v4-only-listeners.rb

#!/usr/bin/env ruby
# Print everything that's listening on 127.0.0.1 but not ::1 or
# listening on 0.0.0.0 but not ::

v4_to_v6 = { "127.0.0.1" => "::1", "0.0.0.0" => "::"}
sockets = {}

IO.popen('sudo ss -Hnlp -A tcp,udp') do |ss|
  while (line = ss.gets) do
    fields = line.split
    proto = fields[0]
    local = fields[4].split(':')
    port = local.pop.to_i
    addr = local.join(':')
    addr = addr == '*' ? '0.0.0.0' : addr
    service = 'unknown'

    if fields.length > 6 then
      if m = fields[6].match(/pid=(\d+)/) then
        pid = m.captures[0]
        service = `systemctl status #{pid}`.split("\n")[0].split(' ')[1]
      end
    end

    unless sockets.key? addr ; sockets[addr] = {} end
    unless sockets[addr].key? proto ; sockets[addr][proto] = {} end

    sockets[addr][proto][port] = service
  end
end

v4_to_v6.keys.sort.each do |v4|
  v6 = v4_to_v6[v4]
  sockets[v4].keys.sort.each do |proto|
    sockets[v4][proto].keys.sort.each do |port|
      unless sockets.key?(v6) && sockets[v6].key?(proto) && sockets[v6][proto].key?(port)
        puts "#{sockets[v4][proto][port]} listening on #{v4}:#{port} but not #{v6}"
      end
    end
  end
end