Make _messages a broadcast stream

Author: szantogab

packages/graphql/lib/src/links/websocket_link/websocket_client.dart

@@ -636,8 +636,13 @@ class GraphQLWebSocketChannel extends StreamChannelMixin<dynamic>
   Stream<GraphQLSocketMessage>? _messages;
 
   /// Stream of messages from the endpoint parsed as GraphQLSocketMessages
-  Stream<GraphQLSocketMessage> get messages => _messages ??=
-      stream.map<GraphQLSocketMessage>(GraphQLSocketMessage.parse);
+  Stream<GraphQLSocketMessage> get messages {
+    if (_messages == null) _messages = stream.map((event) {
+      return GraphQLSocketMessage.parse(event);
+    }).asBroadcastStream();
+
+    return _messages!;
+  }
 
   String? get protocol => _webSocket.protocol;