index.js

var debug = require('debug')('simple-peer')
var getBrowserRTC = require('get-browser-rtc')
var randombytes = require('randombytes')
var stream = require('readable-stream')
var queueMicrotask = require('queue-microtask') // TODO: remove when Node 10 is not supported

var MAX_BUFFERED_AMOUNT = 64 * 1024
var ICECOMPLETE_TIMEOUT = 5 * 1000
var CHANNEL_CLOSING_TIMEOUT = 5 * 1000

// HACK: Filter trickle lines when trickle is disabled #354
function filterTrickle (sdp) {
  return sdp.replace(/a=ice-options:trickle\s\n/g, '')
}

function makeError (message, code) {
  var err = new Error(message)
  err.code = code
  return err
}

function warn (message) {
  console.warn(message)
}

/**
 * WebRTC peer connection. Same API as node core `net.Socket`, plus a few extra methods.
 * Duplex stream.
 * @param {Object} opts
 */
class Peer extends stream.Duplex {
  constructor (opts) {
    opts = Object.assign({
      allowHalfOpen: false
    }, opts)

    super(opts)

    this._id = randombytes(4).toString('hex').slice(0, 7)
    this._debug('new peer %o', opts)

    this.channelName = opts.initiator
      ? opts.channelName || randombytes(20).toString('hex')
      : null

    this.initiator = opts.initiator || false
    this.channelConfig = opts.channelConfig || Peer.channelConfig
    this.config = Object.assign({}, Peer.config, opts.config)
    this.offerOptions = opts.offerOptions || {}
    this.answerOptions = opts.answerOptions || {}
    this.sdpTransform = opts.sdpTransform || (sdp => sdp)
    this.streams = opts.streams || (opts.stream ? [opts.stream] : []) // support old "stream" option
    this.trickle = opts.trickle !== undefined ? opts.trickle : true
    this.allowHalfTrickle = opts.allowHalfTrickle !== undefined ? opts.allowHalfTrickle : false
    this.iceCompleteTimeout = opts.iceCompleteTimeout || ICECOMPLETE_TIMEOUT

    this.destroyed = false
    this._connected = false

    this.remoteAddress = undefined
    this.remoteFamily = undefined
    this.remotePort = undefined
    this.localAddress = undefined
    this.localFamily = undefined
    this.localPort = undefined

    this._wrtc = (opts.wrtc && typeof opts.wrtc === 'object')
      ? opts.wrtc
      : getBrowserRTC()

    if (!this._wrtc) {
      if (typeof window === 'undefined') {
        throw makeError('No WebRTC support: Specify `opts.wrtc` option in this environment', 'ERR_WEBRTC_SUPPORT')
      } else {
        throw makeError('No WebRTC support: Not a supported browser', 'ERR_WEBRTC_SUPPORT')
      }
    }

    this._pcReady = false
    this._channelReady = false
    this._iceComplete = false // ice candidate trickle done (got null candidate)
    this._iceCompleteTimer = null // send an offer/answer anyway after some timeout
    this._channel = null
    this._pendingCandidates = []

    this._isNegotiating = !this.initiator // is this peer waiting for negotiation to complete?
    this._batchedNegotiation = false // batch synchronous negotiations
    this._queuedNegotiation = false // is there a queued negotiation request?
    this._sendersAwaitingStable = []
    this._senderMap = new Map()
    this._firstStable = true
    this._closingInterval = null

    this._remoteTracks = []
    this._remoteStreams = []

    this._chunk = null
    this._cb = null
    this._interval = null

    try {
      this._pc = new (this._wrtc.RTCPeerConnection)(this.config)
    } catch (err) {
      queueMicrotask(() => this.destroy(makeError(err, 'ERR_PC_CONSTRUCTOR')))
      return
    }

