webrtc-adapter/src/js/edge/rtcpeerconnection_shim.js

A shim to insulate apps from WebRTC spec changes and browser prefix differences

/*
 *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree.
 */
 /* eslint-env node */
'use strict';

var SDPUtils = require('sdp');

// sort tracks such that they follow an a-v-a-v...
// pattern.
function sortTracks(tracks) {
  var audioTracks = tracks.filter(function(track) {
    return track.kind === 'audio';
  });
  var videoTracks = tracks.filter(function(track) {
    return track.kind === 'video';
  });
  tracks = [];
  while (audioTracks.length || videoTracks.length) {
    if (audioTracks.length) {
      tracks.push(audioTracks.shift());
    }
    if (videoTracks.length) {
      tracks.push(videoTracks.shift());
    }
  }
  return tracks;
}

// Edge does not like
// 1) stun:
// 2) turn: that does not have all of turn:host:port?transport=udp
// 3) turn: with ipv6 addresses
// 4) turn: occurring muliple times
function filterIceServers(iceServers, edgeVersion) {
  var hasTurn = false;
  iceServers = JSON.parse(JSON.stringify(iceServers));
  return iceServers.filter(function(server) {
    if (server && (server.urls || server.url)) {
      var urls = server.urls || server.url;
      if (server.url && !server.urls) {
        console.warn('RTCIceServer.url is deprecated! Use urls instead.');
      }
      var isString = typeof urls === 'string';
      if (isString) {
        urls = [urls];
      }
      urls = urls.filter(function(url) {
        var validTurn = url.indexOf('turn:') === 0 &&
            url.indexOf('transport=udp') !== -1 &&
            url.indexOf('turn:[') === -1 &&
            !hasTurn;

        if (validTurn) {
          hasTurn = true;
          return true;
        }
        return url.indexOf('stun:') === 0 && edgeVersion >= 14393;
      });

      delete server.url;
      server.urls = isString ? urls[0] : urls;
      return !!urls.length;
    }
    return false;
  });
}

// Determines the intersection of local and remote capabilities.
function getCommonCapabilities(localCapabilities, remoteCapabilities) {
  var commonCapabilities = {
    codecs: [],
    headerExtensions: [],
    fecMechanisms: []
  };

  var findCodecByPayloadType = function(pt, codecs) {
    pt = parseInt(pt, 10);
    for (var i = 0; i < codecs.length; i++) {
      if (codecs[i].payloadType === pt ||
          codecs[i].preferredPayloadType === pt) {
        return codecs[i];
      }
    }
  };

  var rtxCapabilityMatches = function(lRtx, rRtx, lCodecs, rCodecs) {
    var lCodec = findCodecByPayloadType(lRtx.parameters.apt, lCodecs);
    var rCodec = findCodecByPayloadType(rRtx.parameters.apt, rCodecs);
    return lCodec && rCodec &&
        lCodec.name.toLowerCase() === rCodec.name.toLowerCase();
  };

  localCapabilities.codecs.forEach(function(lCodec) {
    for (var i = 0; i < remoteCapabilities.codecs.length; i++) {
      var rCodec = remoteCapabilities.codecs[i];
      if (lCodec.name.toLowerCase() === rCodec.name.toLowerCase() &&
          lCodec.clockRate === rCodec.clockRate) {
        if (lCodec.name.toLowerCase() === 'rtx' &&
            lCodec.parameters && rCodec.parameters.apt) {
          // for RTX we need to find the local rtx that has a apt
          // which points to the same local codec as the remote one.
          if (!rtxCapabilityMatches(lCodec, rCodec,
              localCapabilities.codecs, remoteCapabilities.codecs)) {
            continue;
          }
        }
        rCodec = JSON.parse(JSON.stringify(rCodec)); // deepcopy
        // number of channels is the highest common number of channels
        rCodec.numChannels = Math.min(lCodec.numChannels,
            rCodec.numChannels);
        // push rCodec so we reply with offerer payload type
        commonCapabilities.codecs.push(rCodec);

        // determine common feedback mechanisms
        rCodec.rtcpFeedback = rCodec.rtcpFeedback.filter(function(fb) {
          for (var j = 0; j < lCodec.rtcpFeedback.length; j++) {
            if (lCodec.rtcpFeedback[j].type === fb.type &&
                lCodec.rtcpFeedback[j].parameter === fb.parameter) {
              return true;
            }
          }
          return false;
        });
        // FIXME: also need to determine .parameters
        //  see https://github.com/openpeer/ortc/issues/569
        break;
      }
    }
  });

  localCapabilities.headerExtensions.forEach(function(lHeaderExtension) {
    for (var i = 0; i < remoteCapabilities.headerExtensions.length;
         i++) {
      var rHeaderExtension = remoteCapabilities.headerExtensions[i];
      if (lHeaderExtension.uri === rHeaderExtension.uri) {
        commonCapabilities.headerExtensions.push(rHeaderExtension);
        break;
      }
    }
  });

  // FIXME: fecMechanisms
  return commonCapabilities;
}

// is action=setLocalDescription with type allowed in signalingState
function isActionAllowedInSignalingState(action, type, signalingState) {
  return {
    offer: {
      setLocalDescription: ['stable', 'have-local-offer'],
      setRemoteDescription: ['stable', 'have-remote-offer']
    },
    answer: {
      setLocalDescription: ['have-remote-offer', 'have-local-pranswer'],
      setRemoteDescription: ['have-local-offer', 'have-remote-pranswer']
    }
  }[type][action].indexOf(signalingState) !== -1;
}

module.exports = function(window, edgeVersion) {
  var RTCPeerConnection = function(config) {
    var self = this;

    var _eventTarget = document.createDocumentFragment();
    ['addEventListener', 'removeEventListener', 'dispatchEvent']
        .forEach(function(method) {
          self[method] = _eventTarget[method].bind(_eventTarget);
        });

    this.needNegotiation = false;

