#!/usr/bin/env ruby
 
require 'open-uri'
require 'ping'
 
Signal.trap('INT') { exit }
 
ServiceBaseUrl = 'http://just-dnslookup.com/'
ServiceUrl = "#{ServiceBaseUrl}index.php?vh=%s&c=&s=dns+lookup!"
 
domain = ARGV.first.to_s.strip
 
port_to_test = ARGV.last.to_i
port_to_test = 80 unless (1..65535).include? port_to_test
 
if domain == ''
  puts <<-TEXT
Usage: #{File.basename $0} <host> [port]
 
Find out reachable IP addresses for given host by 2 steps:
 
* Query just-dnslookup.com to get an IP address list for the host.
* Use a TCP echo (not an ICMP echo) to determine if they are reachable.
 
Port are optional, default to 80.
TEXT
  exit
end
 
puts 'Querying just-dnslookup.com...'
 
urls = []
begin
  open(ServiceUrl % domain) do |f|
    urls = f.read.scan(/xmlreqGET\s*\(\s*['"]\s*([^'"]+)['"]/).flatten.collect do |path|
      "#{ServiceBaseUrl}#{path}"
    end
  end
rescue Timeout::Error
  puts "\nMaybe just-dnslookup.com not reachable or this script need an update."
  exit
rescue Errno::ECONNRESET
  puts %(\nThe host string "#{domain}" seems be blocked as a keyword by GFW.)
  exit
end
 
ip_list = []
 
urls.each do |url|
  country_code = url.match(/&cp=(\w+)/)[1]
  puts "Querying just-dnslookup.com with country code #{country_code}..."
  begin
    open(url) do |f|
      data = f.read
      if data['::']
        data = data.split('::')
        ip_list << data.first if data.last['good']
      else
        puts " Unexpected response for country code #{country_code}:"
        puts " #{data.inspect}"
      end
    end
  rescue Timeout::Error, Errno::ECONNRESET
  end
end
 
ip_list.sort!.uniq!
 
if ip_list.empty?
  puts <<-TEXT
 
No IP addresses collected, maybe just-dnslookup.com not reachable or this
script need an update.
TEXT
  exit
end
 
ENV.delete 'http_proxy'
 
ip_table = {}
ip_list.each do |ip|
 
  start_time = Time.now
  if Ping.pingecho(ip, 2, port_to_test)
    ip_table[Time.now - start_time] = ip
  end
end
 
if ip_table.empty?
  puts "\nAll IP addresses of #{domain} are not reachable."
else
  puts "\nReachable IP addresses of #{domain}:"
  puts 'IP | TCP echo time (ms)'
  ip_table.sort.each do |item|
    printf "%-16s| %.1f\n", item.last, item.first * 1000
  end
end