adapter.js

/*
 *  Copyright (c) 2016 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.
 */

/* More information about these options at jshint.com/docs/options */
/* jshint browser: true, camelcase: true, curly: true, devel: true,
   eqeqeq: true, forin: false, globalstrict: true, node: true,
   quotmark: single, undef: true, unused: strict */
/* global mozRTCIceCandidate, mozRTCPeerConnection, Promise,
mozRTCSessionDescription, webkitRTCPeerConnection, MediaStreamTrack,
MediaStream, RTCIceGatherer, RTCIceTransport, RTCDtlsTransport,
RTCRtpSender, RTCRtpReceiver*/
/* exported trace,requestUserMedia */

'use strict';

var getUserMedia = null;
var attachMediaStream = null;
var reattachMediaStream = null;
var webrtcDetectedBrowser = null;
var webrtcDetectedVersion = null;
var webrtcMinimumVersion = null;
var webrtcUtils = {
  log: function() {
    // suppress console.log output when being included as a module.
    if (typeof module !== 'undefined' ||
        typeof require === 'function' && typeof define === 'function') {
      return;
    }
    console.log.apply(console, arguments);
  },
  extractVersion: function(uastring, expr, pos) {
    var match = uastring.match(expr);
    return match && match.length >= pos && parseInt(match[pos], 10);
  }
};

function trace(text) {
  // This function is used for logging.
  if (text[text.length - 1] === '\n') {
    text = text.substring(0, text.length - 1);
  }
  if (window.performance) {
    var now = (window.performance.now() / 1000).toFixed(3);
    webrtcUtils.log(now + ': ' + text);
  } else {
    webrtcUtils.log(text);
  }
}

if (typeof window === 'object') {
  if (window.HTMLMediaElement &&
    !('srcObject' in window.HTMLMediaElement.prototype)) {
    // Shim the srcObject property, once, when HTMLMediaElement is found.
    Object.defineProperty(window.HTMLMediaElement.prototype, 'srcObject', {
      get: function() {
        // If prefixed srcObject property exists, return it.
        // Otherwise use the shimmed property, _srcObject
        return 'mozSrcObject' in this ? this.mozSrcObject : this._srcObject;
      },
      set: function(stream) {
        if ('mozSrcObject' in this) {
          this.mozSrcObject = stream;
        } else {
          // Use _srcObject as a private property for this shim
          this._srcObject = stream;
          // TODO: revokeObjectUrl(this.src) when !stream to release resources?
          this.src = URL.createObjectURL(stream);
        }
      }
    });
  }
  // Proxy existing globals
  getUserMedia = window.navigator && window.navigator.getUserMedia;
}

// Attach a media stream to an element.
attachMediaStream = function(element, stream) {
  element.srcObject = stream;
};

reattachMediaStream = function(to, from) {
  to.srcObject = from.srcObject;
};

if (typeof window === 'undefined' || !window.navigator) {
  webrtcUtils.log('This does not appear to be a browser');
  webrtcDetectedBrowser = 'not a browser';
} else if (navigator.mozGetUserMedia) {
  webrtcUtils.log('This appears to be Firefox');

  webrtcDetectedBrowser = 'firefox';

  // the detected firefox version.
  webrtcDetectedVersion = webrtcUtils.extractVersion(navigator.userAgent,
      /Firefox\/([0-9]+)\./, 1);

  // the minimum firefox version still supported by adapter.
  webrtcMinimumVersion = 31;

  // Shim for RTCPeerConnection on older versions.
  if (!window.RTCPeerConnection) {
    window.RTCPeerConnection = function(pcConfig, pcConstraints) {
      if (webrtcDetectedVersion < 38) {
        // .urls is not supported in FF < 38.
        // create RTCIceServers with a single url.
        if (pcConfig && pcConfig.iceServers) {
          var newIceServers = [];
          for (var i = 0; i < pcConfig.iceServers.length; i++) {
            var server = pcConfig.iceServers[i];
            if (server.hasOwnProperty('urls')) {
              for (var j = 0; j < server.urls.length; j++) {
                var newServer = {
                  url: server.urls[j]
                };
                if (server.urls[j].indexOf('turn') === 0) {
                  newServer.username = server.username;
                  newServer.credential = server.credential;
                }
                newIceServers.push(newServer);
              }
            } else {
              newIceServers.push(pcConfig.iceServers[i]);
            }
          }
          pcConfig.iceServers = newIceServers;
        }
      }
      return new mozRTCPeerConnection(pcConfig, pcConstraints); // jscs:ignore requireCapitalizedConstructors
    };

    // wrap static methods. Currently just generateCertificate.
    if (mozRTCPeerConnection.generateCertificate) {
      Object.defineProperty(window.RTCPeerConnection, 'generateCertificate', {
        get: function() {
          if (arguments.length) {
            return mozRTCPeerConnection.generateCertificate.apply(null,
                arguments);
          } else {
            return mozRTCPeerConnection.generateCertificate;
          }
        }
      });
    }

    window.RTCSessionDescription = mozRTCSessionDescription;
    window.RTCIceCandidate = mozRTCIceCandidate;
  }

  // getUserMedia constraints shim.
  getUserMedia = function(constraints, onSuccess, onError) {
    var constraintsToFF37 = function(c) {
      if (typeof c !== 'object' || c.require) {
        return c;
      }
      var require = [];
      Object.keys(c).forEach(function(key) {
        if (key === 'require' || key === 'advanced' || key === 'mediaSource') {
          return;
        }
        var r = c[key] = (typeof c[key] === 'object') ?
            c[key] : {ideal: c[key]};
        if (r.min !== undefined ||
            r.max !== undefined || r.exact !== undefined) {
          require.push(key);
        }
        if (r.exact !== undefined) {
          if (typeof r.exact === 'number') {
            r.min = r.max = r.exact;
          } else {
            c[key] = r.exact;
          }
          delete r.exact;
        }
        if (r.ideal !== undefined) {
          c.advanced = c.advanced || [];
          var oc = {};
          if (typeof r.ideal === 'number') {
            oc[key] = {min: r.ideal, max: r.ideal};
          } else {
            oc[key] = r.ideal;
          }
          c.advanced.push(oc);
          delete r.ideal;
          if (!Object.keys(r).length) {
            delete c[key];
          }
        }
      });
      if (require.length) {
        c.require = require;
      }
      return c;
    };
    if (webrtcDetectedVersion < 38) {
      webrtcUtils.log('spec: ' + JSON.stringify(constraints));
      if (constraints.audio) {
        constraints.audio = constraintsToFF37(constraints.audio);
      }
      if (constraints.video) {
        constraints.video = constraintsToFF37(constraints.video);
      }
      webrtcUtils.log('ff37: ' + JSON.stringify(constraints));
    }
    return navigator.mozGetUserMedia(constraints, onSuccess, onError);
  };

  navigator.getUserMedia = getUserMedia;

