minitalk

Inter-process communication using only UNIX signals — encoding data at the bit level.

🇧🇷 Leia em Português

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Why this project matters

"This project taught me how processes communicate at the OS level — using signals, PIDs, and bitwise operations. I understood what IPC (Inter-Process Communication) really means, a concept present in every operating system, distributed system, and even container orchestration platform."

Signal-based IPC is foundational knowledge for understanding how processes coordinate in Unix-like systems — the backbone of every Linux server in production today.

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How it works

Two separate programs communicate exclusively through UNIX signals (SIGUSR1 and SIGUSR2):

CLIENT                          SERVER
  |                               |
  | --- SIGUSR1 (bit = 1) ------> |
  | --- SIGUSR2 (bit = 0) ------> |
  | --- SIGUSR1 (bit = 1) ------> |
  |        ... 8 signals ...      |
  |                               | assembles byte → prints character
  | <-- SIGUSR1 (acknowledgment)  |

• SIGUSR1 represents bit 1
• SIGUSR2 represents bit 0
• Each character is transmitted as 8 signals (one per bit)
• The server reconstructs bytes using bit-shift operations
• On null character received, the server sends back an acknowledgment signal

Bonus

The bonus version adds acknowledgment signals from server to client after each character, ensuring reliable delivery.

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A standout technical detail

The signal handler uses sigaction with SA_SIGINFO instead of the simpler signal() function. This allows the server to read info->si_pid — the PID of the sending process — directly from the signal metadata, without any shared global state or additional communication channel. A clean, professional approach to handling signals in C.

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Getting Started

git clone https://github.com/gustavofsousa/minitalk_42.git
cd minitalk_42
make

Running

Start the server first:

./server
# Output: PID: 12345

Send a message from the client:

./client 12345 "Hello, World!"

Bonus version

make bonus
./server_bonus
./client_bonus <PID> "Your message here"

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Project structure

minitalk_42/
├── server.c          # Signal receiver — assembles and prints messages
├── client.c          # Signal sender — encodes and transmits strings
├── server_bonus.c    # Server with acknowledgment
├── client_bonus.c    # Client with acknowledgment
├── libft/            # Personal C library (dependency)
└── Makefile

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Skills demonstrated

• UNIX signals (SIGUSR1, SIGUSR2, sigaction, kill, pause)
• Bitwise operations for encoding/decoding data
• Inter-Process Communication (IPC)
• Process identification (PID)
• Reliable communication protocols design

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License

This project was developed as part of the 42 School curriculum.

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Made with ☕ at 42 Rio de Janeiro