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UDP with sequence numbers

由 六月ゝ 毕业季﹏ 提交于 2019-12-23 04:40:45

问题


I am trying to implement a Reliable UDP protocol for a class assignment in Java. I have managed to add the acknowledgments to every datagram packet that is received, but I am having trouble implementing Sequence Numbers in the datagram packets that I am sending.

Can anyone suggest an easy method to implement this?

@EJP I have tried implementing what you just suggested. This is my code till now (its still very raw - i was using hit and try method to implement it)

Server side

    public class TestServer extends Activity {

private DatagramSocket serverSocket;
Thread serverThread = null;
byte[] incomingData;
byte[] outgoingData;
//int numBytesRead = 0;
int ackSent = 0;
int numPackRecv = 0;
int BUF_SIZE = 1024;
String msg = "ACK";
BufferedInputStream data=null;
BufferedOutputStream out =null;

public static final int SERVERPORT = 6000;

String outputFile = "/sdcard/Movies/asddcopy.mp4";

@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_test_server);

    this.serverThread = new Thread(new ServerThread());
    this.serverThread.start();

}

@Override
protected void onStop() {
    super.onStop();
    try {
        serverSocket.close();
    } catch (Exception e) {
        Log.d("SERVER", "Inside onStop()");
        Log.d("SERVER", Log.getStackTraceString(e));
    }
}

class ServerThread implements Runnable {

    @SuppressLint("NewApi")
    public void run() {

        try {
            serverSocket = new DatagramSocket(SERVERPORT);
            incomingData = new byte[BUF_SIZE];
            //outgoingData = new byte[512];
            outgoingData = msg.getBytes();

            long startRxPackets = TrafficStats.getUidRxPackets(Process.myUid());
            long startTime = System.nanoTime();

            out = new BufferedOutputStream(new FileOutputStream(outputFile, true));


            while (!Thread.currentThread().isInterrupted()) {

                //serverSocket.setSoTimeout(5000);
                while (true) {
                    try{
                        //DatagramPacket incomingPacket = new DatagramPacket(incomingData, incomingData.length);
                        DatagramPacket incomingPacket = new DatagramPacket(incomingData, BUF_SIZE);

                        serverSocket.receive(incomingPacket);
                        byte[] data = incomingPacket.getData();
                        //out.write(data,0,incomingPacket.getLength());
                        //String msg = new String(incomingPacket.getData());

                        ByteArrayInputStream in = new ByteArrayInputStream(data);
                        ObjectInputStream is = new ObjectInputStream(in);

                        if (is == null) {
                            is = new ObjectInputStream(in);
                        }
                        Message msg = (Message) is.readObject();
                        System.out.println(msg.getSeqNo());
                        /*if ("END".equals(msg.substring(0, 3).trim())) {
                            Log.d("SERVER", "Inside END condition");
                            break;
                        }*/
                        out.write(msg.getData(),0,msg.getData().length);
                        numPackRecv += 1;

                        Log.d("SERVER", "Packet Received: " + numPackRecv);

                        InetAddress client = incomingPacket.getAddress();
                        int client_port = incomingPacket.getPort();
                        DatagramPacket outgoingPacket = new DatagramPacket(outgoingData, outgoingData.length, client, client_port);
                        serverSocket.send(outgoingPacket);
                        ackSent += 1;

                        //Log.d("SERVER","Packet Received: " + numPackRecv + " :: " + "Ack Sent: " + ackSent);
                    }catch(Exception e) {
                        Log.d("SERVER", "Inside run() ex1");
                        Log.d("SERVER", Log.getStackTraceString(e));
                        break;

                    }
                }

                out.close();

                serverSocket.disconnect();
                serverSocket.close();

                Log.d("SERVER", "Transfer Complete");
                 Log.d("SERVER", "Actual Time elapsed = " + (System.nanoTime() - startTime)/Math.pow(10, 9) + " s");
                 Log.d("SERVER", "Total Packets Received = " + Long.toString(TrafficStats.getUidRxPackets(Process.myUid()) - startRxPackets));
                 Log.d("SERVER", "Packets Received from Socket = " + numPackRecv);
                 break;
            }
            out.close();
            serverSocket.disconnect();
            serverSocket.close();

            /* Log.d("SERVER", "Transfer Complete");
             Log.d("SERVER", "Actual Time elapsed = " + (System.nanoTime() - startTime)/Math.pow(10, 9) + " s");
             Log.d("SERVER", "Total Packets Received = " + Long.toString(TrafficStats.getUidRxPackets(Process.myUid()) - startRxPackets));
             Log.d("SERVER", "Packets Received from Socket = " + numPackRecv);*/

        }catch (Exception e) {
            Log.d("SERVER", "Inside run() ex2");
            Log.d("SERVER", Log.getStackTraceString(e));
            serverSocket.disconnect();
            serverSocket.close();
            }
        }
    }

This is the Client side

    public class TestClient extends Activity { private DatagramSocket clientSocket;
    byte[] incomingData;
    int BUF_SIZE = 500;
    int numBytesRead = 0;
    int numPackSent = 0;

    private static final int SERVERPORT = 6000;
    private static final String SERVER_IP = "10.0.0.22";

    String inFile = "/sdcard/Movies/asdd.mp4";

