borrow-mac

#!/usr/bin/env ruby

def assert_command_exists(cmd)
  ENV['PATH'].split(File::PATH_SEPARATOR).each do |path|
    exe = File.join(path, cmd)
    return exe if File.executable?(exe) && File.file?(exe)
  end
  abort "#{cmd} not found"
end

def sh(*args)
  puts("$ #{args.join(" ")}")
  system(*args)
end

def process_tcpdump(iface, stream)
  stats = Hash.new(0)
  top5 = []

  begin
    stream.each do |line|
      fields = line.split(/\s+/)
      next unless fields.size > 1
      mac = fields[1]
      next unless mac =~ /^([0-9A-Fa-f]{2}[:-]){5}([0-9A-Fa-f]{2})$/
      stats[mac] += 1
      top5 = stats.sort_by {|_, v| v}[0, 5]
      system("clear")
      puts("Least commonly used mac addresses")
      top5.each_with_index do |p, i|
        puts("#{i + 1}. #{p[0]} : #{p[1]} packets")
      end
      puts("\nReceived packets: #{stats.values.inject(:+)}")
      puts("Seen devices: #{stats.size}")
    end
  rescue IOError, Interrupt
    return if top5.size < 1
    print "apply address (1-#{top5.size}) "
    num = STDIN.gets.to_i
    if 1 <= num && num <= top5.size
      sh("ip", "link", "set", "dev", iface, "down")
      sh("ip", "link", "set", "dev", iface, "address", top5[num - 1][0])
      sh("ip", "link", "set", "dev", iface, "up")
    end
  end
end

def main(args)
  tcpdump = assert_command_exists("tcpdump")
  assert_command_exists("ip")
  ping = assert_command_exists("ping")

  if args.size < 1
    $stderr.puts "USAGE: #{$0} <interface>"
    exit(1)
  end

  iface = args[0]

  IO.popen([tcpdump, "-n", "-l", "-e", "-i", iface]) do |stream|
    # lets find all devices pretty quickly by using multicast ping
    IO.popen ([ping, "-c", "6", "-6", "ff02::1%#{iface}"]) do |stdout|
      # discard output
      stdout.read
    end
    abort "ping failed" unless $? != 2
    process_tcpdump(iface, stream)
  end
rescue Interrupt
end

main(ARGV)