13 files changed, 783 insertions, 0 deletions
diff --git a/same/src/main/java/com/orbekk/net/BroadcastListener.java b/same/src/main/java/com/orbekk/net/BroadcastListener.java
new file mode 100644
index 0000000..c0b66e0
--- /dev/null
+++ b/same/src/main/java/com/orbekk/net/BroadcastListener.java
@@ -0,0 +1,53 @@
+package com.orbekk.net;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.SocketException;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class BroadcastListener {
+    private int port;
+    private Logger logger = LoggerFactory.getLogger(getClass());
+    
+    public BroadcastListener(int port) {
+        this.port = port;
+    }
+    
+    public DatagramPacket listen() {
+        logger.debug("Waiting for broadcast on port " + port);
+        DatagramSocket socket;
+        try {
+            socket = new DatagramSocket(port);
+        } catch (SocketException e) {
+            logger.warn("Failed to create socket.", e.fillInStackTrace());
+            return null;
+        }
+        try {
+            socket.setBroadcast(true);
+        } catch (SocketException e) {
+            logger.warn("Exception: {}", e);
+        }
+        byte[] buffer = new byte[2048];
+        DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
+        try {
+            socket.receive(packet);
+        } catch (IOException e) {
+            logger.warn("Exception when listening for broadcast: {}", e);
+            return null;
+        }
+        
+        String address = packet.getAddress().getHostAddress();
+        logger.debug("Received broadcast from " + address +
+                ": " + new String(packet.getData()));
+        return packet;
+    }
+    
+    public static void main(String[] args) {
+        int port = Integer.parseInt(args[0]);
+        BroadcastListener listener = new BroadcastListener(port);
+        System.out.println("Received broadcast: " + listener.listen());
+    }
+}
diff --git a/same/src/main/java/com/orbekk/net/Broadcaster.java b/same/src/main/java/com/orbekk/net/Broadcaster.java
new file mode 100644
index 0000000..95e279c
--- /dev/null
+++ b/same/src/main/java/com/orbekk/net/Broadcaster.java
@@ -0,0 +1,77 @@
+package com.orbekk.net;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.InterfaceAddress;
+import java.net.NetworkInterface;
+import java.net.SocketException;
+import java.util.Enumeration;
+import java.util.LinkedList;
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public class Broadcaster {
+    private Logger logger = LoggerFactory.getLogger(getClass());
+    
+    public List<InetAddress> getBroadcastAddresses() {
+        List<InetAddress> broadcastAddresses = new LinkedList<InetAddress>();
+        
+        Enumeration<NetworkInterface> interfaces;
+        try {
+            interfaces = NetworkInterface.getNetworkInterfaces();
+        } catch (SocketException e) {
+            logger.warn("Network problem?", e.fillInStackTrace());
+            return broadcastAddresses;
+        }
+        while (interfaces.hasMoreElements()) {
+            NetworkInterface iface = interfaces.nextElement();
+            try {
+                if (iface.isLoopback()) {
+                    logger.debug("Ignoring looback device " + iface.getName());
+                    continue;
+                }
+                for (InterfaceAddress address : iface.getInterfaceAddresses()) {
+                    InetAddress broadcast = address.getBroadcast();
+                    if (broadcast != null) {
+                        broadcastAddresses.add(broadcast);
+                    }
+                }
+            } catch (SocketException e) {
+                logger.info("Ignoring interface " + iface.getName(), e.fillInStackTrace());
+            }
+        }
+        return broadcastAddresses;
+    }
+
+    public boolean sendBroadcast(int port, byte[] data) {
+        boolean successful = false;
+        for (InetAddress broadcastAddress : getBroadcastAddresses()) {
+            try {
+                DatagramSocket socket = new DatagramSocket();
+                socket.setBroadcast(true);
+                DatagramPacket packet = new DatagramPacket(data, data.length, broadcastAddress, port);
+                socket.send(packet);
+                successful = true;
+            } catch (SocketException e) {
+                logger.warn("Failed to send broadcast to " + broadcastAddress +
+                        ". ", e.fillInStackTrace());
+            } catch (IOException e) {
+                logger.warn("Error when sending broadcast to " +
+                        broadcastAddress + ".", e.fillInStackTrace());
+            }
+        }
+        return successful;
+    }
+    
+    public static void main(String[] args) {
+        int port = Integer.parseInt(args[0]);
+        Broadcaster broadcaster = new Broadcaster();
