run Sinatra app on demand

load.rb

# usage:
#
# ruby load.rb ruby /path/to/sinatra_ondemand.rb
#
# or (with rbenv):
#
# ruby load.rb /bin/zsh -c "RBENV_VERSION=1.9.3-rc1 ruby /path/to/sinatra_ondemand.rb"

require 'launch_agent'

agent = LaunchAgent::Base.new(*ARGV)
agent['Sockets'] = {
  'Socket' => {
    'SockServiceName' => '19000'
  }
}
agent['inetdCompatibility'] = {
  'Wait' => false
}
agent['ProgramArguments'] = ARGV
agent['Label'] = agent.job_id

agent.send(agent.loaded? ? :unload : :load)

sinatra_ondemand.rb

#!/usr/bin/env ruby
# based on http://paste.mifo.sk/snippets/starting-sinatra-through-xinetd

require 'thin'
require 'socket'
require 'sinatra'
require 'rack-musicindex'

# git clone https://github.com/youpy/vkcom.git
# cd vkcom
# rake build
# gem install pkg/vkcom-x-x-x.gem
require 'vkcom'

server_thread = Thread.new do
  # find unused port
  TCPServer.new('0.0.0.0', 0).tap {|s| @port = s.addr[1] }.close

  @thin = Thin::Server.new('0.0.0.0', @port, { :"max-persistent-conns" => 0 }) do
    set :run, false
    set :logging, false

    use Rack::MusicIndex, {
      '/JD' => '/Users/youpy/Downloads/JD',
      '/Downloads' => '/Users/youpy/Downloads/',
      '/Dropbox/Downloads' => '/Users/youpy/Dropbox/Downloads/'
    }

    get '/vkcom/:name' do
      content_type 'application/xml;charset=utf-8'
      Vkcom::Renderer::XML.new(Vkcom::Site.new('http://vk.com/%s' % params[:name])).render
    end

    # deprecated
    %w/id383659 webwave hyperboreavw vprwv badwaves/.each do |name|
      get '/%s' % name do
        redirect '/vkcom/%s' % name, 302
      end
    end

    run Sinatra::Application
  end

  @thin.silent = true
  @thin.maximum_persistent_connections = 0
  @thin.start
end

client_thread = Thread.new do
  begin
    socket = TCPSocket.open('0.0.0.0', @port) if @port
    sleep 0.5
  rescue Errno::ECONNREFUSED
  end until socket

  buf = ''
  finished = false

  while true
    break if finished

    rs, ws = IO.select([$stdin, socket], [socket])

    rs.each do |r|
      if r == $stdin
        data = r.read(1)
        if data
          buf += data
        end
      else
        data = r.recv(1024)
        print data
        finished = true if data.size == 0
      end
    end

    ws.each do |w|
      w.write(buf)
      buf = ''
    end
  end

  server_thread.kill
end

[client_thread, server_thread].each do |t|
  t.join
end