Description
Socket Programming with Python
Introduction
You are tasked with implementing the client side of a network application designed according to the client-server
application architecture. (The server is already implemented and running on a remote machine.) The description
of the application and of its application layer protocol is provided below.
In this assignment, you must use Python 3 to write your client.
Application and Application Layer Protocol
Overview
The application concerns remote evaluation of simple arithmetical expressions using only one of the operators
+, -, * and / (no parenthesis or other operators). Examples: 3 + 5, 5 * 8, etc. After an initial greeting message
used by your client to start the connection to the server, the server asks your client to evaluate a (server-chosen,
unspecified) number of expressions one after the other.
Each of these expressions will be sent as a separate message.
For each expression message, the server expects a response message containing the result of the evaluation of the
expression. If your program is able to correctly evaluate all the expressions, then the server will return a secret flag
to the client. This flag is unique to each student, and should be saved for submission (see Section Submission).
The message containing the flag will signify the end of the communication session. At this point, the client can
close the connection to the server, and the application terminates.
Protocol Actions and Messages
Upon starting, the client must setup a TCP connection with the server. Then, the client must send the
introductory message to the server. The server will respond with an expression message. The client must evaluate
the expression and send back a result message. If the result is incorrect, the server will send back a failure message
and close the connection to the client (this means that your client is not correctly designed and you have to modify
it and try again). Otherwise, the server will either send another expression message or, if enough expressions
have been evaluated, a success message. The success carries the secret flag, which you should save and keep for
submission.
The application uses the following types of messages:
• The introductory message is sent from the client to the server to signal the start of communications. It is also
used authenticate the sender. This message uses the following format:
EECE7374 INTR nuid
Where nuid is your Northeastern University identification number. Make sure to enter your NU ID number
as a string that includes all leading zeroes.
• The expression message is sent from the server to the client, carrying the expression to be evaluated. This
message uses the following format:
EECE7374 EXPR expression
Where expression is the expression to be evaluated.
1
• The result message is sent from the client to the server, carrying the result of the last expression to be
evaluated. This message uses the following format:
EECE7374 RSLT result
Where result is the value of the evaluated expression.
• The failure message is sent from the server to the client to indicate that the last expression was evaluated
incorrectly. After the server sends this message it closes the connection to the client. This message has the
following format:
EECE7374 FAIL
• The success message is sent from the server to the client, indicating that the application has completed
successfully. It carries the secret flag for submission. This message uses the following format:
EECE7374 SUCC flag
Where flag is the secret flag.
All of these messages must be case-sensitive strings that have been encoded using UTF-8.
Servers
The server is running on a remote machine with the host name kopi.ece.neu.edu. The server uses the port
numbers in the range [5203, 5212]. If you experience difficulty connecting to a port, try another. The server will be
listening for TCP connection requests. Therefore, ensure that the client uses TCP sockets.
Testing
A sample server sample server.py is available to test your client locally, on your machine, as you design the
client. This server behaves almost exactly like the actual server. However, the secret flag it returns is not the one
required for the assignment. You can test your client by setting your host-name to localhost and the port number
to the same as the one in the sample server. This way, you can test your client as many times as you like, without
needing to worry about connectivity or server load.
Submission
To receive full credit for the assignment, you need to provide this secret flag in your assignment submission,
along with the source code for your client. For your submission, please name your source file as follows:
FirstName LastName Proj.py
Where FirstName and LastName are your first and last names, respectively. It is very important that your
submission complies with this naming format. Any other file name will result in a loss of points.
In your source file, please include a comment header that contains:
• A comprehensive description of your high-level approach to the client design. Here, you need to explain what
your program is doing and how it is doing that. This needs to be written as if you are trying to explain your
program to someone who has not taken this course.
• Your NU ID number, clearly labelled.
• The secret flag that you obtained by running this program, also clearly labelled.
This header can be succinct, but please make sure that all of the information in this header is accurate.
Please ensure that your file can be run! If your submission is not a Python 3 source file and cannot be
run from the command line (or IDE of your choice), then you will lose points.
You may resubmit your source file as many times as you want. However, only the last submission will be graded.
2
Grading
Points will be given to your solution based on the following:
• Filename: 5 points. You will receive full points if your file is named correctly.
• Code works: 35 points. You will receive full points if your code runs without errors.
• High-level approach: 25 points. You will receive full points if you provide sufficient details on how you designed
the client.
• NU ID: 5 points. You will receive full points if the listed NU ID is correct.
• Secret flag: 30 points. You will receive full points if the listed secret flag is the correct one.
3
