minitalk

A small client and server pair that sends a text message between two processes using nothing but UNIX signals. The client turns each character into its 8 bits and fires one signal per bit, SIGUSR1 for a 0 and SIGUSR2 for a 1. The server catches those signals, rebuilds each byte bit by bit, and prints the message as it arrives. Built as the 42 "minitalk" project.

Requirements

A C compiler, make, and a POSIX signals implementation. Builds and runs on both macOS and Linux. The vendored libft builds automatically.

Build

make

Produces two binaries, server and client.

Run

Start the server. It prints its process ID and waits.

./server

Server PID = [12345]
Waiting for messages...

In another terminal, send a message by passing the server's PID and the string.

./client 12345 "Hello from minitalk"

The server prints the message as the bits come in. It keeps running and waits for the next message until you stop it with Ctrl-C.

How it works

• The client validates the PID (digits only, and an existing process) before sending anything.
• For each character it walks the 8 bits from most significant to least, sending SIGUSR1 for a 0 bit and SIGUSR2 for a 1 bit.
• After each bit the client waits for the server to acknowledge it (the server sends a signal back) before sending the next one, with a short delay between bits. This keeps the two sides in step so no bit is lost.
• The server keeps a static bit counter and a byte under construction in its signal handler. Each signal sets or clears one bit, and once 8 have arrived the finished character is printed and the counter resets.
• A null byte marks the end of the string, at which point the server prints a blank line and waits for the next message.