+        String message = "Broadcast from Java broadcaster.";
+        broadcaster.sendBroadcast(port, message.getBytes());
+    }
+}
diff --git a/same/src/main/java/com/orbekk/net/HttpUtil.java b/same/src/main/java/com/orbekk/net/HttpUtil.java
new file mode 100644
index 0000000..b4bb887
--- /dev/null
+++ b/same/src/main/java/com/orbekk/net/HttpUtil.java
@@ -0,0 +1,26 @@
+package com.orbekk.net;
+
+import java.io.IOException;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLConnection;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class HttpUtil {
+    private static final Logger logger =
+            LoggerFactory.getLogger(HttpUtil.class);
+
+    public static void sendHttpRequest(String url) {
+        try {
+            URL pingUrl = new URL(url);
+            pingUrl.openStream();
+            // URLConnection connection = pingUrl.openConnection();
+            // connection.connect();
+        } catch (MalformedURLException e) {
+            logger.warn("Unable to send ping to {}: {}.", url, e);
+        } catch (IOException e) {
+            logger.warn("Error when sending ping: {}", e);
+        }
+    }
+}
diff --git a/same/src/main/java/com/orbekk/rpc/App.java b/same/src/main/java/com/orbekk/rpc/App.java
new file mode 100644
index 0000000..0e9dce3
--- /dev/null
+++ b/same/src/main/java/com/orbekk/rpc/App.java
@@ -0,0 +1,47 @@
+package com.orbekk.rpc;
+
+import com.googlecode.jsonrpc4j.JsonRpcServer;
+import com.orbekk.same.ConnectionManagerImpl;
+import com.orbekk.same.SameState;
+import com.orbekk.same.SameService;
+import com.orbekk.same.SameServiceImpl;
+import org.eclipse.jetty.server.Server;
+
+public class App {
+    public static void main(String[] args) {
+        if (args.length < 3) {
+            System.err.println("Arguments: port networkName clientId");
+            System.exit(1);
+        }
+        int port = Integer.parseInt(args[0]);
+        String networkName = args[1];
+        String clientId = args[2];
+
+        ConnectionManagerImpl connections = new ConnectionManagerImpl();
+
+        SameState sameState = new SameState(networkName, clientId,
+                connections);
+        sameState.start();
+
+        SameServiceImpl service = new SameServiceImpl(sameState);
+        JsonRpcServer jsonServer = new JsonRpcServer(service,
+                SameService.class);   
+    
+        Server server = new Server(port);
+        RpcHandler rpcHandler = new RpcHandler(jsonServer, sameState);
+        server.setHandler(rpcHandler);
+
+        try {
+            server.start();
+        } catch (Exception e) {
+            System.out.println("Could not start jetty server.");
+            e.printStackTrace();
+        }
+        
+        try {
+            server.join();
+        } catch (InterruptedException e) {
+            System.out.println("Interrupt");
+        }
+    }
+}
diff --git a/same/src/main/java/com/orbekk/rpc/Client.java b/same/src/main/java/com/orbekk/rpc/Client.java
new file mode 100644
index 0000000..225347a
--- /dev/null
+++ b/same/src/main/java/com/orbekk/rpc/Client.java
@@ -0,0 +1,66 @@
+package com.orbekk.rpc;
+
+import com.googlecode.jsonrpc4j.JsonRpcServer;
+import com.orbekk.same.ConnectionManagerImpl;
+import com.orbekk.same.SameState;
+import com.orbekk.same.SameService;
+import com.orbekk.same.SameServiceImpl;
+import com.orbekk.net.HttpUtil;
+import org.eclipse.jetty.server.Server;
+
+public class Client {
+    
+    public static void main(String[] args) {
+        if (args.length < 4) {
+            System.err.println("Arguments: port clientId thisNetworkName " +
+                    "remoteNetworkAddr");
+            System.exit(1);
+        }
+        int port = Integer.parseInt(args[0]);
+        String clientId = args[1];
+        String networkName = args[2];
+        String remoteAddr = args[3];
+
+        ConnectionManagerImpl connections = new ConnectionManagerImpl();
+
+        SameState sameState = new SameState(networkName, clientId,
+                connections);
+        sameState.start();
+
+        SameServiceImpl service = new SameServiceImpl(sameState);
+        JsonRpcServer jsonServer = new JsonRpcServer(service,
+                SameService.class);   
+    
+        Server server = new Server(port);
+        RpcHandler rpcHandler = new RpcHandler(jsonServer, sameState);
+        server.setHandler(rpcHandler);
+
+        try {
+            server.start();
+        } catch (Exception e) {
+            System.out.println("Could not start jetty server.");
+            e.printStackTrace();
+        }
+
+        while (sameState.getUrl() == null) {
+            HttpUtil.sendHttpRequest(remoteAddr + "ping?port=" + port);
+            try {
+                Thread.sleep(500);
+            } catch (InterruptedException e) {
+                // Ignore interrupt in wait loop.
