steno 0.1.0

steno: ^0.1.0 copied to clipboard

example/steno_example.dart

// A walking tour of the steno API. Run with:
//
//   dart run example/steno_example.dart
//
// You should see colored, structured output for each section.

// ignore_for_file: avoid_print

import 'package:steno/steno.dart';

Future<void> main() async {
  // 1. Pick a profile. Development gives you colored, verbose output.
  Steno.configure(LoggerProfile.development());

  final root = Steno.get('app');
  root.info('app started', fields: {'pid': 4242});

  // 2. Child loggers carry default fields and tags.
  final auth = root.child('auth', fields: {'module': 'auth'});
  auth.debug('hashing password');
  auth.info('user signed in', fields: {'userId': 'u_42'}, tags: ['auth']);

  // 3. Scopes attach inherited fields to every event inside the body —
  //    even across awaits.
  await LogScope.run({'requestId': 'r_001'}, () async {
    auth.info('parsing token');
    await Future<void>.delayed(const Duration(milliseconds: 5));
    auth.info('token ok'); // still carries requestId
  });

  // 4. Spans measure operations and propagate trace ids automatically.
  await auth.runSpan('verify-token', (span) async {
    span.setField('audience', 'web');
    await Future<void>.delayed(const Duration(milliseconds: 12));
    auth.info('token claims ok'); // inherits the span's trace id
  });

  // 5. Reconfigure on the fly. Switch to JSON for production-style output.
  Steno.configure(LoggerProfile.production().copyWith(
    minLevel: LogLevel.info,
  ));
  root.info('switched to production profile', fields: {
    'password': 'should-be-redacted',
    'userId': 'u_42',
  });

  // 6. Errors are first-class. Try/catch produces a real LogEvent.
  try {
    throw StateError('something blew up');
  } catch (e, st) {
    root.error('handled exception', error: e, stackTrace: st);
  }

  // 7. Lazy field building only runs if the level is enabled.
  root.debug('this is dropped at info level',
      fieldsBuilder: () => <String, Object?>{'expensive': _bigPayload()});

  // 8. Diagnostics are exposed via Steno.health.
  print('--- health ---');
  print(Steno.health.snapshot());

  await Steno.flush();
}

Map<String, Object?> _bigPayload() {
  print('_bigPayload was called — would not run if log level was debug');
  return {'k': 'v'};
}