42 Minitalk

Summary:

The purpose of this project is to code a small data exchange program using UNIX signals.

Foreword:

The cis-3-Hexen-1-ol, also known as (Z)-3-hexen-1-ol and leaf alcohol, is a colorless oily liquid with an intense grassy-green odor of freshly cut green grass and leaves. It is produced in small amounts by most plants and it acts as an attractant to many predatory insects. cis-3-Hexen-1-ol is a very important aroma compound that is used in fruit and vegetable flavors and in perfumes. The yearly production is about 30 tonnes.

Bitwise operation

Signals in C

Subject PDF

Clone

Open a terminal and run following command:

git clone <repository url>

Run

Go to the created repository and run following command:

make

To start run following command :

./server

After opening another terminal in the same folder, run the following command :

./client <client PID> <string to sent>

Finally, run this one to delete the outputs files and the librairy created :

make fclean

Bonus

Run the followings commands :

make bonus

Then :

./server

And :

./client <client PID> <string to sent>

Finally, run this one to delete the outputs files and the librairy created :

make fclean

Explanations

Each characters of the string are sent bits by bits thanks to bitwise operators. In C, a character has a size of one byte (8 bits). The bits are sent from the client to server by using the signals SIGUSR1 and SIGUSR2, each standing for the 0 and 1 respectively. In the bonus part, when the server will receive the null-terminator character from the client. It will send back a signal to client. Thanks to the bitwise operators, the programs support the unicode characters. Which was not possible with my initial implementation :

• Where I was first converting each characters into its binary value (in a string format).
• Then I was going through the created string and using the same signals when encountering either 0 or 1.

Sigaction function

In order to send back a signal from the server to the client, I have used the sigaction function, with which I am able to get the pid of the sending process (in this case the client). Here is its structure :

struct sigaction {
	void     (*sa_handler)(int);
	void     (*sa_sigaction)(int, siginfo_t *, void *);
	sigset_t   sa_mask;
	int        sa_flags;
	void     (*sa_restorer)(void);
};