Seq integration

Seq is a structured log server compatible with CLEF (Compact Log Event Format). The package includes SinkSeq to send events directly from Flutter.

Basic setup

final seqSink = SinkSeq(
  'https://seq.example.com',
  apiKey: 'your-api-key',
  deviceIdentifier: 'app-mobile-v1',
);

logger.addSink(seqSink);

Parameters

Parameter	Required	Description
seqUrl	Yes	Absolute URL of the Seq server
apiKey	No	Key sent in the X-Seq-ApiKey header
deviceIdentifier	No	Device identifier in the CLEF event
client	No	Injected http.Client (useful in tests)

Endpoint and format

The sink sends POST to:

{seqUrl}/api/events/raw?clef

• Content-Type: application/vnd.serilog.clef
• Body: one CLEF JSON object per request

Reserved fields in the event:

• @t — timestamp
• @mt — message template
• @l — level
• DeviceIdentifier — device identifier

data properties are merged without overwriting reserved fields.

Lifecycle

When SinkSeq creates the http.Client internally, call close() when discarding the sink in long-lived apps:

@override
void dispose() {
  seqSink.close();
  super.dispose();
}

If you inject a custom client, the sink does not close it — lifecycle stays with the creator.

Error handling

Network failures or HTTP responses outside 200–201 are logged with print only in debug mode (kDebugMode). In release, failures are silent to avoid impacting UX.

Trailing slash URLs

URLs with a trailing slash are normalized correctly when building the endpoint (Uri.resolve).

URL validation

seqUrl must be an absolute URL. Invalid URLs throw ArgumentError in all builds (including release).

Example with multiple sinks

final logger = StructureLogger();

logger.addSink(SimpleLineSink()); // dev
logger.addSink(SinkSeq(
  'https://seq.example.com',
  apiKey: const String.fromEnvironment('SEQ_API_KEY'),
  deviceIdentifier: 'checkout-app',
));

Tests

Inject a mock http.Client to verify requests without a real network. See test/log_sinks/sink_seq_test.dart in the repository.