Send]@java[UdpMessage.send] and Received messages.
@@@ note
There is a small performance benefit in using connection based UDP API over the connectionless one. If there is a SecurityManager enabled on the system, every connectionless message send has to go through a security check, while in the case of connection-based UDP the security check is cached after connect, thus writes do not suffer an additional performance penalty.
@@@
Akka provides a way to control various options of @javadocDatagramChannel through the @apidoc[akka.io.Inet.SocketOption] interface. The example below shows how to setup a receiver of multicast messages using IPv6 protocol.
To select a Protocol Family you must extend @apidoc[akka.io.Inet.DatagramChannelCreator]
class which @scala[extends]@java[implements] @apidoc[akka.io.Inet.SocketOption]. Provide custom logic
for opening a datagram channel by overriding create method.
Scala : @@snip ScalaUdpMulticast.scala { #inet6-protocol-family }
Java : @@snip JavaUdpMulticast.java { #inet6-protocol-family }
Another socket option will be needed to join a multicast group.
Scala : @@snip ScalaUdpMulticast.scala { #multicast-group }
Java : @@snip JavaUdpMulticast.java { #multicast-group }
Socket options must be provided to @scala[@scaladocBind]@java[@javadocUdpMessage.bind] message.
Scala : @@snip ScalaUdpMulticast.scala { #bind }
Java : @@snip JavaUdpMulticast.java { #bind }