Flutter异常捕获 | 从bugsnag源码学习如何追溯异常产生路径

void main() async => bugsnag.start(
      runApp: () => runApp(const ExampleApp()),
      // 需要到bugsang后台注册账号申请一个api_key
      apiKey: 'add_your_api_key_here',
      projectPackages: const BugsnagProjectPackages.only({'bugsnag_example'}),
      // onError callbacks can be used to modify or reject certain events
      //...
    );

class ExampleApp extends StatelessWidget {
  const ExampleApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      navigatorObservers: [BugsnagNavigatorObserver()],
      initialRoute: '/',
      routes: {
        '/': (context) => const ExampleHomeScreen(),
        '/native-crashes': (context) => const NativeCrashesScreen(),
      },
    );
  }
}

// Use leaveBreadcrumb() to log potentially useful events in order to
  // understand what happened in your app before each error.
  void _leaveBreadcrumb() async =>
      bugsnag.leaveBreadcrumb('This is a custom breadcrumb',
          // Additional data can be attached to breadcrumbs as metadata
          metadata: {'from': 'a', 'to': 'z'});

import 'package:bugsnag_breadcrumbs_http/bugsnag_breadcrumbs_http.dart' as http;
void _networkFailure() async =>
      http.post(Uri.parse('https://example.com/invalid'));

Future<void> start({
    FutureOr<void> Function()? runApp,
    //... Tag1 一堆额外参数
  }) async {
    //...
    //开始就想着用对端SDK，这里当然少不了初始化通道
    _runWithErrorDetection(
      detectDartErrors,
      () => WidgetsFlutterBinding.ensureInitialized(),
    );

    //...

    await ChannelClient._channel.invokeMethod('start', <String, dynamic>{
      //... Tag2:这里将Tag1处的额外参数传给了对端SDK
      
    });

   //Tag3:dart error的处理类，其中全部都是通过channel来桥接的
    final client = ChannelClient(detectDartErrors);
    client._onErrorCallbacks.addAll(onError);
    this.client = client;

    
    _runWithErrorDetection(detectDartErrors, () => runApp?.call());
  }

  void _runWithErrorDetection(
    bool errorDetectionEnabled,
    FutureOr<void> Function() block,
  ) async {
    if (errorDetectionEnabled) {
      //多么熟悉的味道，
      await runZonedGuarded(() async {
        await block();
      }, _reportZonedError);
    } else {
      await block();
    }
  }

//最终_reportZonedError会执行到_notifyInternal
void _notifyUnhandled(dynamic error, StackTrace? stackTrace) {
    _notifyInternal(error, true, null, stackTrace, null);
  }

ChannelClient(bool autoDetectErrors) {
    if (autoDetectErrors) {
      FlutterError.onError = _onFlutterError;
    }
  }

void _onFlutterError(FlutterErrorDetails details) {
    _notifyInternal(details.exception, true, details, details.stack, null);
    //...
  }

Future<void> _notifyInternal(
    dynamic error,
    bool unhandled,
    FlutterErrorDetails? details,
    StackTrace? stackTrace,
    BugsnagOnErrorCallback? callback,
  ) async {
    final errorPayload =
        BugsnagErrorFactory.instance.createError(error, stackTrace);
    final event = await _createEvent(
      errorPayload,
      details: details,
      unhandled: unhandled,
      deliver: _onErrorCallbacks.isEmpty && callback == null,
    );

   //...

    await _deliverEvent(event);
  }

//我说什么来着：连最基本的Event构造，都是在对端。
Future<BugsnagEvent?> _createEvent(
    BugsnagError error, {
    FlutterErrorDetails? details,
    required bool unhandled,
    required bool deliver,
  }) async {
    final buildID = error.stacktrace.first.codeIdentifier;
    //...
    };
    //调用了对端通道方法来实现。
    final eventJson = await _channel.invokeMethod(
      'createEvent',
      {
        'error': error,
        'flutterMetadata': metadata,
        'unhandled': unhandled,
        'deliver': deliver
      },
    );

    if (eventJson != null) {
      return BugsnagEvent.fromJson(eventJson);
    }

    return null;
  }

Future<void> _deliverEvent(BugsnagEvent event) =>
      _channel.invokeMethod('deliverEvent', event);

   这个是我自己想的一个词，该需求目的是能完整记录用户操作的整个行为路径，这样达到清晰指导用户操作过程，对问题的定位很有帮助。可以理解成一个小型的埋点系统，只是该埋点系统只是针对异常来做的。

Future<void> leaveBreadcrumb(
    String message, {
    Map<String, Object>? metadata,
    BugsnagBreadcrumbType type = BugsnagBreadcrumbType.manual,
  }) async {
    final crumb = BugsnagBreadcrumb(message, type: type, metadata: metadata);
    await _channel.invokeMethod('leaveBreadcrumb', crumb);
  }

class ExampleApp extends StatelessWidget {
  const ExampleApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      navigatorObservers: [BugsnagNavigatorObserver()],
      //...
    );
  }
}

----[BugsnagNavigatorObserver]----->
// BugsnagNavigatorObserver extends NavigatorObserver
BugsnagNavigatorObserver({
    //...
  }) : _navigatorName = (navigatorName != null) ? navigatorName : 'navigator';

  @override
  void didReplace({Route<dynamic>? newRoute, Route<dynamic>? oldRoute}) {
    _leaveBreadcrumb('Route replaced on', {
      if (oldRoute != null) 'oldRoute': _routeMetadata(oldRoute),
      if (newRoute != null) 'newRoute': _routeMetadata(newRoute),
    });
    //...
  }

  //....其他回调函数

  void _leaveBreadcrumb(String function, Map<String, Object> metadata) {
    if (leaveBreadcrumbs) {
      bugsnag.leaveBreadcrumb(
        _operationDescription(function),
        type: BugsnagBreadcrumbType.navigation,
        metadata: metadata,
      );
    }
  }

import 'package:bugsnag_breadcrumbs_http/bugsnag_breadcrumbs_http.dart' as http;
void _networkFailure() async =>
      http.post(Uri.parse('https://example.com/invalid'));

----[bugsnag_breadcrumbs_http.dart]---->
Future<http.Response> post(Uri url,
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
    _withClient((client) =>
        client.post(url, headers: headers, body: body, encoding: encoding));

Future<T> _withClient<T>(Future<T> Function(Client) fn) async {
  var client = Client();
  try {
    return await fn(client);
  } finally {
    client.close();
  }
}

---->[client.dart]---->
class Client extends http.BaseClient {
  /// The wrapped client.
  final http.Client _inner;

  Client() : _inner = http.Client();

  Client.withClient(http.Client client) : _inner = client;

  @override
  Future<http.StreamedResponse> send(http.BaseRequest request) async {
    final stopwatch = Stopwatch()..start();
    try {
      final response = await _inner.send(request);
      //拦截点：这里监听发送成功
      await _requestFinished(request, stopwatch, response);
      return response;
    } catch (e) {
      //拦截点：这里监听发送失败
      await _requestFinished(request, stopwatch);
      rethrow;
    }
  }

  Future<void> _requestFinished(
    http.BaseRequest request,
    Stopwatch stopwatch, [
    http.StreamedResponse? response,
  ]) =>
      _leaveBreadcrumb(Breadcrumb.build(_inner, request, stopwatch, response));
}