Proof of concept connect() port scanner using Ruby's async gems.

async_port_scanner.rb

require 'bundler/inline'

gemfile do
  gem 'async-io', '~> 1.30'
end

require 'async'
require 'async/queue'
require 'async/io'

pool_size  = 100
scan_queue = Async::LimitedQueue.new(pool_size)

host  = 'scanme.nmap.org'
ports = (1..65535)

Async do |task|
  task.async do
    ports.each do |port|
      scan_queue.enqueue([host, port])
    end

    pool_size.times { scan_queue.enqueue(nil) }
  end

  workers = pool_size.times.map do
    task.async do
      while (host, port = scan_queue.dequeue)
        endpoint = Async::IO::Endpoint.tcp(host,port)

        begin
          endpoint.connect do |connection|
            puts ">>> Open port found #{host}:#{port}"
          end
        rescue Errno::ECONNREFUSED,
               Errno::ETIMEDOUT
        rescue Errno::EHOSTUNREACH
          sleep(1)
          retry
        end
      end
    end
  end

  workers.each(&:wait)
end