Flutter Dio: Do not log error to Sentry on Cancel Token error

I have some cases in which I am cancelling the token for certain API requests. This is treated by Sentry as an error and being logged into Sentry.

I would like cancel token errors to not be logged.

I tried the following:

await SentryFlutter.init(
    (options) {
      const sentryDsn = String.fromEnvironment('SENTRYDSN',
          defaultValue:
              '[READACTED]');
      

  options.dsn = sentryDsn;
  options.tracesSampleRate = 1.0;
  options.reportPackages = false;
  options.beforeSend = (event, hint) {
    if (hint is DioException && isCancelTokenError(hint)) {
      return null;
    }
    return event;
  };
},

This has not worked. Any help is appreciated.

SentryEvent keeps a copy of the originating error at SentryEvent.throwable, so a more correct beforeSend callback would look like:

(event, hint) {
  if (event.throwable is DioException && CancelToken.isCancel(event.throwable)) {
    return null;
  }   

  return event;
}

where CancelToken.isCancel is provided by Dio.

Putting this together into a minimal demonstration:

import 'package:dio/dio.dart';
import 'package:sentry/sentry.dart';
import 'package:sentry_dio/sentry_dio.dart';

void main() {
  Sentry.init((options) {
    options.beforeSend = (event, hint) {
      if (event.throwable is DioException &&
          CancelToken.isCancel(event.throwable)) {
        return null;
      }

      return event;
    };
    options.dsn = 'https://example@sentry.io/example';
    options.diagnosticLevel = SentryLevel.debug;
    options.log = (level, message, {exception, logger, stackTrace}) {
      print(message);
    };
  }, appRunner: () {
    final dio = Dio();

    dio.addSentry();

    final token = CancelToken();
    dio.get<String>('https://wrong-url.dev/', cancelToken: token);
    token.cancel();
  });
}

which logs, among other things, the following, showing that the event is dropped due to beforeSend returning null:

SentryEvent was dropped by beforeSend callback