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+<code java>
+package nfs;
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+/**
+ * this is used to call a server and wait for a response, taking into account that messages can be lost.
+ * The calling message is supposed to be in a datagram packet and the answer itself is given back as a datagram packet
+ *
+ * @author marcod
+ *
+ */
+public class UDPServerComm {
+	/**
+	 * parameters to reach the server
+	 */
+	InetAddress    serverAddress = null;
+	int            serverPort = 0;
+	DatagramSocket ds = null;
+	/**
+	 * number of retries when a message fails to get an aswer
+	 */
+	int retries = 10;
+	/**
+	 * timeout used to wait an answer from the server
+	 */
+	int timeoutSeconds = 5;
+	/**
+	 * limit of the size of the datagram packet payload (just for this exercise)
+	 */
+	public static final int LIMIT = 8192;
+	/**
+	 * constructor, intializes the parameters needed to communicate with the server: the address and the port
+	 * @param serverName name of the machine running the server
+	 * @param port port used by the server to listen messages
+	 */
+	public UDPServerComm(String serverName, int port) {
+		try {
+			serverAddress = InetAddress.getByName(serverName);
+			serverPort = port;
+			ds = new DatagramSocket();
+		} catch(Exception e) {
+			e.printStackTrace();
+		}
+		return;
+	}
+	/**
+	 * used to set the number of times we have to retransmit before actually failing
+	 * @param n number of time to retransmit
+	 */
+	public void setRetries(int n) {
+		retries = n;
+	}
+	/**
+	 * sets the seconds used before timeouting a request
+	 * @param n the number of seconds the answer is awaited before getting the timeout
+	 */
+	public void setTimeoutSeconds(int n) {
+		timeoutSeconds = n;
+	}
+	/**
+	 * this is the main method: sends the server the datagram packet and waits for an answer, setting proper timeouts
+	 * and retransmitting, if the case
+	 * @param dp the datagram to be sent to the server
+	 * @return the datagram aswered by the server
+	 */
+	public DatagramPacket call(DatagramPacket dp) {
+		DatagramPacket answer = new DatagramPacket(new byte[LIMIT], LIMIT);
+		// prepare the datagram to be sent
+		dp.setAddress(serverAddress);
+		dp.setPort(serverPort);
+		try {
+			// the start waiting for an answer
+			boolean done = false;
+			// set retries to default value
+			int nretry = retries;
+			// set timeout
+			ds.setSoTimeout(timeoutSeconds*1000);
+			do {
+				try {
+					// now send the datagram
+					ds.send(dp);
+					// wait for the answer
+					ds.receive(answer);
+					// got! we are done!
+					done = true;
+				} catch(InterruptedIOException e) { // if the receive timeouts ...
+					nretry--;					    // decrease retry no.
+					if(nretry == 0)                 // in case we reached the limit
+						return null;                // just return a null
+				}
+			} while(!done);
+		} catch (IOException e) {
+			e.printStackTrace();
+		}
+		return answer;
+	}
+}
+</code>