index.js

module.exports = Peer

var debug = require('debug')('simple-peer')
var getBrowserRTC = require('get-browser-rtc')
var inherits = require('inherits')
var randombytes = require('randombytes')
var stream = require('readable-stream')

var MAX_BUFFERED_AMOUNT = 64 * 1024

inherits(Peer, stream.Duplex)

/**
 * WebRTC peer connection. Same API as node core `net.Socket`, plus a few extra methods.
 * Duplex stream.
 * @param {Object} opts
 */
function Peer (opts) {
  var self = this
  if (!(self instanceof Peer)) return new Peer(opts)

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

  opts = Object.assign({
    allowHalfOpen: false
  }, opts)

  stream.Duplex.call(self, opts)

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

  // Needed by _transformConstraints, so set this early
  self._isChromium = typeof window !== 'undefined' && !!window.webkitRTCPeerConnection

  self.initiator = opts.initiator || false
  self.channelConfig = opts.channelConfig || Peer.channelConfig
  self.config = opts.config || Peer.config
  self.constraints = self._transformConstraints(opts.constraints || Peer.constraints)
  self.offerConstraints = self._transformConstraints(opts.offerConstraints || {})
  self.answerConstraints = self._transformConstraints(opts.answerConstraints || {})
  self.sdpTransform = opts.sdpTransform || function (sdp) { return sdp }
  self.streams = opts.streams || (opts.stream ? [opts.stream] : []) // support old "stream" option
  self.trickle = opts.trickle !== undefined ? opts.trickle : true

  self.destroyed = false
  self.connected = false

  self.remoteAddress = undefined
  self.remoteFamily = undefined
  self.remotePort = undefined
  self.localAddress = undefined
  self.localPort = undefined

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

  if (!self._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')
    }
  }

  self._pcReady = false
  self._channelReady = false
  self._iceComplete = false // ice candidate trickle done (got null candidate)
  self._channel = null
  self._pendingCandidates = []

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

  self._remoteTracks = []
  self._remoteStreams = []

  self._chunk = null
  self._cb = null
  self._interval = null

  self._pc = new (self._wrtc.RTCPeerConnection)(self.config, self.constraints)
  if (self._isChromium || (self._wrtc && self._wrtc.electronDaemon)) { // HACK: Electron and Chromium need a promise shim
    shimPromiseAPI(self._wrtc.RTCPeerConnection, self._pc)
  }

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

  self._pc.oniceconnectionstatechange = function () {
    self._onIceStateChange()
  }
  self._pc.onicegatheringstatechange = function () {
    self._onIceStateChange()
  }
  self._pc.onsignalingstatechange = function () {
    self._onSignalingStateChange()
  }
  self._pc.onicecandidate = function (event) {
    self._onIceCandidate(event)
  }

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

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

  if ('addTrack' in self._pc) {
    if (self.streams) {
      self.streams.forEach(function (stream) {
        self.addStream(stream)
      })
    }
    self._pc.ontrack = function (event) {
      self._onTrack(event)
    }
  }

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

  self._onFinishBound = function () {
    self._onFinish()
  }
  self.once('finish', self._onFinishBound)
}

Peer.WEBRTC_SUPPORT = !!getBrowserRTC()

/**
 * Expose config, constraints, and data channel config for overriding all Peer
 * instances. Otherwise, just set opts.config, opts.constraints, 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'
    }
  ]
}
Peer.constraints = {}
Peer.channelConfig = {}

Object.defineProperty(Peer.prototype, 'bufferSize', {
  get: function () {
    var self = this
    return (self._channel && self._channel.bufferedAmount) || 0
  }
})

Peer.prototype.address = function () {
  var self = this
  return { port: self.localPort, family: 'IPv4', address: self.localAddress }
}