    // We prefer feature detection whenever possible, but sometimes that's not
    // possible for certain implementations.
    this._isReactNativeWebrtc = typeof this._pc._peerConnectionId === 'number'

    this._pc.oniceconnectionstatechange = () => {
      this._onIceStateChange()
    }
    this._pc.onicegatheringstatechange = () => {
      this._onIceStateChange()
    }
    this._pc.onconnectionstatechange = () => {
      this._onConnectionStateChange()
    }
    this._pc.onsignalingstatechange = () => {
      this._onSignalingStateChange()
    }
    this._pc.onicecandidate = event => {
      this._onIceCandidate(event)
    }

    // Other spec events, unused by this implementation:
    // - onconnectionstatechange
    // - onicecandidateerror
    // - onfingerprintfailure
    // - onnegotiationneeded

    if (this.initiator) {
      this._setupData({
        channel: this._pc.createDataChannel(this.channelName, this.channelConfig)
      })
    } else {
      this._pc.ondatachannel = event => {
        this._setupData(event)
      }
    }

    if (this.streams) {
      this.streams.forEach(stream => {
        this.addStream(stream)
      })
    }
    this._pc.ontrack = event => {
      this._onTrack(event)
    }

    if (this.initiator) {
      this._needsNegotiation()
    }

    this._onFinishBound = () => {
      this._onFinish()
    }
    this.once('finish', this._onFinishBound)
  }

  get bufferSize () {
    return (this._channel && this._channel.bufferedAmount) || 0
  }

  // HACK: it's possible channel.readyState is "closing" before peer.destroy() fires
  // https://bugs.chromium.org/p/chromium/issues/detail?id=882743
  get connected () {
    return (this._connected && this._channel.readyState === 'open')
  }

  address () {
    return { port: this.localPort, family: this.localFamily, address: this.localAddress }
  }

  signal (data) {
    if (this.destroyed) throw makeError('cannot signal after peer is destroyed', 'ERR_SIGNALING')
    if (typeof data === 'string') {
      try {
        data = JSON.parse(data)
      } catch (err) {
        data = {}
      }
    }
    this._debug('signal()')

    if (data.renegotiate && this.initiator) {
      this._debug('got request to renegotiate')
      this._needsNegotiation()
    }
    if (data.transceiverRequest && this.initiator) {
      this._debug('got request for transceiver')
      this.addTransceiver(data.transceiverRequest.kind, data.transceiverRequest.init)
    }
    if (data.candidate) {
      if (this._pc.localDescription && this._pc.localDescription.type && this._pc.remoteDescription && this._pc.remoteDescription.type) {
        this._addIceCandidate(data.candidate)
      } else {
        this._pendingCandidates.push(data.candidate)
      }
    }
    if (data.sdp) {
      this._pc.setRemoteDescription(new (this._wrtc.RTCSessionDescription)(data))
        .then(() => {
          if (this.destroyed) return

          this._pendingCandidates.forEach(candidate => {
            this._addIceCandidate(candidate)
          })
          this._pendingCandidates = []

          if (this._pc.remoteDescription.type === 'offer') this._createAnswer()
        })
        .catch(err => {
          this.destroy(makeError(err, 'ERR_SET_REMOTE_DESCRIPTION'))
        })
    }
    if (!data.sdp && !data.candidate && !data.renegotiate && !data.transceiverRequest) {
      this.destroy(makeError('signal() called with invalid signal data', 'ERR_SIGNALING'))
    }
  }

  _addIceCandidate (candidate) {
    var iceCandidateObj = new this._wrtc.RTCIceCandidate(candidate)
    this._pc.addIceCandidate(iceCandidateObj)
      .catch(err => {
        if (!iceCandidateObj.address || iceCandidateObj.address.endsWith('.local')) {
          warn('Ignoring unsupported ICE candidate.')
        } else {
          this.destroy(makeError(err, 'ERR_ADD_ICE_CANDIDATE'))
        }
      })
  }

