Programming Assignment 2 Solution

Objective of this assignment:

    • Develop and implement a simple application using UDP sockets.
What you need to do:

    • Implement a simple UDP Client-Server application

Objective:

The objective is to implement a simple client-server application using a safe method: start from a simple working code for the client and the server. You must slowly and carefully bend (modify) little by little the client and server alternatively until you achieve your ultimate goal. You must bend and expand the client and the server alternatively the way a blacksmith forges iron. From time to time save your working client and server code such that you can rollback to the latest working code in case of nasty bugs (hard bugs occur often when socket programming).

For this programming assignment, you are advised to start from the Friend client and server application. The Friend client-server code is available on Canvas with this programming assignment. For this assignment, you must implement a simple polynomial calculator server using UDP. For simplicity, we will limit this client-server application to compute 3rd degree polynomials:
  (  ) = ⬚  )  ) +  +  + + ,  +  - with 0 ≤  0 ≤ 64 and 0 ≤    ≤ 64
for all    0 ≤  ≤ 3.
Part A: Datagram Socket Programming

The objective is to design and implement a Polynomial Calculator Server (CS). This calculator server will compute the polynomial P(x) when the client sends it a 9-byte request with this format:

Field

Total Message Length (TML)  Request ID






Checksum
Size  (byte)
1
2






1
1



1
1
1
1
1
























Where

    1) TML is the Total Message Length (in bytes) including TML. It is an integer representing the total number of bytes of the message. If the message is correct, TML should always be equal to 9. TML size is one byte long.

    2) Request ID is the request ID. This number is generated by the client to differentiate requests. You may use a variable randomly initialized by the client and increment it each time the client generates a new request. Request ID size is 2 bytes long.

    3) x is a number is the number for which we want to compute P(x). x's size is one byte.

    4) is the ith polynomial coefficient  0 with 0 ≤  0 ≤ 64 for all  0 ≤  ≤ 3.   ′   size is one byte.
    5) Checksum is an 8-bit Internet checksum computed as specified in the appendix of this assignment. Checksum

size is one byte.
Note that only a stream of 72 bits (9 bytes) will be sent.

Hint: create a class object Request like "Friend", but with the information needed for a request.
Below are two examples of requests


  (  ) =

)
+6  +12


= 5

Request 1: suppose the Client wants to compute




for

.











TML

Request ID











Checksum




0x09

0x0001












0xDB








0x05

0x01
0x00
0x06

0x0C























2






The client will then send the binary stream (expressed here byte by byte in hexadecimal for convenience):
0x09 0x00 0x01 0x05 0x01 0x00 0x06 0x0C 0xDB



+22  +7

= 13

TML

Request ID











  (  ) = 15  
+

for

.
Request 2: suppose the Client wants to compute
























Checksum




--
--











--







Complete the above table to find the binary stream to be sent(expressed here byte by byte in hexadecimal ..):



    • Note that given the polynomial definition, we could halve the size of a message. To be compatible, do not try to minimize
2 Checksum may be inaccurate



0x09 .......








The Server will respond with a message with this format:




Total Message Length (TML)

Request ID

Error Code

Result

Checksum
one byte

2 bytes

1 byte

4 bytes

one byte


Where

    1) TML is the Total Message Length (in bytes) including TML. It is an integer representing the total numbers of bytes in the message.
    2) Request ID is the request ID. This number is the number that was sent as Request ID in the request sent by the client. This allows the client to match a response to its request.

    3) Error Code is 0 if the request was valid, 127 if the request was invalid (Length not matching TML), and 63 if the checksum does not match..
    4) Result is the value of the polynomial   (  )requested.
    5) Checksum is an 8-bit Internet checksum computed as specified in the appendix of this assignment.


