Description
1. Introduction
In this assignment, starting from the simplest chat functionalities, you will develop more
comprehensive servers for messaging applications, including elementary security features and
current state of the chat-room. This will require that various processes in different machines
are able to work with each other, and recuperate in case of asynchronous messaging and
failure. This chat program is based on a client server model consisting of one chat server and
multiple chat clients over TCP connections. The server is mainly used to authenticate the chat
clients and direct the chat messages (online or offline) to one another. Besides, the server also
has to support certain commands that the clients can use. Detailed specifications of the
functionalities are given under Section 2.
2. Specifications
a. You should write your program in one of the following languages
C/C++
Java
Python
b. You should write a server program and a client program. The server program will be
run first followed by multiple instances of the client program (Each instance supports
one client). They will be run from the terminals on the same and/or different hosts.
c. Server program
You should have a file “user_pass.txt” that contains the valid combination of
usernames and passwords that it can use to authenticate the clients (or client
programs). In each line, the first term in the username and the second term in the
password. Use the following usernames-passwords to populate your file.
Columbia 116bway
SEAS winterbreakisover
csee4119 lotsofexams
foobar passpass
windows withglass
Google hasglasses
facebook wastingtime
wikipedia donation
network seemsez
The server program will be invoked as
% Server
Ex: java Server 4119
python Server.py 4119
When starting up, server reads a list of username-password combinations from
“user_pass.txt” and then listens on a given port (4119 in the above example) and
waits for clients to connect.
Authentication
o When a new chat client requests for a connection, the server should prompt the
client to input his username and password and should authenticate the user
(using the username-password combinations from “user_pass.txt”).
o If the combination is correct, the chat client should be “logged in” and a
welcome message may be displayed.
o If the password is incorrect, the server should ask the user to try again until
there are 3 consecutive failures. In this case, the server should drop this
connection and block access only for this user from the failed attempt IP
address for 60 seconds. Please define 60 seconds using the variable
“BLOCK_TIME” (we will be changing this value while testing your code!).
Commands
o After the client is logged in, the server should support the commands
presented in Table 1. An example is presented in the Appendix.
o If the server cannot recognize some command, an error message should be
displayed.
Table 1: Commands
Command Functionality
whoelse Displays name of other connected users
wholasthr Displays name of only those users that connected within the last
hour.
broadcast Broadcasts to all connected users
message Private to a
block Blocks the from sending any messages. If is self,
display error.
unblock Unblocks the who has been previously blocked. If
was not already blocked, display error.
logout Log out this user.
d. Client program
The client program will be invoked as
% Client
Ex: java Client 10.6.31.102 4119
python Client.py 10.6.31.102 4119
User should be able to connect to a given server and login themselves by entering
a valid username and password.
For the sake of simplicity, prohibit concurrent duplicate users. Ex.: While the
user Columbia is already logged in, make sure that Columbia cannot log in from
another console.
After logging in, users should be able to give any of the commands specified in
Table 1 to the server. Your program should be able to display what the server
responds at the terminal.
o A client must be able to view other users who are currently online
o A client must be able to view other users who were online in the past one
hour. When defining this one hour, use the variable “LAST_HOUR” (we
will be changing this value to less than an hour while testing your code!).
o The client should be able to send and receive private messages with other
clients VIA the SERVER. If the receiving user is not online, the server
must store the message and deliver it to the receiver when the user comes
online. This is the off-line chat functionality.
o A client can broadcast a message to all logged in users at any time. (Offline chat function is not needed for broadcast messages.)
o Since this is a simple chat program, all messages may be displayed in same
console only. A separate console (or UI) for each private messaging is not
compulsory.
o A client can block a user from sending any further messages.
o A client can also unblock a user that was earlier blocked.
o When all work is done, user should be able to logout from the server.
o Also, if a client is inactive (i.e. the client has not issued any command) for
30 minutes, the server should automatically log this user out. Please define
30 minutes using the variable “TIME_OUT”.
e. Any innovative and useful features can be developed. This is your chance for earning
some for extra credit!
NOTE: All messages between clients MUST be sent VIA the SERVER.