  // Shim for mediaDevices on older versions.
  if (!navigator.mediaDevices) {
    navigator.mediaDevices = {getUserMedia: requestUserMedia,
      addEventListener: function() { },
      removeEventListener: function() { }
    };
  }
  navigator.mediaDevices.enumerateDevices =
      navigator.mediaDevices.enumerateDevices || function() {
    return new Promise(function(resolve) {
      var infos = [
        {kind: 'audioinput', deviceId: 'default', label: '', groupId: ''},
        {kind: 'videoinput', deviceId: 'default', label: '', groupId: ''}
      ];
      resolve(infos);
    });
  };

  if (webrtcDetectedVersion < 41) {
    // Work around http://bugzil.la/1169665
    var orgEnumerateDevices =
        navigator.mediaDevices.enumerateDevices.bind(navigator.mediaDevices);
    navigator.mediaDevices.enumerateDevices = function() {
      return orgEnumerateDevices().then(undefined, function(e) {
        if (e.name === 'NotFoundError') {
          return [];
        }
        throw e;
      });
    };
  }
} else if (navigator.webkitGetUserMedia && window.webkitRTCPeerConnection) {
  webrtcUtils.log('This appears to be Chrome');

  webrtcDetectedBrowser = 'chrome';

  // the detected chrome version.
  webrtcDetectedVersion = webrtcUtils.extractVersion(navigator.userAgent,
      /Chrom(e|ium)\/([0-9]+)\./, 2);

  // the minimum chrome version still supported by adapter.
  webrtcMinimumVersion = 38;

  // The RTCPeerConnection object.
  window.RTCPeerConnection = function(pcConfig, pcConstraints) {
    // Translate iceTransportPolicy to iceTransports,
    // see https://code.google.com/p/webrtc/issues/detail?id=4869
    if (pcConfig && pcConfig.iceTransportPolicy) {
      pcConfig.iceTransports = pcConfig.iceTransportPolicy;
    }

    var pc = new webkitRTCPeerConnection(pcConfig, pcConstraints); // jscs:ignore requireCapitalizedConstructors
    var origGetStats = pc.getStats.bind(pc);
    pc.getStats = function(selector, successCallback, errorCallback) { // jshint ignore: line
      var self = this;
      var args = arguments;

      // If selector is a function then we are in the old style stats so just
      // pass back the original getStats format to avoid breaking old users.
      if (arguments.length > 0 && typeof selector === 'function') {
        return origGetStats(selector, successCallback);
      }

      var fixChromeStats = function(response) {
        var standardReport = {};
        var reports = response.result();
        reports.forEach(function(report) {
          var standardStats = {
            id: report.id,
            timestamp: report.timestamp,
            type: report.type
          };
          report.names().forEach(function(name) {
            standardStats[name] = report.stat(name);
          });
          standardReport[standardStats.id] = standardStats;
        });

        return standardReport;
      };

      if (arguments.length >= 2) {
        var successCallbackWrapper = function(response) {
          args[1](fixChromeStats(response));
        };

        return origGetStats.apply(this, [successCallbackWrapper, arguments[0]]);
      }

      // promise-support
      return new Promise(function(resolve, reject) {
        if (args.length === 1 && selector === null) {
          origGetStats.apply(self, [
              function(response) {
                resolve.apply(null, [fixChromeStats(response)]);
              }, reject]);
        } else {
          origGetStats.apply(self, [resolve, reject]);
        }
      });
    };

    return pc;
  };

  // wrap static methods. Currently just generateCertificate.
  if (webkitRTCPeerConnection.generateCertificate) {
    Object.defineProperty(window.RTCPeerConnection, 'generateCertificate', {
      get: function() {
        if (arguments.length) {
          return webkitRTCPeerConnection.generateCertificate.apply(null,
              arguments);
        } else {
          return webkitRTCPeerConnection.generateCertificate;
        }
      }
    });
  }

  // add promise support
  ['createOffer', 'createAnswer'].forEach(function(method) {
    var nativeMethod = webkitRTCPeerConnection.prototype[method];
    webkitRTCPeerConnection.prototype[method] = function() {
      var self = this;
      if (arguments.length < 1 || (arguments.length === 1 &&
          typeof(arguments[0]) === 'object')) {
        var opts = arguments.length === 1 ? arguments[0] : undefined;
        return new Promise(function(resolve, reject) {
          nativeMethod.apply(self, [resolve, reject, opts]);
        });
      } else {
        return nativeMethod.apply(this, arguments);
      }
    };
  });

  ['setLocalDescription', 'setRemoteDescription',
      'addIceCandidate'].forEach(function(method) {
    var nativeMethod = webkitRTCPeerConnection.prototype[method];
    webkitRTCPeerConnection.prototype[method] = function() {
      var args = arguments;
      var self = this;
      return new Promise(function(resolve, reject) {
        nativeMethod.apply(self, [args[0],
            function() {
              resolve();
              if (args.length >= 2) {
                args[1].apply(null, []);
              }
            },
            function(err) {
              reject(err);
              if (args.length >= 3) {
                args[2].apply(null, [err]);
              }
            }]
          );
      });
    };
  });