+            }
+        }
+        
+        SameService remoteService = connections.getConnection(remoteAddr);
+        remoteService.notifyNetwork("NoNetwork");
+        remoteService.participateNetwork("FirstNetwork",
+                sameState.getClientId(), sameState.getUrl());
+
+        try {
+            server.join();
+        } catch (InterruptedException e) {
+            System.out.println("Interrupt");
+        }
+
+    }
+}
diff --git a/same/src/main/java/com/orbekk/rpc/RpcHandler.java b/same/src/main/java/com/orbekk/rpc/RpcHandler.java
new file mode 100644
index 0000000..0bafad4
--- /dev/null
+++ b/same/src/main/java/com/orbekk/rpc/RpcHandler.java
@@ -0,0 +1,52 @@
+package com.orbekk.rpc;
+
+import com.googlecode.jsonrpc4j.JsonRpcServer;
+import com.orbekk.net.HttpUtil;
+import com.orbekk.same.UrlReceiver;
+import java.io.IOException;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.eclipse.jetty.server.Request;
+import org.eclipse.jetty.server.handler.AbstractHandler;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class RpcHandler extends AbstractHandler {
+    private Logger logger = LoggerFactory.getLogger(getClass());
+    private JsonRpcServer rpcServer;
+    private UrlReceiver urlReceiver;
+    
+    public RpcHandler(JsonRpcServer rpcServer,
+            UrlReceiver urlReceiver) {
+        this.rpcServer = rpcServer;
+        this.urlReceiver = urlReceiver;
+    }
+    
+    @Override
+    public synchronized void handle(String target, Request baseRequest,
+            HttpServletRequest request, HttpServletResponse response)
+            throws IOException, ServletException {
+        logger.info("Handling request to target: " + target);
+
+        if (urlReceiver != null) {
+            String sameServiceUrl = "http://" + request.getLocalAddr() + 
+                ":" + request.getLocalPort() + "/SameService.json";
+            urlReceiver.setUrl(sameServiceUrl);
+            urlReceiver = null;
+        }
+
+        if (target.equals("/ping")) {
+            int remotePort = Integer.parseInt(request.getParameter("port"));
+            String pongUrl = "http://" + request.getRemoteAddr() + ":" +
+                remotePort + "/pong";
+            logger.info("Got ping. Sending pong to {}", pongUrl);
+            HttpUtil.sendHttpRequest(pongUrl);
+        } else if (target.equals("/pong")) {
+            logger.info("Received pong from {}", request.getRemoteAddr());
+        } else {
+            rpcServer.handle(request, response);
+        }
+        baseRequest.setHandled(true);
+    }
+}
diff --git a/same/src/main/java/com/orbekk/same/ConnectionManager.java b/same/src/main/java/com/orbekk/same/ConnectionManager.java
new file mode 100644
index 0000000..985f6f0
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/ConnectionManager.java
@@ -0,0 +1,10 @@
+package com.orbekk.same;
+
+/**
+ * An interface that returns a connection for a participant.
+ *
+ * When testing, this interface can be mocked to use local participants only.