  /**
   * Send text/binary data to the remote peer.
   * @param {ArrayBufferView|ArrayBuffer|Buffer|string|Blob} chunk
   */
  send (chunk) {
    this._channel.send(chunk)
  }

  /**
   * Add a Transceiver to the connection.
   * @param {String} kind
   * @param {Object} init
   */
  addTransceiver (kind, init) {
    this._debug('addTransceiver()')

    if (this.initiator) {
      try {
        this._pc.addTransceiver(kind, init)
        this._needsNegotiation()
      } catch (err) {
        this.destroy(makeError(err, 'ERR_ADD_TRANSCEIVER'))
      }
    } else {
      this.emit('signal', { // request initiator to renegotiate
        transceiverRequest: { kind, init }
      })
    }
  }

  /**
   * Add a MediaStream to the connection.
   * @param {MediaStream} stream
   */
  addStream (stream) {
    this._debug('addStream()')

    stream.getTracks().forEach(track => {
      this.addTrack(track, stream)
    })
  }

  /**
   * Add a MediaStreamTrack to the connection.
   * @param {MediaStreamTrack} track
   * @param {MediaStream} stream
   */
  addTrack (track, stream) {
    this._debug('addTrack()')

    var submap = this._senderMap.get(track) || new Map() // nested Maps map [track, stream] to sender
    var sender = submap.get(stream)
    if (!sender) {
      sender = this._pc.addTrack(track, stream)
      submap.set(stream, sender)
      this._senderMap.set(track, submap)
      this._needsNegotiation()
    } else if (sender.removed) {
      throw makeError('Track has been removed. You should enable/disable tracks that you want to re-add.', 'ERR_SENDER_REMOVED')
    } else {
      throw makeError('Track has already been added to that stream.', 'ERR_SENDER_ALREADY_ADDED')
    }
  }

  /**
   * Replace a MediaStreamTrack by another in the connection.
   * @param {MediaStreamTrack} oldTrack
   * @param {MediaStreamTrack} newTrack
   * @param {MediaStream} stream
   */
  replaceTrack (oldTrack, newTrack, stream) {
    this._debug('replaceTrack()')

    var submap = this._senderMap.get(oldTrack)
    var sender = submap ? submap.get(stream) : null
    if (!sender) {
      throw makeError('Cannot replace track that was never added.', 'ERR_TRACK_NOT_ADDED')
    }
    if (newTrack) this._senderMap.set(newTrack, submap)

    if (sender.replaceTrack != null) {
      sender.replaceTrack(newTrack)
    } else {
      this.destroy(makeError('replaceTrack is not supported in this browser', 'ERR_UNSUPPORTED_REPLACETRACK'))
    }
  }

  /**
   * Remove a MediaStreamTrack from the connection.
   * @param {MediaStreamTrack} track
   * @param {MediaStream} stream
   */
  removeTrack (track, stream) {
    this._debug('removeSender()')

    var submap = this._senderMap.get(track)
    var sender = submap ? submap.get(stream) : null
    if (!sender) {
      throw makeError('Cannot remove track that was never added.', 'ERR_TRACK_NOT_ADDED')
    }
    try {
      sender.removed = true
      this._pc.removeTrack(sender)
    } catch (err) {
      if (err.name === 'NS_ERROR_UNEXPECTED') {
        this._sendersAwaitingStable.push(sender) // HACK: Firefox must wait until (signalingState === stable) https://bugzilla.mozilla.org/show_bug.cgi?id=1133874
      } else {
        this.destroy(makeError(err, 'ERR_REMOVE_TRACK'))
      }
    }
    this._needsNegotiation()
  }

  /**
   * Remove a MediaStream from the connection.
   * @param {MediaStream} stream
   */
  removeStream (stream) {
    this._debug('removeSenders()')

    stream.getTracks().forEach(track => {
      this.removeTrack(track, stream)
    })
  }

