fix(infra): avoid data loss (#6111)

packages/frontend/workspace-impl/src/cloud/sync.ts

@@ -12,6 +12,8 @@ import { base64ToUint8Array, uint8ArrayToBase64 } from '../utils/base64';
 
 const logger = new DebugLogger('affine:storage:socketio');
 
+(window as any)._TEST_SIMULATE_SYNC_LAG = Promise.resolve();
+
 export class AffineSyncStorage implements SyncStorage {
   name = 'affine-cloud';
 
@@ -57,6 +59,9 @@ export class AffineSyncStorage implements SyncStorage {
     docId: string,
     state: Uint8Array
   ): Promise<{ data: Uint8Array; state?: Uint8Array } | null> {
+    // for testing
+    await (window as any)._TEST_SIMULATE_SYNC_LAG;
+
     const stateVector = state ? await uint8ArrayToBase64(state) : undefined;
 
     logger.debug('doc-load-v2', {

packages/frontend/workspace-impl/src/local/sync-sqlite.ts

@@ -20,6 +20,13 @@ export class SQLiteSyncStorage implements SyncStorage {
     );
 
     if (update) {
+      if (
+        update.byteLength === 0 ||
+        (update.byteLength === 2 && update[0] === 0 && update[1] === 0)
+      ) {
+        return null;
+      }
+
       return {
         data: update,
         state: encodeStateVectorFromUpdate(update),