Simple port scanner written in Ruby

port_scanner.rb

#!/usr/bin/env ruby

require 'socket'
require 'timeout'
require 'thread'

$stdout.sync = true

DEBUG = false   # Debug mode

PARALLEL = 120  # Number of port scanning thread
TIMEOUT = 5     # Timeout in sec.

DATEFORMAT = '%Y-%m-%d %H:%M:%S.%4N'
#DATEFORMAT = '%H:%M:%S.%4N'

$mutex = Mutex.new    # Giant lock ;p
$threads = Array.new  # All threads

def msg(str, type = 'MSG')
  return '[' + Time.now.strftime(DATEFORMAT) + '] [' + type.strip + '] ' + str.strip
end
def dbg(str)
  if DEBUG
    $threads << Thread.new do
      $mutex.synchronize do
        warn msg(str, 'DEBUG')
      end
    end
  end
end
def err(str)
  abort msg(str, 'ERROR')
end

def scan(host = '127.0.0.1', port = 80)
  begin
    Timeout.timeout(TIMEOUT) do
      TCPSocket.open(host, port)
    end
  rescue Timeout::Error, Errno::ETIMEDOUT
    return :STEALTH
  rescue Errno::ECONNREFUSED
    return :CLOSE
  rescue
    return :FAIL
  end

  return :OPEN
end

def report(result)
  puts 'Ports (except for CLOSE):'

  cnt = 0
  result.each_pair do |p, r|
    case r
    when :OPEN, :STEALTH, :FAIL
      puts "#{'%5d' % p} : #{r}"
      cnt += 1
    end
  end

  if cnt < 1
    puts '  No data for output.'
  end
end


case ARGV[0]
when nil
    host = '127.0.0.1'
when '-h', '-?', '--help', '--version'
  puts <<MAN
$ ./#{File.basename(__FILE__)} [ host [ start_port [ end_port ] ] ]

Examples:
  ./#{File.basename(__FILE__)}                     ... Scan 127.0.0.1,   port 1 - 65535
  ./#{File.basename(__FILE__)} 203.0.113.1         ... Scan 203.0.113.1, port 1 - 65535
  ./#{File.basename(__FILE__)} 203.0.113.1 80      ... Scan 203.0.113.1, port 80
  ./#{File.basename(__FILE__)} 203.0.113.1 20 500  ... Scan 203.0.113.1, port 20 - 500
MAN

  exit
else
  host = ARGV[0].strip
end

if ARGV[1].nil?
  s_port = 1
  e_port = 65535
else
  s_port = ARGV[1].to_i

  if ARGV[2].nil?
    e_port = s_port
  else
    e_port = ARGV[2].to_i
  end
end

if s_port < 1 || s_port > 65535
  err 'Start port must be between 1 and 65535.'
end
if e_port < 1 || e_port > 65535
  err 'End port must be between 1 and 65535.'
end

result = Hash.new   # Result
queue  = Queue.new  # Work Queue
s_port.upto(e_port) do |p|
  result[p] = nil

  q = { 'host' => host, 'port' => p }
  queue.push q
end


begin
  dbg "Starting to scan... [ #{host} ]"

  # Create worker threaeds
  PARALLEL.times do
    $threads << Thread.new do
      while ! queue.empty?
        w = queue.pop

        dbg "Scanning Port #{w['port']} ..."
        r = scan(w['host'], w['port'])

        result[w['port']] = r
      end
    end
  end

  $threads.each do |t|
    t.join
  end
rescue Interrupt
  dbg 'Interrupt.'
  dbg "Please take a moment to finish all working threads (Max = #{TIMEOUT}sec.)."

  queue.clear
  $threads.each do |t|
    t.join
  end
ensure
  dbg 'Finish!!'
  report(result)
end