  _needsNegotiation () {
    this._debug('_needsNegotiation')
    if (this._batchedNegotiation) return // batch synchronous renegotiations
    this._batchedNegotiation = true
    queueMicrotask(() => {
      this._batchedNegotiation = false
      this._debug('starting batched negotiation')
      this.negotiate()
    })
  }

  negotiate () {
    if (this.initiator) {
      if (this._isNegotiating) {
        this._queuedNegotiation = true
        this._debug('already negotiating, queueing')
      } else {
        this._debug('start negotiation')
        setTimeout(() => { // HACK: Chrome crashes if we immediately call createOffer
          this._createOffer()
        }, 0)
      }
    } else {
      if (!this._isNegotiating) {
        this._debug('requesting negotiation from initiator')
        this.emit('signal', { // request initiator to renegotiate
          renegotiate: true
        })
      }
    }
    this._isNegotiating = true
  }

  // TODO: Delete this method once readable-stream is updated to contain a default
  // implementation of destroy() that automatically calls _destroy()
  // See: https://github.com/nodejs/readable-stream/issues/283
  destroy (err) {
    this._destroy(err, () => {})
  }

  _destroy (err, cb) {
    if (this.destroyed) return

    this._debug('destroy (error: %s)', err && (err.message || err))

    this.readable = this.writable = false

    if (!this._readableState.ended) this.push(null)
    if (!this._writableState.finished) this.end()

    this.destroyed = true
    this._connected = false
    this._pcReady = false
    this._channelReady = false
    this._remoteTracks = null
    this._remoteStreams = null
    this._senderMap = null

    clearInterval(this._closingInterval)
    this._closingInterval = null

    clearInterval(this._interval)
    this._interval = null
    this._chunk = null
    this._cb = null

    if (this._onFinishBound) this.removeListener('finish', this._onFinishBound)
    this._onFinishBound = null

    if (this._channel) {
      try {
        this._channel.close()
      } catch (err) {}

      this._channel.onmessage = null
      this._channel.onopen = null
      this._channel.onclose = null
      this._channel.onerror = null
    }
    if (this._pc) {
      try {
        this._pc.close()
      } catch (err) {}

      this._pc.oniceconnectionstatechange = null
      this._pc.onicegatheringstatechange = null
      this._pc.onsignalingstatechange = null
      this._pc.onicecandidate = null
      this._pc.ontrack = null
      this._pc.ondatachannel = null
    }
    this._pc = null
    this._channel = null

    if (err) this.emit('error', err)
    this.emit('close')
    cb()
  }

  _setupData (event) {
    if (!event.channel) {
      // In some situations `pc.createDataChannel()` returns `undefined` (in wrtc),
      // which is invalid behavior. Handle it gracefully.
      // See: https://github.com/feross/simple-peer/issues/163
      return this.destroy(makeError('Data channel event is missing `channel` property', 'ERR_DATA_CHANNEL'))
    }

    this._channel = event.channel
    this._channel.binaryType = 'arraybuffer'

    if (typeof this._channel.bufferedAmountLowThreshold === 'number') {
      this._channel.bufferedAmountLowThreshold = MAX_BUFFERED_AMOUNT
    }

    this.channelName = this._channel.label

    this._channel.onmessage = event => {
      this._onChannelMessage(event)
    }
    this._channel.onbufferedamountlow = () => {
      this._onChannelBufferedAmountLow()
    }
    this._channel.onopen = () => {
      this._onChannelOpen()
    }
    this._channel.onclose = () => {
      this._onChannelClose()
    }
    this._channel.onerror = err => {
      this.destroy(makeError(err, 'ERR_DATA_CHANNEL'))
    }

    // HACK: Chrome will sometimes get stuck in readyState "closing", let's check for this condition
    // https://bugs.chromium.org/p/chromium/issues/detail?id=882743
    var isClosing = false
    this._closingInterval = setInterval(() => { // No "onclosing" event
      if (this._channel && this._channel.readyState === 'closing') {
        if (isClosing) this._onChannelClose() // closing timed out: equivalent to onclose firing
        isClosing = true
      } else {
        isClosing = false
      }
    }, CHANNEL_CLOSING_TIMEOUT)
  }

