RTCPeerConnection.prototype.createAnswer = function()

in monitoring-stack-cdk/resources/frontend/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);
      };