    this.onicecandidate = null;
    this.onaddstream = null;
    this.ontrack = null;
    this.onremovestream = null;
    this.onsignalingstatechange = null;
    this.oniceconnectionstatechange = null;
    this.onicegatheringstatechange = null;
    this.onnegotiationneeded = null;
    this.ondatachannel = null;
    this.canTrickleIceCandidates = null;

    this.localStreams = [];
    this.remoteStreams = [];
    this.getLocalStreams = function() {
      return self.localStreams;
    };
    this.getRemoteStreams = function() {
      return self.remoteStreams;
    };

    this.localDescription = new window.RTCSessionDescription({
      type: '',
      sdp: ''
    });
    this.remoteDescription = new window.RTCSessionDescription({
      type: '',
      sdp: ''
    });
    this.signalingState = 'stable';
    this.iceConnectionState = 'new';
    this.iceGatheringState = 'new';

    this.iceOptions = {
      gatherPolicy: 'all',
      iceServers: []
    };
    if (config && config.iceTransportPolicy) {
      switch (config.iceTransportPolicy) {
        case 'all':
        case 'relay':
          this.iceOptions.gatherPolicy = config.iceTransportPolicy;
          break;
        default:
          // don't set iceTransportPolicy.
          break;
      }
    }
    this.usingBundle = config && config.bundlePolicy === 'max-bundle';

    if (config && config.iceServers) {
      this.iceOptions.iceServers = filterIceServers(config.iceServers,
          edgeVersion);
    }
    this._config = config || {};

    // per-track iceGathers, iceTransports, dtlsTransports, rtpSenders, ...
    // everything that is needed to describe a SDP m-line.
    this.transceivers = [];

    // since the iceGatherer is currently created in createOffer but we
    // must not emit candidates until after setLocalDescription we buffer
    // them in this array.
    this._localIceCandidatesBuffer = [];

    this._sdpSessionId = SDPUtils.generateSessionId();
  };

  RTCPeerConnection.prototype._emitGatheringStateChange = function() {
    var event = new Event('icegatheringstatechange');
    this.dispatchEvent(event);
    if (this.onicegatheringstatechange !== null) {
      this.onicegatheringstatechange(event);
    }
  };

  RTCPeerConnection.prototype._emitBufferedCandidates = function() {
    var self = this;
    var sections = SDPUtils.splitSections(self.localDescription.sdp);
    // FIXME: need to apply ice candidates in a way which is async but
    // in-order
    this._localIceCandidatesBuffer.forEach(function(event) {
      var end = !event.candidate || Object.keys(event.candidate).length === 0;
      if (end) {
        for (var j = 1; j < sections.length; j++) {
          if (sections[j].indexOf('\r\na=end-of-candidates\r\n') === -1) {
            sections[j] += 'a=end-of-candidates\r\n';
          }
        }
      } else {
        sections[event.candidate.sdpMLineIndex + 1] +=
            'a=' + event.candidate.candidate + '\r\n';
      }
      self.localDescription.sdp = sections.join('');
      self.dispatchEvent(event);
      if (self.onicecandidate !== null) {
        self.onicecandidate(event);
      }
      if (!event.candidate && self.iceGatheringState !== 'complete') {
        var complete = self.transceivers.every(function(transceiver) {
          return transceiver.iceGatherer &&
              transceiver.iceGatherer.state === 'completed';
        });
        if (complete && self.iceGatheringStateChange !== 'complete') {
          self.iceGatheringState = 'complete';
          self._emitGatheringStateChange();
        }
      }
    });
    this._localIceCandidatesBuffer = [];
  };

  RTCPeerConnection.prototype.getConfiguration = function() {
    return this._config;
  };

  // internal helper to create a transceiver object.
  // (whih is not yet the same as the WebRTC 1.0 transceiver)
  RTCPeerConnection.prototype._createTransceiver = function(kind) {
    var hasBundleTransport = this.transceivers.length > 0;
    var transceiver = {
      track: null,
      iceGatherer: null,
      iceTransport: null,
      dtlsTransport: null,
      localCapabilities: null,
      remoteCapabilities: null,
      rtpSender: null,
      rtpReceiver: null,
      kind: kind,
      mid: null,
      sendEncodingParameters: null,
      recvEncodingParameters: null,
      stream: null,
      wantReceive: true
    };
    if (this.usingBundle && hasBundleTransport) {
      transceiver.iceTransport = this.transceivers[0].iceTransport;
      transceiver.dtlsTransport = this.transceivers[0].dtlsTransport;
    } else {
      var transports = this._createIceAndDtlsTransports();
      transceiver.iceTransport = transports.iceTransport;
      transceiver.dtlsTransport = transports.dtlsTransport;
    }
    this.transceivers.push(transceiver);
    return transceiver;
  };

  RTCPeerConnection.prototype.addTrack = function(track, stream) {
    var transceiver;
    for (var i = 0; i < this.transceivers.length; i++) {
      if (!this.transceivers[i].track &&
          this.transceivers[i].kind === track.kind) {
        transceiver = this.transceivers[i];
      }
    }
    if (!transceiver) {
      transceiver = this._createTransceiver(track.kind);
    }

    transceiver.track = track;
    transceiver.stream = stream;
    transceiver.rtpSender = new window.RTCRtpSender(track,
        transceiver.dtlsTransport);

    this._maybeFireNegotiationNeeded();
    return transceiver.rtpSender;
  };

  RTCPeerConnection.prototype.addStream = function(stream) {
    var self = this;
    if (edgeVersion >= 15025) {
      this.localStreams.push(stream);
      stream.getTracks().forEach(function(track) {
        self.addTrack(track, stream);
      });
    } else {
      // Clone is necessary for local demos mostly, attaching directly
      // to two different senders does not work (build 10547).
      // Fixed in 15025 (or earlier)
      var clonedStream = stream.clone();
      stream.getTracks().forEach(function(track, idx) {
        var clonedTrack = clonedStream.getTracks()[idx];
        track.addEventListener('enabled', function(event) {
          clonedTrack.enabled = event.enabled;
        });
      });
      clonedStream.getTracks().forEach(function(track) {
        self.addTrack(track, clonedStream);
      });
      this.localStreams.push(clonedStream);
    }
    this._maybeFireNegotiationNeeded();
  };