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

  if (data.renegotiate) {
    self._debug('got request to renegotiate')
    self._needsNegotiation()
  }
  if (data.candidate) {
    if (self._pc.remoteDescription && self._pc.remoteDescription.type) self._addIceCandidate(data.candidate)
    else self._pendingCandidates.push(data.candidate)
  }
  if (data.sdp) {
    self._pc.setRemoteDescription(new (self._wrtc.RTCSessionDescription)(data)).then(function () {
      if (self.destroyed) return

      self._pendingCandidates.forEach(function (candidate) {
        self._addIceCandidate(candidate)
      })
      self._pendingCandidates = []

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

Peer.prototype._addIceCandidate = function (candidate) {
  var self = this
  try {
    self._pc.addIceCandidate(
      new self._wrtc.RTCIceCandidate(candidate),
      noop,
      function (err) { self.destroy(makeError(err, 'ERR_ADD_ICE_CANDIDATE')) }
    )
  } catch (err) {
    self.destroy(makeError('error adding candidate: ' + err.message, 'ERR_ADD_ICE_CANDIDATE'))
  }
}

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

/**
 * Add a MediaStream to the connection.
 * @param {MediaStream} stream
 */
Peer.prototype.addStream = function (stream) {
  var self = this

  self._debug('addStream()')

  stream.getTracks().forEach(function (track) {
    self.addTrack(track, stream)
  })
}

/**
 * Add a MediaStreamTrack to the connection.
 * @param {MediaStreamTrack} track
 * @param {MediaStream} stream
 */
Peer.prototype.addTrack = function (track, stream) {
  var self = this

  self._debug('addTrack()')

  var sender = self._pc.addTrack(track, stream)
  var submap = self._senderMap.get(track) || new WeakMap() // nested WeakMaps map [track, stream] to sender
  submap.set(stream, sender)
  self._senderMap.set(track, submap)
  self._needsNegotiation()
}

/**
 * Remove a MediaStreamTrack from the connection.
 * @param {MediaStreamTrack} track
 * @param {MediaStream} stream
 */
Peer.prototype.removeTrack = function (track, stream) {
  var self = this

  self._debug('removeSender()')

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

/**
 * Remove a MediaStream from the connection.
 * @param {MediaStream} stream
 */
Peer.prototype.removeStream = function (stream) {
  var self = this

  self._debug('removeSenders()')

  stream.getTracks().forEach(function (track) {
    self.removeTrack(track, stream)
  })
}

Peer.prototype._needsNegotiation = function () {
  var self = this

  self._debug('_needsNegotiation')
  if (self._batchedNegotiation) return // batch synchronous renegotiations
  self._batchedNegotiation = true
  setTimeout(function () {
    self._batchedNegotiation = false
    self._debug('starting batched negotiation')
    self.negotiate()
  }, 0)
}

Peer.prototype.negotiate = function () {
  var self = this

  if (self.initiator) {
    if (self._isNegotiating) {
      self._queuedNegotiation = true
      self._debug('already negotiating, queueing')
    } else {
      self._debug('start negotiation')
      self._createOffer()
    }
  } else {
    if (!self._isNegotiating) {
      self._debug('requesting negotiation from initiator')
      self.emit('signal', { // request initiator to renegotiate
        renegotiate: true
      })
    }
  }
  self._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
Peer.prototype.destroy = function (err) {
  var self = this
  self._destroy(err, function () {})
}

Peer.prototype._destroy = function (err, cb) {
  var self = this
  if (self.destroyed) return

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

  self.readable = self.writable = false

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

  self.destroyed = true
  self.connected = false
  self._pcReady = false
  self._channelReady = false
  self._remoteTracks = null
  self._remoteStreams = null
  self._senderMap = null

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

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

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

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

    self._pc.oniceconnectionstatechange = null
    self._pc.onicegatheringstatechange = null
    self._pc.onsignalingstatechange = null
    self._pc.onicecandidate = null
    if ('addTrack' in self._pc) {
      self._pc.ontrack = null
    }
    self._pc.ondatachannel = null
  }
  self._pc = null
  self._channel = null

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

Peer.prototype._setupData = function (event) {
  var self = this
  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 self.destroy(makeError('Data channel event is missing `channel` property', 'ERR_DATA_CHANNEL'))
  }

