RTCPeerConnection.prototype.createAnswer = function()

in release/connect-rtc.js [4409:4503]
83 lines of code
22 McCabe index (conditional complexity)

  RTCPeerConnection.prototype.createAnswer = function() {
    var pc = this;

    if (pc._isClosed) {
      return Promise.reject(makeError('InvalidStateError',
          'Can not call createAnswer after close'));
    }

    if (!(pc.signalingState === 'have-remote-offer' ||
        pc.signalingState === 'have-local-pranswer')) {
      return Promise.reject(makeError('InvalidStateError',
          'Can not call createAnswer in signalingState ' + pc.signalingState));
    }

    var sdp = SDPUtils.writeSessionBoilerplate(pc._sdpSessionId,
        pc._sdpSessionVersion++);
    if (pc.usingBundle) {
      sdp += 'a=group:BUNDLE ' + pc.transceivers.map(function(t) {
        return t.mid;
      }).join(' ') + '\r\n';
    }
    sdp += 'a=ice-options:trickle\r\n';

    var mediaSectionsInOffer = SDPUtils.getMediaSections(
        pc._remoteDescription.sdp).length;
    pc.transceivers.forEach(function(transceiver, sdpMLineIndex) {
      if (sdpMLineIndex + 1 > mediaSectionsInOffer) {
        return;
      }
      if (transceiver.rejected) {
        if (transceiver.kind === 'application') {
          if (transceiver.protocol === 'DTLS/SCTP') { // legacy fmt
            sdp += 'm=application 0 DTLS/SCTP 5000\r\n';
          } else {
            sdp += 'm=application 0 ' + transceiver.protocol +
                ' webrtc-datachannel\r\n';
          }
        } else if (transceiver.kind === 'audio') {
          sdp += 'm=audio 0 UDP/TLS/RTP/SAVPF 0\r\n' +
              'a=rtpmap:0 PCMU/8000\r\n';
        } else if (transceiver.kind === 'video') {
          sdp += 'm=video 0 UDP/TLS/RTP/SAVPF 120\r\n' +
              'a=rtpmap:120 VP8/90000\r\n';
        }
        sdp += 'c=IN IP4 0.0.0.0\r\n' +
            'a=inactive\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) {
            transceiver.sendEncodingParameters[0].rtx = {
              ssrc: transceiver.sendEncodingParameters[0].ssrc + 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 += writeMediaSection(transceiver, commonCapabilities,
          'answer', transceiver.stream, pc._dtlsRole);
      if (transceiver.rtcpParameters &&
          transceiver.rtcpParameters.reducedSize) {
        sdp += 'a=rtcp-rsize\r\n';
      }
    });

    var desc = new window.RTCSessionDescription({
      type: 'answer',
      sdp: sdp
    });
    return Promise.resolve(desc);
  };