creating first structure of cinema backend server

Signed-off-by: Peter Siegmund <developer@mars3142.org>

server/cinema/lib/feature/websocket/websocket.service.dart

@@ -0,0 +1,28 @@
+import 'package:injectable/injectable.dart';
+import 'package:shelf/shelf.dart';
+import 'package:shelf_web_socket/shelf_web_socket.dart';
+
+@LazySingleton()
+class WebSocketService {
+  final List<dynamic> _clients = [];
+
+  Handler get handler => webSocketHandler((webSocket, _) {
+    _clients.add(webSocket);
+    print('Client connected, total: ${_clients.length}');
+
+    webSocket.stream.listen(
+      (message) {
+        webSocket.sink.add('echo $message');
+      },
+      onDone: () {
+        _clients.remove(webSocket);
+        print('Client disconnected, total: ${_clients.length}');
+      },
+      onError: (error) {
+        _clients.remove(webSocket);
+        print('Client error: $error');
+      },
+      cancelOnError: true,
+    );
+  });
+}