client.js

const debug = require('debug')('bittorrent-tracker:client')
const EventEmitter = require('events')
const once = require('once')
const parallel = require('run-parallel')
const Peer = require('simple-peer')

const common = require('./lib/common')
const HTTPTracker = require('./lib/client/http-tracker') // empty object in browser
const UDPTracker = require('./lib/client/udp-tracker') // empty object in browser
const WebSocketTracker = require('./lib/client/websocket-tracker')

/**
 * BitTorrent tracker client.
 *
 * Find torrent peers, to help a torrent client participate in a torrent swarm.
 *
 * @param {Object} opts                          options object
 * @param {string|Buffer} opts.infoHash          torrent info hash
 * @param {string|Buffer} opts.peerId            peer id
 * @param {string|Array.<string>} opts.announce  announce
 * @param {number} opts.port                     torrent client listening port
 * @param {function} opts.getAnnounceOpts        callback to provide data to tracker
 * @param {number} opts.rtcConfig                RTCPeerConnection configuration object
 * @param {number} opts.userAgent                User-Agent header for http requests
 * @param {number} opts.wrtc                     custom webrtc impl (useful in node.js)
 */
class Client extends EventEmitter {
  constructor (opts = {}) {
    super()

    if (!opts.peerId) throw new Error('Option `peerId` is required')
    if (!opts.infoHash) throw new Error('Option `infoHash` is required')
    if (!opts.announce) throw new Error('Option `announce` is required')
    if (!process.browser && !opts.port) throw new Error('Option `port` is required')

    this.peerId = typeof opts.peerId === 'string'
      ? opts.peerId
      : opts.peerId.toString('hex')
    this._peerIdBuffer = Buffer.from(this.peerId, 'hex')
    this._peerIdBinary = this._peerIdBuffer.toString('binary')

    this.infoHash = typeof opts.infoHash === 'string'
      ? opts.infoHash.toLowerCase()
      : opts.infoHash.toString('hex')
    this._infoHashBuffer = Buffer.from(this.infoHash, 'hex')
    this._infoHashBinary = this._infoHashBuffer.toString('binary')

    debug('new client %s', this.infoHash)

    this.destroyed = false

    this._port = opts.port
    this._getAnnounceOpts = opts.getAnnounceOpts
    this._rtcConfig = opts.rtcConfig
    this._userAgent = opts.userAgent

    // Support lazy 'wrtc' module initialization
    // See: https://github.com/webtorrent/webtorrent-hybrid/issues/46
    this._wrtc = typeof opts.wrtc === 'function' ? opts.wrtc() : opts.wrtc

    let announce = typeof opts.announce === 'string'
      ? [opts.announce]
      : opts.announce == null ? [] : opts.announce

    // Remove trailing slash from trackers to catch duplicates
    announce = announce.map(announceUrl => {
      announceUrl = announceUrl.toString()
      if (announceUrl[announceUrl.length - 1] === '/') {
        announceUrl = announceUrl.substring(0, announceUrl.length - 1)
      }
      return announceUrl
    })
    // remove duplicates by converting to Set and back
    announce = Array.from(new Set(announce))

    const webrtcSupport = this._wrtc !== false && (!!this._wrtc || Peer.WEBRTC_SUPPORT)

    const nextTickWarn = err => {
      process.nextTick(() => {
        this.emit('warning', err)
      })
    }

    this._trackers = announce
      .map(announceUrl => {
        let parsedUrl
        try {
          parsedUrl = new URL(announceUrl)
        } catch (err) {
          nextTickWarn(new Error(`Invalid tracker URL: ${announceUrl}`))
          return null
        }

        const port = parsedUrl.port
        if (port < 0 || port > 65535) {
          nextTickWarn(new Error(`Invalid tracker port: ${announceUrl}`))
          return null
        }

        const protocol = parsedUrl.protocol
        if ((protocol === 'http:' || protocol === 'https:') &&
            typeof HTTPTracker === 'function') {
          return new HTTPTracker(this, announceUrl)
        } else if (protocol === 'udp:' && typeof UDPTracker === 'function') {
          return new UDPTracker(this, announceUrl)
        } else if ((protocol === 'ws:' || protocol === 'wss:') && webrtcSupport) {
          // Skip ws:// trackers on https:// sites because they throw SecurityError
          if (protocol === 'ws:' && typeof window !== 'undefined' &&
              window.location.protocol === 'https:') {
            nextTickWarn(new Error(`Unsupported tracker protocol: ${announceUrl}`))
            return null
          }
          return new WebSocketTracker(this, announceUrl)
        } else {
          nextTickWarn(new Error(`Unsupported tracker protocol: ${announceUrl}`))
          return null
        }
      })
      .filter(Boolean)
  }