+ */
+public interface ConnectionManager {
+    SameService getConnection(String url);
+}
diff --git a/same/src/main/java/com/orbekk/same/ConnectionManagerImpl.java b/same/src/main/java/com/orbekk/same/ConnectionManagerImpl.java
new file mode 100644
index 0000000..841d5fa
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/ConnectionManagerImpl.java
@@ -0,0 +1,31 @@
+package com.orbekk.same;
+
+import com.googlecode.jsonrpc4j.JsonRpcHttpClient;
+import com.googlecode.jsonrpc4j.ProxyUtil;
+import java.net.MalformedURLException;
+import java.net.URL;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class ConnectionManagerImpl implements ConnectionManager {
+
+    private Logger logger = LoggerFactory.getLogger(getClass());
+
+    public ConnectionManagerImpl() {
+    }
+
+    @Override
+    public SameService getConnection(String url) {
+        SameService service = null;
+        try {
+            JsonRpcHttpClient client = new JsonRpcHttpClient(new URL(url));
+            service = ProxyUtil.createProxy(
+                    this.getClass().getClassLoader(),
+                    SameService.class,
+                    client);
+        } catch (MalformedURLException e) {
+            logger.warn("Unable to create client for {}, {}", url, e);
+        }
+        return service;
+    }
+}
diff --git a/same/src/main/java/com/orbekk/same/SameService.java b/same/src/main/java/com/orbekk/same/SameService.java
new file mode 100644
index 0000000..8f239da
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/SameService.java
@@ -0,0 +1,40 @@
+package com.orbekk.same;
+
+import java.util.Map;
+
+public interface SameService {
+    /**
+     * A notification that 'networkName' exists.
+     *
+     * This is called by any participant of a network after a broadcast
+     * has been performed.
+     */
+    void notifyNetwork(String networkName);
+
+    /**
+     * A request from the callee to participate in 'networkName'.
+     */
+    void participateNetwork(String networkName, String clientId, String url);
+
+    /**
+     * Notification of participation in network.
+     */
+    void notifyParticipation(String networkName, String masterId);
+
+    /**
+     * New state.
+     * 
+     * When sent to a non-master from the master, use 'newState' as the
+     * current state.
+     *
+     * When sent to a master, broadcast the new state to all clients.
+     */
+    void setState(String newState);
+
+    /**
+     * Notify all nodes of network participants.
+     *
+     * Only sent from master to non-master.
+     */
+    void setParticipants(Map<String, String> participants);
+}
diff --git a/same/src/main/java/com/orbekk/same/SameServiceImpl.java b/same/src/main/java/com/orbekk/same/SameServiceImpl.java
new file mode 100644
index 0000000..27579b5
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/SameServiceImpl.java
@@ -0,0 +1,60 @@
+package com.orbekk.same;
+
+import java.util.Map;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class SameServiceImpl implements SameService {
+    private Logger logger = LoggerFactory.getLogger(getClass());
+    private SameState sameState;
+
+    public SameServiceImpl(SameState sameState) {
+        this.sameState = sameState;
+    }
+
+    @Override
+    public void notifyNetwork(String networkName) {
+        logger.info("Notification from network " + networkName);
+    }
+
+    @Override
+    public void participateNetwork(String networkName, String clientId,
+            String url) {
+        if (!networkName.equals(sameState.getNetworkName())) {
+            logger.warn("Client tried to join {}, but network name is {}.",
+                    networkName, sameState.getNetworkName());
+            return;
+        }
+        if (clientId.equals("") || url.equals("")) {
+            logger.warn("Missing client info: ClientId({}), URL({}).",
+                    clientId, url);
+            return;
+        }
+        sameState.addParticipant(clientId, url);
+    }
+
+    @Override
+    public void notifyParticipation(String networkName, String masterId) {
+        logger.info("Joining network {}. Master is {}", networkName, masterId);
+        // int i = 1;
+        // for (Map.Entry<String, String> e : participants.entrySet()) {
+        //     String clientId = e.getKey();
+        //     String url = e.getValue();
+        //     logger.info("  {} participant {}: {}, {}",
+        //             new Object[]{networkName, i, clientId, url});
+        //     i++;
+        // }
+        sameState.joinNetwork(networkName, masterId);
+    }
+
+    @Override
+    public void setParticipants(Map<String, String> participants) {
+        sameState.setParticipants(participants);
+    }
+
+    @Override
+    public void setState(String newState) {
+        sameState.setState(newState);
+    }
+}
diff --git a/same/src/main/java/com/orbekk/same/SameState.java b/same/src/main/java/com/orbekk/same/SameState.java
new file mode 100644
index 0000000..c9cd216
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/SameState.java
@@ -0,0 +1,233 @@
+package com.orbekk.same;
+
+import java.util.List;
+import java.util.LinkedList;
+import java.util.Map;
+import java.util.HashMap;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The implementation of a 'Same' state.
+ *
+ * This class manages the current state of the Same protocol.
