rosbridge_dart_client

Subscribe-only Dart client for the rosbridge_suite JSON-over-WebSocket protocol. Connects to a rosbridge_server ROS 2 node and surfaces topic-subscribe streams as Stream<Map<String, dynamic>>. Pure Dart, no transport-layer lock-in.

Why this package exists

A driver-assist app built on the ROS 2 Navigation Stack already has nav2 nodes publishing safety state on ROS 2 topics. To consume those streams from a Dart / Flutter app, the integrator needs a rosbridge_server bridge node + a Dart-side WebSocket client. This package fills the Dart-side client with a subscribe-only minimum scope: enough to consume nav2 collision-state topics through nav2_safety_layer without authoring the protocol layer.

Driver impact chain (≤4 hops)

ROS 2 Navigation Stack node (e.g. nav2 Collision Monitor)
  -> rosbridge_server WebSocket bridge
    -> RosbridgeClient (this package; subscribe-only)
      -> integrator HMI (composing nav2_safety_layer for advisories)
        -> driver in unexpected snow

Four hops, with the driver as the terminal beneficiary.

Quick start

a. Install + import

dependencies:
  rosbridge_dart_client: ^0.1.0

import 'package:rosbridge_dart_client/rosbridge_dart_client.dart';

b. Connect + subscribe

final client = RosbridgeClient(uri: Uri.parse('ws://localhost:9090'));
await client.connect();

final sub = client.subscribe(
  topic: '/collision_monitor/state',
  type: 'nav2_msgs/msg/CollisionMonitorState',
).listen((json) {
  print('Got collision-monitor state: $json');
  // map json to typed record via Nav2CollisionMonitorState.fromJson
  // from the nav2_safety_layer package
});

// later — close the connection
await client.close();

c. Compose with nav2_safety_layer

import 'package:nav2_safety_layer/nav2_safety_layer.dart';
import 'package:navigation_safety_core/navigation_safety_core.dart';
import 'package:rosbridge_dart_client/rosbridge_dart_client.dart';

final ros = RosbridgeClient(uri: Uri.parse('ws://localhost:9090'));
await ros.connect();

final layer = Nav2SafetyLayer(
  profile: DriverProfile.snowZoneExperienced,
  throttle: AlertDensityThrottle(alertsPerMinuteCap: 60),
);
layer.advisories.listen((advisory) => print('Advisory: $advisory'));

ros.subscribe(
  topic: '/collision_monitor/state',
  type: 'nav2_msgs/msg/CollisionMonitorState',
).listen((json) {
  layer.onMonitorState(Nav2CollisionMonitorState.fromJson(json));
});

That's the 3-package full chain.

Out of scope for 0.1.0

This package ships a deliberately minimum scope so the surface stays auditable:

• op:publish outbound (publish-to-topic from Dart) — not supported
• op:call_service (service calls) — not supported
• op:advertise / op:unadvertise — not supported
• Action goals / action clients — not supported
• PNG-compressed messages — not supported
• Authentication helpers — not built-in; integrator wraps auth into the WebSocket connect URI if needed

When integrator demand for these surfaces materializes, they will be added in subsequent minor versions without breaking the 0.1.0 subscribe surface.

What this is NOT

• Not a roslibdart replacement. This package targets a specific consumer pattern (subscribe-only consumption of typed ROS 2 message streams) rather than the full roslibdart surface (publish, service, action). Integrators wanting publish or service surfaces wire a different bridge.
• Not a rosbridge_server. This is the Dart-side client only. The integrator runs rosbridge_server on their ROS 2 system.
• Not an L2+ automation or control surface. Subscribe-only — no outbound actuator messages.
• Not a typed message decoder. The Stream returns Map<String, dynamic> — caller maps to typed records (e.g. via Nav2CollisionMonitorState.fromJson from nav2_safety_layer).

License

BSD-3-Clause. See LICENSE.