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 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 each piece alternatively the way a black-smith forges iron. From time to time save your working client and server such that you can roll-back to the latest working code in case of problems.

For this programming assignment, you are advised to start from the Friend client and server application to implement a calculator server. You must implement the calculator server using UDP.

Part A: Datagram Socket Programming

The objective is to design a Calculating Server (CS). This calculating server performs bitwise boolean and arithmetic computations requested by a client on 16-bit signed integers. Your server must offer the following operations:

    1) addition (+), 2) subtraction (-), 3) multiplication (*), 4) division (/), 5) Shift Right (>>), 6) Shift Left (<<), and one-complement (NOT) (~).
A client request will have the following format:

Field

TML

Request ID

Op Code
Number Operands
Operand 1

Operand 2
Size (bytes)

1

1

1
1
2

2

Where

    1) TML is the Total Message Length (in bytes) including TML. It is an integer representing the total number of bytes in the message.
    2) Request ID is the request ID. This number is generated by the client to differentiate requests. You may use a variable randomly initialized and incremented each time a request is sent.

    3) Op Code is a number specifying the desired operation following this table

 Operation  +  -   *  /   >>  <<  ~ 

OpCode    0    1    2    3    4    5    6

    4) Number Operands is the number of operands: 2 for (+, -, *, /) and shifts. It is 1 for ~ (NOT).

    5) Operand 1: this number is the first or unique operand for all operations.
    6) Operand 2: this number is the second operand for operations (+, -, *, /, <<, >>). It is the number of bits to shift by for the shift operations. This operand does NOT exist for the ~ (NOT) operation.

Operands are sent in the network byte order (i.e., big endian).

Hint: create a class object Request like "Friend", but with the information needed for a request.

Below are two examples of requests
Request 1: suppose the Client requests to perform the operation 240 >> 4, i.e., shift the number 240 right by 4 bits (if this is the 7th request):

 0x08  0x07  0x04  0x02  0x00  0xF0  0x00  0x04 


Request 2: suppose the Client requests to perform the operation 240 – 160  (if this is the 9th request):

0x08    0x09    0x01    0x02    0x00    0xF0    0x00    0xA0


The Server will respond with a message with this format:


Total Message Length (TML)
Request ID
Error Code

Result
one byte
1 byte
1 byte

4 bytes


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.

    3) Error Code is 0 if the request was valid, and 127 if the request was invalid (Length not matching TML).
    4) Result is the result of the requested operation.


In response to Request 1 below

 0x08  0x07  0x04  0x02  0x00  0xF0  0x00  0x04 


the server will send back:

 0x07  0x07  0x00  0x00  0x00  0x00  0x0F 


In response to Request 2,

 0x08  0x09  0x01  0x02  0x00  0xF0  0x00  0xA0 


the server would send back:

 0x07  0x09  0x00  0x00  0x00  0x00  0x50 


    a) Repetitive Server: Write a datagram Calculating 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:

        i. 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 an Opcode, an Operand1 and if needed an Operand2 where OpCode is the opcode of the requested operation (See the opcode table). Operand1 and Operand2 (if applicable) are the operands. For each entry from the user, your program must perform the following operations:
        ii. form a message as described above
        iii. send the message to the server and wait for a response
        iv. print all the message one byte at a time in hexadecimal (for debugging purpose)
        v. print out the response of the server in a manner convenient for a typical Facebook user: the request ID and the response
        vi. print out the round trip time (time between the transmission of the request and the reception of the response)

        vii. prompt the user for a new request.


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 calculator 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 EACHyour source program separately (standalone). In addition, put all the source programs in a folder that you name with your group ID. Zip the folder and submit it TOO.

    • Electronic copy of the report (including your answers) (standalone). Submit the file as a Microsoft Word or PDF file.

Grading

    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.