pretend-to-be-my-switch: MAC address spoofing for OS X

pretend-to-be-my-switch

#!/usr/bin/env ruby

# Spoofs your MAC address, but only while the script is running.
#
# Put your native MAC address at ~/.mac-native in "aa:bb:cc:dd:ee:ff" format.
# Put your Switch's MAC address at ~/.mac-switch in "aa:bb:cc:dd:ee:ff" format.
#
# Run this script with `sudo`. It will change your WiFi MAC address. Kill the
# script and it'll change the MAC address back just before exiting.
#
# Why?
#
# You're on vacation and wanting to play a Switch game in your hotel room. The
# Switch is _supposed_ to handle captive portals properly, but in practice (at
# least for me) it doesn't work most of the time, so if that happens to me:
#
# 1. I open my laptop and run `sudo pretend-to-be-my-switch` in a terminal
#    window.
# 2. I join the hotel WiFi network and do the captive portal dance.
# 3. Once I'm connected, I kill the script with Ctrl-C.
# 4. I reattempt connection from the Switch, and this time it should succeed.
#
# If you try to re-join the network from your laptop after killing the script,
# you'll see the captive portal again, because to the network you're an
# entirely new device.
#
# CAVEATS:
#
# * Make sure to look up your native MAC address: `ifconfig en0 | grep ether`
# * If the device you want to spoof isn't en0, you'll have to hack the script.
# * Google suggests that the spoofing only lasts until a reboot, so if the
#   script doesn't exit cleanly somehow, a reboot should set your MAC address
#   back to normal. Failing that, a clean launch and exit of the script will
#   explicitly set your MAC address to the original value.

require 'pathname'

MAC_SWITCH = Pathname.new(ENV['HOME']).join('.mac-switch').read
MAC_NATIVE = Pathname.new(ENV['HOME']).join('.mac-native').read

unless ENV['USER'] == 'root'
  STDERR.puts "Must run as root!"
  Process.exit!
end

def change_mac(mac)
  puts "Changing mac address to: #{mac}"
  `sudo ifconfig en0 ether #{mac}`
end

Signal.trap('INT') do
  change_mac(MAC_NATIVE)
  Process.exit(0)
end

Signal.trap('TERM') do
  change_mac(MAC_NATIVE)
  Process.exit(0)
end

change_mac(MAC_SWITCH)

sleep(60) while true