In response to Request 1 above, the server will send back:

 0x09  0x00  0x01  0x00  0x00  0x00  0x00  0xA7  0x4E  i.e, the stream 0x09 0x00 0x01 0x00 0x00 0x00 0x00 0xA7 0x4E



In response to Request 2, the server will send back:

0x09

i.e, the stream 0x09 -- --


        a) Repetitive Server: Write a datagram Polynomial Calculator Server (ServerUDP.java) in java. This server must respond to requests as described above. The server must run on port (10010+GID) and could run on any machine on the Internet. GID is your group ID that was assigned to you. The server must accept a command line of the form: java ServerUDP portnumber where portnumber is the port where the server should be working. For example, if your Group ID (GID) is 13 then your server must listen on Port # 10023.

        b) Write a datagram client (ClientUDP.java) in java:

    6) Accepts a command line of the form: java ClientUDP servername PortNumber where servername is the server name and PortNumber is the port number of the server. Your program must prompt the user to ask for the number x, and the coefficient 0 for all such that 0 ≤ ≤ 3. For each entry from the user, your program must perform the following operations:

            i. form a message m as described above
            ii. send the message to the server and wait for a response
            iii. print all the message one byte at a time in hexadecimal (for debugging/grading purpose)
            iv. print out the response of the server in a manner convenient for a typical Facebook user: the original polynomial, the value of x and the numerical resultl P(x).

            v. print out the round trip time (time between the transmission of the request and the reception of the response)
            vi. prompt the user for a new request. (Design some way to allow the user to end the client
program)
Five points will be deducted for any requirement not met.

How to get started?

    1) Download all files (UDP sockets) to run the "Friend" application used in Module 2 to illustrate how any class object can be exchanged: Friend.java, FriendBinConst.java, FriendDecoder.java, FriendDecoderBin.java, SendUDP.java, and RecvUDP.java.

    2) Compile these files and execute the UDP server and client. Make sure they work
    3) Create a new folder called Request and duplicate inside it ALL files related to the Friend class object
    4) Inside the Folder Request, change ALL occurrences of "Friend" with "Request" including the file names.
    3) Adapt each file to your application. Replace the fields used by Friend with the fields used by a request.
    4) Aim to have the client send one request and have the server understand it (just like what we did with a friend

object).
    5) When your server will receive and print out correctly a request, then you need to send back a response...
    6) Create a class object Response....


Report

    • Write a report. The report should not exceed half a page.

    • Your report must state whether your programs work or not (this must be just ONE sentence). If your program does not work, explain the obstacles encoutered.

What you need to turn in:

    • Electronic copy of each source program separately (standalone). In addition, put all the source programs in one folder that you name with your group ID. Zip the folder and submit it TOO.
    • Electronic copy of the report (including your answers if appropriate) (standalone). Submit the file as a Microsoft Word or a PDF file.

Grading
Your code will be compiled, executed, tested, and graded on Engineering Tux machines. Insure that your code works well on Tux machines.

    1) UDP client is worth 40% if it works well: communicates with YOUR server.

    2) UDP client is worth 10% extra if it works well with a working server from any of your classmates.

    1) UDP server is worth 40% if it works well: communicates with YOUR client.

    2) UDP server is worth 10% extra if it works well with a working client from any of your classmates.

Note that five points will be deducted for any requirement not met.


Appendix: How To Compute an n-bit Checksum

Consider a stream R of bits to send.  An n-bit Internet Checksum of the stream S is computed as follows:

    1) Break the stream R of bits in n-bit words w1, w2, ..., and wm.

    2) Compute the n-bit word S = w1 + w2, if there is a carry then set S = S + 1

    3) Compute S = S + w3, if there is a carry then set S = S + 1

........

    n) Compute S = S + wn, if there is a carry then set S = S + 1 Finally, the Internet Checksum = ~S (one-complement of S)

Example: suppose you must send the stream R =  0101110001111010 0101.

To compute a 4-bit checksum,

    1) Break the stream R of bits in 4-bit words w1, w2, ..., and wm. In this case, we will obtain: w1, w2, w3, w4, and w5 with w1 = 0101, w2 = 1100, w3 = 0111 w4 = 1010 and w5 = 0101

Go to Step 2.... Compute the n-bit word S = w1 + w2, if there is a carry then set S = S + 1 .....



How to check that your checksum is right?: if you add all words wi and the checksum, the sum should be equal to 111....1 (all ones).