MultiChat

A Multicast based chat application that works in a LAN environment. Any user can join multiple courses. A user can send a message to any of his/her registered course and will also receive messages sent to those courses.

Getting Started

Compilation

Use make to compile the code. It will generate an executable named mchat.

Running the MultiChat

$ ./mchat <path to course-data file>

For example, if the course-data file is named course-info.txt and is stored in the current directory, to run the application,

$ ./mchat course-info.txt

Optional loopback argument

The mchat application also accepts an optional argument to set loopback. (Loopback is disabled by default).

For example, if the course-data file named course-info.txt is stored in the current directory and you want to allow loopback, run application as,

$ ./mchat course-info.txt 1

Format for the course-data file

This file contains a list of all courses that can be currently taken along with their ComCode (a 4 digit unique code). This file helps the client to generate group IP address based on the course code. The course-data file should have the following format,

<k = Number of Courses>
<C1 COMCODE>,<C1 COURSE CODE>,<C1 COURSE TITLE>
<C2 COMCODE>,<C2 COURSE CODE>,<C2 COURSE TITLE>
..
..
..
<Ck COMCODE>,<Ck COURSE CODE>,<Ck COURSE TITLE>

For example,

6
1092,CS F213,OBJECT ORIENTED PROG
1090,CS F214,LOGIC IN COMPUTER SC
1093,CS F215,DIGITAL DESIGN
1091,CS F222,DISCR STRUC FOR COMP SCI
1316,CS F301,PRINCIPLES OF PROGG LANG
2266,CS F320,FOUNDATIONS OF DATA SCIENCE

(A sample file containing this information for all courses offered in First Semester 2019-20 is included.)

Commands

The program gives these options to a user,

1. Send Message
2. Join new course
3. Leave a course
4. Exit

Enter the corresponding option number to select an option.

Default settings

These default settings are defined in the first few lines of the code and can be changed from there.

• Maximum message length is set to 2047 bytes.
• Port for the Multicast socket is set to 6000.
• BaseIP for multicast groups is set to 238.101.
• Loopback of Messages is disabled.

Working

Generation of multicast group IP Address

All the group IP Addresses are generated based on the ComCode of a course. All IPs have a format of 238.101.1xx.1xx.

The procedure used to generate an IP address from a course ComCode is,

char *genIpFromComCode(int comCode){
    char *multicastIP = allocString(16);
    sprintf(multicastIP,"%s.1%d.1%d",baseIP,comCode/100,comCode%100);
    return multicastIP;
}

For example, if a course has ComCode equal to 1092, then the corresponding group IP will be 238.101.110.192.

Generation of a Message

A message entered by a user is padded with some extra characters to improve the message readability. An example message is shown below,

- - - - - - - - - - - - - - - - - - - -
MESSAGE FROM IS F462
- - - - - - - - - - - - - - - - - - - -
This is a test message.
- - - - - - - - - - - - - - - - - - - -

Receiving Messages

A separate child process is run to accept messages from the subscribed groups and print them to console. This process is killed when 4. Exit option is selected or SIGINT signal is given by the user.