feat: Log explanatory warning if origins option is undefined

src/server/index.test.ts

@@ -13,6 +13,10 @@ import type { StorageAPI } from '../types';
 
 const game = { seed: 0 };
 
+const warn = jest.spyOn(console, 'warn').mockImplementation(() => {});
+beforeEach(warn.mockReset);
+afterAll(warn.mockRestore);
+
 jest.mock('../core/logger', () => ({
   info: () => {},
   error: () => {},
@@ -80,6 +84,18 @@ describe('new', () => {
     const server = Server({ games: [game], authenticateCredentials });
     expect(server.db).not.toBeNull();
   });
+
+  test('logs a warning if origins not set', () => {
+    Server({ games: [{}] });
+    expect(warn).toHaveBeenCalledWith(
+      expect.stringContaining('Server `origins` option is not set.')
+    );
+  });
+
+  test('does not log a warning if origins set', () => {
+    Server({ games: [{}], origins: [] });
+    expect(warn).not.toHaveBeenCalled();
+  });
 });
 
 describe('run', () => {

src/server/index.ts

@@ -104,6 +104,14 @@ export function Server({
   if (transport === undefined) {
     transport = new SocketIO({ https });
   }
+  if (origins === undefined) {
+    console.warn(
+      'Server `origins` option is not set.\n' +
+        'Since boardgame.io@0.45, CORS is not enabled by default and you must ' +
+        'explicitly set the origins that are allowed to connect to the server.\n' +
+        'See https://boardgame.io/documentation/#/api/Server'
+    );
+  }
   transport.init(app, games, origins);
 
   const router = createRouter({ db, games, uuid, auth });