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:
- Add all appropriate packet sanity checks: timeouts, host/port, size, opcode, and block number
- Generate output (to System.out)
- Terminate when a packet of size less than 512 is received
- Support arbitrary window sizes
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.
- 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.
- Add sanity checks, for (in order) host/port, packet size, opcode, and block number.
- 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.
-
Add support for an arbitrary window size.
- [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.