Show HN: Peer-to-Peer Messaging

A decentralized messaging application for local area networks. Uses UDP multicast for automatic peer discovery and TCP for direct peer-to-peer communication.

A functional P2P messaging application for LANs. We demonstrate how peers can discover each other and exchange messages without any central coordination. All communication happens directly between clients.

Working:

• UDP multicast-based peer discovery (IPv4 only)
• Direct TCP messaging between discovered peers
• Multiple instances on the same machine (SO_REUSEPORT)

Limitations:

• Local network only (no NAT traversal)
• No encryption (cleartext over TCP)
• No message persistence
• No group chat (only 1-to-1 messaging)

Discovery Layer (UDP Multicast):

• Multicast group: 239.255.255.250:6789
• Periodic announcements every 5 seconds
• Peer timeout after 15 seconds of silence
• JSON-serialized discovery messages

Messaging Layer (TCP):

• Each peer listens on a dynamically assigned port
• Direct socket connections for message delivery
• Line-delimited JSON over TCP
• Concurrent connection handling via Tokio

Requires Rust 1.70 or later.

Start multiple instances on the same network:

Discovery happens automatically. After a few seconds, peers will appear in each other's peer lists.

Commands:

• /peers - Show discovered peers
• /send <nickname> <message> - Send a message
• /quit - Exit

Example:

Messages appear in the recipient's terminal with a timestamp.

Peers send periodic announcements to 239.255.255.250:6789:

The peer registry maintains a list of all recently-seen peers. Peers are removed if they haven't announced in 15 seconds.

Messages are sent over TCP as line-delimited JSON:

Each peer maintains a TCP listener. To send a message, a peer:

1. Looks up the recipient in the peer registry
2. Opens a TCP connection to their address
3. Sends the JSON message followed by \n
4. Closes the connection

This is inefficient but simple.