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P2P-Chat-App
Workshop 3 - 08.03.2026 Ali Gokcek - 2021400012 Tested my program by myself with another MacOS computer. Readme and inline comments were extended and the code got licensed for open-sourcing (will make it public after the deadline).
P2P chat application over local WiFi using Python. Peer discovery uses UDP broadcast; messages use TCP unicast.
Protocol
| Type | Transport | Fields | Purpose |
|---|---|---|---|
ASK |
UDP broadcast | SENDER_IP |
Announce presence to subnet |
REPLY |
TCP unicast | RECEIVER_NAME, RECEIVER_IP |
Respond to discovery |
MESSAGE |
TCP unicast | SENDER_IP, SENDER_NAME, PAYLOAD (max 2 KB) |
Send a chat message |
Project Structure
├── config.py # Tunable constants (port, timeouts, intervals, CIDR range)
├── network.py # NetworkManager — UDP broadcast, TCP send/receive, listeners
├── p2p_chat.py # P2PChat — protocol handlers, peer management, CLI (entry point)
└── requirements.txt
Requirements
- Python 3.7+
- macOS (uses
ipconfig getifaddr en0for IP detection) - Peers must be on the same WiFi / local subnet
- No external dependencies — stdlib only
Usage
python3 p2p_chat.py
Commands
| Command | Description |
|---|---|
/peers |
List known peers |
/send <name@ip> <msg> |
Send a message to a peer |
/help |
Show help |
/quit |
Exit |
Example Session
Your name: alice
Identity : alice@192.168.1.10
Port : 12487
> /peers
- bob@192.168.1.42
> /send bob@192.168.1.42 Hello!
You → bob: Hello!
[-] Peer left: bob@192.168.1.42
> /quit
Configuration
Constants can be adjusted in config.py:
| Constant | Default | Description |
|---|---|---|
PORT |
12487 | Port used for both UDP broadcast and TCP unicast |
MAX_PAYLOAD_BYTES |
2048 | Maximum message payload size in bytes |
SEND_TIMEOUT_SEC |
3 | TCP connect/send timeout in seconds |
CIDR_RANGE |
24 | Subnet mask used to compute the broadcast address |
BROADCAST_INTERVAL |
10 | Seconds between automatic ASK broadcasts |
PEER_TIMEOUT |
30 | Seconds of silence before a peer is evicted |
REAPER_INTERVAL |
5 | How often the reaper checks for stale peers |
License
BSD 2-Clause © 2026 Ali Gökçek — see LICENSE for full text.
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