Dart: try catch not catching the exception from a function that uses 'rethrow'

Question

I'm trying to use the library livekit_client to create a chat room, I'm trying to handle the exception when the connection fails, this is the code I'm using to connect and catch the error:

try {
      room.connect(
        'ws://localhost:7880',
        'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjEwNjcxMzA2NDgzLCJpc3MiOiJkZXZrZXkiLCJuYW1lIjoidXNlcjEiLCJuYmYiOjE2NzEzMDY0ODMsInN1YiI6InVzZXIxIiwidmlkZW8iOnsicm9vbSI6Im15LWZpcnN0LXJvb20iLCJyb29tSm9pbiI6dHJ1ZX19.SQ2OSWl1CG7UVbui_vmChfmUkYvT3QxKgXd9Yh167ws',
        roomOptions: _roomOptions,
        fastConnectOptions: FastConnectOptions(
          microphone: const TrackOption(enabled: true),
          camera: const TrackOption(enabled: true),
        ),
      );
    } catch (e) {
      print('connection error $e');
    }

but the exception is not being handled and instead the debugger stops at the exception source inside the library files specifically this code:

} catch (error) {
      logger.fine('Connect Error $error');
      _updateConnectionState(ConnectionState.disconnected);
      rethrow;
    }

it stops at the 'rethrow' line

so is 'try catch' has some specifc limitations when used with functions that use 'rethrow'? why is it not catching the exception?

full test code :

import 'package:flutter/material.dart';
import 'package:livekit_client/livekit_client.dart';
import 'package:logging/logging.dart';

void main(List<String> args) {
  Logger.root.level = Level.ALL; // defaults to Level.INFO
  Logger.root.onRecord.listen((record) {
    print('${record.level.name}: ${record.time}: ${record.message}');
  });
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  Room room = Room();
  final RoomOptions _roomOptions = const RoomOptions(
    adaptiveStream: true,
    dynacast: true,
    defaultVideoPublishOptions: VideoPublishOptions(
      simulcast: true,
    ),
    defaultScreenShareCaptureOptions:
        ScreenShareCaptureOptions(useiOSBroadcastExtension: true),
  );

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    print('initializing');
    try {
      room.connect(
        'ws://localhost:7880',
        'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjEwNjcxMzA2NDgzLCJpc3MiOiJkZXZrZXkiLCJuYW1lIjoidXNlcjEiLCJuYmYiOjE2NzEzMDY0ODMsInN1YiI6InVzZXIxIiwidmlkZW8iOnsicm9vbSI6Im15LWZpcnN0LXJvb20iLCJyb29tSm9pbiI6dHJ1ZX19.SQ2OSWl1CG7UVbui_vmChfmUkYvT3QxKgXd9Yh167ws',
        roomOptions: _roomOptions,
        fastConnectOptions: FastConnectOptions(
          microphone: const TrackOption(enabled: true),
          camera: const TrackOption(enabled: true),
        ),
      );
    } catch (e) {
      print('connection error $e');
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(),
    );
  }
}

A debugger might be configured to stop whenever any exception is thrown; that says nothing about whether that exception will later be caught or not, and you haven't shown evidence that it isn't caught. If the exception does go uncaught, then what is the error message? What is the stack trace? — jamesdlin
– jamesdlin, Commented Dec 17, 2022 at 21:50

som-R91 · Accepted Answer · 2022-12-17 21:36:30Z

2

This is just a guess. But is room.connect() an asynchronous method? It connects to an online server so it must return a Future. Try adding an await keyword. Also, note that you cannot write async/await in the initState method. So maybe try connecting to the server from the main() method, or use a provider.

Your code should look something like this:-

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  try {
    await room.connect();
  } catch (error) {
    // handle error.
  }
  runApp(MyApp());
}

answered Dec 17, 2022 at 21:36

som-R91

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