Add a helper function to ensure we have the correct datastore installed

app/bin/server_common.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library pub_dartlang_org.server_common;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:gcloud/datastore.dart';
@@ skipping 89 matching lines @@
   registerScopeExitCallback(authClient.close);
 
   final datastore = new DatastoreImpl(authClient, projectId);
   registerDatastoreService(datastore);
 
   final db = new DatastoreDB(datastore);
   registerDbService(db);
 
   return db;
 }
+
+/// Wrapper function used to work around issue with running gRPC datastore on
+/// MacOS.
+///
+/// On
+///    * linux this function simply returns `fun(dbService)`
+///
+///    * macos this function makes a new service scope, optionally builds an
+///      apiary datastore and registers an apiary datastore in the new service
+///      scope
+///
+Future withCorrectDatastore(Future fun(DatastoreDB db), DatastoreDB savedDb) {
+  if (Platform.isMacOS) {
+    return fork(() async {
+      registerDbService(savedDb ?? await initializeApiaryDatastore());
+      return fun(dbService);
+    });
+  } else {
+    assert(dbService != null);
+    return fun(dbService);
+  }
+}