udp-tracker.js

module.exports = UDPTracker

var BN = require('bn.js')
var compact2string = require('compact2string')
var debug = require('debug')('bittorrent-tracker:udp-tracker')
var dgram = require('dgram')
var EventEmitter = require('events').EventEmitter
var hat = require('hat')
var inherits = require('inherits')
var url = require('url')

var common = require('./common')

var TIMEOUT = 15000

inherits(UDPTracker, EventEmitter)

/**
 * UDP torrent tracker client (for an individual tracker)
 *
 * @param {Client} client       parent bittorrent tracker client
 * @param {string} announceUrl  announce url of tracker
 * @param {Object} opts         options object
 */
function UDPTracker (client, announceUrl, opts) {
  var self = this
  EventEmitter.call(self)
  debug('new udp tracker %s', announceUrl)

  self.client = client
  self.destroyed = false

  self._opts = opts
  self._announceUrl = announceUrl
  self._intervalMs = self.client._intervalMs // use client interval initially
  self._interval = null
  self._cleanupFns = []
}

UDPTracker.prototype.announce = function (opts) {
  var self = this
  self._request(opts)
}

UDPTracker.prototype.scrape = function (opts) {
  var self = this
  opts._scrape = true
  self._request(opts) // udp scrape uses same announce url
}

// TODO: Improve this interface
UDPTracker.prototype.setInterval = function (intervalMs) {
  var self = this
  clearInterval(self._interval)

  self._intervalMs = intervalMs
  if (intervalMs) {
    // HACK
    var update = self.announce.bind(self, self.client._defaultAnnounceOpts())
    self._interval = setInterval(update, self._intervalMs)
  }
}

UDPTracker.prototype.destroy = function () {
  var self = this
  if (self.destroyed) return
  self.destroyed = true

  self._cleanupFns.slice(0).forEach(function (cleanup) {
    cleanup()
  })
  self._cleanupFns = []
}

UDPTracker.prototype._request = function (opts) {
  var self = this
  if (!opts) opts = {}
  var parsedUrl = url.parse(self._announceUrl)
  var transactionId = genTransactionId()
  var socket = dgram.createSocket('udp4')

  var cleanup = function () {
    self._cleanupFns.splice(self._cleanupFns.indexOf(cleanup), 1)
    if (timeout) {
      clearTimeout(timeout)
      timeout = null
    }
    socket.removeListener('error', onError)
    socket.removeListener('message', onSocketMessage)
    socket.on('error', noop) // ignore all future errors
    try { socket.close() } catch (err) {}
    socket = null
  }
  self._cleanupFns.push(cleanup)

  // does not matter if `stopped` event arrives, so supress errors & cleanup after timeout
  var ms = opts.event === 'stopped' ? TIMEOUT / 10 : TIMEOUT
  var timeout = setTimeout(function () {
    timeout = null
    if (opts.event === 'stopped') cleanup()
    else onError(new Error('tracker request timed out (' + opts.event + ')'))
  }, ms)
  if (timeout.unref) timeout.unref()

  send(Buffer.concat([
    common.CONNECTION_ID,
    common.toUInt32(common.ACTIONS.CONNECT),
    transactionId
  ]))

  socket.on('error', onError)
  socket.on('message', onSocketMessage)

  function onSocketMessage (msg) {
    if (self.destroyed) return
    if (msg.length < 8 || msg.readUInt32BE(4) !== transactionId.readUInt32BE(0)) {
      return onError(new Error('tracker sent invalid transaction id'))
    }

    var action = msg.readUInt32BE(0)
    debug('UDP response %s, action %s', self._announceUrl, action)
    switch (action) {
      case 0: // handshake
        if (msg.length < 16) return onError(new Error('invalid udp handshake'))

        if (opts._scrape) scrape(msg.slice(8, 16))
        else announce(msg.slice(8, 16), opts)

        return

      case 1: // announce
        cleanup()
        if (msg.length < 20) return onError(new Error('invalid announce message'))

