Minitalk

#📝/42/Core_Curriculum/Minitalk #📝/Computer_Science/Programming/C

General concepts of the project

The objective of this project is to create a client-server program that can communicate with each other using UNIX signals. The client program sends a string message to the server program, which receives the message and displays it on the standard output.

• The purpose of this project is to code a small data exchange program using UNIX signals.
• The client will send information (a string) to the server using UNIX signals.
• The server must correctly receive and interpret this information, then display it.
• Server sends signal back, comfirming that the message got delivered.

Compilation:

To compile the client program, use the following command:

make client

To compile the server program, use the following command:

make server

Running the Programs

To run the server program, execute the following command:

./server

The server program will start listening for incoming signals.

To run the client program, execute the following command:

./client [server PID] [message]

Replace [server PID] with the process ID of the server program and [message] with the message you want to send to the server.

For example, if the server PID is 1234 and you want to send the message "Hello, World!" to the server, execute the following command:

./client 1234 "Hello, World!"

Resources:

Allowed functions

• write() | ft_printf() | pause() | sleep() | usleep() | exit() | malloc() | free() | libft functions

New functions

• signal(): It's a function in C programming language that is used to set up a signal handler for a specific signal. A signal handler is a function that is called when a signal is sent to the program.
• sigaction(): It's a function in C programming language that is used to set up a signal handler for a specific signal. It's safer than the signal() function because it provides more control over how the signal is handled.
• sigemptyset(): It's a function in C programming language that is used to initialize a signal set to empty. A signal set is a collection of signals that can be blocked or unblocked by the program.
• sigaddset(): It's a function in C programming language that is used to add a signal to a signal set. Once a signal is added to a signal set, it can be blocked or unblocked by the program.
• kill(): It's a function in C programming language that is used to send a signal to a process or a group of processes. The signal can be used to terminate a process or to interrupt its execution.
• getpid(): It's a function in C programming language that is used to get the process ID of the current process. The process ID is a unique identifier assigned to each process by the operating system.

Signals in C

A signal is a software interrupt that is sent to a process by the operating system in an event such as when a user presses ctrl-c in terminal. Signals are asynchronous notifications delivered to your script when specific events occur.

Signals allow the manipulation of a process from outside its domain, as well as allowing the process to manipulate itself or copies of itself (children). There are two general types of signals: those that cause termination of a process and those that do not. Signals which cause termination of a program might result from an irrecoverable error or might be the result of a user at a terminal typing the interrupt character. (CTRL + C)Signals are use when a process is stopped because it wishes to access its control terminal while in the background (see tty(4)). Signals are optionally generated when a process resumes after being stopped, when the status of child processes changes, or when input is ready at the control terminal. Most signals result in the termination of the process receiving them, if no action is taken; some signals instead cause the process receiving them to be stopped, or are simply discarded if the process has not requested otherwise. Except for the SIGKILL and SIGSTOP signals, the signal() function allows for a signal to be caught, to be ignored, or to generate an interrupt. These signals are defined in the file <signal.h>

No	Name	Default Action	Description
1	SIGHUP	terminate process	terminal line hangup
2	SIGINT	terminate process	interrupt program
3	SIGQUIT	create core image	quit program
4	SIGILL	create core image	illegal instruction
...	...	...	...
30	==SIGUSR1==	terminate process	==User defined signal 1==
31	==SIGUSR2==	terminate process	==User defined signal 2==

This table represents all the UNIX signals. As you can see there is a lot of things that can be done with signals. However we are allowed to use in our project only SIGUSR1 and SIGUSR2.

Comunnication between client and the server

Two arguments are passed to the client executable - PID of the server and message to be sent. Each value of chars making up the message are send as binary via sigusr1 and sigusr2. Take look at code implementation. Coments there will guide you with how the character is converted into binary value and sent to the server.