asynchronous port scanner in ruby

async_port_scanner.rb

require 'async/io'
require 'async/await'
require 'async/semaphore'

class PortScanner
  include Async::Await
  include Async::IO

  def initialize(host: '127.0.0.1', ports:)
    @host      = host
    @ports     = ports
    @semaphore = Async::Semaphore.new(`ulimit -n`.to_i)
  end

  def scan_port(port, timeout: 0.5)
    timeout(timeout) do 
      Async::IO::Endpoint.tcp(@host, port).connect do |peer|
        peer.close 
        puts "#{port} open"
      end
    end
  rescue Errno::ECONNREFUSED, Async::TimeoutError
    puts "#{port} closed"
  rescue Errno::EMFILE
    sleep timeout
    retry 
  end

  async def start(timeout: 0.5)
    @ports.map do |port|
      @semaphore.async do
        scan_port(port, timeout: timeout)
      end
    end.collect(&:result)
  end
end

scanner = PortScanner.new(ports: (1..1024))

scanner.start

@picatz Because of the way async works - scanner.start will wait until all tasks complete anyway.

If you add

require 'async/semaphore'

def initialize
    @semaphore = Async::Semaphore.new(`ulimit -n`.to_i)
...
end

# remove async from def scan_port

async def start(timeout: 0.5)
    @ports.map{|port|
        @semaphore.async do
            scan_port(port, timeout: timeout)}
        end
    end.collect(&:result)
end

You should avoid the need for handling Errno::EMFILE.

You need to use async v1.9.1 for this to work.

@ioquatix Async::Semaphore seems to be a nice abstraction to help clean up the code and provide a similar semantic for people that understand Ruby's multi-threading APIs. 👌

However, I still seem to reach the too many files limit since, I'd assume, other operations on my system have files that are open. So, I still end up hitting Errno::EMFILE, or using it to keep track of the situation myself with raise Errno::EMFILE while @open_fds >= @fd_limit which I don't mind doing in this case -- I think.