  // getUserMedia constraints shim.
  var constraintsToChrome = function(c) {
    if (typeof c !== 'object' || c.mandatory || c.optional) {
      return c;
    }
    var cc = {};
    Object.keys(c).forEach(function(key) {
      if (key === 'require' || key === 'advanced' || key === 'mediaSource') {
        return;
      }
      var r = (typeof c[key] === 'object') ? c[key] : {ideal: c[key]};
      if (r.exact !== undefined && typeof r.exact === 'number') {
        r.min = r.max = r.exact;
      }
      var oldname = function(prefix, name) {
        if (prefix) {
          return prefix + name.charAt(0).toUpperCase() + name.slice(1);
        }
        return (name === 'deviceId') ? 'sourceId' : name;
      };
      if (r.ideal !== undefined) {
        cc.optional = cc.optional || [];
        var oc = {};
        if (typeof r.ideal === 'number') {
          oc[oldname('min', key)] = r.ideal;
          cc.optional.push(oc);
          oc = {};
          oc[oldname('max', key)] = r.ideal;
          cc.optional.push(oc);
        } else {
          oc[oldname('', key)] = r.ideal;
          cc.optional.push(oc);
        }
      }
      if (r.exact !== undefined && typeof r.exact !== 'number') {
        cc.mandatory = cc.mandatory || {};
        cc.mandatory[oldname('', key)] = r.exact;
      } else {
        ['min', 'max'].forEach(function(mix) {
          if (r[mix] !== undefined) {
            cc.mandatory = cc.mandatory || {};
            cc.mandatory[oldname(mix, key)] = r[mix];
          }
        });
      }
    });
    if (c.advanced) {
      cc.optional = (cc.optional || []).concat(c.advanced);
    }
    return cc;
  };

  getUserMedia = function(constraints, onSuccess, onError) {
    if (constraints.audio) {
      constraints.audio = constraintsToChrome(constraints.audio);
    }
    if (constraints.video) {
      constraints.video = constraintsToChrome(constraints.video);
    }
    webrtcUtils.log('chrome: ' + JSON.stringify(constraints));
    return navigator.webkitGetUserMedia(constraints, onSuccess, onError);
  };
  navigator.getUserMedia = getUserMedia;

  if (!navigator.mediaDevices) {
    navigator.mediaDevices = {getUserMedia: requestUserMedia,
                              enumerateDevices: function() {
      return new Promise(function(resolve) {
        var kinds = {audio: 'audioinput', video: 'videoinput'};
        return MediaStreamTrack.getSources(function(devices) {
          resolve(devices.map(function(device) {
            return {label: device.label,
                    kind: kinds[device.kind],
                    deviceId: device.id,
                    groupId: ''};
          }));
        });
      });
    }};
  }

  // A shim for getUserMedia method on the mediaDevices object.
  // TODO(KaptenJansson) remove once implemented in Chrome stable.
  if (!navigator.mediaDevices.getUserMedia) {
    navigator.mediaDevices.getUserMedia = function(constraints) {
      return requestUserMedia(constraints);
    };
  } else {
    // Even though Chrome 45 has navigator.mediaDevices and a getUserMedia
    // function which returns a Promise, it does not accept spec-style
    // constraints.
    var origGetUserMedia = navigator.mediaDevices.getUserMedia.
        bind(navigator.mediaDevices);
    navigator.mediaDevices.getUserMedia = function(c) {
      webrtcUtils.log('spec:   ' + JSON.stringify(c)); // whitespace for alignment
      c.audio = constraintsToChrome(c.audio);
      c.video = constraintsToChrome(c.video);
      webrtcUtils.log('chrome: ' + JSON.stringify(c));
      return origGetUserMedia(c);
    };
  }

  // Dummy devicechange event methods.
  // TODO(KaptenJansson) remove once implemented in Chrome stable.
  if (typeof navigator.mediaDevices.addEventListener === 'undefined') {
    navigator.mediaDevices.addEventListener = function() {
      webrtcUtils.log('Dummy mediaDevices.addEventListener called.');
    };
  }
  if (typeof navigator.mediaDevices.removeEventListener === 'undefined') {
    navigator.mediaDevices.removeEventListener = function() {
      webrtcUtils.log('Dummy mediaDevices.removeEventListener called.');
    };
  }

  // Attach a media stream to an element.
  attachMediaStream = function(element, stream) {
    if (webrtcDetectedVersion >= 43) {
      element.srcObject = stream;
    } else if (typeof element.src !== 'undefined') {
      element.src = URL.createObjectURL(stream);
    } else {
      webrtcUtils.log('Error attaching stream to element.');
    }
  };
  reattachMediaStream = function(to, from) {
    if (webrtcDetectedVersion >= 43) {
      to.srcObject = from.srcObject;
    } else {
      to.src = from.src;
    }
  };

} else if (navigator.mediaDevices && navigator.userAgent.match(
    /Edge\/(\d+).(\d+)$/)) {
  webrtcUtils.log('This appears to be Edge');
  webrtcDetectedBrowser = 'edge';

  webrtcDetectedVersion = webrtcUtils.extractVersion(navigator.userAgent,
      /Edge\/(\d+).(\d+)$/, 2);

  // The minimum version still supported by adapter.
  // This is the build number for Edge.
  webrtcMinimumVersion = 10547;

  if (window.RTCIceGatherer) {
    // Generate an alphanumeric identifier for cname or mids.
    // TODO: use UUIDs instead? https://gist.github.com/jed/982883
    var generateIdentifier = function() {
      return Math.random().toString(36).substr(2, 10);
    };

    // The RTCP CNAME used by all peerconnections from the same JS.
    var localCName = generateIdentifier();

    // SDP helpers - to be moved into separate module.
    var SDPUtils = {};

    // Splits SDP into lines, dealing with both CRLF and LF.
    SDPUtils.splitLines = function(blob) {
      return blob.trim().split('\n').map(function(line) {
        return line.trim();
      });
    };

    // Splits SDP into sessionpart and mediasections. Ensures CRLF.
    SDPUtils.splitSections = function(blob) {
      var parts = blob.split('\r\nm=');
      return parts.map(function(part, index) {
        return (index > 0 ? 'm=' + part : part).trim() + '\r\n';
      });
    };

    // Returns lines that start with a certain prefix.
    SDPUtils.matchPrefix = function(blob, prefix) {
      return SDPUtils.splitLines(blob).filter(function(line) {
        return line.indexOf(prefix) === 0;
      });
    };

    // Parses an ICE candidate line. Sample input:
    // candidate:702786350 2 udp 41819902 8.8.8.8 60769 typ relay raddr 8.8.8.8 rport 55996"
    SDPUtils.parseCandidate = function(line) {
      var parts;
      // Parse both variants.
      if (line.indexOf('a=candidate:') === 0) {
        parts = line.substring(12).split(' ');
      } else {
        parts = line.substring(10).split(' ');
      }

      var candidate = {
        foundation: parts[0],
        component: parts[1],
        protocol: parts[2].toLowerCase(),
        priority: parseInt(parts[3], 10),
        ip: parts[4],
        port: parseInt(parts[5], 10),
        // skip parts[6] == 'typ'
        type: parts[7]
      };

      for (var i = 8; i < parts.length; i += 2) {
        switch (parts[i]) {
          case 'raddr':
            candidate.relatedAddress = parts[i + 1];
            break;
          case 'rport':
            candidate.relatedPort = parseInt(parts[i + 1], 10);
            break;
          case 'tcptype':
            candidate.tcpType = parts[i + 1];
            break;
          default: // Unknown extensions are silently ignored.
            break;
        }
      }
      return candidate;
    };

