Python Chat Application

A simple multi-threaded Python chat app with server and client components, featuring TLS transport encryption, user accounts with password authentication, and persistent message history.

Features

• TLS transport encryption (stdlib ssl module, no external dependencies)
• User accounts with password hashing (PBKDF2-HMAC-SHA256 via hashlib)
• Message history replayed on join (SQLite via sqlite3)
• Multi-user support with nicknames
• Real-time message broadcasting
• Length-prefixed socket framing so messages are not split or merged by TCP
• Graceful connection and shutdown handling

Requirements

• Python 3.8+
• OpenSSL (for generating the server certificate — usually pre-installed)
• Works on macOS, Linux, and Windows
• Clients and server must be reachable over the network

Quick Start

1. Clone the repository

git clone https://github.com/yourusername/simple-chat-client
cd simple-chat-client

2. (Optional) Install as a package

pip install .

This installs chat-server and chat-client console scripts.

3. Generate a TLS certificate (server side, one time)

python generate_cert.py

This creates cert.pem and key.pem in the current directory. Keep key.pem private. Distribute cert.pem to clients only if you want them to verify the server identity with --ca-cert.

For clients that connect by LAN IP or DNS name, include that name in the certificate:

python generate_cert.py --san 192.168.0.103 --san DNS:chat.local

4. Start the server

# Direct
python server.py

# After pip install
chat-server

# With options
chat-server --host 0.0.0.0 --port 65432 --cert cert.pem --key key.pem --db chat.db

5. Start a client

# Direct (interactive prompts)
python chat.py

# After pip install
chat-client

# With flags (skips prompts)
chat-client --host 192.168.0.103 --port 65432 --nickname Alice --ca-cert cert.pem

On first connect, a new nickname triggers registration (choose a password). On subsequent connects, the same nickname triggers login (enter your password).

Client Commands

Command	Action
/quit	Disconnect gracefully
Ctrl+C	Force quit

Server Options

Flag	Default	Description
--host	0.0.0.0	Bind address
--port	65432	TCP port
--cert	cert.pem	TLS certificate
--key	key.pem	TLS private key
--db	chat.db	SQLite database path

Client Options

Flag	Default	Description
--host	(prompted)	Server IP address
--port	(prompted)	Server port
--nickname	(prompted)	Your chat nickname
--ca-cert	(none)	Server cert for verification
--no-check-hostname	false	Verify the cert but skip hostname matching

Nicknames may contain letters, numbers, underscores, and hyphens, up to 32 characters. Messages are limited to 2,000 characters.

Security Notes

• All traffic is encrypted in transit with TLS.
• Passwords are never stored in plaintext — PBKDF2-HMAC-SHA256 with a random salt and 100,000 iterations.
• The default TLS configuration skips certificate verification on the client side (suitable only for quick local/private testing). Pass --ca-cert cert.pem to verify the server certificate and hostname.
• If you use --ca-cert with a self-signed certificate, generate the certificate with subjectAltName entries for the hostname or IP clients will use.
• This is not end-to-end encrypted — the server decrypts messages to broadcast them.

File Overview

simple-chat-client/
├── simplechat/
│   ├── __init__.py    # Package metadata
│   ├── server.py      # ChatServer class + main()
│   ├── client.py      # ChatClient class + main()
│   ├── db.py          # SQLite helpers (users, messages)
│   ├── protocol.py    # Length-prefixed socket framing
│   └── validation.py  # Shared nickname/message validation
├── server.py          # Shim: python server.py still works
├── chat.py            # Shim: python chat.py still works
├── generate_cert.py   # One-time TLS cert generator
├── pyproject.toml     # pip install configuration
├── packaging/
│   └── systemd/        # User and system service unit files
└── docs/
    └── background.md  # Running the server persistently

Running the Server in the Background

For persistent deployment (VPS, Raspberry Pi, etc.) see docs/background.md, which covers screen, nohup, systemd, and launchctl.

Running Tests

python -m unittest discover -v
python -m compileall -q .

Contributing

1. Fork the repository
2. Create your branch: git checkout -b feature/AmazingFeature
3. Commit your changes: git commit -m 'Add some AmazingFeature'
4. Push to the branch: git push origin feature/AmazingFeature
5. Open a Pull Request

License

MIT — see the LICENSE file for details.