    @Override
    public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test_client);      

new Thread(new ClientThread()).start();
    }

    public void onClick(View view) {

new workInProgress().execute("");
    }

    private class workInProgress extends AsyncTask<Object, Object, Object> {

@SuppressLint("NewApi")
@Override
protected Object doInBackground(Object... params) {

    try {

        Log.d("CLIENT", "Sending a file to the server...");
        BufferedInputStream inputBuf = new BufferedInputStream(new FileInputStream(inFile));
        //byte[] fileBytes = new byte[(int) inFile.length()];
        byte[] fileBytes = new byte[BUF_SIZE];

        incomingData = new byte[BUF_SIZE];
        double numPktToSend = Math.ceil(inFile.length()*1.0/BUF_SIZE);
        //Log.d("CLIENT", "Total packets to be sent = " + numPktToSend);

        int sleepCycle = 1;
        long sysPackSent = 0;
        //long startTxPackets = TrafficStats.getTotalTxPackets();
        long startTxPackets = TrafficStats.getUidTxPackets(Process.myUid());
        Log.d("CLIENT", "startTxPacks: " + startTxPackets);
        long packDrops = 0;
        long startTime = System.nanoTime();
        long count=0;
        long ackRec=0;
        int seqNo = 0;

        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        ObjectOutputStream os = new ObjectOutputStream(outStream);


        while((numBytesRead = inputBuf.read(fileBytes)) != -1) {
            //DatagramPacket packet = new DatagramPacket(fileBytes, fileBytes.length);
             if (os == null) {
                    os = new ObjectOutputStream(outStream);
             }
             Message msg = new Message(++seqNo, fileBytes, false);   
             os.writeObject(msg);
             os.flush();
             os.reset();

             byte[] data = outStream.toByteArray();
             DatagramPacket packet = new DatagramPacket(data, data.length);
            clientSocket.send(packet);
            numPackSent += 1;

            //Log.d("CLIENT", "No of packets sent = " + numPackSent);

            sysPackSent = TrafficStats.getUidTxPackets(Process.myUid()) - startTxPackets;

            try{
                clientSocket.setSoTimeout(5000);
                packet = new DatagramPacket(incomingData, incomingData.length);
                clientSocket.receive(packet);
                String recAck = new String(packet.getData());
                ackRec++;
            }
            catch(Exception e) {
                //Log.d("CLIENT", Log.getStackTraceString(e));
            }

            packDrops = numPackSent - ackRec;
            if (packDrops > count) {
                sleepCycle = Math.min(16, sleepCycle * 2);
                count = packDrops;
                Log.d("CLIENT",String.valueOf(sleepCycle) + " :: " + numPackSent);
            } else {
                sleepCycle = Math.max(sleepCycle - 1, 1);
            }
            Thread.sleep(sleepCycle);

        }

        if (numBytesRead == -1) {
            fileBytes = "END".getBytes();
            Log.d("CLIENT", "Sending END Packet");
            clientSocket.send(new DatagramPacket(fileBytes, fileBytes.length));
        }


        Log.d("CLIENT", "Actual Time elapsed = " + (System.nanoTime() - startTime)/Math.pow(10, 9) + " s");
        Log.d("CLIENT", "Total Packets Transmitted = " + Long.toString(sysPackSent));
        Log.d("CLIENT", "No of packets dropped = " + String.valueOf(packDrops));
        Log.d("CLIENT", "Packets Pushed to Socket = " + numPackSent);
        Log.d("CLIENT", "Number of Acknoledgments received " +ackRec);

        inputBuf.close();
        os.close();
        outStream.close();
        clientSocket.disconnect();
        clientSocket.close();

        Log.d("CLIENT", "Sending file.. Complete!!!");



} catch (Exception e) {
    Log.d("CLIENT", Log.getStackTraceString(e));
    clientSocket.disconnect();
    clientSocket.close();
}

    return null;
}

    }

    class ClientThread implements Runnable  {

@Override
public void run() {

    try {
        InetAddress serverAddr = InetAddress.getByName(SERVER_IP);
        clientSocket = new DatagramSocket();
        clientSocket.connect(serverAddr, SERVERPORT);
        Log.d("CLIENT", "Connection Successful");
    } catch (UnknownHostException e1) {
        Log.d("CLIENT", "Inside run() UnknownHostEx");
        Log.d("CLIENT", Log.getStackTraceString(e1));
    } catch (IOException e1) {
        Log.d("CLIENT", "Inside run() IOEx");
        Log.d("CLIENT", Log.getStackTraceString(e1));
    }

}

    }

I am getting a few errors at the Server side:

  1. I am receiving the same sequence number for each packet (i.e. 1)
  2. I am not sure about the buffer size for the incoming packet, as I am using 500 bytes at Client side and 1024 at the Sever. And if I take 500 bytes in both the codes I get a End of File exception.

I would really appreciate if you could suggest better ways to implement the same thing! Thanks :)

Thanks!


回答1:


  1. Create a ByteArrayOutputStream.
  2. Wrap it in a DataOutputStream
  3. Use DataOutputStream.writeInt() to write the sequence number.
  4. Use write() to write the data.
  5. Construct the DatagramPacket from the byte array returned by the ByteArrayOutputStream.

At the receiver, do exactly the reverse, using the complementary classes and methods in each case. What those are is left as an exercise for the reader.




回答2:


The simplest method would probably be to a look at the TCP protocol, and stick all the TCP headers into the start of each of your UDP packets.



来源：https://stackoverflow.com/questions/22889264/udp-with-sequence-numbers

标签
java
sockets
udp
client-server
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