  _read () {}

  _write (chunk, encoding, cb) {
    if (this.destroyed) return cb(makeError('cannot write after peer is destroyed', 'ERR_DATA_CHANNEL'))

    if (this._connected) {
      try {
        this.send(chunk)
      } catch (err) {
        return this.destroy(makeError(err, 'ERR_DATA_CHANNEL'))
      }
      if (this._channel.bufferedAmount > MAX_BUFFERED_AMOUNT) {
        this._debug('start backpressure: bufferedAmount %d', this._channel.bufferedAmount)
        this._cb = cb
      } else {
        cb(null)
      }
    } else {
      this._debug('write before connect')
      this._chunk = chunk
      this._cb = cb
    }
  }

  // When stream finishes writing, close socket. Half open connections are not
  // supported.
  _onFinish () {
    if (this.destroyed) return

    // Wait a bit before destroying so the socket flushes.
    // TODO: is there a more reliable way to accomplish this?
    const destroySoon = () => {
      setTimeout(() => this.destroy(), 1000)
    }

    if (this._connected) {
      destroySoon()
    } else {
      this.once('connect', destroySoon)
    }
  }

  _startIceCompleteTimeout () {
    if (this.destroyed) return
    if (this._iceCompleteTimer) return
    this._debug('started iceComplete timeout')
    this._iceCompleteTimer = setTimeout(() => {
      if (!this._iceComplete) {
        this._iceComplete = true
        this._debug('iceComplete timeout completed')
        this.emit('iceTimeout')
        this.emit('_iceComplete')
      }
    }, this.iceCompleteTimeout)
  }

  _createOffer () {
    if (this.destroyed) return

    this._pc.createOffer(this.offerOptions)
      .then(offer => {
        if (this.destroyed) return
        if (!this.trickle && !this.allowHalfTrickle) offer.sdp = filterTrickle(offer.sdp)
        offer.sdp = this.sdpTransform(offer.sdp)

        const sendOffer = () => {
          if (this.destroyed) return
          var signal = this._pc.localDescription || offer
          this._debug('signal')
          this.emit('signal', {
            type: signal.type,
            sdp: signal.sdp
          })
        }

        const onSuccess = () => {
          this._debug('createOffer success')
          if (this.destroyed) return
          if (this.trickle || this._iceComplete) sendOffer()
          else this.once('_iceComplete', sendOffer) // wait for candidates
        }

        const onError = err => {
          this.destroy(makeError(err, 'ERR_SET_LOCAL_DESCRIPTION'))
        }

        this._pc.setLocalDescription(offer)
          .then(onSuccess)
          .catch(onError)
      })
      .catch(err => {
        this.destroy(makeError(err, 'ERR_CREATE_OFFER'))
      })
  }

  _requestMissingTransceivers () {
    if (this._pc.getTransceivers) {
      this._pc.getTransceivers().forEach(transceiver => {
        if (!transceiver.mid && transceiver.sender.track && !transceiver.requested) {
          transceiver.requested = true // HACK: Safari returns negotiated transceivers with a null mid
          this.addTransceiver(transceiver.sender.track.kind)
        }
      })
    }
  }

  _createAnswer () {
    if (this.destroyed) return

    this._pc.createAnswer(this.answerOptions)
      .then(answer => {
        if (this.destroyed) return
        if (!this.trickle && !this.allowHalfTrickle) answer.sdp = filterTrickle(answer.sdp)
        answer.sdp = this.sdpTransform(answer.sdp)

        const sendAnswer = () => {
          if (this.destroyed) return
          var signal = this._pc.localDescription || answer
          this._debug('signal')
          this.emit('signal', {
            type: signal.type,
            sdp: signal.sdp
          })
          if (!this.initiator) this._requestMissingTransceivers()
        }

        const onSuccess = () => {
          if (this.destroyed) return
          if (this.trickle || this._iceComplete) sendAnswer()
          else this.once('_iceComplete', sendAnswer)
        }

        const onError = err => {
          this.destroy(makeError(err, 'ERR_SET_LOCAL_DESCRIPTION'))
        }

        this._pc.setLocalDescription(answer)
          .then(onSuccess)
          .catch(onError)
      })
      .catch(err => {
        this.destroy(makeError(err, 'ERR_CREATE_ANSWER'))
      })
  }

