add support for shared web workers

Author: stevensJourney

packages/powersync_core/lib/src/sync/options.dart

@@ -125,13 +125,15 @@ extension type ResolvedSyncOptions(SyncOptions source) {
       syncImplementation: other.syncImplementation,
       includeDefaultStreams:
           other.includeDefaultStreams ?? includeDefaultStreams,
+      appMetadata: other.appMetadata ?? appMetadata,
     );
 
     final didChange = !_mapEquality.equals(newOptions.params, params) ||
         newOptions.crudThrottleTime != crudThrottleTime ||
         newOptions.retryDelay != retryDelay ||
         newOptions.syncImplementation != source.syncImplementation ||
-        newOptions.includeDefaultStreams != includeDefaultStreams;
+        newOptions.includeDefaultStreams != includeDefaultStreams ||
+        !_mapEquality.equals(newOptions.appMetadata, appMetadata);
     return (ResolvedSyncOptions(newOptions), didChange);
   }
 

packages/powersync_core/lib/src/web/sync_worker.dart

@@ -94,6 +94,11 @@ class _ConnectedClient {
                 null => SyncClientImplementation.defaultClient,
                 final name => SyncClientImplementation.values.byName(name),
               },
+              appMetadata: switch (request.appMetadataEncoded) {
+                null => null,
+                final encodedAppMetadata => Map<String, String>.from(
+                    jsonDecode(encodedAppMetadata) as Map<String, dynamic>),
+              },
             );
 
             _runner = _worker.referenceSyncTask(

packages/powersync_core/lib/src/web/sync_worker_protocol.dart

@@ -80,6 +80,7 @@ extension type StartSynchronization._(JSObject _) implements JSObject {
     required String schemaJson,
     String? syncParamsEncoded,
     UpdateSubscriptions? subscriptions,
+    String? appMetadataEncoded,
   });
 
   external String get databaseName;
@@ -90,6 +91,7 @@ extension type StartSynchronization._(JSObject _) implements JSObject {
   external String get schemaJson;
   external String? get syncParamsEncoded;
   external UpdateSubscriptions? get subscriptions;
+  external String? get appMetadataEncoded;
 }
 
 @anonymous
@@ -483,6 +485,10 @@ final class WorkerCommunicationChannel {
           final params => jsonEncode(params),
         },
         subscriptions: UpdateSubscriptions(-1, streams),
+        appMetadataEncoded: switch (options.source.appMetadata) {
+          null => null,
+          final appMetadata => jsonEncode(appMetadata),
+        },
       ),
     ));
     await completion;