  RTCPeerConnection.prototype.removeStream = function(stream) {
    var idx = this.localStreams.indexOf(stream);
    if (idx > -1) {
      this.localStreams.splice(idx, 1);
      this._maybeFireNegotiationNeeded();
    }
  };

  RTCPeerConnection.prototype.getSenders = function() {
    return this.transceivers.filter(function(transceiver) {
      return !!transceiver.rtpSender;
    })
    .map(function(transceiver) {
      return transceiver.rtpSender;
    });
  };

  RTCPeerConnection.prototype.getReceivers = function() {
    return this.transceivers.filter(function(transceiver) {
      return !!transceiver.rtpReceiver;
    })
    .map(function(transceiver) {
      return transceiver.rtpReceiver;
    });
  };

  // Create ICE gatherer and hook it up.
  RTCPeerConnection.prototype._createIceGatherer = function(mid,
      sdpMLineIndex) {
    var self = this;
    var iceGatherer = new window.RTCIceGatherer(self.iceOptions);
    iceGatherer.onlocalcandidate = function(evt) {
      var event = new Event('icecandidate');
      event.candidate = {sdpMid: mid, sdpMLineIndex: sdpMLineIndex};

      var cand = evt.candidate;
      var end = !cand || Object.keys(cand).length === 0;
      // Edge emits an empty object for RTCIceCandidateComplete‥
      if (end) {
        // polyfill since RTCIceGatherer.state is not implemented in
        // Edge 10547 yet.
        if (iceGatherer.state === undefined) {
          iceGatherer.state = 'completed';
        }
      } else {
        // RTCIceCandidate doesn't have a component, needs to be added
        cand.component = 1;
        event.candidate.candidate = SDPUtils.writeCandidate(cand);
      }

      // update local description.
      var sections = SDPUtils.splitSections(self.localDescription.sdp);
      if (!end) {
        sections[event.candidate.sdpMLineIndex + 1] +=
            'a=' + event.candidate.candidate + '\r\n';
      } else {
        sections[event.candidate.sdpMLineIndex + 1] +=
            'a=end-of-candidates\r\n';
      }
      self.localDescription.sdp = sections.join('');
      var transceivers = self._pendingOffer ? self._pendingOffer :
          self.transceivers;
      var complete = transceivers.every(function(transceiver) {
        return transceiver.iceGatherer &&
            transceiver.iceGatherer.state === 'completed';
      });

      // Emit candidate if localDescription is set.
      // Also emits null candidate when all gatherers are complete.
      switch (self.iceGatheringState) {
        case 'new':
          if (!end) {
            self._localIceCandidatesBuffer.push(event);
          }
          if (end && complete) {
            self._localIceCandidatesBuffer.push(
                new Event('icecandidate'));
          }
          break;
        case 'gathering':
          self._emitBufferedCandidates();
          if (!end) {
            self.dispatchEvent(event);
            if (self.onicecandidate !== null) {
              self.onicecandidate(event);
            }
          }
          if (complete) {
            self.dispatchEvent(new Event('icecandidate'));
            if (self.onicecandidate !== null) {
              self.onicecandidate(new Event('icecandidate'));
            }
            self.iceGatheringState = 'complete';
            self._emitGatheringStateChange();
          }
          break;
        case 'complete':
          // should not happen... currently!
          break;
        default: // no-op.
          break;
      }
    };
    return iceGatherer;
  };

  // Create ICE transport and DTLS transport.
  RTCPeerConnection.prototype._createIceAndDtlsTransports = function() {
    var self = this;
    var iceTransport = new window.RTCIceTransport(null);
    iceTransport.onicestatechange = function() {
      self._updateConnectionState();
    };

    var dtlsTransport = new window.RTCDtlsTransport(iceTransport);
    dtlsTransport.ondtlsstatechange = function() {
      self._updateConnectionState();
    };
    dtlsTransport.onerror = function() {
      // onerror does not set state to failed by itself.
      Object.defineProperty(dtlsTransport, 'state',
          {value: 'failed', writable: true});
      self._updateConnectionState();
    };

    return {
      iceTransport: iceTransport,
      dtlsTransport: dtlsTransport
    };
  };

  // Destroy ICE gatherer, ICE transport and DTLS transport.
  // Without triggering the callbacks.
  RTCPeerConnection.prototype._disposeIceAndDtlsTransports = function(
      sdpMLineIndex) {
    var iceGatherer = this.transceivers[sdpMLineIndex].iceGatherer;
    if (iceGatherer) {
      delete iceGatherer.onlocalcandidate;
      delete this.transceivers[sdpMLineIndex].iceGatherer;
    }
    var iceTransport = this.transceivers[sdpMLineIndex].iceTransport;
    if (iceTransport) {
      delete iceTransport.onicestatechange;
      delete this.transceivers[sdpMLineIndex].iceTransport;
    }
    var dtlsTransport = this.transceivers[sdpMLineIndex].dtlsTransport;
    if (dtlsTransport) {
      delete dtlsTransport.ondtlsstatechange;
      delete dtlsTransport.onerror;
      delete this.transceivers[sdpMLineIndex].dtlsTransport;
    }
  };

