feat(internal-plugin-mercury): add mercuryTimeOffset

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;
+    if (typeof wsWriteTimestamp === 'number' && wsWriteTimestamp > 0) {
+      this.mercuryTimeOffset = Date.now() - wsWriteTimestamp;
+    }
+  },
+
   _reconnect(webSocketUrl) {
     this.logger.info(`${this.namespace}: reconnecting`);
 

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

@@ -295,6 +295,7 @@ export default class Socket extends EventEmitter {
     try {
       const data = JSON.parse(event.data);
       const sequenceNumber = parseInt(data.sequenceNumber, 10);
+      const wsWriteTimestamp = parseInt(data.wsWriteTimestamp, 10);
 
       this.logger.debug(`socket,${this._domain}: sequence number: `, sequenceNumber);
       if (this.expectedSequenceNumber && sequenceNumber !== this.expectedSequenceNumber) {
@@ -308,7 +309,7 @@ export default class Socket extends EventEmitter {
       // Yes, it's a little weird looking; we want to emit message events that
       // look like normal socket message events, but event.data cannot be
       // modified and we don't actually care about anything but the data property
-      const processedEvent = {data};
+      const processedEvent = {data, wsWriteTimestamp};
 
       this._acknowledge(processedEvent);
       if (data.type === 'pong') {

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';

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

@@ -750,13 +750,15 @@ describe('plugin-mercury', () => {
           data: JSON.stringify({
             sequenceNumber: 3,
             id: 'mockid',
+            wsWriteTimestamp: 1735689600000,
           }),
         });
 
         assert.calledWith(spy, {
           data: {
             sequenceNumber: 3,
             id: 'mockid',
+            wsWriteTimestamp: 1735689600000,
           },
         });
       });
@@ -790,13 +792,15 @@ describe('plugin-mercury', () => {
           data: JSON.stringify({
             sequenceNumber: 5,
             id: 'mockid',
+            wsWriteTimestamp: 1735689600000,
           }),
         });
         assert.called(socket._acknowledge);
         assert.calledWith(socket._acknowledge, {
           data: {
             sequenceNumber: 5,
             id: 'mockid',
+            wsWriteTimestamp: 1735689600000,
           },
         });
       });