Programming Project (due: December 5, more or less)
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 (updated Nov 14), and
wclient.java (now working), which contains
an outline of the actual program.
The outline gets as far as sending the REQ packet
and printing some diagnostics.
Only wclient.java should be modified;
you should not have to make changes to wumppkt.java.
Your assignment is to do the following, by modifying and extending
the wclient.java outline file:
- Implement the basic transfer
- Add all appropriate packet sanity checks: timeouts, host/port, size, opcode, and block number
- Generate output. The transferred file is to be written to
System.out. A status message about every packet is to be written to
System.err. Do not confuse these!
- Terminate when a packet of size less than 512 is received
- Implement an appropriate "dallying" strategy
- send an ERROR packet if it receives a packet from
the wrong port. The appropriate ERRCODE in this case is EBADPORT.
- Add support for window sizes > 1.
An outline of the program main loop, with notes,
is now available here
.
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 dallying and error packets.
After the client has received the
file, dallying means to wait 2.0 - 3.0 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.
Error packets are to be sent to any sender of an apparent data packet
that comes from the wrong port.
-
Add support for arbitrary window sizes last, after everything else is working.
You can test your program by contacting the server (to be announced; probably ulam2.cs.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.