zapchat (Python)

Terminal-native LAN chat. No accounts, no cloud, no servers — just your local network.

This is the Python distribution of zapchat. It speaks the same discovery protocol as the Node.js version, so a Python user and an npm user on the same Wi-Fi can chat with each other.

Since zapchat 6.0 the Python client runs the same encrypted wire protocol v2 as the Node.js client: ephemeral X25519 key exchange, all TCP frames sealed with AES-256-GCM, handshakes signed by a long-term Ed25519 identity key with TOFU pinning. Cross-stack chat needs no flags on either side. The only dependency this adds is cryptography. Links to genuinely old peers (zapchat ≤ 5 Python clients) stay possible but remain opt-in plaintext on both stacks: run with --allow-plaintext to accept them (the link is then unencrypted v1 and /status says so).

Install

pip install zapchat

Run

zapchat

That is it. Everyone on the same network who runs zapchat shows up automatically, and you can start chatting.

zapchat 6.0.0 — LAN chat, no accounts, no server
  you are sam on #general (tcp:45913)
  waiting for people on this network... (ctrl+c to quit, /help)
* alex connected
10:24 alex: morning all
10:25 sam: morning! which room are we using today?

Commands

How it works

• Every instance sends a small UDP beacon (multicast + subnet broadcast) announcing its username, room and TCP port — in both wire versions, so pre-6.0 peers are still discovered.
• Beacons are how instances find each other; then they open direct TCP connections and run the encrypted protocol v2 handshake (the same one the npm client uses) before any message flows.
• Rooms are derived, not stored: a room exists while somebody is in it.
• There is no server of any kind. If the LAN works, zapchat works.

Works with the npm version of zapchat on the same network (same beacons, same encrypted message protocol, no flags needed either way). Actions (/me) use the same CTCP-style framing as the npm client, so an npm user sees * sam waves exactly like a Python user does.

Privacy

• No accounts, no telemetry, no cloud: the only network traffic is UDP beacons and TCP messages on your local network.
• Config is one small JSON file (your username, a random client id, the last room, your identity key and peer key pins). Chat history stays in memory.
• Messages on a link are end-to-end encrypted with AES-256-GCM; peers are authenticated by TOFU key pinning, so an impostor with a changed key is refused loudly. This protects LAN traffic — it is still not anonymous.
• The exception is an opt-in link to a legacy peer (--allow-plaintext): that one link is unencrypted and /status warns about it.

Requirements

• Python 3.9+ with the cryptography package (installed automatically by pip)
• Windows, macOS, Linux

License

MIT © Samarth Chugh (Sam3360)