  // Start the RTP Sender and Receiver for a transceiver.
  RTCPeerConnection.prototype._transceive = function(transceiver,
      send, recv) {
    var params = getCommonCapabilities(transceiver.localCapabilities,
        transceiver.remoteCapabilities);
    if (send && transceiver.rtpSender) {
      params.encodings = transceiver.sendEncodingParameters;
      params.rtcp = {
        cname: SDPUtils.localCName,
        compound: transceiver.rtcpParameters.compound
      };
      if (transceiver.recvEncodingParameters.length) {
        params.rtcp.ssrc = transceiver.recvEncodingParameters[0].ssrc;
      }
      transceiver.rtpSender.send(params);
    }
    if (recv && transceiver.rtpReceiver) {
      // remove RTX field in Edge 14942
      if (transceiver.kind === 'video'
          && transceiver.recvEncodingParameters
          && edgeVersion < 15019) {
        transceiver.recvEncodingParameters.forEach(function(p) {
          delete p.rtx;
        });
      }
      params.encodings = transceiver.recvEncodingParameters;
      params.rtcp = {
        cname: transceiver.rtcpParameters.cname,
        compound: transceiver.rtcpParameters.compound
      };
      if (transceiver.sendEncodingParameters.length) {
        params.rtcp.ssrc = transceiver.sendEncodingParameters[0].ssrc;
      }
      transceiver.rtpReceiver.receive(params);
    }
  };

  RTCPeerConnection.prototype.setLocalDescription = function(description) {
    var self = this;

    if (!isActionAllowedInSignalingState('setLocalDescription',
        description.type, this.signalingState)) {
      var e = new Error('Can not set local ' + description.type +
          ' in state ' + this.signalingState);
      e.name = 'InvalidStateError';
      if (arguments.length > 2 && typeof arguments[2] === 'function') {
        window.setTimeout(arguments[2], 0, e);
      }
      return Promise.reject(e);
    }

    var sections;
    var sessionpart;
    if (description.type === 'offer') {
      // FIXME: What was the purpose of this empty if statement?
      // if (!this._pendingOffer) {
      // } else {
      if (this._pendingOffer) {
        // VERY limited support for SDP munging. Limited to:
        // * changing the order of codecs
        sections = SDPUtils.splitSections(description.sdp);
        sessionpart = sections.shift();
        sections.forEach(function(mediaSection, sdpMLineIndex) {
          var caps = SDPUtils.parseRtpParameters(mediaSection);
          self._pendingOffer[sdpMLineIndex].localCapabilities = caps;
        });
        this.transceivers = this._pendingOffer;
        delete this._pendingOffer;
      }
    } else if (description.type === 'answer') {
      sections = SDPUtils.splitSections(self.remoteDescription.sdp);
      sessionpart = sections.shift();
      var isIceLite = SDPUtils.matchPrefix(sessionpart,
          'a=ice-lite').length > 0;
      sections.forEach(function(mediaSection, sdpMLineIndex) {
        var transceiver = self.transceivers[sdpMLineIndex];
        var iceGatherer = transceiver.iceGatherer;
        var iceTransport = transceiver.iceTransport;
        var dtlsTransport = transceiver.dtlsTransport;
        var localCapabilities = transceiver.localCapabilities;
        var remoteCapabilities = transceiver.remoteCapabilities;

        var rejected = SDPUtils.isRejected(mediaSection);

        if (!rejected && !transceiver.isDatachannel) {
          var remoteIceParameters = SDPUtils.getIceParameters(
              mediaSection, sessionpart);
          var remoteDtlsParameters = SDPUtils.getDtlsParameters(
              mediaSection, sessionpart);
          if (isIceLite) {
            remoteDtlsParameters.role = 'server';
          }

          if (!self.usingBundle || sdpMLineIndex === 0) {
            iceTransport.start(iceGatherer, remoteIceParameters,
                isIceLite ? 'controlling' : 'controlled');
            dtlsTransport.start(remoteDtlsParameters);
          }

          // Calculate intersection of capabilities.
          var params = getCommonCapabilities(localCapabilities,
              remoteCapabilities);

          // Start the RTCRtpSender. The RTCRtpReceiver for this
          // transceiver has already been started in setRemoteDescription.
          self._transceive(transceiver,
              params.codecs.length > 0,
              false);
        }
      });
    }

    this.localDescription = {
      type: description.type,
      sdp: description.sdp
    };
    switch (description.type) {
      case 'offer':
        this._updateSignalingState('have-local-offer');
        break;
      case 'answer':
        this._updateSignalingState('stable');
        break;
      default:
        throw new TypeError('unsupported type "' + description.type +
            '"');
    }

    // If a success callback was provided, emit ICE candidates after it
    // has been executed. Otherwise, emit callback after the Promise is
    // resolved.
    var hasCallback = arguments.length > 1 &&
      typeof arguments[1] === 'function';
    if (hasCallback) {
      var cb = arguments[1];
      window.setTimeout(function() {
        cb();
        if (self.iceGatheringState === 'new') {
          self.iceGatheringState = 'gathering';
          self._emitGatheringStateChange();
        }
        self._emitBufferedCandidates();
      }, 0);
    }
    var p = Promise.resolve();
    p.then(function() {
      if (!hasCallback) {
        if (self.iceGatheringState === 'new') {
          self.iceGatheringState = 'gathering';
          self._emitGatheringStateChange();
        }
        // Usually candidates will be emitted earlier.
        window.setTimeout(self._emitBufferedCandidates.bind(self), 500);
      }
    });
    return p;
  };

