How to stream a file download with em-http

test-em-http.rb

require 'em-http'
require 'eventmachine'

url = ARGV[0]
puts "going to try to download #{url}"

EventMachine.run do
  req = EventMachine::HttpRequest.new(url).get
  File.unlink("really_big_file") if File.exist?("really_big_file")

  req.headers do |headers|
    if headers.status != 200
      puts "Failed to download! Status: #{headers.status}"
      req.close
      EM.stop
    end
  end

  req.stream do |chunk|
    File.open("really_big_file", 'a') do |fd|
      fd.write(chunk)
    end
  end

  req.callback do
    puts "File downloaded successfully it seems"
    EM.stop
  end

  req.errback do
    req.close
    puts "Argh! Error downloading the thing"
  end
end