nav2_safety_layer

Pure-Dart bridge layering navigation_safety_core driver-cognition primitives over the ROS 2 Navigation Stack (nav2) Collision Monitor and Collision Detector state messages. No transport lock-in. The integrator wires any ROS-Dart bridge of choice (roslibdart, rosbridge over WebSocket, MQTT bridge, custom Dart wrapper) and pushes typed records into the layer.

Why this package exists

A driver-assist app built on the ROS 2 Navigation Stack already has nav2's Collision Monitor and Collision Detector publishing action-class state every cycle. An integrator building a nav2-based ROS 2 + Flutter dashboard ends up handcoding the same polygon-name + action-type → driver-cognition mapping every time. This package centralizes that mapping with a caution-add-only invariant and a profile-tuned density throttle so the driver in unexpected snow does not face alert-fatigue from a chatty monitor.

Driver impact chain (≤4 hops)

nav2 Collision Monitor / Detector node (ROS 2)
  -> integrator's ROS-Dart bridge (roslibdart, rosbridge, etc.)
    -> Nav2SafetyLayer (this package)
      -> driver in unexpected snow on a nav2-stack-served vehicle

Four hops, with the driver as the terminal beneficiary.

Quick start

a. Install + import

dependencies:
  nav2_safety_layer: ^0.1.0
  navigation_safety_core: ^0.10.0
  # plus the ROS-Dart bridge of your choice

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

b. Wire the layer to your bridge's stream

final layer = Nav2SafetyLayer(
  profile: DriverProfile.snowZoneExperienced,
  throttle: AlertDensityThrottle.forProfile(DriverProfile.snowZoneExperienced),
);

// Subscribe to advisory strings the HMI surfaces:
layer.advisories.listen((advisory) {
  // surface to driver via your HMI
});

// Wire nav2's CollisionMonitorState topic via your ROS-Dart bridge:
//   bridge.subscribe('/collision_monitor/state', (rawJson) {
//     layer.onMonitorState(Nav2CollisionMonitorState.fromJson(rawJson));
//   });
//   bridge.subscribe('/collision_detector/state', (rawJson) {
//     layer.onDetectorState(Nav2CollisionDetectorState.fromJson(rawJson));
//   });

c. Map without rate-limiting

If the integrator already has its own throttle / dedup pipeline, the mapper can be used statically without a layer:

final advisory = Nav2SafetyMapper.toAdvisory(
  state,
  DriverProfile.snowZoneExperienced,
); // null when state.actionType == doNothing

Mapping discipline

• Caution-add-only invariant. Unknown action_type integers degrade to Nav2CollisionAction.doNothing rather than asserting a specific behavior the publisher did not intend.
• Verbatim relay (Article 17 β). Polygon names from the publisher are surfaced verbatim in the advisory body so the driver-facing HMI can display the publisher's exact polygon naming.
• Profile-tuned density throttle. The integrator chooses the throttle's cap class via AlertDensityThrottle.forProfile(...); the default literature-anchored caps in navigation_safety_core apply.

Standards mapping

Standard	Mapping
SAE J3016	L0 / L1 supportive. No L2+ claim. Advisories inform; the driver decides.
ISO 26262	Product-quality scope at the package boundary. The integrator performs the hazard analysis at the closed-loop boundary.
JIS / JASO	Not mapped at this scope.

What this is NOT

• Not a ROS-Dart bridge. This package does not implement rosbridge, MQTT, or any other transport. The integrator supplies the bridge.
• Not a control surface. Advisory strings are driver-facing language; the package does not actuate the vehicle.
• Not an L2+ automation or handover-class supervision package.
• Not a polygon authoring tool. Polygon names come from the upstream nav2 Collision Monitor / Collision Detector configuration; this package preserves them verbatim, it does not author them.

License

BSD-3-Clause. See LICENSE.