  RTCPeerConnection.prototype.setRemoteDescription = function(description) {
    var self = this;

    if (!isActionAllowedInSignalingState('setRemoteDescription',
        description.type, this.signalingState)) {
      var e = new Error('Can not set remote ' + description.type +
          ' in state ' + this.signalingState);
      e.name = 'InvalidStateError';
      if (arguments.length > 2 && typeof arguments[2] === 'function') {
        window.setTimeout(arguments[2], 0, e);
      }
      return Promise.reject(e);
    }

    var streams = {};
    var receiverList = [];
    var sections = SDPUtils.splitSections(description.sdp);
    var sessionpart = sections.shift();
    var isIceLite = SDPUtils.matchPrefix(sessionpart,
        'a=ice-lite').length > 0;
    var usingBundle = SDPUtils.matchPrefix(sessionpart,
        'a=group:BUNDLE ').length > 0;
    this.usingBundle = usingBundle;
    var iceOptions = SDPUtils.matchPrefix(sessionpart,
        'a=ice-options:')[0];
    if (iceOptions) {
      this.canTrickleIceCandidates = iceOptions.substr(14).split(' ')
          .indexOf('trickle') >= 0;
    } else {
      this.canTrickleIceCandidates = false;
    }

    sections.forEach(function(mediaSection, sdpMLineIndex) {
      var lines = SDPUtils.splitLines(mediaSection);
      var kind = SDPUtils.getKind(mediaSection);
      var rejected = SDPUtils.isRejected(mediaSection);
      var protocol = lines[0].substr(2).split(' ')[2];

      var direction = SDPUtils.getDirection(mediaSection, sessionpart);
      var remoteMsid = SDPUtils.parseMsid(mediaSection);

      var mid = SDPUtils.getMid(mediaSection) || SDPUtils.generateIdentifier();

      // Reject datachannels which are not implemented yet.
      if (kind === 'application' && protocol === 'DTLS/SCTP') {
        self.transceivers[sdpMLineIndex] = {
          mid: mid,
          isDatachannel: true
        };
        return;
      }

      var transceiver;
      var iceGatherer;
      var iceTransport;
      var dtlsTransport;
      var rtpReceiver;
      var sendEncodingParameters;
      var recvEncodingParameters;
      var localCapabilities;

      var track;
      // FIXME: ensure the mediaSection has rtcp-mux set.
      var remoteCapabilities = SDPUtils.parseRtpParameters(mediaSection);
      var remoteIceParameters;
      var remoteDtlsParameters;
      if (!rejected) {
        remoteIceParameters = SDPUtils.getIceParameters(mediaSection,
            sessionpart);
        remoteDtlsParameters = SDPUtils.getDtlsParameters(mediaSection,
            sessionpart);
        remoteDtlsParameters.role = 'client';
      }
      recvEncodingParameters =
          SDPUtils.parseRtpEncodingParameters(mediaSection);

      var rtcpParameters = SDPUtils.parseRtcpParameters(mediaSection);

      var isComplete = SDPUtils.matchPrefix(mediaSection,
          'a=end-of-candidates', sessionpart).length > 0;
      var cands = SDPUtils.matchPrefix(mediaSection, 'a=candidate:')
          .map(function(cand) {
            return SDPUtils.parseCandidate(cand);
          })
          .filter(function(cand) {
            return cand.component === '1' || cand.component === 1;
          });

      // Check if we can use BUNDLE and dispose transports.
      if ((description.type === 'offer' || description.type === 'answer') &&
          !rejected && usingBundle && sdpMLineIndex > 0 &&
          self.transceivers[sdpMLineIndex]) {
        self._disposeIceAndDtlsTransports(sdpMLineIndex);
        self.transceivers[sdpMLineIndex].iceGatherer =
            self.transceivers[0].iceGatherer;
        self.transceivers[sdpMLineIndex].iceTransport =
            self.transceivers[0].iceTransport;
        self.transceivers[sdpMLineIndex].dtlsTransport =
            self.transceivers[0].dtlsTransport;
        if (self.transceivers[sdpMLineIndex].rtpSender) {
          self.transceivers[sdpMLineIndex].rtpSender.setTransport(
              self.transceivers[0].dtlsTransport);
        }
        if (self.transceivers[sdpMLineIndex].rtpReceiver) {
          self.transceivers[sdpMLineIndex].rtpReceiver.setTransport(
              self.transceivers[0].dtlsTransport);
        }
      }
      if (description.type === 'offer' && !rejected) {
        transceiver = self.transceivers[sdpMLineIndex] ||
            self._createTransceiver(kind);
        transceiver.mid = mid;

        if (!transceiver.iceGatherer) {
          transceiver.iceGatherer = usingBundle && sdpMLineIndex > 0 ?
              self.transceivers[0].iceGatherer :
              self._createIceGatherer(mid, sdpMLineIndex);
        }

        if (isComplete && cands.length &&
            (!usingBundle || sdpMLineIndex === 0)) {
          transceiver.iceTransport.setRemoteCandidates(cands);
        }

        localCapabilities = window.RTCRtpReceiver.getCapabilities(kind);

        // filter RTX until additional stuff needed for RTX is implemented
        // in adapter.js
        if (edgeVersion < 15019) {
          localCapabilities.codecs = localCapabilities.codecs.filter(
              function(codec) {
                return codec.name !== 'rtx';
              });
        }

        sendEncodingParameters = [{
          ssrc: (2 * sdpMLineIndex + 2) * 1001
        }];

        if (direction === 'sendrecv' || direction === 'sendonly') {
          rtpReceiver = new window.RTCRtpReceiver(transceiver.dtlsTransport,
              kind);

          track = rtpReceiver.track;
          // FIXME: does not work with Plan B.
          if (remoteMsid) {
            if (!streams[remoteMsid.stream]) {
              streams[remoteMsid.stream] = new window.MediaStream();
              Object.defineProperty(streams[remoteMsid.stream], 'id', {
                get: function() {
                  return remoteMsid.stream;
                }
              });
            }
            Object.defineProperty(track, 'id', {
              get: function() {
                return remoteMsid.track;
              }
            });
            streams[remoteMsid.stream].addTrack(track);
            receiverList.push([track, rtpReceiver,
              streams[remoteMsid.stream]]);
          } else {
            if (!streams.default) {
              streams.default = new window.MediaStream();
            }
            streams.default.addTrack(track);
            receiverList.push([track, rtpReceiver, streams.default]);
          }
        }

        transceiver.localCapabilities = localCapabilities;
        transceiver.remoteCapabilities = remoteCapabilities;
        transceiver.rtpReceiver = rtpReceiver;
        transceiver.rtcpParameters = rtcpParameters;
        transceiver.sendEncodingParameters = sendEncodingParameters;
        transceiver.recvEncodingParameters = recvEncodingParameters;