+ */
+public class SameState extends Thread implements UrlReceiver {
+    private Logger logger = LoggerFactory.getLogger(getClass());
+    private ConnectionManager connections;
+
+    // TODO: Change the name of State.
+    private com.orbekk.same.State state =
+            new com.orbekk.same.State();
+
+    /**
+     * The client id of this participant.
+     */
+    private String clientId;
+
+    /**
+     * Stopping condition for this thread.
+     */
+    private boolean stopped = false;
+
+    private String _setState = null;
+    private Map<String, String> _setParticipants = null;
+
+    private Map<String, String> pendingParticipants =
+            new HashMap<String, String>();
+
+    public SameState(String networkName, String clientId,
+            ConnectionManager connections) {
+        state.setNetworkName(networkName);
+        this.clientId = clientId;
+        this.connections = connections;
+        state.setMasterId(clientId);
+        state.getParticipants().put(clientId, null);
+    }
+
+    public String getMasterId() {
+        return state.getMasterId();
+    }
+
+    public synchronized Map<String, String> getParticipants() {
+        return state.getParticipants();
+    }
+
+    /**
+     * Reset this SameService to an initial state.
+     *
+     * TODO: Implement fully.
+     */
+    private synchronized void resetState() {
+        state = new com.orbekk.same.State();
+        pendingParticipants.clear();
+    }
+
+    public synchronized void joinNetwork(String networkName, String masterId) {
+        resetState();
+        state.setNetworkName(networkName);
+        state.setMasterId(masterId);
+        logger.info("Joined network {}.", networkName);
+    }
+
+    public String getClientId() {
+        return clientId;
+    }
+
+    public String getNetworkName() {
+        return state.getNetworkName();
+    }
+
+    public String getCurrentState() {
+        return state.getData();
+    }
+
+    /**
+     * TODO: Move to a separate library.
+     */
+    public void librarySetNewState(String newState) {
+        connections.getConnection(
+                state.getParticipants().get(state.getMasterId()))
+                .setState(newState);
+    }
+
+    public String getUrl() {
+        return state.getParticipants().get(clientId);
+    }
+
+    @Override
+    public void setUrl(String url) {
+        logger.info("My URL is {}", url);
+        state.getParticipants().put(clientId, url);
+    }
+
+    public synchronized void addParticipant(String clientId, String url) {
+        logger.info("PendingParticipant.add: {} ({})", clientId, url);
+        pendingParticipants.put(clientId, url);
+        notifyAll();
+    }
+
+    public synchronized void setParticipants(Map<String, String> participants) {
+        logger.info("Pending operation: _setParticipants");
+        _setParticipants = participants;
+        notifyAll();
+    }
+
+    public synchronized void setState(String newState) {
+        logger.info("Pending operation: _setState");
+        _setState = newState;
+        notifyAll();
+    }
+
+    private synchronized void handleSetParticipants() {
+        if (_setParticipants != null) {
+            if (isMaster()) {
+                logger.error("{}: Master received setParticipants.", clientId);
+            } else {
+                logger.info("{}: New participants committed.", clientId);
+                state.getParticipants().clear();
+                state.getParticipants().putAll(_setParticipants);
+            }
+        }
+        _setParticipants = null;
+    }
+
+    public synchronized void handleSetState() {
+        if (_setState != null) {
+            if (isMaster()) {
+                broadcast(new ServiceOperation() {
+                    @Override void run(SameService service) {
+                        service.setState(_setState);
+                    }
+                });
+            }
+            state.setData(_setState);
+            _setState = null;
+        }
+    }
+
+    private boolean isMaster() {
+        return state.getMasterId().equals(clientId);
+    }
+
+    private synchronized void handleNewParticipants() {
+        if (!isMaster()) {
+            for (Map.Entry<String, String> e : pendingParticipants.entrySet()) {
+                SameService master = connections.getConnection(
+                        state.getParticipants().get(state.getMasterId()));
+                logger.info("Redirecting participant request to {}",
+                        state.getMasterId());
+                String clientId = e.getKey();
+                String url = e.getValue();
+                master.participateNetwork(state.getNetworkName(), clientId,
+                        url);
+            }
+        } else {
+            state.getParticipants().putAll(pendingParticipants);
+            for (Map.Entry<String, String> e :
+                    pendingParticipants.entrySet()) {
+                String clientId = e.getKey();
+                String url = e.getValue();
+                logger.info("New participant: {} URL({})", clientId, url);
+                SameService remoteService = connections.getConnection(url);
+                remoteService.notifyParticipation(state.getNetworkName(),
+                        state.getMasterId());
+                broadcast(new ServiceOperation(){
+                    @Override void run(SameService service) {
+                        service.setParticipants(state.getParticipants());
+                    }
+                });
+            }
+        }
+        pendingParticipants.clear();
+    }
+
+    /**
+     * This method runs the pending commands to SameState.
