user_passkey.rb

# Generating a unique passkey for each user(to use with XBT Tracker) and injecting it in the torrent file.
# This is for Rails.

require 'bencode' # sudo gem install bencode
require 'digest/sha1'

class TorrentsController < ApplicationController

def download_example_torrent
  # Decode the torrent file using the bencode gem
  decoded_torrent = BEncode.load_file("public/files/example.torrent") # This would normally be dynamic and fetched from the DB...
  
  # Generate the info_hash
  info_hash = ([Digest::SHA1.hexdigest(decoded_torrent["info"].bencode)].pack("H*")).downcase

  uid = current_user.id # This assumes an Authlogic authentication system. Adjust accordingly!

  torrent_pass_private_key = "1294e7bc8ca465b124319c70538c1f16"	# This will usually be fetched from the xbt_config table
  torrent_pass_version = 0 # This will usually be fetched from the xbt_users table

  # Generate the passkey, following the XBT Tracker algorithm
  substring = (Digest::SHA1.hexdigest("%s %d %d %s" % [torrent_pass_private_key, torrent_pass_version, uid, info_hash]).slice(0..23))
  passkey = ("%08x%s" % [uid, substring])

  # Tweak the announce URL for to include the passkey		
  announce_url = URI.parse("http://localhost:2710/announce")
  announce_url.path = "/" + passkey + announce_url.path
  
  decoded_torrent["announce"] = announce_url.to_s # New format: http://localhost:2710/passkey/announce

  # Reencode the torrent metadata
  torrent_data = decoded_torrent.bencode

  # Stream the modified torrent file to the user!
  send_data torrent_data, :filename => "passkeyed.torrent", :type => "application/x-bittorrent"
end

end