Server.java
package com.t4b.demo.gobackn;
import java.net.*;
import java.io.*;
import java.util.*;
public class Server {
public static void main(String args[]) throws Exception {
ServerSocket server = new ServerSocket(6262);
System.out.println("Server established.");
Socket client = server.accept();
ObjectOutputStream oos = new ObjectOutputStream(client.getOutputStream());
ObjectInputStream ois = new ObjectInputStream(client.getInputStream());
System.out.println("Client is now connected.");
int x = (Integer) ois.readObject();
int k = (Integer) ois.readObject();
int j = 0;
int i = (Integer) ois.readObject();
boolean flag = true;
Random r = new Random(6);
int mod = r.nextInt(6);
while (mod == 1 || mod == 0)
mod = r.nextInt(6);
while (true) {
int c = k;
for (int h = 0; h <= x; h++) {
System.out.print("|" + c + "|");
c = (c + 1) % x;
}
System.out.println();
System.out.println();
if (k == j) {
System.out.println("Frame " + k + " recieved" + "\n" + "Data:" + j);
j++;
System.out.println();
}
else
System.out.println("Frames recieved not in correct order" + "\n" + " Expected farme:" + j + "\n"
+ " Recieved frame no :" + k);
System.out.println();
if (j % mod == 0 && flag) {
System.out.println("Error found. Acknowledgement not sent. ");
flag = !flag;
j--; // it was like j-;
} else if (k == j - 1) {
oos.writeObject(k);
System.out.println("Acknowledgement sent");
}
System.out.println();
if (j % mod == 0)
flag = !flag;
k = (Integer) ois.readObject();
if (k == -1)
break;
i = (Integer) ois.readObject();
}
System.out.println("Client finished sending data. Exiting");
oos.writeObject(-1);
}
}
Client.java
package com.t4b.demo.gobackn;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
public class Client {
public static void main(String args[]) throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Enter the value of m : ");
int m = Integer.parseInt(br.readLine());
int x = (int) ((Math.pow(2, m)) - 1);
System.out.print("Enter no. of frames to be sent:");
int count = Integer.parseInt(br.readLine());
int data[] = new int[count];
int h = 0;
for (int i = 0; i < count; i++) {
System.out.print("Enter data for frame no " + h + " => ");
data[i] = Integer.parseInt(br.readLine());
h = (h + 1) % x;
}
Socket client = new Socket("localhost", 6262);
ObjectInputStream ois = new ObjectInputStream(client.getInputStream());
ObjectOutputStream oos = new ObjectOutputStream(client.getOutputStream());
System.out.println("Connected with server.");
boolean flag = false;
GoBackNListener listener = new GoBackNListener(ois, x);
listener = new GoBackNListener(ois, x);
listener.t.start();
int strt = 0;
h = 0;
oos.writeObject(x);
do {
int c = h;
for (int i = h; i < count; i++) {
System.out.print("|" + c + "|");
c = (c + 1) % x;
}
System.out.println();
System.out.println();
h = strt;
for (int i = strt; i < x; i++) {
System.out.println("Sending frame:" + h);
h = (h + 1) % x;
System.out.println();
oos.writeObject(i);
oos.writeObject(data[i]);
Thread.sleep(100);
}
listener.t.join(3500);
if (listener.reply != x - 1) {
System.out.println(
"No reply from server in 3.5 seconds. Resending data from frame no " + (listener.reply + 1));
System.out.println();
strt = listener.reply + 1;
flag = false;
} else {
System.out.println("All elements sent successfully. Exiting");
flag = true;
}
} while (!flag);
oos.writeObject(-1);
}
}
class GoBackNListener implements Runnable {
Thread t;
ObjectInputStream ois;
int reply, x;
GoBackNListener(ObjectInputStream o, int i) {
t = new Thread(this);
ois = o;
reply = -2;
x = i;
}
@Override
public void run() {
try {
int temp = 0;
while (reply != -1) {
reply = (Integer) ois.readObject();
if (reply != -1 && reply != temp + 1)
reply = temp;
if (reply != -1) {
temp = reply;
System.out.println("Acknowledgement of frame no " + (reply % x) + " recieved.");
System.out.println();
}
}
reply = temp;
} catch (Exception e) {
System.out.println("Exception => " + e);
}
}
}
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