WebSockets transport: error calling onReceive, error: type 'List<dynamic>' is not a subtype of type 'List<Object>?'

[Igor]

Hi, I can reproduce the issue

Server code (dotnet core 3.1):

 await Clients.Caller.SendAsync("someMessage", JsonConvert.SerializeObject(new
          {
                some_data= id.ToString(),
                some_other_data = somethingElse.ToString()
          }));

Client code:

import 'package:signalr_netcore/signalr_client.dart';

//all logs are enabled
Logger.root.level = Level.ALL;

Logger.root.onRecord.listen((record) {
      print('${record.level.name}: ${record.time}: ${record.message}');
    });

//specify hub connection options
final httpConnectionOptions = new HttpConnectionOptions(
          accessTokenFactory: () async => await getUserToken(),
          logger: transportProtLogger,
          httpClient: WebSupportingHttpClient(null,
              httpClientCreateCallback: _httpClientCreateCallback),
          logMessageContent: true);


//build the hub connection
final hubConnection = HubConnectionBuilder()
               .withUrl(mainServer + '/myHub', options: httpConnectionOptions)
               .configureLogging(hubProtLogger)
               .withAutomaticReconnect(
                    retryDelays: [2000, 5000, 10000, 20000, 50000]).build();

//...

 _hubConnection.on('someMessage', _handleSomeMessage);

//...


 void _handleSomeMessage(List<Object>? args) {
//This would never call, due to the following error in the logs:
2I/flutter (11935): SEVERE: 2021-10-09 00:33:20.786183: (WebSockets transport) error calling onReceive, error: type 'List<dynamic>' is not a subtype of type 'List<Object>?'

}

After some digging I figured out that error goes from JsonHubProtocol class where invocation message got parsed, e.g. :
signalr_core\json_hub_protocol.dart

class JsonHubProtocol implements IHubProtocol {

//....

static InvocationMessage _getInvocationMessageFromJson(
      Map<String, dynamic> jsonData) {
    final MessageHeaders? headers =
        createMessageHeadersFromJson(jsonData["headers"]);
    final message = InvocationMessage(
        jsonData["target"],

//Here jsonData produces List<dynamic> instead of List<Object>
        jsonData["arguments"],

        jsonData["streamIds"],
        headers,
        jsonData["invocationId"]);

    _assertNotEmptyString(
        message.target, "Invalid payload for Invocation message.");
    if (message.invocationId != null) {
      _assertNotEmptyString(
          message.invocationId, "Invalid payload for Invocation message.");
    }

    return message;
  }

So possible fix would be just add a cast to Object:

        jsonData["arguments"]?.cast<Object>().toList(),

[Farshid Sefidgaran]

Hi @golovin-igor
Thanks for your Pull Request.
It is already approved and published.
I am going to close this issue.

Regards