Download a file with EventMachine

em_download_test.rb

require 'rubygems'
require 'eventmachine'
require 'em-http'

# Learning EM: file download with progress.
# See http://rubylearning.com/blog/2010/10/01/an-introduction-to-eventmachine-and-how-to-avoid-callback-spaghetti/
# for a brilliant introduction to EM.
EM.run do
  
  # just an innocent eclipse file of 2megs from a reasonably fast but not balzing fast server.
  @file_download_url= ENV['file_download_url'] || "http://www.intalio.org/public/maven2/org/eclipse/jdt/ecj/3.5.1/ecj-3.5.1.jar"
  @download_size = -1
  @downloaded_size=0
  
  download_uri = URI.parse(@file_download_url)
  @file = open(download_uri.path.split('/').last, "wb")
  download_url_no_userinfo = "#{download_uri.scheme}://#{download_uri.host}#{download_uri.path}"
  http = EM::HttpRequest.new(download_url_no_userinfo)
          .get(:head => download_uri.user.nil? ? {}
             : {'authorization' => [download_uri.user, download_uri.password]})
  
  http.errback { p 'Uh oh'; @file.close; EM.stop }
  
  http.callback {
    @file.close
    unless http.response_header.status == 200
      puts "Call failed with response code #{http.response_header.status}"
    end
    EM.stop
  }

  http.headers do |hash|
    p [:headers, hash]
    @download_size = hash["CONTENT_LENGTH"].to_i unless hash["CONTENT_LENGTH"].nil?
  end
  
  http.stream do |chunk|
    @downloaded_size+=chunk.length
    @file.write(chunk)
  end
  
  EM.add_periodic_timer(1) do # #{@downloaded_size * 100 / @download_size}%
    if @downloaded_size == -1
      if @download_size == 0
        p "The download has not started"
      else
        p "Downloading #{@file.path} 0%: total size #{@download_size} bytes. Total size unknown"
      end
    else
        if @download_size == 0
          p "Downloading #{@file.path} #{@downloaded_size} out of #{@download_size}. Total size unknown"
        else
          p "Downloading #{@file.path} #{@downloaded_size} out of #{@download_size}: #{@downloaded_size * 100 / @download_size}%"
        end
    end
  end
  
end ## EM Loop