UDP Socket Communication in C

This project demonstrates how to implement UDP-based client-server communication using the C programming language. It includes basic socket setup, message exchange, asynchronous I/O using select(), and a stress test simulating 10,000 clients.

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📌 Features

• ✅ Basic UDP client and server using sendto() and recvfrom()
• ✅ Asynchronous, non-blocking server using select()
• ✅ Performance/stress testing with 10,000 simulated UDP messages
• ✅ Prints client IP and port on each request
• ✅ Designed to run in a local development environment (127.0.0.1)

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📁 Project Structure

udp-communication/
├── src/
│   ├── UDPClient.c               # Simple client that sends and receives a message
│   └── UDPServer.c               # Simple server that replies to each client
│
├── advanced/
│   └── ServerMultipleClient.c    # Non-blocking server using select()
│
├── tests/
│   └── 10kClient.c               # Simulates 10,000 clients sending messages
│
└── README.md

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🚀 Getting Started

🔧 Requirements

• GCC (or any C compiler)
• Unix-like environment (Linux, WSL, macOS)

🛠 Compile

gcc src/UDPServer.c -o server
gcc src/UDPClient.c -o client
gcc advanced/ServerMultipleClient.c -o server_select
gcc tests/10kClient.c -o stress_test

▶️ Run

In separate terminals or processes:

./server           # Basic server
./client           # Basic client

# OR

./server_select    # Non-blocking select() based server
./stress_test      # Sends 10,000 UDP messages

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🧠 What I Learned

• How to use low-level socket APIs in C: socket(), bind(), sendto(), recvfrom()
• Difference between TCP and UDP (connectionless, unordered, fast)
• Using select() and fcntl() to implement non-blocking I/O
• How to simulate massive numbers of clients for load testing
• IP/port parsing and diagnostic logging

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🧪 Sample Output

Server with select() running on port 8080...
Received from 127.0.0.1:48730 → Client No 1
Received from 127.0.0.1:48731 → Client No 2
...

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🧼 Extras (Optional)

Add the following to your .gitignore to keep your repo clean:

.vscode/
*.out
*.o

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📬 Contact

Developed as part of my summer internship at Movita
📧 aenesozturk@gmail.com
🌐 https://github.com/aenesozturk

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📝 License

This project is open source and free to use under the MIT License.