developing tftp application in java

HI guys,
I'm trying to develop a tftp application in java.This is the specification i want:
Task is to implement a modified version of TFTP, as follows:
1- version will still run on top of UDP,
2-However, instead of having each packet be acknowledged before sending the next one, you will implement a TCP type of functionality: packets can be sent without waiting for an acknowledgement. The receiver has to keep track of sequence numbers and implement some type of ordering to �restore� the original format of the file. The sender should be informed of missing packets through duplicate ACKs, as we saw in class.
3-You only have to implement the binary type of data transmission.
4-Your TFTP server should be multi-threaded, i.e., it should support multiple client requests. This is done by creating a new thread for each client request that is received.
5-Your application should survive short outages. Transferring a large file and
disconnecting your Internet connection for a short time can test this. Upon reconnection, your client and the server should be able to pick up where they left off.
I have created four files:
1)tftpClient:The client
2)tftpServer:the server
3)tftpTransfer:It performs packet transfer and stuff
4)UdpData

erforms udp packet functionality

tftpClient:
import java.net.*;
import java.io.*;
import java.util.*;
public class tftpClient {
public static void main(String argv[]) {
String host= argv[0],fileName=argv[1],line;
int replyLen,blockNum;
try {
// Process command line args.....
InetAddress server = InetAddress.getByName(host);
// DatagramSocket sock = new DatagramSocket(2000,InetAddress.getLocalHost());
DatagramSocket sock = new DatagramSocket();
FileOutputStream outFile = new FileOutputStream(fileName);
// Create the request packet and send it off
UdpData reqData = new UdpData(4+fileName.length()+5); // 5==len("octet")
reqData.putInt(2,0); // RREQ opcode
reqData.putString(fileName,2); // Requested file
reqData.putString("octet",2+fileName.length()+1); // Trans mode
DatagramPacket pack = reqData.mkPacket(server,2000); // 69==TFTP port
sock.send(pack);
System.out.println("host:"+server.toString());
System.out.println("sent on socket:"+sock);
// Create the ACK packet
UdpData ackData = new UdpData(4);
ackData.putInt(4,0); // ACK opcode
DatagramPacket ackPack = ackData.mkPacket(server,2000);
// Create a packet to receive the data
UdpData recData = new UdpData(516); // 516==max pak len
pack = recData.mkPacket();
System.out.println("receiving packet");
for(int pakLen=516; pakLen==516; ) {
sock.receive(pack);
pakLen=pack.getLength();
System.out.println("still...."+sock.toString());
if (recData.getInt(0)==3) { // If a DATA pak then...
blockNum=recData.getInt(2);
outFile.write(recData.getData(),4,pakLen-4);
ackData.putInt(blockNum,2);
ackPack = ackData.mkPacket(server,pack.getPort());
sock.send(ackPack);
}
else
throw new Exception();
};
outFile.close();
sock.close();
}
catch (Exception e) { System.out.println("tftp session failed"); }
}
}
2)tftpServer:
import java.net.*;
import java.io.*;
import java.util.*;
public class tftpServer {
// Tftp opcodes (RFC 1350)
public static final int tftpRRQ=1;
public static final int tftpWRQ=2;
public static final int tftpDATA=3;
public static final int tftpACK=4;
public static final int tftpERROR=5;
public static final int maxTftpPakLen=516;
public static void main(String argv[]) {
try {
DatagramSocket sock = new DatagramSocket(2000);
System.out.println("Server Ready. Listening on port: "+sock.getLocalPort());
for(;

