a dead simple torrent tracker in ruby

tracker.rb

require 'bencode'
require 'sinatra'

torrents = {}

get '/announce' do
  compact = (params[:compact] || '1') == '1'
  no_peer_id = params[:no_peer_id] == '1'
  event = params[:event] || 'empty'
  numwant = (request[:numwant] || 50).to_i

  complete = params[:left].to_i == 0

  torrents[params[:info_hash]] ||= { peers: {}, snatches: 0 }

  pcomplete = 0
  pincomplete = 0

  peerids = torrents[params[:info_hash]][:peers].keys.shuffle
  peerlist = compact ? '' : []

  while numwant > 0 and not peerids.empty?
    peerid = peerids.shift
    peer = torrents[params[:info_hash]][:peers][peerid]
    unless complete and peer[:complete]
      if compact
        peerlist << (peer[:ip].split('.').map(&:to_i) + [peer[:port]]).pack('CCCCS>')
      else
        peer = {
          'ip' => peer[:ip],
          'port' => peer[:port]
        }
        peer['peer id'] = peerid unless no_peer_id
      end

      numwant -= 1
    end

    if peer[:complete]
      pcomplete += 1
    else
      pincomplete += 1
    end
  end

  torrents[params[:info_hash]][:peers][params[:peer_id]] = {
    ip: params[:ip] || request.ip,
    port: params[:port].to_i,
    complete: complete
  }

  torrents[params[:info_hash]][:snatches] += 1 if event == 'complete'

  puts "#{params[:info_hash].unpack('H*').first} #{pcomplete} #{pincomplete}"

  {
    'interval' => 10,
    'min interval' => 1,
    'complete' => pcomplete,
    'incomplete' => pincomplete,
    'peers' => peerlist
  }.bencode
end

get '/scrape' do
  files = {}
  (params[:info_hash] ? [params[:info_hash]] : torrents.keys).each do |info_hash|
    t = torrents[info_hash]
    files[info_hash] = {
      complete: t[:peers].values.count { |p| p[:complete] },
      downloaded: t[:snatches],
      incomplete: t[:peers].values.count { |p| not p[:complete] }
    }
  end

  files.each do |i, t|
    puts "#{i.unpack('H*').first} downloaded=#{t[:downloaded]} complete=#{t[:complete]} incomplete=#{t[:incomplete]}"
  end

  { files: files }.bencode
end