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

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

  self.channelName = self._channel.label

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

Peer.prototype._read = function () {}

Peer.prototype._write = function (chunk, encoding, cb) {
  var self = this
  if (self.destroyed) return cb(makeError('cannot write after peer is destroyed', 'ERR_DATA_CHANNEL'))

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

// When stream finishes writing, close socket. Half open connections are not
// supported.
Peer.prototype._onFinish = function () {
  var self = this
  if (self.destroyed) return

  if (self.connected) {
    destroySoon()
  } else {
    self.once('connect', destroySoon)
  }

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

Peer.prototype._createOffer = function () {
  var self = this
  if (self.destroyed) return

  self._pc.createOffer(self.offerConstraints).then(function (offer) {
    if (self.destroyed) return
    offer.sdp = self.sdpTransform(offer.sdp)
    self._pc.setLocalDescription(offer).then(onSuccess).catch(onError)

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

    function onError (err) {
      self.destroy(makeError(err, 'ERR_SET_LOCAL_DESCRIPTION'))
    }

    function sendOffer () {
      var signal = self._pc.localDescription || offer
      self._debug('signal')
      self.emit('signal', {
        type: signal.type,
        sdp: signal.sdp
      })
    }
  }).catch(function (err) { self.destroy(makeError(err, 'ERR_CREATE_OFFER')) })
}

Peer.prototype._createAnswer = function () {
  var self = this
  if (self.destroyed) return

  self._pc.createAnswer(self.answerConstraints).then(function (answer) {
    if (self.destroyed) return
    answer.sdp = self.sdpTransform(answer.sdp)
    self._pc.setLocalDescription(answer).then(onSuccess).catch(onError)

    function onSuccess () {
      if (self.destroyed) return
      if (self.trickle || self._iceComplete) sendAnswer()
      else self.once('_iceComplete', sendAnswer)
    }

    function onError (err) {
      self.destroy(makeError(err, 'ERR_SET_LOCAL_DESCRIPTION'))
    }

    function sendAnswer () {
      var signal = self._pc.localDescription || answer
      self._debug('signal')
      self.emit('signal', {
        type: signal.type,
        sdp: signal.sdp
      })
    }
  }).catch(function (err) { self.destroy(makeError(err, 'ERR_CREATE_ANSWER')) })
}

Peer.prototype._onIceStateChange = function () {
  var self = this
  if (self.destroyed) return
  var iceConnectionState = self._pc.iceConnectionState
  var iceGatheringState = self._pc.iceGatheringState

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

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

Peer.prototype.getStats = function (cb) {
  var self = this

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

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

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

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

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

Peer.prototype._maybeReady = function () {
  var self = this
  self._debug('maybeReady pc %s channel %s', self._pcReady, self._channelReady)
  if (self.connected || self._connecting || !self._pcReady || !self._channelReady) return

  self._connecting = true

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

    self.getStats(function (err, items) {
      if (self.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(function (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
        }
      })

      items.forEach(function (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)
        }
      })

      function setSelectedCandidatePair (selectedCandidatePair) {
        foundSelectedCandidatePair = true

        var local = localCandidates[selectedCandidatePair.localCandidateId]

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

        var remote = remoteCandidates[selectedCandidatePair.remoteCandidateId]

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

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

      // 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 {
        self._connecting = false
        self.connected = true
      }

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

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

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

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

Peer.prototype._onInterval = function () {
  var self = this
  if (!self._cb || !self._channel || self._channel.bufferedAmount > MAX_BUFFERED_AMOUNT) {
    return
  }
  self._onChannelBufferedAmountLow()
}