  _onConnectionStateChange () {
    if (this.destroyed) return
    if (this._pc.connectionState === 'failed') {
      this.destroy(makeError('Connection failed.', 'ERR_CONNECTION_FAILURE'))
    }
  }

  _onIceStateChange () {
    if (this.destroyed) return
    var iceConnectionState = this._pc.iceConnectionState
    var iceGatheringState = this._pc.iceGatheringState

    this._debug(
      'iceStateChange (connection: %s) (gathering: %s)',
      iceConnectionState,
      iceGatheringState
    )
    this.emit('iceStateChange', iceConnectionState, iceGatheringState)

    if (iceConnectionState === 'connected' || iceConnectionState === 'completed') {
      this._pcReady = true
      this._maybeReady()
    }
    if (iceConnectionState === 'failed') {
      this.destroy(makeError('Ice connection failed.', 'ERR_ICE_CONNECTION_FAILURE'))
    }
    if (iceConnectionState === 'closed') {
      this.destroy(makeError('Ice connection closed.', 'ERR_ICE_CONNECTION_CLOSED'))
    }
  }

  getStats (cb) {
    // statreports can come with a value array instead of properties
    const flattenValues = report => {
      if (Object.prototype.toString.call(report.values) === '[object Array]') {
        report.values.forEach(value => {
          Object.assign(report, value)
        })
      }
      return report
    }

    // Promise-based getStats() (standard)
    if (this._pc.getStats.length === 0) {
      this._pc.getStats()
        .then(res => {
          var reports = []
          res.forEach(report => {
            reports.push(flattenValues(report))
          })
          cb(null, reports)
        }, err => cb(err))

    // Two-parameter callback-based getStats() (deprecated, former standard)
    } else if (this._isReactNativeWebrtc) {
      this._pc.getStats(null, res => {
        var reports = []
        res.forEach(report => {
          reports.push(flattenValues(report))
        })
        cb(null, reports)
      }, err => cb(err))

    // Single-parameter callback-based getStats() (non-standard)
    } else if (this._pc.getStats.length > 0) {
      this._pc.getStats(res => {
        // If we destroy connection in `connect` callback this code might happen to run when actual connection is already closed
        if (this.destroyed) return

        var reports = []
        res.result().forEach(result => {
          var report = {}
          result.names().forEach(name => {
            report[name] = result.stat(name)
          })
          report.id = result.id
          report.type = result.type
          report.timestamp = result.timestamp
          reports.push(flattenValues(report))
        })
        cb(null, reports)
      }, err => cb(err))

    // Unknown browser, skip getStats() since it's anyone's guess which style of
    // getStats() they implement.
    } else {
      cb(null, [])
    }
  }

  _maybeReady () {
    this._debug('maybeReady pc %s channel %s', this._pcReady, this._channelReady)
    if (this._connected || this._connecting || !this._pcReady || !this._channelReady) return

    this._connecting = true

    // HACK: We can't rely on order here, for details see https://github.com/js-platform/node-webrtc/issues/339
    const findCandidatePair = () => {
      if (this.destroyed) return

      this.getStats((err, items) => {
        if (this.destroyed) return

        // Treat getStats error as non-fatal. It's not essential.
        if (err) items = []

        var remoteCandidates = {}
        var localCandidates = {}
        var candidatePairs = {}
        var foundSelectedCandidatePair = false