        var interval = msg.readUInt32BE(8)
        if (interval && !self._opts.interval && self._intervalMs !== 0) {
          // use the interval the tracker recommends, UNLESS the user manually specifies an
          // interval they want to use
          self.setInterval(interval * 1000)
        }

        self.client.emit('update', {
          announce: self._announceUrl,
          complete: msg.readUInt32BE(16),
          incomplete: msg.readUInt32BE(12)
        })

        var addrs
        try {
          addrs = compact2string.multi(msg.slice(20))
        } catch (err) {
          return self.client.emit('warning', err)
        }
        addrs.forEach(function (addr) {
          self.client.emit('peer', addr)
        })
        break

      case 2: // scrape
        cleanup()
        if (msg.length < 20 || (msg.length - 8) % 12 !== 0) {
          return onError(new Error('invalid scrape message'))
        }
        var infoHashes = (Array.isArray(opts.infoHash) && opts.infoHash.length > 0)
          ? opts.infoHash.map(function (infoHash) { return infoHash.toString('hex') })
          : (opts.infoHash || self.client._infoHash).toString('hex')

        for (var i = 0, len = (msg.length - 8) / 12; i < len; i += 1) {
          self.client.emit('scrape', {
            announce: self._announceUrl,
            infoHash: infoHashes[i],
            complete: msg.readUInt32BE(8 + (i * 12)),
            downloaded: msg.readUInt32BE(12 + (i * 12)),
            incomplete: msg.readUInt32BE(16 + (i * 12))
          })
        }
        break

      case 3: // error
        cleanup()
        if (msg.length < 8) return onError(new Error('invalid error message'))
        self.client.emit('warning', new Error(msg.slice(8).toString()))
        break

      default:
        onError(new Error('tracker sent invalid action'))
        break
    }
  }

  function onError (err) {
    if (self.destroyed) return
    cleanup()
    if (err.message) err.message += ' (' + self._announceUrl + ')'
    // errors will often happen if a tracker is offline, so don't treat it as fatal
    self.client.emit('warning', err)
  }

  function send (message) {
    if (!parsedUrl.port) {
      parsedUrl.port = 80
    }
    socket.send(message, 0, message.length, parsedUrl.port, parsedUrl.hostname)
  }

  function announce (connectionId, opts) {
    opts = opts || {}
    transactionId = genTransactionId()

    send(Buffer.concat([
      connectionId,
      common.toUInt32(common.ACTIONS.ANNOUNCE),
      transactionId,
      self.client._infoHash,
      self.client._peerId,
      toUInt64(opts.downloaded || 0),
      opts.left != null ? toUInt64(opts.left) : new Buffer('FFFFFFFFFFFFFFFF', 'hex'),
      toUInt64(opts.uploaded || 0),
      common.toUInt32(common.EVENTS[opts.event] || 0),
      common.toUInt32(0), // ip address (optional)
      common.toUInt32(0), // key (optional)
      common.toUInt32(opts.numWant || common.DEFAULT_ANNOUNCE_PEERS),
      toUInt16(self.client._port || 0)
    ]))
  }

  function scrape (connectionId) {
    transactionId = genTransactionId()

    var infoHash = (Array.isArray(opts.infoHash) && opts.infoHash.length > 0)
      ? Buffer.concat(opts.infoHash)
      : (opts.infoHash || self.client._infoHash)

    send(Buffer.concat([
      connectionId,
      common.toUInt32(common.ACTIONS.SCRAPE),
      transactionId,
      infoHash
    ]))
  }
}

function genTransactionId () {
  return new Buffer(hat(32), 'hex')
}

function toUInt16 (n) {
  var buf = new Buffer(2)
  buf.writeUInt16BE(n, 0)
  return buf
}

var MAX_UINT = 4294967295

function toUInt64 (n) {
  if (n > MAX_UINT || typeof n === 'string') {
    var bytes = new BN(n).toArray()
    while (bytes.length < 8) {
      bytes.unshift(0)
    }
    return new Buffer(bytes)
  }
  return Buffer.concat([common.toUInt32(0), common.toUInt32(n)])
}

function noop () {}