3. Deliverables:
Submission will be done on courseworks. Please post a single _.zip (Ex.
zz1111_java.zip) file to the Programming Assignment 1 folder. The file should include the
following:
README.txt: This file should contain the following.
a. A brief description of your code
b. Details on development environment
c. Instructions on how to run your code
d. Sample commands to invoke your code
e. Description of an additional functionalities and how they should be
executed/tested.
Makefile: The make file is used to build your application. Please try to keep this as
simple as possible. If you don’t know how to write a makefile, read this quick tutorial
http://www.cs.colby.edu/maxwell/courses/tutorials/maketutor/.
Source code and related files (like user_pass.txt). (Make sure your code is
commented!)
4. Testing, Sample Run, and Grading
Please make sure that your programs compile and run correctly. To grade your
program, we will extract the received zip file, type make and run the programs using
the same syntax given in Section 2. Please make sure that your submission
successfully passes this simple procedure.
TA’s will compile and test the code you submit on CLIC machines. It is your
responsibility to make sure your code is compliable and runnable on CLIC machines.
The CLIC lab has following setup: Java 1.6, gcc version 4.6.3, python 2.7.3
Do not simply submit the entire eclipse/your favourite project folder. Submit only the
relevant files.
Although we mainly observe the functionality and correctness of your program, we
might examine your source code a little. Too poorly structured code or humanunreadable code may result in a score penalty
Here is a sample run showing how we will be testing your code:
Terminal 1
>make
>java server 4119 // You don’t have to use Java, and 4119 here is just an
// example. We may test on other unoccupied ports
Terminal 2
>java client 10.11.12.13 4119 // 4119 is the port that server listens on
// and 10.11.12.13 is the IP address of the server
// program
>Username: network // After connecting to server, your program should
// prompt “Username: ” and wait for user to put in
// his/her name. Here our user is “network”
>Password: seemsez // again your program should prompt “Password: ” and
// wait for user to put in the password. Since this is a
// introductory assignment, the password displayed as
// plain text is acceptable
>Welcome to simple chat server! // welcome message from the server acknowledging that
// the user has logged in
>Command: // from now on your server should respond to
// commands specified in Table 1
5. Appendix: Example
Consider the following scenario
3 clients – facebook, wikipedia and network are currently logged in.
1 client – windows was logged in, but logged out more than an hour back.
1 client – Google was logged in, but logged out half an hour back.
The following should happen on entering the given commands on the terminal of facebook.
whoelse
Since whoelse should print all the other users currently logged in, the following
should be displayed on the terminal of facebook.
wikipedia
network
wholasthr
Since wholasthr should print all the users who were logged in during the last one
hour, the following should be displayed on the terminal of facebook
wikipedia
network
Google
Note: windows is not displayed!
broadcast hello world
The following should be printed on all the terminals of all the users who are currently
logged in, i.e., wikipedia and network.
facebook: hello world
message wikipedia hi
The following should be printed on the terminal of wikipedia
facebook: hi
message foobar hi
Note that foobar is currently not online. So, once foobar comes online, the following
should be printed on the terminal of foobar
facebook: hi
This is support for offline chat function.
block facebook
An error message like the following should be printed on the terminal of facebook.
Error! You cannot block yourself!
block wikipedia
The following message should be printed on the terminal of facebook.
You have successfully blocked wikipedia from sending you messages.
The following message should be printed on the terminal of wikipedia when it tries to
send a message to facebook using “message facebook hi”.
You cannot send any message to facebook. You have been blocked by the
user.
unblock wikipedia
The following message should be printed on the terminal of facebook.
You have successfully unblocked wikipedia.
logout
facebook should be logged out and the client program supporting this user should
terminate.
Grading rubric
Functionality Max Points awarded /
deducted
Basic client and server programs with following functionality as
per the specifications:
– successful log in
– Multiple clients support (from multiple machines)
– Implementation of whoelse
– Implementation of logout
35
Correct implementation of wholasthr 5
Correct implementation of broadcast 10
Correct implementation of private messaging 10
Correct implementation of offline message 10
Correct implementation of user issued block and unblock 10
Blocking the user from a failed login terminal after 3
unsuccessful logins
5
Automatic “logout” of the client after 30 minutes of inactivity 5
Well documented README, makefile (if required) 5
Code quality 5
Extra feature: The feature should be useful and grading will be
done on its innovation, utility and amount of effort.
Max 10 points per extra
feature. On TA discretion.
Total max extra feature points 20
