Capture stderr data on EventMachine.popen

popen3.rb

#!/usr/bin/env ruby -wW1

require 'eventmachine'

module EventMachine
  # @see http://eventmachine.rubyforge.org/EventMachine.html#M000491
  def self.popen3(cmd, handler=nil, *args)
    klass = klass_from_handler(Connection, handler, *args)
    w     = Shellwords::shellwords(cmd)
    w.unshift(w.first) if w.first

    new_stderr = $stderr.dup
    rd, wr     = IO::pipe

    $stderr.reopen wr
    s = invoke_popen(w)
    $stderr.reopen new_stderr
    
    klass.new(s, *args).tap do |c|
      EM.attach(rd, Popen3StderrHandler, c)
      @conns[s] = c
      yield(c) if block_given?
    end
  end 
  
  class Popen3StderrHandler < EventMachine::Connection
    def initialize(connection)
      @connection = connection
    end
    
    def receive_data(data)
      @connection.receive_stderr(data)
    end
  end  # class::Popen3StderrHandler
  
end # module::EventMachine


class CountRecvr < EventMachine::Connection
  include EventMachine::Deferrable
  
  class << self
    def start(cmd, *args)
      EM.popen3(cmd, self, *args).tap { |o| yield(o) if block_given? }
    end
  end # << self
  
  def initialize(cnt = 5)
    $stderr.puts("#{self.class}.new(#{cnt}) -> #{self}")
    @cnt  = cnt
    @data = ""
  end
  
  def post_init
    $stderr.puts "post init from parent"
    send_data("#{@cnt}\n")
  end
  
  def receive_data(d)
    puts "receive data from child: #{d.dump}"
    @data << d
    @data.include?("#{self}") && raise("stderr is shared by parent and child!")
  end
  
  alias :receive_stderr :receive_data
  
  def unbind
    get_status.exitstatus == 0 ? succeed(@data, self) : fail(@data, self)
  end
end # class::CountRecvr < EventMachine::Connection


# @see http://eventmachine.rubyforge.org/EventMachine.html#M000491
# @see https://gist.github.com/535644
EM.run {
  CountRecvr.start(%q{ruby -e' gets.to_i.times{ |i| $stderr.puts i+1; sleep 1 }'}, ARGV[0] || 3) do |cntr|
    cntr.callback { EM.stop }
    cntr.errback  { EM.stop }
  end
}