feat(internal-plugin-mercury): add mercuryTimeOffset (#4035)

Author: lialang-cisco

packages/@webex/internal-plugin-mercury/src/mercury.js

@@ -41,6 +41,10 @@ const Mercury = WebexPlugin.extend({
     },
     socket: 'object',
     localClusterServiceUrls: 'object',
+    mercuryTimeOffset: {
+      default: undefined,
+      type: 'number',
+    },
   },
 
   derived: {
@@ -197,6 +201,7 @@ const Mercury = WebexPlugin.extend({
 
     socket.on('close', (...args) => this._onclose(...args));
     socket.on('message', (...args) => this._onmessage(...args));
+    socket.on('pong', (...args) => this._setTimeOffset(...args));
     socket.on('sequence-mismatch', (...args) => this._emit('sequence-mismatch', ...args));
     socket.on('ping-pong-latency', (...args) => this._emit('ping-pong-latency', ...args));
 
@@ -486,6 +491,7 @@ const Mercury = WebexPlugin.extend({
   },
 
   _onmessage(event) {
+    this._setTimeOffset(event);
     const envelope = event.data;
 
     if (process.env.ENABLE_MERCURY_LOGGING) {
@@ -529,6 +535,13 @@ const Mercury = WebexPlugin.extend({
       });
   },
 
+  _setTimeOffset(event) {
+    const {wsWriteTimestamp} = event.data;
+    if (typeof wsWriteTimestamp === 'number' && wsWriteTimestamp > 0) {
+      this.mercuryTimeOffset = Date.now() - wsWriteTimestamp;
+    }
+  },
+
   _reconnect(webSocketUrl) {
     this.logger.info(`${this.namespace}: reconnecting`);
 

packages/@webex/internal-plugin-mercury/test/unit/spec/mercury.js

@@ -773,6 +773,41 @@ describe('plugin-mercury', () => {
       });
     });
 
+    describe('#_setTimeOffset', () => {
+      it('sets mercuryTimeOffset based on the difference between wsWriteTimestamp and now', () => {
+        const event = {
+          data: {
+            wsWriteTimestamp: Date.now() - 60000,
+          }          
+        };
+        assert.isUndefined(mercury.mercuryTimeOffset);
+        mercury._setTimeOffset(event);
+        assert.isDefined(mercury.mercuryTimeOffset);
+        assert.isTrue(mercury.mercuryTimeOffset > 0);
+      });
+      it('handles negative offsets', () => {
+        const event = {
+          data: {
+            wsWriteTimestamp: Date.now() + 60000,
+          }          
+        };
+        mercury._setTimeOffset(event);
+        assert.isTrue(mercury.mercuryTimeOffset < 0);
+      });
+      it('handles invalid wsWriteTimestamp', () => {
+        const invalidTimestamps = [null, -1, 'invalid', undefined];
+        invalidTimestamps.forEach(invalidTimestamp => {
+          const event = {
+            data: {
+              wsWriteTimestamp: invalidTimestamp,
+            }          
+          };
+          mercury._setTimeOffset(event);
+          assert.isUndefined(mercury.mercuryTimeOffset);
+        });
+      });
+    });
+    
     describe('#_prepareUrl()', () => {
       beforeEach(() => {
         webex.internal.device.webSocketUrl = 'ws://example.com';