  /**
   * Send a `start` announce to the trackers.
   * @param {Object} opts
   * @param {number=} opts.uploaded
   * @param {number=} opts.downloaded
   * @param {number=} opts.left (if not set, calculated automatically)
   */
  start (opts) {
    opts = this._defaultAnnounceOpts(opts)
    opts.event = 'started'
    debug('send `start` %o', opts)
    this._announce(opts)

    // start announcing on intervals
    this._trackers.forEach(tracker => {
      tracker.setInterval()
    })
  }

  /**
   * Send a `stop` announce to the trackers.
   * @param {Object} opts
   * @param {number=} opts.uploaded
   * @param {number=} opts.downloaded
   * @param {number=} opts.numwant
   * @param {number=} opts.left (if not set, calculated automatically)
   */
  stop (opts) {
    opts = this._defaultAnnounceOpts(opts)
    opts.event = 'stopped'
    debug('send `stop` %o', opts)
    this._announce(opts)
  }

  /**
   * Send a `complete` announce to the trackers.
   * @param {Object} opts
   * @param {number=} opts.uploaded
   * @param {number=} opts.downloaded
   * @param {number=} opts.numwant
   * @param {number=} opts.left (if not set, calculated automatically)
   */
  complete (opts) {
    if (!opts) opts = {}
    opts = this._defaultAnnounceOpts(opts)
    opts.event = 'completed'
    debug('send `complete` %o', opts)
    this._announce(opts)
  }

  /**
   * Send a `update` announce to the trackers.
   * @param {Object} opts
   * @param {number=} opts.uploaded
   * @param {number=} opts.downloaded
   * @param {number=} opts.numwant
   * @param {number=} opts.left (if not set, calculated automatically)
   */
  update (opts) {
    opts = this._defaultAnnounceOpts(opts)
    if (opts.event) delete opts.event
    debug('send `update` %o', opts)
    this._announce(opts)
  }

  _announce (opts) {
    this._trackers.forEach(tracker => {
      // tracker should not modify `opts` object, it's passed to all trackers
      tracker.announce(opts)
    })
  }

  /**
   * Send a scrape request to the trackers.
   * @param {Object} opts
   */
  scrape (opts) {
    debug('send `scrape`')
    if (!opts) opts = {}
    this._trackers.forEach(tracker => {
      // tracker should not modify `opts` object, it's passed to all trackers
      tracker.scrape(opts)
    })
  }

  setInterval (intervalMs) {
    debug('setInterval %d', intervalMs)
    this._trackers.forEach(tracker => {
      tracker.setInterval(intervalMs)
    })
  }

  destroy (cb) {
    if (this.destroyed) return
    this.destroyed = true
    debug('destroy')

    const tasks = this._trackers.map(tracker => cb => {
      tracker.destroy(cb)
    })

    parallel(tasks, cb)

    this._trackers = []
    this._getAnnounceOpts = null
  }

  _defaultAnnounceOpts (opts = {}) {
    if (opts.numwant == null) opts.numwant = common.DEFAULT_ANNOUNCE_PEERS

    if (opts.uploaded == null) opts.uploaded = 0
    if (opts.downloaded == null) opts.downloaded = 0

    if (this._getAnnounceOpts) opts = Object.assign({}, opts, this._getAnnounceOpts())

    return opts
  }
}

/**
 * Simple convenience function to scrape a tracker for an info hash without needing to
 * create a Client, pass it a parsed torrent, etc. Support scraping a tracker for multiple
 * torrents at the same time.
 * @params {Object} opts
 * @param  {string|Array.<string>} opts.infoHash
 * @param  {string} opts.announce
 * @param  {function} cb
 */
Client.scrape = (opts, cb) => {
  cb = once(cb)

  if (!opts.infoHash) throw new Error('Option `infoHash` is required')
  if (!opts.announce) throw new Error('Option `announce` is required')

  const clientOpts = Object.assign({}, opts, {
    infoHash: Array.isArray(opts.infoHash) ? opts.infoHash[0] : opts.infoHash,
    peerId: Buffer.from('01234567890123456789'), // dummy value
    port: 6881 // dummy value
  })

  const client = new Client(clientOpts)
  client.once('error', cb)
  client.once('warning', cb)

  let len = Array.isArray(opts.infoHash) ? opts.infoHash.length : 1
  const results = {}
  client.on('scrape', data => {
    len -= 1
    results[data.infoHash] = data
    if (len === 0) {
      client.destroy()
      const keys = Object.keys(results)
      if (keys.length === 1) {
        cb(null, results[keys[0]])
      } else {
        cb(null, results)
      }
    }
  })

  opts.infoHash = Array.isArray(opts.infoHash)
    ? opts.infoHash.map(infoHash => {
      return Buffer.from(infoHash, 'hex')
    })
    : Buffer.from(opts.infoHash, 'hex')
  client.scrape({ infoHash: opts.infoHash })
  return client
}

module.exports = Client