    // Translates a candidate object into SDP candidate attribute.
    SDPUtils.writeCandidate = function(candidate) {
      var sdp = [];
      sdp.push(candidate.foundation);
      sdp.push(candidate.component);
      sdp.push(candidate.protocol.toUpperCase());
      sdp.push(candidate.priority);
      sdp.push(candidate.ip);
      sdp.push(candidate.port);

      var type = candidate.type;
      sdp.push('typ');
      sdp.push(type);
      if (type !== 'host' && candidate.relatedAddress &&
          candidate.relatedPort) {
        sdp.push('raddr');
        sdp.push(candidate.relatedAddress); // was: relAddr
        sdp.push('rport');
        sdp.push(candidate.relatedPort); // was: relPort
      }
      if (candidate.tcpType && candidate.protocol.toLowerCase() === 'tcp') {
        sdp.push('tcptype');
        sdp.push(candidate.tcpType);
      }
      return 'candidate:' + sdp.join(' ');
    };

    // Parses an rtpmap line, returns RTCRtpCoddecParameters. Sample input:
    // a=rtpmap:111 opus/48000/2
    SDPUtils.parseRtpMap = function(line) {
      var parts = line.substr(9).split(' ');
      var parsed = {
        payloadType: parseInt(parts.shift(), 10) // was: id
      };

      parts = parts[0].split('/');

      parsed.name = parts[0];
      parsed.clockRate = parseInt(parts[1], 10); // was: clockrate
      parsed.numChannels = parts.length === 3 ? parseInt(parts[2], 10) : 1; // was: channels
      return parsed;
    };

    // Generate an a=rtpmap line from RTCRtpCodecCapability or RTCRtpCodecParameters.
    SDPUtils.writeRtpMap = function(codec) {
      var pt = codec.payloadType;
      if (codec.preferredPayloadType !== undefined) {
        pt = codec.preferredPayloadType;
      }
      return 'a=rtpmap:' + pt + ' ' + codec.name + '/' + codec.clockRate +
          (codec.numChannels !== 1 ? '/' + codec.numChannels : '') + '\r\n';
    };

    // Parses an ftmp line, returns dictionary. Sample input:
    // a=fmtp:96 vbr=on;cng=on
    // Also deals with vbr=on; cng=on
    SDPUtils.parseFmtp = function(line) {
      var parsed = {};
      var kv;
      var parts = line.substr(line.indexOf(' ') + 1).split(';');
      for (var j = 0; j < parts.length; j++) {
        kv = parts[j].trim().split('=');
        parsed[kv[0].trim()] = kv[1];
      }
      return parsed;
    };

    // Generates an a=ftmp line from RTCRtpCodecCapability or RTCRtpCodecParameters.
    SDPUtils.writeFtmp = function(codec) {
      var line = '';
      var pt = codec.payloadType;
      if (codec.preferredPayloadType !== undefined) {
        pt = codec.preferredPayloadType;
      }
      if (codec.parameters && codec.parameters.length) {
        var params = [];
        Object.keys(codec.parameters).forEach(function(param) {
          params.push(param + '=' + codec.parameters[param]);
        });
        line += 'a=fmtp:' + pt + ' ' + params.join(';') + '\r\n';
      }
      return line;
    };

    // Parses an rtcp-fb line, returns RTCPRtcpFeedback object. Sample input:
    // a=rtcp-fb:98 nack rpsi
    SDPUtils.parseRtcpFb = function(line) {
      var parts = line.substr(line.indexOf(' ') + 1).split(' ');
      return {
        type: parts.shift(),
        parameter: parts.join(' ')
      };
    };
    // Generate a=rtcp-fb lines from RTCRtpCodecCapability or RTCRtpCodecParameters.
    SDPUtils.writeRtcpFb = function(codec) {
      var lines = '';
      var pt = codec.payloadType;
      if (codec.preferredPayloadType !== undefined) {
        pt = codec.preferredPayloadType;
      }
      if (codec.rtcpFeedback && codec.rtcpFeedback.length) {
        // FIXME: special handling for trr-int?
        codec.rtcpFeedback.forEach(function(fb) {
          lines += 'a=rtcp-fb:' + pt + ' ' + fb.type + ' ' + fb.parameter +
              '\r\n';
        });
      }
      return lines;
    };

    // Parses an RFC 5576 ssrc media attribute. Sample input:
    // a=ssrc:3735928559 cname:something
    SDPUtils.parseSsrcMedia = function(line) {
      var sp = line.indexOf(' ');
      var parts = {
        ssrc: line.substr(7, sp - 7),
      };
      var colon = line.indexOf(':', sp);
      if (colon > -1) {
        parts.attribute = line.substr(sp + 1, colon - sp - 1);
        parts.value = line.substr(colon + 1);
      } else {
        parts.attribute = line.substr(sp + 1);
      }
      return parts;
    };

    // Extracts DTLS parameters from SDP media section or sessionpart.
    // FIXME: for consistency with other functions this should only
    //   get the fingerprint line as input. See also getIceParameters.
    SDPUtils.getDtlsParameters = function(mediaSection, sessionpart) {
      var lines = SDPUtils.splitLines(mediaSection);
      lines = lines.concat(SDPUtils.splitLines(sessionpart)); // Search in session part, too.
      var fpLine = lines.filter(function(line) {
        return line.indexOf('a=fingerprint:') === 0;
      })[0].substr(14);
      // Note: a=setup line is ignored since we use the 'auto' role.
      var dtlsParameters = {
        role: 'auto',
        fingerprints: [{
          algorithm: fpLine.split(' ')[0],
          value: fpLine.split(' ')[1]
        }]
      };
      return dtlsParameters;
    };

