package kademlia;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import java.util.Timer;
import java.util.TimerTask;
import kademlia.exceptions.KadServerDownException;
import kademlia.message.KademliaMessageFactory;
import kademlia.message.Message;
import kademlia.message.MessageFactory;
import kademlia.node.Node;
import kademlia.message.Receiver;
/**
* The server that handles sending and receiving messages between nodes on the Kad Network
*
* @author Joshua Kissoon
* @created 20140215
*/
public class KadServer
{
/* Maximum size of a Datagram Packet */
private static final int DATAGRAM_BUFFER_SIZE = 64 * 1024; // 64KB
/* Basic Kad Objects */
private final transient KadConfiguration config;
/* Server Objects */
private final DatagramSocket socket;
private transient boolean isRunning;
private final Map<Integer, Receiver> receivers;
private final Timer timer; // Schedule future tasks
private final Map<Integer, TimerTask> tasks; // Keep track of scheduled tasks
private final Node localNode;
/* Factories */
private final KademliaMessageFactory messageFactory;
private final KadStatistician statistician;
{
isRunning = true;
this.tasks = new HashMap<>();
this.receivers = new HashMap<>();
this.timer = new Timer(true);
}
/**
* Initialize our KadServer
*
* @param udpPort The port to listen on
* @param mFactory Factory used to create messages
* @param localNode Local node on which this server runs on
* @param config
* @param statistician A statistician to manage the server statistics
*
* @throws java.net.SocketException
*/
public KadServer(int udpPort, KademliaMessageFactory mFactory, Node localNode, KadConfiguration config, KadStatistician statistician) throws SocketException
{
this.config = config;
this.socket = new DatagramSocket(udpPort);
this.localNode = localNode;
this.messageFactory = mFactory;
this.statistician = statistician;
/* Start listening for incoming requests in a new thread */
this.startListener();
}
/**
* Starts the listener to listen for incoming messages
*/
private void startListener()
{
new Thread()
{
@Override
public void run()
{
listen();
}
}.start();
}
/**
* Sends a message
*
* @param msg The message to send
* @param to The node to send the message to
* @param recv The receiver to handle the response message
*
* @return Integer The communication ID of this message
*
* @throws IOException
* @throws kademlia.exceptions.KadServerDownException
*/
public synchronized int sendMessage(Node to, Message msg, Receiver recv) throws IOException, KadServerDownException
{
if (!isRunning)
{
throw new KadServerDownException(this.localNode + " - Kad Server is not running.");
}
/* Generate a random communication ID */
int comm = new Random().nextInt();
/* If we have a receiver */
if (recv != null)
{
try
{
/* Setup the receiver to handle message response */
receivers.put(comm, recv);
TimerTask task = new TimeoutTask(comm, recv);
timer.schedule(task, this.config.responseTimeout());
tasks.put(comm, task);
}
catch (IllegalStateException ex)
{
/* The timer is already cancelled so we cannot do anything here really */
}
}
/* Send the message */
sendMessage(to, msg, comm);
return comm;
}
/**
* Method called to reply to a message received
*
* @param to The Node to send the reply to
* @param msg The reply message
* @param comm The communication ID - the one received
*
* @throws java.io.IOException
*/
public synchronized void reply(Node to, Message msg, int comm) throws IOException
{
if (!isRunning)
{
throw new IllegalStateException("Kad Server is not running.");
}
sendMessage(to, msg, comm);
}
/**
* Internal sendMessage method called by the public sendMessage method after a communicationId is generated
*/
private void sendMessage(Node to, Message msg, int comm) throws IOException
{
/* Use a try-with resource to auto-close streams after usage */
try (ByteArrayOutputStream bout = new ByteArrayOutputStream(); DataOutputStream dout = new DataOutputStream(bout);)
{
/* Setup the message for transmission */
dout.writeInt(comm);
dout.writeByte(msg.code());
msg.toStream(dout);
dout.close();
byte[] data = bout.toByteArray();
if (data.length > DATAGRAM_BUFFER_SIZE)
{
throw new IOException("Message is too big");
}
/* Everything is good, now create the packet and send it */
DatagramPacket pkt = new DatagramPacket(data, 0, data.length);
pkt.setSocketAddress(to.getSocketAddress());
socket.send(pkt);
/* Lets inform the statistician that we've sent some data */
this.statistician.sentData(data.length);
}
}
/**
* Listen for incoming messages in a separate thread
*/
private void listen()
{
try
{
while (isRunning)
{
try
{
/* Wait for a packet */
byte[] buffer = new byte[DATAGRAM_BUFFER_SIZE];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
socket.receive(packet);
/* Lets inform the statistician that we've received some data */
this.statistician.receivedData(packet.getLength());
if (this.config.isTesting())
{
/**
* Simulating network latency
* We pause for 1 millisecond/100 bytes
*/
int pause = packet.getLength() / 100;
try
{
Thread.sleep(pause);
}
catch (InterruptedException ex)
{
}
}
/* We've received a packet, now handle it */
try (ByteArrayInputStream bin = new ByteArrayInputStream(packet.getData(), packet.getOffset(), packet.getLength());
DataInputStream din = new DataInputStream(bin);)
{
/* Read in the conversation Id to know which handler to handle this response */
int comm = din.readInt();
byte messCode = din.readByte();
Message msg = messageFactory.createMessage(messCode, din);
din.close();
/* Get a receiver for this message */
Receiver receiver;
if (this.receivers.containsKey(comm))
{
/* If there is a reciever in the receivers to handle this */
synchronized (this)
{
receiver = this.receivers.remove(comm);
TimerTask task = (TimerTask) tasks.remove(comm);
if (task != null)
{
task.cancel();
}
}
}
else
{
/* There is currently no receivers, try to get one */
receiver = messageFactory.createReceiver(messCode, this);
}
/* Invoke the receiver */
if (receiver != null)
{
receiver.receive(msg, comm);
}
}
}
catch (IOException e)
{
//this.isRunning = false;
System.err.println("Server ran into a problem in listener method. Message: " + e.getMessage());
}
}
}
finally
{
if (!socket.isClosed())
{
socket.close();
}
this.isRunning = false;
}
}
/**
* Remove a conversation receiver
*
* @param comm The id of this conversation
*/
private synchronized void unregister(int comm)
{
receivers.remove(comm);
this.tasks.remove(comm);
}
/**
* Stops listening and shuts down the server
*/
public synchronized void shutdown()
{
this.isRunning = false;
this.socket.close();
timer.cancel();
}
/**
* Task that gets called by a separate thread if a timeout for a receiver occurs.
* When a reply arrives this task must be canceled using the <code>cancel()</code>
* method inherited from <code>TimerTask</code>. In this case the caller is
* responsible for removing the task from the <code>tasks</code> map.
* */
class TimeoutTask extends TimerTask
{
private final int comm;
private final Receiver recv;
public TimeoutTask(int comm, Receiver recv)
{
this.comm = comm;
this.recv = recv;
}
@Override
public void run()
{
if (!KadServer.this.isRunning)
{
return;
}
try
{
unregister(comm);
recv.timeout(comm);
}
catch (IOException e)
{
System.err.println("Cannot unregister a receiver. Message: " + e.getMessage());
}
}
}
public void printReceivers()
{
for (Integer r : this.receivers.keySet())
{
System.out.println("Receiver for comm: " + r + "; Receiver: " + this.receivers.get(r));
}
}
public boolean isRunning()
{
return this.isRunning;
}
}
