feat: delay client sync step until server is ready

Author: galaxian85

src/y-socket-io/client.js

@@ -157,7 +157,7 @@ export class SocketIOProvider extends Observable {
 
     this.doc.on('update', this.onUpdateDoc)
 
-    this.socket.on('connect', () => this.onSocketConnection(resyncInterval))
+    this.socket.once('ready-for-sync', () => this.onSocketConnection(resyncInterval))
 
     this.socket.on('disconnect', (event) => this.onSocketDisconnection(event))
 

src/y-socket-io/y-socket-io.js

@@ -171,6 +171,7 @@ export class YSocketIO {
         this.client.getDoc(namespace, 'index').then((doc) => {
           assert(socket.user)
           assert(this.subscriber)
+          socket.emit('ready-for-sync')
           if (
             api.isSmallerRedisId(doc.redisLastId, socket.user.initialRedisSubId)
           ) {