Akka I/O

The I/O extension provides an non-blocking, event driven API that matches the underlying transports mechanism.

Getting Started

Every I/O Driver has a special actor, called the manager, that serves as an entry point for the API. The manager for a particular driver is accessible through an extension method on ActorSystem. The following example shows how to get a reference to the TCP manager.

using Akka.Actor;
using Akka.IO;

...

var system = ActorSystem.Create("example");
var manager = system.Tcp();

TCP Driver

Client Connection

To create a connection an actor sends a Tcp.Connect message to the TCP Manager. Once the connection is established the connection actor sends a Tcp.Connected message to the commander, which registers the connection handler by replying with a Tcp.Register message.

Once this handshake is completed, the handler and connection communicate with Tcp.WriteCommand and Tcp.Received messages.

The following diagram illustrate the actors involved in establishing and handling a connection.

The following example shows a simple Telnet client. The client send lines entered in the console to the TCP connection, and write data received from the network to the console.

public class TelnetClient : UntypedActor
{
    public TelnetClient(string host, int port)
    {
        var endpoint = new DnsEndPoint(host, port);
        Context.System.Tcp().Tell(new Tcp.Connect(endpoint));
    }

    protected override void OnReceive(object message)
    {
        if (message is Tcp.Connected connected)
        {
            Console.WriteLine("Connected to {0}", connected.RemoteAddress);

            // Register self as connection handler
            Sender.Tell(new Tcp.Register(Self));
            ReadConsoleAsync();
            Become(Connected(Sender));
        }
        else if (message is Tcp.CommandFailed)
        {
            Console.WriteLine("Connection failed");
        }
        else Unhandled(message);
    }

    private UntypedReceive Connected(IActorRef connection)
    {
        return message =>
        {
            if (message is Tcp.Received received)  // data received from network
            {
                Console.WriteLine(Encoding.ASCII.GetString(received.Data.ToArray()));
            }
            else if (message is string s)   // data received from console
            {
                connection.Tell(Tcp.Write.Create(ByteString.FromString(s + "\n")));
                ReadConsoleAsync();
            }
            else if (message is Tcp.PeerClosed)
            {
                Console.WriteLine("Connection closed");
            }
            else Unhandled(message);
        };
    }

    private void ReadConsoleAsync()
    {
        Task.Factory.StartNew(self => Console.In.ReadLineAsync().PipeTo((ICanTell)self), Self);
    }
}

Server Connection

To accept connections, an actor sends an Tcp.Bind message to the TCP manager, passing the bind handler in the message. The bind commander will receive a Tcp.Bound message when the connection is listening.

The bind handler will receive a Tcp.Connected message for each accepted connection, and needs to register the connection handler by replying with a Tcp.Register message. Thereafter it proceeds the same as a client connection.

The following diagram illustrate the actor and messages.

The following code example shows a simple server that echo's data received from the network.

public class EchoServer : UntypedActor
{
    public EchoServer(int port)
    {
        Context.System.Tcp().Tell(new Tcp.Bind(Self, new IPEndPoint(IPAddress.Any, port)));
    }

    protected override void OnReceive(object message)
    {
        if (message is Tcp.Bound bound)
        {
            Console.WriteLine("Listening on {0}", bound.LocalAddress);
        }
        else if (message is Tcp.Connected)
        {
            var connection = Context.ActorOf(Props.Create(() => new EchoConnection(Sender)));
            Sender.Tell(new Tcp.Register(connection));
        }
        else Unhandled(message);
    }
}

public class EchoConnection : UntypedActor
{
    private readonly IActorRef _connection;

    public EchoConnection(IActorRef connection)
    {
        _connection = connection;
    }

    protected override void OnReceive(object message)
    {
        if (message is Tcp.Received received)
        {
            if (received.Data[0] == 'x')
                Context.Stop(Self);
            else
                _connection.Tell(Tcp.Write.Create(received.Data));
        }
        else Unhandled(message);
    }
}