    // Serializes DTLS parameters to SDP.
    SDPUtils.writeDtlsParameters = function(params, setupType) {
      var sdp = 'a=setup:' + setupType + '\r\n';
      params.fingerprints.forEach(function(fp) {
        sdp += 'a=fingerprint:' + fp.algorithm + ' ' + fp.value + '\r\n';
      });
      return sdp;
    };
    // Parses ICE information from SDP media section or sessionpart.
    // FIXME: for consistency with other functions this should only
    //   get the ice-ufrag and ice-pwd lines as input.
    SDPUtils.getIceParameters = function(mediaSection, sessionpart) {
      var lines = SDPUtils.splitLines(mediaSection);
      lines = lines.concat(SDPUtils.splitLines(sessionpart)); // Search in session part, too.
      var iceParameters = {
        usernameFragment: lines.filter(function(line) {
          return line.indexOf('a=ice-ufrag:') === 0;
        })[0].substr(12),
        password: lines.filter(function(line) {
          return line.indexOf('a=ice-pwd:') === 0;
        })[0].substr(10)
      };
      return iceParameters;
    };

    // Serializes ICE parameters to SDP.
    SDPUtils.writeIceParameters = function(params) {
      return 'a=ice-ufrag:' + params.usernameFragment + '\r\n' +
          'a=ice-pwd:' + params.password + '\r\n';
    };

    // Parses the SDP media section and returns RTCRtpParameters.
    SDPUtils.parseRtpParameters = function(mediaSection) {
      var description = {
        codecs: [],
        headerExtensions: [],
        fecMechanisms: [],
        rtcp: []
      };
      var lines = SDPUtils.splitLines(mediaSection);
      var mline = lines[0].split(' ');
      for (var i = 3; i < mline.length; i++) { // find all codecs from mline[3..]
        var pt = mline[i];
        var rtpmapline = SDPUtils.matchPrefix(
            mediaSection, 'a=rtpmap:' + pt + ' ')[0];
        if (rtpmapline) {
          var codec = SDPUtils.parseRtpMap(rtpmapline);
          var fmtps = SDPUtils.matchPrefix(
              mediaSection, 'a=fmtp:' + pt + ' ');
          // Only the first a=fmtp:<pt> is considered.
          codec.parameters = fmtps.length ? SDPUtils.parseFmtp(fmtps[0]) : {};
          codec.rtcpFeedback = SDPUtils.matchPrefix(
              mediaSection, 'a=rtcp-fb:' + pt + ' ')
            .map(SDPUtils.parseRtcpFb);
          description.codecs.push(codec);
        }
      }
      // FIXME: parse headerExtensions, fecMechanisms and rtcp.
      return description;
    };

    // Generates parts of the SDP media section describing the capabilities / parameters.
    SDPUtils.writeRtpDescription = function(kind, caps) {
      var sdp = '';

      // Build the mline.
      sdp += 'm=' + kind + ' ';
      sdp += caps.codecs.length > 0 ? '9' : '0'; // reject if no codecs.
      sdp += ' UDP/TLS/RTP/SAVPF ';
      sdp += caps.codecs.map(function(codec) {
        if (codec.preferredPayloadType !== undefined) {
          return codec.preferredPayloadType;
        }
        return codec.payloadType;
      }).join(' ') + '\r\n';

      sdp += 'c=IN IP4 0.0.0.0\r\n';
      sdp += 'a=rtcp:9 IN IP4 0.0.0.0\r\n';

      // Add a=rtpmap lines for each codec. Also fmtp and rtcp-fb.
      caps.codecs.forEach(function(codec) {
        sdp += SDPUtils.writeRtpMap(codec);
        sdp += SDPUtils.writeFtmp(codec);
        sdp += SDPUtils.writeRtcpFb(codec);
      });
      // FIXME: add headerExtensions, fecMechanismş and rtcp.
      sdp += 'a=rtcp-mux\r\n';
      return sdp;
    };

    SDPUtils.writeSessionBoilerplate = function() {
      // FIXME: sess-id should be an NTP timestamp.
      return 'v=0\r\n' +
          'o=thisisadapterortc 8169639915646943137 2 IN IP4 127.0.0.1\r\n' +
          's=-\r\n' +
          't=0 0\r\n';
    };

    SDPUtils.writeMediaSection = function(transceiver, caps, type, stream) {
      var sdp = SDPUtils.writeRtpDescription(transceiver.kind, caps);

      // Map ICE parameters (ufrag, pwd) to SDP.
      sdp += SDPUtils.writeIceParameters(
          transceiver.iceGatherer.getLocalParameters());

      // Map DTLS parameters to SDP.
      sdp += SDPUtils.writeDtlsParameters(
          transceiver.dtlsTransport.getLocalParameters(),
          type === 'offer' ? 'actpass' : 'active');

      sdp += 'a=mid:' + transceiver.mid + '\r\n';

      if (transceiver.rtpSender && transceiver.rtpReceiver) {
        sdp += 'a=sendrecv\r\n';
      } else if (transceiver.rtpSender) {
        sdp += 'a=sendonly\r\n';
      } else if (transceiver.rtpReceiver) {
        sdp += 'a=recvonly\r\n';
      } else {
        sdp += 'a=inactive\r\n';
      }

      // FIXME: for RTX there might be multiple SSRCs. Not implemented in Edge yet.
      if (transceiver.rtpSender) {
        var msid = 'msid:' + stream.id + ' ' +
            transceiver.rtpSender.track.id + '\r\n';
        sdp += 'a=' + msid;
        sdp += 'a=ssrc:' + transceiver.sendSsrc + ' ' + msid;
      }
      // FIXME: this should be written by writeRtpDescription.
      sdp += 'a=ssrc:' + transceiver.sendSsrc + ' cname:' +
          localCName + '\r\n';
      return sdp;
    };

    // Gets the direction from the mediaSection or the sessionpart.
    SDPUtils.getDirection = function(mediaSection, sessionpart) {
      // Look for sendrecv, sendonly, recvonly, inactive, default to sendrecv.
      var lines = SDPUtils.splitLines(mediaSection);
      for (var i = 0; i < lines.length; i++) {
        switch (lines[i]) {
          case 'a=sendrecv':
          case 'a=sendonly':
          case 'a=recvonly':
          case 'a=inactive':
            return lines[i].substr(2);
        }
      }
      if (sessionpart) {
        return SDPUtils.getDirection(sessionpart);
      }
      return 'sendrecv';
    };

