> For the complete documentation index, see [llms.txt](https://42-guide.gitbook.io/42-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://42-guide.gitbook.io/42-guide/core-curriculum/rank-02/integrations/what-to-do.md).

# What to do ?

### 1. Understanding the Project

#### Objective

* **Create a server program** that listens for incoming messages.
* **Create a client program** that sends messages to the server.
* **Use UNIX signals** (SIGUSR1 and SIGUSR2) for communication.

***

### 2. What are Signals?

**Signals** are software interrupts that notify a process of events. Some commonly used signals include:

* **SIGINT (2)**: Interrupt signal (Ctrl+C).
* **SIGKILL (9)**: Forces a process to terminate.
* **SIGTERM (15)**: Requests a process to terminate.
* **SIGUSR1 (10)** and **SIGUSR2 (12)**: User-defined signals, used in Minitalk.

In Minitalk, **SIGUSR1** and **SIGUSR2** are used to transmit binary data (1s and 0s).

***

### 3. How Does It Work?

Since signals can only send a small amount of information (only which signal was sent), we need to encode characters as binary and send them bit by bit.

#### Basic Process:

1. The client **sends the server the PID** (Process ID).
2. The client **converts the message into binary**.
3. The client **sends each bit of each character** using **SIGUSR1** (0) and **SIGUSR2** (1).
4. The server **receives the bits** and **reconstructs the original message**.

***

### 4. Step-by-Step Implementation

#### 4.1 Server

The server will:

* Print its own PID (so the client knows where to send data).
* Listen for **SIGUSR1** and **SIGUSR2** signals.
* Decode the binary message into characters.
* Print the received message.

**4.1.1 Server Code Explanation**

* Use `getpid()` to print the server PID.
* Use `signal()` or `sigaction()` to listen for **SIGUSR1** and **SIGUSR2**.
* Construct each character bit by bit (8 bits = 1 character).
* Print the final message.

#### 4.2 Client

The client will:

* Get the server's PID as an argument.
* Convert the message into binary.
* Send each bit to the server using **SIGUSR1** (0) and **SIGUSR2** (1).
* Introduce a small delay between signals to ensure processing.

**4.2.1 Client Code Explanation**

* Convert each character into its binary representation.
* Send one bit at a time using `kill(server_pid, SIGUSR1/SIGUSR2)`.
* Wait for a short delay to avoid overwhelming the server.


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