        items.forEach(item => {
          // TODO: Once all browsers support the hyphenated stats report types, remove
          // the non-hypenated ones
          if (item.type === 'remotecandidate' || item.type === 'remote-candidate') {
            remoteCandidates[item.id] = item
          }
          if (item.type === 'localcandidate' || item.type === 'local-candidate') {
            localCandidates[item.id] = item
          }
          if (item.type === 'candidatepair' || item.type === 'candidate-pair') {
            candidatePairs[item.id] = item
          }
        })

        const setSelectedCandidatePair = selectedCandidatePair => {
          foundSelectedCandidatePair = true

          var local = localCandidates[selectedCandidatePair.localCandidateId]

          if (local && (local.ip || local.address)) {
            // Spec
            this.localAddress = local.ip || local.address
            this.localPort = Number(local.port)
          } else if (local && local.ipAddress) {
            // Firefox
            this.localAddress = local.ipAddress
            this.localPort = Number(local.portNumber)
          } else if (typeof selectedCandidatePair.googLocalAddress === 'string') {
            // TODO: remove this once Chrome 58 is released
            local = selectedCandidatePair.googLocalAddress.split(':')
            this.localAddress = local[0]
            this.localPort = Number(local[1])
          }
          if (this.localAddress) {
            this.localFamily = this.localAddress.includes(':') ? 'IPv6' : 'IPv4'
          }

          var remote = remoteCandidates[selectedCandidatePair.remoteCandidateId]

          if (remote && (remote.ip || remote.address)) {
            // Spec
            this.remoteAddress = remote.ip || remote.address
            this.remotePort = Number(remote.port)
          } else if (remote && remote.ipAddress) {
            // Firefox
            this.remoteAddress = remote.ipAddress
            this.remotePort = Number(remote.portNumber)
          } else if (typeof selectedCandidatePair.googRemoteAddress === 'string') {
            // TODO: remove this once Chrome 58 is released
            remote = selectedCandidatePair.googRemoteAddress.split(':')
            this.remoteAddress = remote[0]
            this.remotePort = Number(remote[1])
          }
          if (this.remoteAddress) {
            this.remoteFamily = this.remoteAddress.includes(':') ? 'IPv6' : 'IPv4'
          }

          this._debug(
            'connect local: %s:%s remote: %s:%s',
            this.localAddress, this.localPort, this.remoteAddress, this.remotePort
          )
        }

        items.forEach(item => {
          // Spec-compliant
          if (item.type === 'transport' && item.selectedCandidatePairId) {
            setSelectedCandidatePair(candidatePairs[item.selectedCandidatePairId])
          }

          // Old implementations
          if (
            (item.type === 'googCandidatePair' && item.googActiveConnection === 'true') ||
            ((item.type === 'candidatepair' || item.type === 'candidate-pair') && item.selected)
          ) {
            setSelectedCandidatePair(item)
          }
        })

        // Ignore candidate pair selection in browsers like Safari 11 that do not have any local or remote candidates
        // But wait until at least 1 candidate pair is available
        if (!foundSelectedCandidatePair && (!Object.keys(candidatePairs).length || Object.keys(localCandidates).length)) {
          setTimeout(findCandidatePair, 100)
          return
        } else {
          this._connecting = false
          this._connected = true
        }

        if (this._chunk) {
          try {
            this.send(this._chunk)
          } catch (err) {
            return this.destroy(makeError(err, 'ERR_DATA_CHANNEL'))
          }
          this._chunk = null
          this._debug('sent chunk from "write before connect"')

          var cb = this._cb
          this._cb = null
          cb(null)
        }

        // If `bufferedAmountLowThreshold` and 'onbufferedamountlow' are unsupported,
        // fallback to using setInterval to implement backpressure.
        if (typeof this._channel.bufferedAmountLowThreshold !== 'number') {
          this._interval = setInterval(() => this._onInterval(), 150)
          if (this._interval.unref) this._interval.unref()
        }

        this._debug('connect')
        this.emit('connect')
      })
    }
    findCandidatePair()
  }