    // ORTC defines an RTCIceCandidate object but no constructor.
    // Not implemented in Edge.
    if (!window.RTCIceCandidate) {
      window.RTCIceCandidate = function(args) {
        return args;
      };
    }
    // ORTC does not have a session description object but
    // other browsers (i.e. Chrome) that will support both PC and ORTC
    // in the future might have this defined already.
    if (!window.RTCSessionDescription) {
      window.RTCSessionDescription = function(args) {
        return args;
      };
    }

    window.RTCPeerConnection = function(config) {
      var self = this;

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

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

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

      this.iceOptions = {
        gatherPolicy: 'all',
        iceServers: []
      };
      if (config && config.iceTransportPolicy) {
        switch (config.iceTransportPolicy) {
          case 'all':
          case 'relay':
            this.iceOptions.gatherPolicy = config.iceTransportPolicy;
            break;
          case 'none':
            // FIXME: remove once implementation and spec have added this.
            throw new TypeError('iceTransportPolicy "none" not supported');
        }
      }
      if (config && config.iceServers) {
        // Edge does not like
        // 1) stun:
        // 2) turn: that does not have all of turn:host:port?transport=udp
        // 3) an array of urls
        config.iceServers.forEach(function(server) {
          if (server.urls) {
            var url;
            if (typeof(server.urls) === 'string') {
              url = server.urls;
            } else {
              url = server.urls[0];
            }
            if (url.indexOf('transport=udp') !== -1) {
              self.iceServers.push({
                username: server.username,
                credential: server.credential,
                urls: url
              });
            }
          }
        });
      }

      // 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 = [];
    };

    window.RTCPeerConnection.prototype._emitBufferedCandidates = function() {
      var self = this;
      // FIXME: need to apply ice candidates in a way which is async but in-order
      this._localIceCandidatesBuffer.forEach(function(event) {
        if (self.onicecandidate !== null) {
          self.onicecandidate(event);
        }
      });
      this._localIceCandidatesBuffer = [];
    };

    window.RTCPeerConnection.prototype.addStream = function(stream) {
      // Clone is necessary for local demos mostly, attaching directly
      // to two different senders does not work (build 10547).
      this.localStreams.push(stream.clone());
      this._maybeFireNegotiationNeeded();
    };

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

    // Determines the intersection of local and remote capabilities.
    window.RTCPeerConnection.prototype._getCommonCapabilities =
        function(localCapabilities, remoteCapabilities) {
      var commonCapabilities = {
        codecs: [],
        headerExtensions: [],
        fecMechanisms: []
      };
      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 &&
              lCodec.numChannels === rCodec.numChannels) {
            // push rCodec so we reply with offerer payload type
            commonCapabilities.codecs.push(rCodec);

            // FIXME: also need to determine intersection between
            // .rtcpFeedback and .parameters
            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;
    };

    // Create ICE gatherer, ICE transport and DTLS transport.
    window.RTCPeerConnection.prototype._createIceAndDtlsTransports =
        function(mid, sdpMLineIndex) {
      var self = this;
      var iceGatherer = new RTCIceGatherer(self.iceOptions);
      var iceTransport = new RTCIceTransport(iceGatherer);
      iceGatherer.onlocalcandidate = function(evt) {
        var event = {};
        event.candidate = {sdpMid: mid, sdpMLineIndex: sdpMLineIndex};

        var cand = evt.candidate;
        // Edge emits an empty object for RTCIceCandidateComplete‥
        if (!cand || Object.keys(cand).length === 0) {
          // polyfill since RTCIceGatherer.state is not implemented in Edge 10547 yet.
          if (iceGatherer.state === undefined) {
            iceGatherer.state = 'completed';
          }

          // Emit a candidate with type endOfCandidates to make the samples work.
          // Edge requires addIceCandidate with this empty candidate to start checking.
          // The real solution is to signal end-of-candidates to the other side when
          // getting the null candidate but some apps (like the samples) don't do that.
          event.candidate.candidate =
              'candidate:1 1 udp 1 0.0.0.0 9 typ endOfCandidates';
        } else {
          // RTCIceCandidate doesn't have a component, needs to be added
          cand.component = iceTransport.component === 'RTCP' ? 2 : 1;
          event.candidate.candidate = SDPUtils.writeCandidate(cand);
        }

        var complete = self.transceivers.every(function(transceiver) {
          return transceiver.iceGatherer &&
              transceiver.iceGatherer.state === 'completed';
        });
        // FIXME: update .localDescription with candidate and (potentially) end-of-candidates.
        //     To make this harder, the gatherer might emit candidates before localdescription
        //     is set. To make things worse, gather.getLocalCandidates still errors in
        //     Edge 10547 when no candidates have been gathered yet.

        if (self.onicecandidate !== null) {
          // Emit candidate if localDescription is set.
          // Also emits null candidate when all gatherers are complete.
          if (self.localDescription && self.localDescription.type === '') {
            self._localIceCandidatesBuffer.push(event);
            if (complete) {
              self._localIceCandidatesBuffer.push({});
            }
          } else {
            self.onicecandidate(event);
            if (complete) {
              self.onicecandidate({});
            }
          }
        }
      };
      iceTransport.onicestatechange = function() {
        self._updateConnectionState();
      };

      var dtlsTransport = new RTCDtlsTransport(iceTransport);
      dtlsTransport.ondtlsstatechange = function() {
        self._updateConnectionState();
      };
      dtlsTransport.onerror = function() {
        // onerror does not set state to failed by itself.
        dtlsTransport.state = 'failed';
        self._updateConnectionState();
      };

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

    // Start the RTP Sender and Receiver for a transceiver.
    window.RTCPeerConnection.prototype._transceive = function(transceiver,
        send, recv) {
      var params = this._getCommonCapabilities(transceiver.localCapabilities,
          transceiver.remoteCapabilities);
      if (send && transceiver.rtpSender) {
        params.encodings = [{
          ssrc: transceiver.sendSsrc
        }];
        params.rtcp = {
          cname: localCName,
          ssrc: transceiver.recvSsrc
        };
        transceiver.rtpSender.send(params);
      }
      if (recv && transceiver.rtpReceiver) {
        params.encodings = [{
          ssrc: transceiver.recvSsrc
        }];
        params.rtcp = {
          cname: transceiver.cname,
          ssrc: transceiver.sendSsrc
        };
        transceiver.rtpReceiver.receive(params);
      }
    };

    window.RTCPeerConnection.prototype.setLocalDescription =
        function(description) {
      var self = this;
      if (description.type === 'offer') {
        if (!this._pendingOffer) {
        } else {
          this.transceivers = this._pendingOffer;
          delete this._pendingOffer;
        }
      } else if (description.type === 'answer') {
        var sections = SDPUtils.splitSections(self.remoteDescription.sdp);
        var sessionpart = sections.shift();
        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 = mediaSection.split('\n', 1)[0]
              .split(' ', 2)[1] === '0';

          if (!rejected) {
            var remoteIceParameters = SDPUtils.getIceParameters(mediaSection,
                sessionpart);
            iceTransport.start(iceGatherer, remoteIceParameters, 'controlled');

            var remoteDtlsParameters = SDPUtils.getDtlsParameters(mediaSection,
              sessionpart);
            dtlsTransport.start(remoteDtlsParameters);