        // Start the RTCRtpReceiver now. The RTPSender is started in
        // setLocalDescription.
        self._transceive(self.transceivers[sdpMLineIndex],
            false,
            direction === 'sendrecv' || direction === 'sendonly');
      } else if (description.type === 'answer' && !rejected) {
        transceiver = self.transceivers[sdpMLineIndex];
        iceGatherer = transceiver.iceGatherer;
        iceTransport = transceiver.iceTransport;
        dtlsTransport = transceiver.dtlsTransport;
        rtpReceiver = transceiver.rtpReceiver;
        sendEncodingParameters = transceiver.sendEncodingParameters;
        localCapabilities = transceiver.localCapabilities;

        self.transceivers[sdpMLineIndex].recvEncodingParameters =
            recvEncodingParameters;
        self.transceivers[sdpMLineIndex].remoteCapabilities =
            remoteCapabilities;
        self.transceivers[sdpMLineIndex].rtcpParameters = rtcpParameters;

        if (!usingBundle || sdpMLineIndex === 0) {
          if ((isIceLite || isComplete) && cands.length) {
            iceTransport.setRemoteCandidates(cands);
          }
          iceTransport.start(iceGatherer, remoteIceParameters,
              'controlling');
          dtlsTransport.start(remoteDtlsParameters);
        }

        self._transceive(transceiver,
            direction === 'sendrecv' || direction === 'recvonly',
            direction === 'sendrecv' || direction === 'sendonly');

        if (rtpReceiver &&
            (direction === 'sendrecv' || direction === 'sendonly')) {
          track = rtpReceiver.track;
          if (remoteMsid) {
            if (!streams[remoteMsid.stream]) {
              streams[remoteMsid.stream] = new window.MediaStream();
            }
            streams[remoteMsid.stream].addTrack(track);
            receiverList.push([track, rtpReceiver, streams[remoteMsid.stream]]);
          } else {
            if (!streams.default) {
              streams.default = new window.MediaStream();
            }
            streams.default.addTrack(track);
            receiverList.push([track, rtpReceiver, streams.default]);
          }
        } else {
          // FIXME: actually the receiver should be created later.
          delete transceiver.rtpReceiver;
        }
      }
    });

    this.remoteDescription = {
      type: description.type,
      sdp: description.sdp
    };
    switch (description.type) {
      case 'offer':
        this._updateSignalingState('have-remote-offer');
        break;
      case 'answer':
        this._updateSignalingState('stable');
        break;
      default:
        throw new TypeError('unsupported type "' + description.type +
            '"');
    }
    Object.keys(streams).forEach(function(sid) {
      var stream = streams[sid];
      if (stream.getTracks().length) {
        self.remoteStreams.push(stream);
        var event = new Event('addstream');
        event.stream = stream;
        self.dispatchEvent(event);
        if (self.onaddstream !== null) {
          window.setTimeout(function() {
            self.onaddstream(event);
          }, 0);
        }

        receiverList.forEach(function(item) {
          var track = item[0];
          var receiver = item[1];
          if (stream.id !== item[2].id) {
            return;
          }
          var trackEvent = new Event('track');
          trackEvent.track = track;
          trackEvent.receiver = receiver;
          trackEvent.streams = [stream];
          self.dispatchEvent(trackEvent);
          if (self.ontrack !== null) {
            window.setTimeout(function() {
              self.ontrack(trackEvent);
            }, 0);
          }
        });
      }
    });

    // check whether addIceCandidate({}) was called within four seconds after
    // setRemoteDescription.
    window.setTimeout(function() {
      if (!(self && self.transceivers)) {
        return;
      }
      self.transceivers.forEach(function(transceiver) {
        if (transceiver.iceTransport &&
            transceiver.iceTransport.state === 'new' &&
            transceiver.iceTransport.getRemoteCandidates().length > 0) {
          console.warn('Timeout for addRemoteCandidate. Consider sending ' +
              'an end-of-candidates notification');
          transceiver.iceTransport.addRemoteCandidate({});
        }
      });
    }, 4000);

    if (arguments.length > 1 && typeof arguments[1] === 'function') {
      window.setTimeout(arguments[1], 0);
    }
    return Promise.resolve();
  };

  RTCPeerConnection.prototype.close = function() {
    this.transceivers.forEach(function(transceiver) {
      /* not yet
      if (transceiver.iceGatherer) {
        transceiver.iceGatherer.close();
      }
      */
      if (transceiver.iceTransport) {
        transceiver.iceTransport.stop();
      }
      if (transceiver.dtlsTransport) {
        transceiver.dtlsTransport.stop();
      }
      if (transceiver.rtpSender) {
        transceiver.rtpSender.stop();
      }
      if (transceiver.rtpReceiver) {
        transceiver.rtpReceiver.stop();
      }
    });
    // FIXME: clean up tracks, local streams, remote streams, etc
    this._updateSignalingState('closed');
  };

  // Update the signaling state.
  RTCPeerConnection.prototype._updateSignalingState = function(newState) {
    this.signalingState = newState;
    var event = new Event('signalingstatechange');
    this.dispatchEvent(event);
    if (this.onsignalingstatechange !== null) {
      this.onsignalingstatechange(event);
    }
  };

  // Determine whether to fire the negotiationneeded event.
  RTCPeerConnection.prototype._maybeFireNegotiationNeeded = function() {
    var self = this;
    if (this.signalingState !== 'stable' || this.needNegotiation === true) {
      return;
    }
    this.needNegotiation = true;
    window.setTimeout(function() {
      if (self.needNegotiation === false) {
        return;
      }
      self.needNegotiation = false;
      var event = new Event('negotiationneeded');
      self.dispatchEvent(event);
      if (self.onnegotiationneeded !== null) {
        self.onnegotiationneeded(event);
      }
    }, 0);
  };