Peer.prototype._onSignalingStateChange = function () {
  var self = this
  if (self.destroyed) return

  if (self._pc.signalingState === 'stable') {
    self._isNegotiating = false

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

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

    self._debug('negotiate')
    self.emit('negotiate')
  }

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

Peer.prototype._onIceCandidate = function (event) {
  var self = this
  if (self.destroyed) return
  if (event.candidate && self.trickle) {
    self.emit('signal', {
      candidate: {
        candidate: event.candidate.candidate,
        sdpMLineIndex: event.candidate.sdpMLineIndex,
        sdpMid: event.candidate.sdpMid
      }
    })
  } else if (!event.candidate) {
    self._iceComplete = true
    self.emit('_iceComplete')
  }
}

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

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

Peer.prototype._onChannelOpen = function () {
  var self = this
  if (self.connected || self.destroyed) return
  self._debug('on channel open')
  self._channelReady = true
  self._maybeReady()
}

Peer.prototype._onChannelClose = function () {
  var self = this
  if (self.destroyed) return
  self._debug('on channel close')
  self.destroy()
}

Peer.prototype._onTrack = function (event) {
  var self = this
  if (self.destroyed) return

  event.streams.forEach(function (eventStream) {
    self._debug('on track')
    self.emit('track', event.track, eventStream)

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

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

    self._remoteStreams.push(eventStream)
    setTimeout(function () {
      self.emit('stream', eventStream) // ensure all tracks have been added
    }, 0)
  })
}

Peer.prototype.setConstraints = function (constraints) {
  var self = this
  if (self.initiator) {
    self.offerConstraints = self._transformConstraints(constraints)
  } else {
    self.answerConstraints = self._transformConstraints(constraints)
  }
}

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

// Transform constraints objects into the new format (unless Chromium)
// TODO: This can be removed when Chromium supports the new format
Peer.prototype._transformConstraints = function (constraints) {
  var self = this

  if (Object.keys(constraints).length === 0) {
    return constraints
  }

  if ((constraints.mandatory || constraints.optional) && !self._isChromium) {
    // convert to new format

    // Merge mandatory and optional objects, prioritizing mandatory
    var newConstraints = Object.assign({}, constraints.optional, constraints.mandatory)

    // fix casing
    if (newConstraints.OfferToReceiveVideo !== undefined) {
      newConstraints.offerToReceiveVideo = newConstraints.OfferToReceiveVideo
      delete newConstraints['OfferToReceiveVideo']
    }

    if (newConstraints.OfferToReceiveAudio !== undefined) {
      newConstraints.offerToReceiveAudio = newConstraints.OfferToReceiveAudio
      delete newConstraints['OfferToReceiveAudio']
    }

    return newConstraints
  } else if (!constraints.mandatory && !constraints.optional && self._isChromium) {
    // convert to old format

    // fix casing
    if (constraints.offerToReceiveVideo !== undefined) {
      constraints.OfferToReceiveVideo = constraints.offerToReceiveVideo
      delete constraints['offerToReceiveVideo']
    }

    if (constraints.offerToReceiveAudio !== undefined) {
      constraints.OfferToReceiveAudio = constraints.offerToReceiveAudio
      delete constraints['offerToReceiveAudio']
    }

    return {
      mandatory: constraints // NOTE: All constraints are upgraded to mandatory
    }
  }

  return constraints
}

// HACK: Minimal shim to force Chrome and WRTC to use their more reliable callback API
function shimPromiseAPI (RTCPeerConnection, pc) {
  pc.createOffer = function (constraints) {
    return new Promise((resolve, reject) => {
      RTCPeerConnection.prototype.createOffer.call(this, resolve, reject, constraints)
    })
  }
  pc.createAnswer = function (constraints) {
    return new Promise((resolve, reject) => {
      RTCPeerConnection.prototype.createAnswer.call(this, resolve, reject, constraints)
    })
  }
  pc.setLocalDescription = function (description) {
    return new Promise((resolve, reject) => {
      RTCPeerConnection.prototype.setLocalDescription.call(this, description, resolve, reject)
    })
  }
  pc.setRemoteDescription = function (description) {
    return new Promise((resolve, reject) => {
      RTCPeerConnection.prototype.setRemoteDescription.call(this, description, resolve, reject)
    })
  }
}

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

function noop () {}