fix(SDP) Do not filter out SSRC 'cname' attributes. (#2695)

* fix(SDP) Do not filter out SSRC 'cname' attributes.
Chrome doesn't generate the a=ssrc line with 'msid' attribute when the track is removed from pc and a renegotiation is triggered. As a result a source-remove is sent to the p2p peer when it shouldn't be causing issues on the receiver when the same source is added back to the conference. Fixes toggleCamera on mobile browser not working as expected.

Author: jallamsetty1

modules/sdp/LocalSdpMunger.js

@@ -96,9 +96,15 @@ export default class LocalSdpMunger {
             }
         }
 
-        // Ignore the 'cname', 'label' and 'mslabel' attributes.
-        mediaSection.ssrcs = mediaSection.ssrcs
-            .filter(ssrc => ssrc.attribute === 'msid' || ssrc.attribute === 'name' || ssrc.attribute === 'videoType');
+        // Ignore the 'label' and 'mslabel' attributes.
+        mediaSection.ssrcs
+            = mediaSection.ssrcs.filter(ssrc => ssrc.attribute !== 'label' && ssrc.attribute !== 'mslabel');
+
+        // Remove the 'cname' attribute on Firefox as a=ssrc line with only 'cname' attribute are present in the SDP
+        // for recvonly SSRCs generated by createAnswer. These do not have to be signaled to the peers.
+        if (browser.isFirefox()) {
+            mediaSection.ssrcs = mediaSection.ssrcs.filter(ssrc => ssrc.attribute !== 'cname');
+        }
 
         // On FF when the user has started muted create answer will generate a recv only SSRC. We don't want to signal
         // this SSRC in order to reduce the load of the xmpp server for large calls. Therefore the SSRC needs to be

modules/sdp/LocalSdpMunger.spec.js

@@ -28,24 +28,7 @@ describe('TransformSdpsForUnifiedPlan', () => {
         localSdpMunger = new LocalSdpMunger(tpc, localEndpointId);
     });
     describe('StripSsrcs', () => {
-        it('should strip ssrcs from an sdp with no msid (i.e., recvonly transceivers)', () => {
-            localSdpMunger.tpc.isP2P = false;
-
-            const sdpStr = transform.write(SampleSdpStrings.recvOnlySdp);
-            const desc = new RTCSessionDescription({
-                type: 'offer',
-                sdp: sdpStr
-            });
-            const transformedDesc = localSdpMunger.transformStreamIdentifiers(desc, {});
-            const newSdp = transform.parse(transformedDesc.sdp);
-            const audioSsrcs = getSsrcLines(newSdp, 'audio');
-            const videoSsrcs = getSsrcLines(newSdp, 'video');
-
-            expect(audioSsrcs.length).toEqual(0);
-            expect(videoSsrcs.length).toEqual(0);
-        });
-
-        describe('should strip cname, label and mslabel from an sdp with msid', () => {
+        describe('should strip label and mslabel from an sdp with msid', () => {
             let audioSsrcs, videoSsrcs;
 
             const transformStreamIdentifiers = () => {
@@ -77,8 +60,8 @@ describe('TransformSdpsForUnifiedPlan', () => {
             it('with source name signaling enabled (injected source name)', () => {
                 transformStreamIdentifiers();
 
-                expect(audioSsrcs.length).toEqual(1 + 1 /* injected source name */);
-                expect(videoSsrcs.length).toEqual(3 + 3 /* injected source name into each ssrc */);
+                expect(audioSsrcs.length).toEqual(2 + 1 /* injected source name */);
+                expect(videoSsrcs.length).toEqual(6 + 3 /* injected source name into each ssrc */);
             });
         });
     });