  // Update the connection state.
  RTCPeerConnection.prototype._updateConnectionState = function() {
    var self = this;
    var newState;
    var states = {
      'new': 0,
      closed: 0,
      connecting: 0,
      checking: 0,
      connected: 0,
      completed: 0,
      disconnected: 0,
      failed: 0
    };
    this.transceivers.forEach(function(transceiver) {
      states[transceiver.iceTransport.state]++;
      states[transceiver.dtlsTransport.state]++;
    });
    // ICETransport.completed and connected are the same for this purpose.
    states.connected += states.completed;

    newState = 'new';
    if (states.failed > 0) {
      newState = 'failed';
    } else if (states.connecting > 0 || states.checking > 0) {
      newState = 'connecting';
    } else if (states.disconnected > 0) {
      newState = 'disconnected';
    } else if (states.new > 0) {
      newState = 'new';
    } else if (states.connected > 0 || states.completed > 0) {
      newState = 'connected';
    }

    if (newState !== self.iceConnectionState) {
      self.iceConnectionState = newState;
      var event = new Event('iceconnectionstatechange');
      this.dispatchEvent(event);
      if (this.oniceconnectionstatechange !== null) {
        this.oniceconnectionstatechange(event);
      }
    }
  };

  RTCPeerConnection.prototype.createOffer = function() {
    var self = this;
    if (this._pendingOffer) {
      throw new Error('createOffer called while there is a pending offer.');
    }
    var offerOptions;
    if (arguments.length === 1 && typeof arguments[0] !== 'function') {
      offerOptions = arguments[0];
    } else if (arguments.length === 3) {
      offerOptions = arguments[2];
    }

    var numAudioTracks = this.transceivers.filter(function(t) {
      return t.kind === 'audio';
    }).length;
    var numVideoTracks = this.transceivers.filter(function(t) {
      return t.kind === 'video';
    }).length;

    // Determine number of audio and video tracks we need to send/recv.
    if (offerOptions) {
      // Reject Chrome legacy constraints.
      if (offerOptions.mandatory || offerOptions.optional) {
        throw new TypeError(
            'Legacy mandatory/optional constraints not supported.');
      }
      if (offerOptions.offerToReceiveAudio !== undefined) {
        if (offerOptions.offerToReceiveAudio === true) {
          numAudioTracks = 1;
        } else if (offerOptions.offerToReceiveAudio === false) {
          numAudioTracks = 0;
        } else {
          numAudioTracks = offerOptions.offerToReceiveAudio;
        }
      }
      if (offerOptions.offerToReceiveVideo !== undefined) {
        if (offerOptions.offerToReceiveVideo === true) {
          numVideoTracks = 1;
        } else if (offerOptions.offerToReceiveVideo === false) {
          numVideoTracks = 0;
        } else {
          numVideoTracks = offerOptions.offerToReceiveVideo;
        }
      }
    }

    this.transceivers.forEach(function(transceiver) {
      if (transceiver.kind === 'audio') {
        numAudioTracks--;
        if (numAudioTracks < 0) {
          transceiver.wantReceive = false;
        }
      } else if (transceiver.kind === 'video') {
        numVideoTracks--;
        if (numVideoTracks < 0) {
          transceiver.wantReceive = false;
        }
      }
    });

    // Create M-lines for recvonly streams.
    while (numAudioTracks > 0 || numVideoTracks > 0) {
      if (numAudioTracks > 0) {
        this._createTransceiver('audio');
        numAudioTracks--;
      }
      if (numVideoTracks > 0) {
        this._createTransceiver('video');
        numVideoTracks--;
      }
    }
    // reorder tracks
    var transceivers = sortTracks(this.transceivers);

    var sdp = SDPUtils.writeSessionBoilerplate(this._sdpSessionId);
    transceivers.forEach(function(transceiver, sdpMLineIndex) {
      // For each track, create an ice gatherer, ice transport,
      // dtls transport, potentially rtpsender and rtpreceiver.
      var track = transceiver.track;
      var kind = transceiver.kind;
      var mid = SDPUtils.generateIdentifier();
      transceiver.mid = mid;

      if (!transceiver.iceGatherer) {
        transceiver.iceGatherer = self.usingBundle && sdpMLineIndex > 0 ?
            transceivers[0].iceGatherer :
            self._createIceGatherer(mid, sdpMLineIndex);
      }

      var localCapabilities = window.RTCRtpSender.getCapabilities(kind);
      // filter RTX until additional stuff needed for RTX is implemented
      // in adapter.js
      if (edgeVersion < 15019) {
        localCapabilities.codecs = localCapabilities.codecs.filter(
            function(codec) {
              return codec.name !== 'rtx';
            });
      }
      localCapabilities.codecs.forEach(function(codec) {
        // work around https://bugs.chromium.org/p/webrtc/issues/detail?id=6552
        // by adding level-asymmetry-allowed=1
        if (codec.name === 'H264' &&
            codec.parameters['level-asymmetry-allowed'] === undefined) {
          codec.parameters['level-asymmetry-allowed'] = '1';
        }
      });

      // generate an ssrc now, to be used later in rtpSender.send
      var sendEncodingParameters = [{
        ssrc: (2 * sdpMLineIndex + 1) * 1001
      }];
      if (track) {
        // add RTX
        if (edgeVersion >= 15019 && kind === 'video') {
          sendEncodingParameters[0].rtx = {
            ssrc: (2 * sdpMLineIndex + 1) * 1001 + 1
          };
        }
      }

      if (transceiver.wantReceive) {
        transceiver.rtpReceiver = new window.RTCRtpReceiver(
          transceiver.dtlsTransport,
          kind
        );
      }

      transceiver.localCapabilities = localCapabilities;
      transceiver.sendEncodingParameters = sendEncodingParameters;
    });

