CS 372 Introduction to Computer Networks Programming Assignment #1


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1. Implement a client-server network application
2. Learn to use the sockets API
3. Use the TCP protocol
4. Refresh programming skills
The Program:
Design and implement a simple chat system that works for one pair of users, i.e., create two
programs: a chat server and a chat client. The final version of your programs must
accomplish the following tasks:
1. chatserve starts on host A.
2. chatserve on host A waits on a port (specified by command-line) for a client request.
3. chatclient starts on host B, specifying host A’s hostname and port number on the
command line.
4. chatclient on host B gets the user’s “handle” by initial query (a one-word name, up to
10 characters). chatclient will display this handle as a prompt on host B, and will
prepend it to all messages sent to host A. e.g., “ SteveO> Hi!!”
5. chatclient on host B sends an initial message to chatserve on host A : PORTNUM.
This causes a connection to be established between Host A and Host B. Host A and
host B are now peers, and may alternate sending and receiving messages. Responses
from host A should have host A’s “handle” prepended.
6. Host A responds to Host B, or closes the connection with the command “\quit”
7. Host B responds to Host A, or closes the connection with the command “\quit”
8. If the connection is not closed, repeat from 6.
9. If the connection is closed, chatserve repeats from 2 (until a SIGINT is received).
• chatserve must be implemented in Java or Python
• chatclient must be implemented in C/C++.
• Of course, your program must be well-modularized and well-documented.
• Your programs must run on an OSU flip server (for example: flip1.engr.oregonstate.edu).
Specify your testing machine in the program documentation.
• Your programs should be able to send messages of up to 500 characters.
• Use the directories in which the programs are running. Don’t hard-code any directories,
since they might be inaccessible to the graders.
• Be sure to cite any references, and credit any collaborators.
• Provide a README.txt with detailed instructions on how to compile, execute, and
control your program.
• Combine all program files into one *.zip archive (no .7z or .gz allowed). The .zip file
should not contain any folders – only files!
page 2 of 2
• For your C implementation, read Beej’s Guide. It has everything you need for this
assignment. You will probably learn the most about socket programming by using C.
• If you are using Python, check http://docs.python.org/release/2.6.5/library/internet.html,
• If you are using Java, check
• It’s OK to hard-code host A’s handle.
• It’s OK to implement this system so that it requires the two users to take turns sending
messages, i.e., when a user sends a message, s/he must wait for a response before sending
the next message.
• When debugging, don’t use the well-known port numbers, because these will already be
in use. I’d suggest using 30020 or 30021, though other students may be using these when
you’re on the servers.
• If you use additional include-files or make-files, be sure to include them in your .zip file.
• You can test these programs using just one computer. Start the server, then start the
client in a new window. You can then switch back and forth between the two terminal
• Project #1 will be accepted up to one week late with a penalty of up to 10% per day.
• If you implement extra credit features, be sure to describe those features in your program
documentation and README.txt or you will not receive any credit.
• There are many possibilities for extra credit. Be sure that your program satisfies the
requirements first, and then do the extra credit in separate files.
• Extra credit possibilities include (but are not limited to) …
 Set up your programs so that either host can make first contact.
 Make it possible for either host to send at any time (while the connection is active)
without “taking turns”.
 Make your server multi-threaded.
 Split the screen to show host B’s typing in one panel, and host A’s responses in the
other panel.
 Make the characters appear on the receiving host as they are being typed on the
sending host (instead of waiting for the entire line to be sent).