A very fast spaghetti-script written in Ruby that downloads files

download.rb

#!/usr/bin/env ruby
# download (Works for me™)
#
# A simple & fast download script that utilizes em-http-request as http client
# Usage: download <url>
#
# The filename is determined either by the GET path or by the Content-Disposition response header if given.
# The script will check if there is an existing file and try to resume the download if possible.
#
# Sometimes writing Spaghetti code can be a lot of fun. Don't use it, I do not want to maintain this script.

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

unless url = ARGV.first
  puts "Usage: download <url>"
  puts "Destination directory is hardcoded to ~/Downloads"
  exit 1
end
filename = File.basename(url)
target = nil
content_length = received_bytes = 0
file = nil
resume_with_range = false

at_exit { file.close if file.kind_of?(File) && !file.closed? }

download = Proc.new do
  EM.run do
    redirects = 0
    request_headers = { 'Accept-Encoding' => 'deflate, gzip' }
    request_headers.merge!({ 'Range' => "bytes=#{received_bytes}-" }) if resume_with_range
    http = EM::HttpRequest.new(url).get(:head => request_headers, :redirects => 10)
    http.headers do
      if http.response_header['LOCATION']
        puts "Hop ##{redirects+=1} to #{http.response_header['LOCATION']}"
      else
        filename = (http.response_header['CONTENT_DISPOSITION'] =~ /filename="(.*)"/ && $1) || filename
        target = File.expand_path(File.join('~/Downloads', filename))

        unless resume_with_range
          unfinished = File.exist?(target) && File.size(target) < content_length
          file = File.exist?(target) ? File.open(target, 'r+') : File.open(target, 'w')
          content_length = http.response_header['CONTENT_LENGTH'].to_i

          if unfinished && http.response_header['ACCEPT_RANGES']
            received_bytes = File.size(target)
            resume_with_range = true
            file.close
            EM.stop
          elsif unfinished
            puts "Restarting download (Unfortunately the server you download from does not support resuming the transfer)"
            file.rewind
          elsif File.exist?(target) && File.size(target) == content_length
            puts "Download already finished"
            file.close
            EM.stop
          end
        else
          if http.response_header['CONTENT_RANGE'] =~ %r{bytes (\d+)-\d+/(\d+)}
            filepos = $1.to_i
            content_length = $2.to_i
          else
            filepos = 0
          end
          
          if filepos == received_bytes
            puts "Resuming the transfer"
            file.reopen(target, 'r+')
            file.seek(filepos)
          else
            puts "Restarting download (Unfortunately the server you download from does not support resuming the transfer)"
            received_bytes = 0
            file.reopen(target, 'w')
          end
        end
        file.sync = true unless file.closed?
      end
    end
    http.stream do |chunk|
      unless file.closed?
        received_bytes += file.write(chunk)
        print "\r#{'%0.2f' % (received_bytes / 1024.0 / 1024.0)}/#{'%0.2f' % (content_length / 1024.0 / 1024.0)} MB"
      end
    end
    http.callback { EM.stop }
    http.errback { EM.stop }
  end
end

download.call
download.call if resume_with_range

puts target