foostat.rb

require 'celluloid/io'
require 'celluloid/autostart'
require 'net/sftp'

class Foo
  include Celluloid::IO

  def initialize
    async.connect_and_stat
  end

  def connect_and_stat
    # without celluloid-io
    #@sftp = Net::SFTP.start('localhost', ENV['USER'])

    # with celluloid-io
    @sftp = Net::SFTP.start('localhost', ENV['USER'], proxy: TCPSocket)
    stat = @sftp.stat!('/etc/passwd')
    p stat
    terminate
  end
end

Foo.run