Programming Project (due Friday, June 29)

Your project will be to implement the BUMP client in java. Here is an overview of the three WUMP protocols (BUMP, HUMP, and CHUMP). Here are the files wumppkt.java, containing the packet format classes, and wclient.java, which contains an outline of the actual program (see below for a slightly different version of the latter). Only the latter file should be modified; you are not to make changes to wumppkt.java. I've added the error code values to wumppkt.java; they were omitted from the handout.

I am investigating a java version difference: some javas accept, for example,
      wp.new REQ("foo");
while other (newer?) versions require
      wp.new wumppkt.REQ("foo");
Here is wclient.java in this alternative format.

Your assignment is to do the following, by modifying and extending the wclient.java outline file:

If your program meets the other requirements but handles only a window size of 1, you will receive a score right on the border between A and B; your exam and homework scores will then tip the balance.

I recommend that you implement this in phases, as follows.

  1. Latch on to the new port: save the port number from Data[1], and make sure all ACKs get sent to this port. THis will mean that the transfer completes. You should also have the output written to System.out, and make sure the client stops when a packet with less than 512 bytes of data is received.
  2. Add sanity checks, for (in order) host/port, packet size, opcode, and block number.
  3. Handle timeouts, by retransmitting the most recently sent packet when the elapsed time exceeds a certain amount (4 seconds?). One way to do this is to keep a DatagramPacket variable LastSent, which can either be reqDG or ackDG, and just resend LastSent. Note that the response to an InterruptedIOException, a "true" timeout, will simply be to continue the loop again.
  4. Add support for an arbitrary window size.
  5. [optional] send an error packet when appropriate, and implement dallying (both below).

You can test your program by contacting the server (at ulam.math.luc.edu) and requesting files. No matter what file you ask for, the file you get is always the same. However, by asking for the following names, you get the indicated behavior:

lose
Lose everything after the first windowful (min 3). It will be retransmitted when you retransmit the previous ACK.
spray
Constant barrage of data[1]. Implies LOSE too. In this case, no timeout events will occur; you must check for elapsed time.
delay
Delays sending packet 1, prompting a duplicate REQ and thus results in multiple server instances on multiple ports.
reorder
Sends the first windowful in the wrong order.
dupdata2
DATA[2] is sent twice
losedata2
DATA[2] is lost on initial send, until you resend ACK[1]
marspacket
A packet from the wrong port (a "martian" port) arrives
badopcode
a packet arrives with an incorrect opcode
nofile
you get an error packet with a NO FILE error code.
Your program should send an ERROR packet if it receives a packet from the wrong port. The appropriate ERRCODE in this case is EBADPORT.

You will receive up to 4 points of extra credit if you implement "dallying", which is the wump analogue of TIMEWAIT. After the client has received the file, dallying means to wait 2.0 timeout intervals (or more) to see if the final data packet is retransmitted. If it is, it means that the final ACK was lost. The dally period gives the client an opportunity to resend the final ACK.