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#!/usr/bin/env ruby

require 'socket'

class PortScanner

  def initialize(host: '0.0.0.0', ports:, batch_size: 1024)

    @host      = host

    @ports     = ports.to_a

    @batch_size = batch_size

  end

  def scan_port(port, timeout)

    peer = Socket.tcp(@host, port, connect_timeout: timeout)

    puts "#{port} #{peer.wait_writable(timeout) ? 'open' : 'timeout'}"

    peer.close

  rescue Errno::ECONNREFUSED

    # puts "#{port} closed"

  rescue SystemCallError => e

    puts "#{port} #{e.message}"

  end

  def start(timeout = 1.0)

    @batch_size.times.map do

      Threadlet.start do

         while port = @ports.shift

           scan_port(port, timeout)

         end

      end

    end.each(&:join)

  end

end

limits = Process.getrlimit(Process::RLIMIT_NOFILE)

batch_size = [512, limits.first].min

host = "127.0.0.1"

scanner = PortScanner.new(host: host, ports: Range.new(1, 65535), batch_size: batch_size)

scanner.start