+     *
+     * It should be called by the worker thread, but can be called directly
+     * for testing purposes to avoid threading in unit tests.
+     */
+    synchronized void internalRun() {
+        handleNewParticipants();
+        handleSetState();
+        handleSetParticipants();
+    }
+
+    public synchronized void run() {
+        while (!stopped) {
+            internalRun();
+            try {
+                wait(1000);
+            } catch (InterruptedException e) {
+                // Ignore interrupt in wait loop.
+            }
+        }
+    }
+
+    public synchronized void stopSame() {
+        try {
+            stopped = true;
+            notifyAll();
+            this.join();
+        } catch (InterruptedException e) {
+            logger.warn("Got InterruptedException while waiting for SameState " +
+                    "to finish. Ignoring.");
+        }
+    }
+
+    public abstract static class ServiceOperation {
+        abstract void run(SameService service);
+    }
+    
+    public synchronized void broadcast(ServiceOperation operation) {
+        for (Map.Entry<String, String> e :
+                state.getParticipants().entrySet()) {
+            String clientId = e.getKey();
+            String url = e.getValue();
+            if (!clientId.equals(this.clientId)) {
+                operation.run(connections.getConnection(url));
+            }
+        }
+    }
+}
diff --git a/same/src/main/java/com/orbekk/same/State.java b/same/src/main/java/com/orbekk/same/State.java
new file mode 100644
index 0000000..70ffa83
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/State.java
@@ -0,0 +1,78 @@
+package com.orbekk.same;
+
+import java.util.Map;
+import java.util.HashMap;
+
+public class State {
+    private long stateIteration = 0;
+    private Map<String, String> participants = new HashMap<String, String>();
+    private String networkName = "";
+    private String masterId = "";
+    private String data = "";
+
+    public long getStateIteration() {
+        return stateIteration;
+    }
+
+    public void setStateIteration(long stateIteration) {
+        this.stateIteration = stateIteration;
+    }
+
+    public Map<String, String> getParticipants() {
+        return participants;
+    }
+
+    public String getNetworkName() {
+        return networkName;
+    }
+
+    public void setNetworkName(String networkName) {
+        this.networkName = networkName;
+    }
+
+    public String getMasterId() {
+        return masterId;
+    }
+
+    public void setMasterId(String masterId) {
+        this.masterId = masterId;
+    }
+
+    public String getData() {
+        return data;
+    }
+
+    public void setData(String data) {
+        this.data = data;
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder participantsString = new StringBuilder();
+        participantsString.append("[");
+        boolean first = true;
+        for (Map.Entry<String, String> e : participants.entrySet()) {
+            if (!first) {
+                participantsString.append(", ");
+            }
+            first = false;
+            participantsString.append(e.getKey())
+                    .append("(")
+                    .append(e.getValue())
+                    .append(")");
+            String clientId = e.getKey();
+            String url = e.getValue();
+        }
+        participantsString.append("]");
+
+        return String.format(
+            "State( \n" +
+            "      stateIteration = %d,\n" +
+            "      networkName    = %s,\n" +
+            "      masterId       = %s,\n" +
+            "      data           = %s,\n" +
+            "      participants   = %s\n" +
+            ")", stateIteration, networkName, masterId, data,
+            participantsString);
+    }
+}
diff --git a/same/src/main/java/com/orbekk/same/UrlReceiver.java b/same/src/main/java/com/orbekk/same/UrlReceiver.java
new file mode 100644
index 0000000..31a0276
--- /dev/null
+++ b/same/src/main/java/com/orbekk/same/UrlReceiver.java
@@ -0,0 +1,10 @@
+package com.orbekk.same;
+
+/**
+ * An interface to get notified of the URL to this computer.
+ *
+ * This interface is used to reliably obtain the URL of this host.
+ */
+public interface UrlReceiver {
+    void setUrl(String url);
+}