    // always offer BUNDLE and dispose on return if not supported.
    if (this._config.bundlePolicy !== 'max-compat') {
      sdp += 'a=group:BUNDLE ' + transceivers.map(function(t) {
        return t.mid;
      }).join(' ') + '\r\n';
    }
    sdp += 'a=ice-options:trickle\r\n';

    transceivers.forEach(function(transceiver, sdpMLineIndex) {
      sdp += SDPUtils.writeMediaSection(transceiver,
          transceiver.localCapabilities, 'offer', transceiver.stream);
      sdp += 'a=rtcp-rsize\r\n';
    });

    this._pendingOffer = transceivers;
    var desc = new window.RTCSessionDescription({
      type: 'offer',
      sdp: sdp
    });
    if (arguments.length && typeof arguments[0] === 'function') {
      window.setTimeout(arguments[0], 0, desc);
    }
    return Promise.resolve(desc);
  };

  RTCPeerConnection.prototype.createAnswer = function() {
    var sdp = SDPUtils.writeSessionBoilerplate(this._sdpSessionId);
    if (this.usingBundle) {
      sdp += 'a=group:BUNDLE ' + this.transceivers.map(function(t) {
        return t.mid;
      }).join(' ') + '\r\n';
    }
    this.transceivers.forEach(function(transceiver, sdpMLineIndex) {
      if (transceiver.isDatachannel) {
        sdp += 'm=application 0 DTLS/SCTP 5000\r\n' +
            'c=IN IP4 0.0.0.0\r\n' +
            'a=mid:' + transceiver.mid + '\r\n';
        return;
      }

      // FIXME: look at direction.
      if (transceiver.stream) {
        var localTrack;
        if (transceiver.kind === 'audio') {
          localTrack = transceiver.stream.getAudioTracks()[0];
        } else if (transceiver.kind === 'video') {
          localTrack = transceiver.stream.getVideoTracks()[0];
        }
        if (localTrack) {
          // add RTX
          if (edgeVersion >= 15019 && transceiver.kind === 'video') {
            transceiver.sendEncodingParameters[0].rtx = {
              ssrc: (2 * sdpMLineIndex + 2) * 1001 + 1
            };
          }
        }
      }

      // Calculate intersection of capabilities.
      var commonCapabilities = getCommonCapabilities(
          transceiver.localCapabilities,
          transceiver.remoteCapabilities);

      var hasRtx = commonCapabilities.codecs.filter(function(c) {
        return c.name.toLowerCase() === 'rtx';
      }).length;
      if (!hasRtx && transceiver.sendEncodingParameters[0].rtx) {
        delete transceiver.sendEncodingParameters[0].rtx;
      }

      sdp += SDPUtils.writeMediaSection(transceiver, commonCapabilities,
          'answer', transceiver.stream);
      if (transceiver.rtcpParameters &&
          transceiver.rtcpParameters.reducedSize) {
        sdp += 'a=rtcp-rsize\r\n';
      }
    });

    var desc = new window.RTCSessionDescription({
      type: 'answer',
      sdp: sdp
    });
    if (arguments.length && typeof arguments[0] === 'function') {
      window.setTimeout(arguments[0], 0, desc);
    }
    return Promise.resolve(desc);
  };

  RTCPeerConnection.prototype.addIceCandidate = function(candidate) {
    if (!candidate) {
      for (var j = 0; j < this.transceivers.length; j++) {
        this.transceivers[j].iceTransport.addRemoteCandidate({});
        if (this.usingBundle) {
          return Promise.resolve();
        }
      }
    } else {
      var mLineIndex = candidate.sdpMLineIndex;
      if (candidate.sdpMid) {
        for (var i = 0; i < this.transceivers.length; i++) {
          if (this.transceivers[i].mid === candidate.sdpMid) {
            mLineIndex = i;
            break;
          }
        }
      }
      var transceiver = this.transceivers[mLineIndex];
      if (transceiver) {
        var cand = Object.keys(candidate.candidate).length > 0 ?
            SDPUtils.parseCandidate(candidate.candidate) : {};
        // Ignore Chrome's invalid candidates since Edge does not like them.
        if (cand.protocol === 'tcp' && (cand.port === 0 || cand.port === 9)) {
          return Promise.resolve();
        }
        // Ignore RTCP candidates, we assume RTCP-MUX.
        if (cand.component &&
            !(cand.component === '1' || cand.component === 1)) {
          return Promise.resolve();
        }
        transceiver.iceTransport.addRemoteCandidate(cand);

        // update the remoteDescription.
        var sections = SDPUtils.splitSections(this.remoteDescription.sdp);
        sections[mLineIndex + 1] += (cand.type ? candidate.candidate.trim()
            : 'a=end-of-candidates') + '\r\n';
        this.remoteDescription.sdp = sections.join('');
      }
    }
    if (arguments.length > 1 && typeof arguments[1] === 'function') {
      window.setTimeout(arguments[1], 0);
    }
    return Promise.resolve();
  };

  RTCPeerConnection.prototype.getStats = function() {
    var promises = [];
    this.transceivers.forEach(function(transceiver) {
      ['rtpSender', 'rtpReceiver', 'iceGatherer', 'iceTransport',
        'dtlsTransport'].forEach(function(method) {
          if (transceiver[method]) {
            promises.push(transceiver[method].getStats());
          }
        });
    });
    var cb = arguments.length > 1 && typeof arguments[1] === 'function' &&
        arguments[1];
    var fixStatsType = function(stat) {
      return {
        inboundrtp: 'inbound-rtp',
        outboundrtp: 'outbound-rtp',
        candidatepair: 'candidate-pair',
        localcandidate: 'local-candidate',
        remotecandidate: 'remote-candidate'
      }[stat.type] || stat.type;
    };
    return new Promise(function(resolve) {
      // shim getStats with maplike support
      var results = new Map();
      Promise.all(promises).then(function(res) {
        res.forEach(function(result) {
          Object.keys(result).forEach(function(id) {
            result[id].type = fixStatsType(result[id]);
            results.set(id, result[id]);
          });
        });
        if (cb) {
          window.setTimeout(cb, 0, results);
        }
        resolve(results);
      });
    });
  };
  return RTCPeerConnection;
};