{
UdpData reqData = new UdpData(maxTftpPakLen);
DatagramPacket reqPak = reqData.mkPacket();
System.out.println("ready to receive request");
sock.receive(reqPak);
System.out.println("received request at socket:"+sock.toString());
if (reqData.getInt(0)==tftpRRQ) {
System.out.println("Display this:");
System.out.println("Request from "+reqPak.getAddress());
tftpTransfer t = new tftpTransfer(reqPak);
}
}
}
catch(Exception e) { System.out.println("Server terminated"); }
}
}
3)tftpTransfer:
import java.net.*;
import java.io.*;
import java.util.*;
class tftpTransfer extends Thread {
protected DatagramSocket sock;
protected InetAddress clientIP;
protected int clientPort;
protected FileInputStream source;
protected UdpData dataPak;
public tftpTransfer(DatagramPacket reqPak) {
try {
sock = new DatagramSocket();
clientIP = reqPak.getAddress();
clientPort = reqPak.getPort();
UdpData reqData = new UdpData(reqPak);
File srcFile = new File(reqData.getString(2));
if (srcFile.exists() && srcFile.isFile() && srcFile.canRead()) {
source = new FileInputStream(srcFile);
dataPak = new UdpData(516); // 516==max pak len
dataPak.putInt(3,0); // 3==DATA opcode
this.start();
}
} catch (Exception e) { System.out.println("Client failed"); };
}
public void run() {
int bytesRead = 512;
DatagramPacket ack = new DatagramPacket(new byte[4],4);
try {
for (int blkNum=0; bytesRead==512; blkNum++) { // 512==max data len
dataPak.putInt(blkNum,2);
bytesRead = source.read(dataPak.getData(),4,512);
sock.send(dataPak.mkPacket(clientIP,clientPort,516)); // 516==max data len + header
sock.receive(ack);
}
} catch (Exception e) { System.out.println("Client failed"); }
try {
source.close();
sock.close();
} catch (Exception e) {};
}
}
4)UdpData.java:
import java.net.*;
import java.io.*;
import java.util.*;
public class UdpData {
private byte data[];
public UdpData(int len) { data = new byte[len]; };
public UdpData(DatagramPacket pack) { data = pack.getData(); }
public byte[] getData() { return data; };
public int length() { return data.length; };
public DatagramPacket mkPacket() { return new DatagramPacket(data,data.length); };
public DatagramPacket mkPacket(int len) { return new DatagramPacket(data,len); };
public DatagramPacket mkPacket(InetAddress dest, int port) {
return new DatagramPacket(data,data.length,dest,port);
};
public DatagramPacket mkPacket(InetAddress dest, int port, int len) {
return new DatagramPacket(data,len,dest,port);
};
public int getInt(int offset) {
// Fix to avoid sign extension
// Remember what the MSB is and then turn it off to avoid sign extension. It is
// then added back to the sum after everything has been converted to integers.
byte lo = data[offset+1];
int signBit = (int)(lo&0x80);
lo&=0x7f;
// Standard TCP/IP byte order is hiByte followed by loByte (big endian)
int hiByte = (int)data[offset];
int loByte = (int)lo;
return (hiByte<<8)+signBit+loByte;
};
public void putInt(int val, int offset) {
int loByte = val%256;
int hiByte = val>>>8;
// Standard TCP/IP byte order is hiByte followed by loByte (big endian)
data[offset] = (byte)hiByte;
data[offset+1] = (byte)loByte;
};
public String getString(int offset) {
StringBuffer strBuf = new StringBuffer();
int curPos = offset;
while (data[curPos]!=0) {
strBuf.append((char)data[curPos]);
curPos++;
}
return new String(strBuf);
};
public void putString(String str, int offset) {
str.getBytes(0,str.length(),data,offset);
data[offset+str.length()]=0;
};
}
BUT I STILL CAN'T GET IT TO WORK.THE CLIENT IS SENDING A REQUEST FOR A FILE FROM THE SERVER AND IT JUST HANGS.THE SERVER IS UP AND WAITING FOR REQUESTS.

CAN ANYONE HELP ME WITH THIS???
THANKS A LOT,
KICHU

Kichu, please do not post the same topic in multiple forums. Closing this. Respondents may answer here TFTP .