🌉 BridgeChat

A multi-protocol chat room where TCP and UDP clients talk to each other — in the same room.

---

📌 About

BridgeChat is a terminal-based chat room server built with Python's socket and threading libraries. It accepts both TCP and UDP clients simultaneously, broadcasting messages across all connected users regardless of which protocol they used to connect.

The project was developed as a Computer Networks (BIL302) assignment and demonstrates practical use of socket programming, concurrent client handling, and protocol-agnostic messaging.

---

✨ Features

• Dual-protocol support — TCP and UDP clients coexist in the same chat room
• Multi-threaded server — each TCP client runs in its own thread; UDP is handled in a single dedicated thread
• Cross-protocol broadcast — a message from a TCP client is delivered to all UDP clients and vice versa
• Username uniqueness — duplicate usernames are rejected across both protocols
• Case-insensitive validation — Nefise and NEFISE are treated as the same user
• Graceful disconnection — TCP clients are detected when their socket closes; UDP clients send Gorusuruz to leave
• Username reuse — once a user leaves, their username becomes available again

---

🗂️ Project Structure

bridgechat/
├── Server.py       # Main server — handles TCP and UDP listeners
├── ClientTCP.py    # TCP client
├── ClientUDP.py    # UDP client
├── testcases.py    # Automated test suite (11 tests, 2 scenario groups)
└── assets/
    ├── server.png
    └── testcases.png

---

⚙️ How It Works

Server (Server.py)

The server starts two listener threads on launch:

• TCP Listener (127.0.0.1:12345) — accepts incoming connections, spawns a new thread per client via handle_tcp_client()
• UDP Listener (127.0.0.1:12346) — processes all datagrams in a single thread; the first datagram from any new address is treated as the username

Both listeners share a broadcast() function that delivers messages to all connected clients across both protocols. A threading.Lock protects the shared tcp_clients and udp_clients dictionaries.

TCP Client (ClientTCP.py)

Connects to the server, completes username registration, then starts a background listener thread. The main thread handles user input and sends messages.

UDP Client (ClientUDP.py)

No persistent connection — the OS assigns a port automatically. The first datagram sent is the username. Subsequent messages are broadcast to the room. Typing Gorusuruz signals the server to remove the user.

---

🚀 Running the Project

1. Start the server:

python Server.py

2. Open a TCP client (one or more terminals):

python ClientTCP.py

3. Open a UDP client (one or more terminals):

python ClientUDP.py

Enter your username when prompted. Messages sent from any client will appear in all other connected clients' terminals, tagged with the sender's name and protocol (e.g., berke[TCP] : merhaba, zeynep[UDP] : merhaba).

To leave: TCP clients can close their terminal (Ctrl+C), UDP clients type Gorusuruz.

---

🧪 Test Scenarios

The test suite (testcases.py) is split into two scenario groups and covers 11 tests in total.

Run:

python testcases.py

When prompted, start the server in a separate terminal and press Enter to continue.

---

Group A — Server Offline Tests

#	Test	Expected Behaviour
01	TCP connection attempt while server is offline	ConnectionRefusedError raised
02	UDP datagram sent while server is offline	Timeout or Windows ICMP rejection

---

Group B — 3 TCP + 3 UDP Clients Connected

These tests use six simultaneous clients:

Protocol	Usernames
TCP	hatice, nefise, berke
UDP	merve, neslihan, zeynep

#	Test	Expected Behaviour
03	Connect all six clients	All receive Hosgeldiniz
04	Cross-protocol messaging (TCP ↔ UDP)	Messages reach all other clients
05	Duplicate username attempt	Server rejects with "zaten sohbet odasında"
06	Case-insensitive duplicate (NEFISE while nefise is online)	Server rejects the duplicate
07	Empty username via TCP	Server ignores or rejects
08	Whitespace-only username via UDP	Server ignores or rejects
09	TCP client disconnect (nefise closes socket)	Server removes user, broadcasts departure
10	UDP client leaves with Gorusuruz (neslihan)	Server removes user, broadcasts departure
11	Reuse of departed username (nefise reconnects)	Hosgeldiniz — username is available again

---

📸 Screenshots

Server Console

Server output showing six clients joining, chatting across protocols, and disconnecting.

---

Test Results

All 11 tests passing across both scenario groups.

---

🔧 Technical Notes

• The server uses SO_REUSEADDR so it can restart without waiting for the OS to release the port.
• UDP does not have a native disconnect mechanism — the Gorusuruz keyword serves as an application-level leave signal.
• On Windows, closing a UDP socket may generate a WinError 10054 (ICMP port unreachable); the server handles this silently.
• The lock object wraps all reads and writes to the shared client dictionaries to prevent race conditions under concurrent access.

---

📋 Requirements

• Python 3.x
• No external libraries — only the standard socket and threading modules

---

TCP delivers your messages reliably. UDP delivers your emotions. BridgeChat handles both.

---

BIL302 — Computer Networks Assignment

⭐ Star this repo if you find it helpful!

Made with ❤️ by zeynpakn