MongoDB Sharded Cluster Support

.changeset/weak-lions-obey.md

@@ -0,0 +1,7 @@
+---
+'@powersync/service-module-mongodb': minor
+'@powersync/service-core': minor
+'@powersync/service-image': minor
+---
+
+Added support for sharded MongoDB replication connections.

modules/module-mongodb/src/replication/ChangeStream.ts

@@ -179,21 +179,23 @@ export class ChangeStream {
 
     // We need to get the snapshot time before taking the initial snapshot.
     const hello = await this.defaultDb.command({ hello: 1 });
-    const snapshotTime = hello.lastWrite?.majorityOpTime?.ts as mongo.Timestamp;
-    if (hello.msg == 'isdbgrid') {
-      throw new ServiceError(
-        ErrorCode.PSYNC_S1341,
-        'Sharded MongoDB Clusters are not supported yet (including MongoDB Serverless instances).'
-      );
-    } else if (hello.setName == null) {
+    // Use the clusterTime for sharded clusters
+    const snapshotTime: mongo.Timestamp = hello.lastWrite?.majorityOpTime?.ts ?? hello.$clusterTime?.clusterTime;
+
+    // Sharded cluster don't provide a setName, but we do support them.
+    // We don't support standalone instances
+    if (hello.msg != 'isdbgrid' && hello.setName == null) {
       throw new ServiceError(
         ErrorCode.PSYNC_S1342,
         'Standalone MongoDB instances are not supported - use a replicaset.'
       );
-    } else if (snapshotTime == null) {
+    }
+
+    if (snapshotTime == null) {
       // Not known where this would happen apart from the above cases
       throw new ReplicationAssertionError('MongoDB lastWrite timestamp not found.');
     }
+
     // We previously used {snapshot: true} for the snapshot session.
     // While it gives nice consistency guarantees, it fails when the
     // snapshot takes longer than 5 minutes, due to minSnapshotHistoryWindowInSeconds

modules/module-mongodb/src/replication/replication-utils.ts

@@ -1,6 +1,6 @@
 import { ErrorCode, ServiceError } from '@powersync/lib-services-framework';
-import { MongoManager } from './MongoManager.js';
 import { PostImagesOption } from '../types/types.js';
+import { MongoManager } from './MongoManager.js';
 
 export const CHECKPOINTS_COLLECTION = '_powersync_checkpoints';
 
@@ -10,12 +10,9 @@ export async function checkSourceConfiguration(connectionManager: MongoManager):
   const db = connectionManager.db;
 
   const hello = await db.command({ hello: 1 });
-  if (hello.msg == 'isdbgrid') {
-    throw new ServiceError(
-      ErrorCode.PSYNC_S1341,
-      'Sharded MongoDB Clusters are not supported yet (including MongoDB Serverless instances).'
-    );
-  } else if (hello.setName == null) {
+  // Sharded cluster don't provide a setName, but we do support them.
+  // We don't support standalone instances
+  if (hello.msg != 'isdbgrid' && hello.setName == null) {
     throw new ServiceError(ErrorCode.PSYNC_S1342, 'Standalone MongoDB instances are not supported - use a replicaset.');
   }