chendo / airchat

AirChat lets you chat to nearby users by abusing the AirDrop interface on OS X.

AirChat

AirChat is a zero-dependency* P2P CLI chat tool that (ab)uses the AirDrop interface to allow chatting across WiFi networks (or no WiFi network).

A RailsCamp AU 20 project.

Features

• Chat to other AirChat users in proximity without being on the same network
• Self-contained - no gems, nothing else to download/install
• Automatically keeps AirDrop active
• Commands: /nick, /who, /me, /quit
• User colours tied to their IPv6 address

Requirements

• OS X with system Ruby 2+ with working AirDrop
• Ruby 2.0 or higher (comes with OS X)
• tcpdump (comes with OS X)

Usage

# Get it
curl -L https://github.com/chendo/airchat/raw/master/airchat.rb > airchat.rb && chmod +x airchat.rb
# or get someone to AirDrop it to you, etc.

# AirChat requires raw access to the /dev/bpf* interface.
# Run using sudo
sudo ./airchat.rb
# OR
# Give permission to /dev/bpf*
sudo chgrp staff /dev/bpf* && sudo chmod g+rw /dev/bpf*  # These permissions will reset on reboot
./airchat.rb

How does it work?

AirChat uses the awdl0 interface to talk to other machines with AirDrop active. However, OS X restricts binding to this interface, and non-AirDrop network traffic is rejected with ICMP Port Unreachable. AirChat gets around this by using tcpdump to receive UDP data, as OS X doesn't stop you from sending packets through that interface.

AirChat broadcasts JSON-encoded messages in UDP to ff02::fb on port 1337.

Caveats/TODO

• Messages are transmitted in plain text.
• No direct messaging
• One channel only (you can specify a different port by modifying the source)
• Message delivery is not guaranteed
• No message repeater functionality

License

MIT.

ANSI RGB magic sauce from the paint gem.