Implement perfect negotiation for WebRTC collision.

Author: jianjunz

src/sdk/p2p/p2pclient.js

@@ -101,7 +101,7 @@ const P2PClient = function(configuration, signalingChannel) {
       return;
     }
     if (connectionIds.has(origin) &&
-        connectionIds.get(origin) != connectionId && !isPolitePeer(origin)) {
+        connectionIds.get(origin) !== connectionId && !isPolitePeer(origin)) {
       Logger.warning(
           // eslint-disable-next-line max-len
           'Collision detected, ignore this message because current endpoint is impolite peer.');
@@ -295,8 +295,8 @@ const P2PClient = function(configuration, signalingChannel) {
     if (!connectionId) {
       const connectionIdLimit = 100000;
       connectionId = Math.round(Math.random() * connectionIdLimit);
-      connectionIds.set(remoteId, connectionId);
     }
+    connectionIds.set(remoteId, connectionId);
     if (!channels.has(remoteId)) {
       // Construct an signaling sender/receiver for P2PPeerConnection.
       const signalingForChannel = Object.create(EventDispatcher);

src/sdk/p2p/peerconnection-channel.js

@@ -93,7 +93,7 @@ class P2PPeerConnectionChannel extends EventDispatcher {
     this._dataSeq = 1; // Sequence number for data channel messages.
     this._sendDataPromises = new Map(); // Key is data sequence number, value is an object has |resolve| and |reject|.
     this._addedTrackIds = []; // Tracks that have been added after receiving remote SDP but before connection is established. Draining these messages when ICE connection state is connected.
-    this._isCaller = true;
+    this._isPolitePeer = localId < remoteId;
     this._infoSent = false;
     this._disposed = false;
     this._createPeerConnection();
@@ -416,6 +416,15 @@ class P2PPeerConnectionChannel extends EventDispatcher {
   _onOffer(sdp) {
     Logger.debug('About to set remote description. Signaling state: ' +
       this._pc.signalingState);
+    if (this._pc.signalingState !== 'stable') {
+      if (this._isPolitePeer) {
+        // Rollback.
+        this._pc.setLocalDescription();
+      } else {
+        // Ignore this offer.
+        return;
+      }
+    }
     sdp.sdp = this._setRtpSenderOptions(sdp.sdp, this._config);
     // Firefox only has one codec in answer, which does not truly reflect its
     // decoding capability. So we set codec preference to remote offer, and let

test/unit/resources/scripts/fake-p2p-signaling.js

@@ -39,7 +39,6 @@ export default class FakeP2PSignalingChannel {
   }
 
   send(targetId, message) {
-    Logger.debug(this.userId + ' -> ' + targetId + ': ' + message);
     return new Promise((resolve, reject) => {
       messageQueue.push({ target: targetId, message, resolve, reject, sender: this.userId });
       setTimeout(() => {

test/unit/resources/scripts/p2p.js

@@ -157,5 +157,27 @@ describe('Unit tests for P2PClient', function() {
       //expect(Promise.all([p2pclient1.send('user2', 'message'), p2pclient2.send('user1', 'message')])).to.be.fulfilled.and.notify(done);
       // TODO: Check messages are received.
     });
+    it('WebRTC collision should be resolved.', async () => {
+      const c1Spy = new sinon.spy();
+      const c2Spy = new sinon.spy();
+      p2pclient1.addEventListener('messagereceived',c1Spy);
+      p2pclient2.addEventListener('messagereceived',c2Spy);
+      await p2pclient1.publish('user2', localStream);
+      // Both sides create PeerConnection. It cannot 100% sure to trigger WebRTC
+      // collision. But it has a high chance that `setRemoteDescription` get
+      // failed. However, even `setRemoteDescription` is failed, the SDK stops
+      // `PeerConnection` silently without firing an event. So this test case
+      // cannot detect failures like this.
+      await Promise.all([
+        p2pclient1.send('user2', 'message'), p2pclient2.send('user1', 'message')
+      ]);
+      await new Promise(resolve => {
+        setTimeout(() => {
+          expect(c1Spy.callCount).to.equal(1);
+          expect(c2Spy.callCount).to.equal(1);
+          resolve();
+        }, 100);
+      });
+    });
   });
 });