            // Calculate intersection of capabilities.
            var params = self._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 = description;
      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();
          self._emitBufferedCandidates();
        }, 0);
      }
      var p = Promise.resolve();
      p.then(function() {
        if (!hasCallback) {
          window.setTimeout(self._emitBufferedCandidates.bind(self), 0);
        }
      });
      return p;
    };

    window.RTCPeerConnection.prototype.setRemoteDescription =
        function(description) {
      var self = this;
      var stream = new MediaStream();
      var sections = SDPUtils.splitSections(description.sdp);
      var sessionpart = sections.shift();
      sections.forEach(function(mediaSection, sdpMLineIndex) {
        var lines = SDPUtils.splitLines(mediaSection);
        var mline = lines[0].substr(2).split(' ');
        var kind = mline[0];
        var rejected = mline[1] === '0';
        var direction = SDPUtils.getDirection(mediaSection, sessionpart);

        var transceiver;
        var iceGatherer;
        var iceTransport;
        var dtlsTransport;
        var rtpSender;
        var rtpReceiver;
        var sendSsrc;
        var recvSsrc;
        var localCapabilities;

        // 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);
        }
        var mid = SDPUtils.matchPrefix(mediaSection, 'a=mid:')[0].substr(6);

        var cname;
        // Gets the first SSRC. Note that with RTX there might be multiple SSRCs.
        var remoteSsrc = SDPUtils.matchPrefix(mediaSection, 'a=ssrc:')
            .map(function(line) {
              return SDPUtils.parseSsrcMedia(line);
            })
            .filter(function(obj) {
              return obj.attribute === 'cname';
            })[0];
        if (remoteSsrc) {
          recvSsrc = parseInt(remoteSsrc.ssrc, 10);
          cname = remoteSsrc.value;
        }

        if (description.type === 'offer') {
          var transports = self._createIceAndDtlsTransports(mid, sdpMLineIndex);

          localCapabilities = RTCRtpReceiver.getCapabilities(kind);
          sendSsrc = (2 * sdpMLineIndex + 2) * 1001;

          rtpReceiver = new RTCRtpReceiver(transports.dtlsTransport, kind);

          // FIXME: not correct when there are multiple streams but that is
          // not currently supported in this shim.
          stream.addTrack(rtpReceiver.track);

          // FIXME: look at direction.
          if (self.localStreams.length > 0 &&
              self.localStreams[0].getTracks().length >= sdpMLineIndex) {
            // FIXME: actually more complicated, needs to match types etc
            var localtrack = self.localStreams[0].getTracks()[sdpMLineIndex];
            rtpSender = new RTCRtpSender(localtrack, transports.dtlsTransport);
          }

          self.transceivers[sdpMLineIndex] = {
            iceGatherer: transports.iceGatherer,
            iceTransport: transports.iceTransport,
            dtlsTransport: transports.dtlsTransport,
            localCapabilities: localCapabilities,
            remoteCapabilities: remoteCapabilities,
            rtpSender: rtpSender,
            rtpReceiver: rtpReceiver,
            kind: kind,
            mid: mid,
            cname: cname,
            sendSsrc: sendSsrc,
            recvSsrc: recvSsrc
          };
          // 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;
          rtpSender = transceiver.rtpSender;
          rtpReceiver = transceiver.rtpReceiver;
          sendSsrc = transceiver.sendSsrc;
          //recvSsrc = transceiver.recvSsrc;
          localCapabilities = transceiver.localCapabilities;

          self.transceivers[sdpMLineIndex].recvSsrc = recvSsrc;
          self.transceivers[sdpMLineIndex].remoteCapabilities =
              remoteCapabilities;
          self.transceivers[sdpMLineIndex].cname = cname;

          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')) {
            stream.addTrack(rtpReceiver.track);
          } else {
            // FIXME: actually the receiver should be created later.
            delete transceiver.rtpReceiver;
          }
        }
      });

      this.remoteDescription = description;
      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 + '"');
      }
      window.setTimeout(function() {
        if (self.onaddstream !== null && stream.getTracks().length) {
          self.remoteStreams.push(stream);
          window.setTimeout(function() {
            self.onaddstream({stream: stream});
          }, 0);
        }
      }, 0);
      if (arguments.length > 1 && typeof arguments[1] === 'function') {
        window.setTimeout(arguments[1], 0);
      }
      return Promise.resolve();
    };

    window.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.
    window.RTCPeerConnection.prototype._updateSignalingState =
        function(newState) {
      this.signalingState = newState;
      if (this.onsignalingstatechange !== null) {
        this.onsignalingstatechange();
      }
    };

    // Determine whether to fire the negotiationneeded event.
    window.RTCPeerConnection.prototype._maybeFireNegotiationNeeded =
        function() {
      // Fire away (for now).
      if (this.onnegotiationneeded !== null) {
        this.onnegotiationneeded();
      }
    };

