http-tracker.js

const arrayRemove = require('unordered-array-remove')
const bencode = require('bencode')
const compact2string = require('compact2string')
const debug = require('debug')('bittorrent-tracker:http-tracker')
const get = require('simple-get')

const common = require('../common')
const Tracker = require('./tracker')

const HTTP_SCRAPE_SUPPORT = /\/(announce)[^/]*$/

/**
 * HTTP 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
 */
class HTTPTracker extends Tracker {
  constructor (client, announceUrl, opts) {
    super(client, announceUrl)

    debug('new http tracker %s', announceUrl)

    // Determine scrape url (if http tracker supports it)
    this.scrapeUrl = null

    const match = this.announceUrl.match(HTTP_SCRAPE_SUPPORT)
    if (match) {
      const pre = this.announceUrl.slice(0, match.index)
      const post = this.announceUrl.slice(match.index + 9)
      this.scrapeUrl = `${pre}/scrape${post}`
    }

    this.cleanupFns = []
    this.maybeDestroyCleanup = null
  }

  announce (opts) {
    if (this.destroyed) return

    const params = Object.assign({}, opts, {
      compact: (opts.compact == null) ? 1 : opts.compact,
      info_hash: this.client._infoHashBinary,
      peer_id: this.client._peerIdBinary,
      port: this.client._port
    })
    if (this._trackerId) params.trackerid = this._trackerId

    this._request(this.announceUrl, params, (err, data) => {
      if (err) return this.client.emit('warning', err)
      this._onAnnounceResponse(data)
    })
  }

  scrape (opts) {
    if (this.destroyed) return

    if (!this.scrapeUrl) {
      this.client.emit('error', new Error(`scrape not supported ${this.announceUrl}`))
      return
    }

    const infoHashes = (Array.isArray(opts.infoHash) && opts.infoHash.length > 0)
      ? opts.infoHash.map(infoHash => {
        return infoHash.toString('binary')
      })
      : (opts.infoHash && opts.infoHash.toString('binary')) || this.client._infoHashBinary
    const params = {
      info_hash: infoHashes
    }
    this._request(this.scrapeUrl, params, (err, data) => {
      if (err) return this.client.emit('warning', err)
      this._onScrapeResponse(data)
    })
  }

  destroy (cb) {
    const self = this
    if (this.destroyed) return cb(null)
    this.destroyed = true
    clearInterval(this.interval)

    // If there are no pending requests, destroy immediately.
    if (this.cleanupFns.length === 0) return destroyCleanup()

    // Otherwise, wait a short time for pending requests to complete, then force
    // destroy them.
    var timeout = setTimeout(destroyCleanup, common.DESTROY_TIMEOUT)

    // But, if all pending requests complete before the timeout fires, do cleanup
    // right away.
    this.maybeDestroyCleanup = () => {
      if (this.cleanupFns.length === 0) destroyCleanup()
    }

    function destroyCleanup () {
      if (timeout) {
        clearTimeout(timeout)
        timeout = null
      }
      self.maybeDestroyCleanup = null
      self.cleanupFns.slice(0).forEach(cleanup => {
        cleanup()
      })
      self.cleanupFns = []
      cb(null)
    }
  }

  _request (requestUrl, params, cb) {
    const self = this
    const u = requestUrl + (!requestUrl.includes('?') ? '?' : '&') +
      common.querystringStringify(params)

    this.cleanupFns.push(cleanup)

    let request = get.concat({
      url: u,
      timeout: common.REQUEST_TIMEOUT,
      headers: {
        'user-agent': this.client._userAgent || ''
      }
    }, onResponse)

    function cleanup () {
      if (request) {
        arrayRemove(self.cleanupFns, self.cleanupFns.indexOf(cleanup))
        request.abort()
        request = null
      }
      if (self.maybeDestroyCleanup) self.maybeDestroyCleanup()
    }

    function onResponse (err, res, data) {
      cleanup()
      if (self.destroyed) return

      if (err) return cb(err)
      if (res.statusCode !== 200) {
        return cb(new Error(`Non-200 response code ${res.statusCode} from ${self.announceUrl}`))
      }
      if (!data || data.length === 0) {
        return cb(new Error(`Invalid tracker response from${self.announceUrl}`))
      }

      try {
        data = bencode.decode(data)
      } catch (err) {
        return cb(new Error(`Error decoding tracker response: ${err.message}`))
      }
      const failure = data['failure reason']
      if (failure) {
        debug(`failure from ${requestUrl} (${failure})`)
        return cb(new Error(failure))
      }

      const warning = data['warning message']
      if (warning) {
        debug(`warning from ${requestUrl} (${warning})`)
        self.client.emit('warning', new Error(warning))
      }

      debug(`response from ${requestUrl}`)

      cb(null, data)
    }
  }

  _onAnnounceResponse (data) {
    const interval = data.interval || data['min interval']
    if (interval) this.setInterval(interval * 1000)

    const trackerId = data['tracker id']
    if (trackerId) {
      // If absent, do not discard previous trackerId value
      this._trackerId = trackerId
    }

    const response = Object.assign({}, data, {
      announce: this.announceUrl,
      infoHash: common.binaryToHex(data.info_hash)
    })
    this.client.emit('update', response)

    let addrs
    if (Buffer.isBuffer(data.peers)) {
      // tracker returned compact response
      try {
        addrs = compact2string.multi(data.peers)
      } catch (err) {
        return this.client.emit('warning', err)
      }
      addrs.forEach(addr => {
        this.client.emit('peer', addr)
      })
    } else if (Array.isArray(data.peers)) {
      // tracker returned normal response
      data.peers.forEach(peer => {
        this.client.emit('peer', `${peer.ip}:${peer.port}`)
      })
    }

    if (Buffer.isBuffer(data.peers6)) {
      // tracker returned compact response
      try {
        addrs = compact2string.multi6(data.peers6)
      } catch (err) {
        return this.client.emit('warning', err)
      }
      addrs.forEach(addr => {
        this.client.emit('peer', addr)
      })
    } else if (Array.isArray(data.peers6)) {
      // tracker returned normal response
      data.peers6.forEach(peer => {
        const ip = /^\[/.test(peer.ip) || !/:/.test(peer.ip)
          ? peer.ip /* ipv6 w/ brackets or domain name */
          : `[${peer.ip}]` /* ipv6 without brackets */
        this.client.emit('peer', `${ip}:${peer.port}`)
      })
    }
  }

  _onScrapeResponse (data) {
    // NOTE: the unofficial spec says to use the 'files' key, 'host' has been
    // seen in practice
    data = data.files || data.host || {}

    const keys = Object.keys(data)
    if (keys.length === 0) {
      this.client.emit('warning', new Error('invalid scrape response'))
      return
    }

    keys.forEach(infoHash => {
      // TODO: optionally handle data.flags.min_request_interval
      // (separate from announce interval)
      const response = Object.assign(data[infoHash], {
        announce: this.announceUrl,
        infoHash: common.binaryToHex(infoHash)
      })
      this.client.emit('scrape', response)
    })
  }
}

HTTPTracker.prototype.DEFAULT_ANNOUNCE_INTERVAL = 30 * 60 * 1000 // 30 minutes

module.exports = HTTPTracker