  _onInterval () {
    if (!this._cb || !this._channel || this._channel.bufferedAmount > MAX_BUFFERED_AMOUNT) {
      return
    }
    this._onChannelBufferedAmountLow()
  }

  _onSignalingStateChange () {
    if (this.destroyed) return

    if (this._pc.signalingState === 'stable' && !this._firstStable) {
      this._isNegotiating = false

      // HACK: Firefox doesn't yet support removing tracks when signalingState !== 'stable'
      this._debug('flushing sender queue', this._sendersAwaitingStable)
      this._sendersAwaitingStable.forEach(sender => {
        this._pc.removeTrack(sender)
        this._queuedNegotiation = true
      })
      this._sendersAwaitingStable = []

      if (this._queuedNegotiation) {
        this._debug('flushing negotiation queue')
        this._queuedNegotiation = false
        this._needsNegotiation() // negotiate again
      }

      this._debug('negotiate')
      this.emit('negotiate')
    }
    this._firstStable = false

    this._debug('signalingStateChange %s', this._pc.signalingState)
    this.emit('signalingStateChange', this._pc.signalingState)
  }

  _onIceCandidate (event) {
    if (this.destroyed) return
    if (event.candidate && this.trickle) {
      this.emit('signal', {
        candidate: {
          candidate: event.candidate.candidate,
          sdpMLineIndex: event.candidate.sdpMLineIndex,
          sdpMid: event.candidate.sdpMid
        }
      })
    } else if (!event.candidate && !this._iceComplete) {
      this._iceComplete = true
      this.emit('_iceComplete')
    }
    // as soon as we've received one valid candidate start timeout
    if (event.candidate) {
      this._startIceCompleteTimeout()
    }
  }

  _onChannelMessage (event) {
    if (this.destroyed) return
    var data = event.data
    if (data instanceof ArrayBuffer) data = Buffer.from(data)
    this.push(data)
  }

  _onChannelBufferedAmountLow () {
    if (this.destroyed || !this._cb) return
    this._debug('ending backpressure: bufferedAmount %d', this._channel.bufferedAmount)
    var cb = this._cb
    this._cb = null
    cb(null)
  }

  _onChannelOpen () {
    if (this._connected || this.destroyed) return
    this._debug('on channel open')
    this._channelReady = true
    this._maybeReady()
  }

  _onChannelClose () {
    if (this.destroyed) return
    this._debug('on channel close')
    this.destroy()
  }

  _onTrack (event) {
    if (this.destroyed) return

    event.streams.forEach(eventStream => {
      this._debug('on track')
      this.emit('track', event.track, eventStream)

      this._remoteTracks.push({
        track: event.track,
        stream: eventStream
      })

      if (this._remoteStreams.some(remoteStream => {
        return remoteStream.id === eventStream.id
      })) return // Only fire one 'stream' event, even though there may be multiple tracks per stream

      this._remoteStreams.push(eventStream)
      queueMicrotask(() => {
        this.emit('stream', eventStream) // ensure all tracks have been added
      })
    })
  }

  _debug () {
    var args = [].slice.call(arguments)
    args[0] = '[' + this._id + '] ' + args[0]
    debug.apply(null, args)
  }
}

Peer.WEBRTC_SUPPORT = !!getBrowserRTC()

/**
 * Expose peer and data channel config for overriding all Peer
 * instances. Otherwise, just set opts.config or opts.channelConfig
 * when constructing a Peer.
 */
Peer.config = {
  iceServers: [
    {
      urls: 'stun:stun.l.google.com:19302'
    },
    {
      urls: 'stun:global.stun.twilio.com:3478?transport=udp'
    }
  ],
  sdpSemantics: 'unified-plan'
}

Peer.channelConfig = {}

module.exports = Peer