    // Update the connection state.
    window.RTCPeerConnection.prototype._updateConnectionState =
        function() {
      var self = this;
      var newState;
      var states = {
        'new': 0,
        closed: 0,
        connecting: 0,
        checking: 0,
        connected: 0,
        completed: 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.connecting > 0 || states.completed > 0) {
        newState = 'connected';
      }

      if (newState !== self.iceConnectionState) {
        self.iceConnectionState = newState;
        if (this.oniceconnectionstatechange !== null) {
          this.oniceconnectionstatechange();
        }
      }
    };

    window.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 tracks = [];
      var numAudioTracks = 0;
      var numVideoTracks = 0;
      // Default to sendrecv.
      if (this.localStreams.length) {
        numAudioTracks = this.localStreams[0].getAudioTracks().length;
        numVideoTracks = this.localStreams[0].getVideoTracks().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) {
          numAudioTracks = offerOptions.offerToReceiveAudio;
        }
        if (offerOptions.offerToReceiveVideo !== undefined) {
          numVideoTracks = offerOptions.offerToReceiveVideo;
        }
      }
      if (this.localStreams.length) {
        // Push local streams.
        this.localStreams[0].getTracks().forEach(function(track) {
          tracks.push({
            kind: track.kind,
            track: track,
            wantReceive: track.kind === 'audio' ?
                numAudioTracks > 0 : numVideoTracks > 0
          });
          if (track.kind === 'audio') {
            numAudioTracks--;
          } else if (track.kind === 'video') {
            numVideoTracks--;
          }
        });
      }
      // Create M-lines for recvonly streams.
      while (numAudioTracks > 0 || numVideoTracks > 0) {
        if (numAudioTracks > 0) {
          tracks.push({
            kind: 'audio',
            wantReceive: true
          });
          numAudioTracks--;
        }
        if (numVideoTracks > 0) {
          tracks.push({
            kind: 'video',
            wantReceive: true
          });
          numVideoTracks--;
        }
      }

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

        var transports = self._createIceAndDtlsTransports(mid, sdpMLineIndex);

        var localCapabilities = RTCRtpSender.getCapabilities(kind);
        var rtpSender;
        var rtpReceiver;

        // generate an ssrc now, to be used later in rtpSender.send
        var sendSsrc = (2 * sdpMLineIndex + 1) * 1001;
        if (track) {
          rtpSender = new RTCRtpSender(track, transports.dtlsTransport);
        }

        if (mline.wantReceive) {
          rtpReceiver = new RTCRtpReceiver(transports.dtlsTransport, kind);
        }

        transceivers[sdpMLineIndex] = {
          iceGatherer: transports.iceGatherer,
          iceTransport: transports.iceTransport,
          dtlsTransport: transports.dtlsTransport,
          localCapabilities: localCapabilities,
          remoteCapabilities: null,
          rtpSender: rtpSender,
          rtpReceiver: rtpReceiver,
          kind: kind,
          mid: mid,
          sendSsrc: sendSsrc,
          recvSsrc: null
        };
        var transceiver = transceivers[sdpMLineIndex];
        sdp += SDPUtils.writeMediaSection(transceiver,
            transceiver.localCapabilities, 'offer', self.localStreams[0]);
      });

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

    window.RTCPeerConnection.prototype.createAnswer = function() {
      var self = this;
      var answerOptions;
      if (arguments.length === 1 && typeof arguments[0] !== 'function') {
        answerOptions = arguments[0];
      } else if (arguments.length === 3) {
        answerOptions = arguments[2];
      }

      var sdp = SDPUtils.writeSessionBoilerplate();
      this.transceivers.forEach(function(transceiver) {
        // Calculate intersection of capabilities.
        var commonCapabilities = self._getCommonCapabilities(
            transceiver.localCapabilities,
            transceiver.remoteCapabilities);

        sdp += SDPUtils.writeMediaSection(transceiver, commonCapabilities,
            'answer', self.localStreams[0]);
      });

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

    window.RTCPeerConnection.prototype.addIceCandidate = function(candidate) {
      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) {
          return;
        }
        // Ignore RTCP candidates, we assume RTCP-MUX.
        if (cand.component !== '1') {
          return;
        }
        // A dirty hack to make samples work.
        if (cand.type === 'endOfCandidates') {
          cand = {};
        }
        transceiver.iceTransport.addRemoteCandidate(cand);
      }
      if (arguments.length > 1 && typeof arguments[1] === 'function') {
        window.setTimeout(arguments[1], 0);
      }
      return Promise.resolve();
    };

    window.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];
      return new Promise(function(resolve) {
        var results = {};
        Promise.all(promises).then(function(res) {
          res.forEach(function(result) {
            Object.keys(result).forEach(function(id) {
              results[id] = result[id];
            });
          });
          if (cb) {
            window.setTimeout(cb, 0, results);
          }
          resolve(results);
        });
      });
    };
  }
} else {
  webrtcUtils.log('Browser does not appear to be WebRTC-capable');
}

// Returns the result of getUserMedia as a Promise.
function requestUserMedia(constraints) {
  return new Promise(function(resolve, reject) {
    getUserMedia(constraints, resolve, reject);
  });
}

var webrtcTesting = {};
try {
  Object.defineProperty(webrtcTesting, 'version', {
    set: function(version) {
      webrtcDetectedVersion = version;
    }
  });
} catch (e) {}

if (typeof module !== 'undefined') {
  var RTCPeerConnection;
  var RTCIceCandidate;
  var RTCSessionDescription;
  if (typeof window !== 'undefined') {
    RTCPeerConnection = window.RTCPeerConnection;
    RTCIceCandidate = window.RTCIceCandidate;
    RTCSessionDescription = window.RTCSessionDescription;
  }
  module.exports = {
    RTCPeerConnection: RTCPeerConnection,
    RTCIceCandidate: RTCIceCandidate,
    RTCSessionDescription: RTCSessionDescription,
    getUserMedia: getUserMedia,
    attachMediaStream: attachMediaStream,
    reattachMediaStream: reattachMediaStream,
    webrtcDetectedBrowser: webrtcDetectedBrowser,
    webrtcDetectedVersion: webrtcDetectedVersion,
    webrtcMinimumVersion: webrtcMinimumVersion,
    webrtcTesting: webrtcTesting,
    webrtcUtils: webrtcUtils
    //requestUserMedia: not exposed on purpose.
    //trace: not exposed on purpose.
  };
} else if ((typeof require === 'function') && (typeof define === 'function')) {
  // Expose objects and functions when RequireJS is doing the loading.
  define([], function() {
    return {
      RTCPeerConnection: window.RTCPeerConnection,
      RTCIceCandidate: window.RTCIceCandidate,
      RTCSessionDescription: window.RTCSessionDescription,
      getUserMedia: getUserMedia,
      attachMediaStream: attachMediaStream,
      reattachMediaStream: reattachMediaStream,
      webrtcDetectedBrowser: webrtcDetectedBrowser,
      webrtcDetectedVersion: webrtcDetectedVersion,
      webrtcMinimumVersion: webrtcMinimumVersion,
      webrtcTesting: webrtcTesting,
      webrtcUtils: webrtcUtils
      //requestUserMedia: not exposed on purpose.
      //trace: not exposed on purpose.
    };
  });
}