ROS / ROS2

# ROS and ROS2 Rules

## Package Structure

- Keep packages focused on one robot capability or integration boundary.
- Use `package.xml` and `CMakeLists.txt` or `setup.py` consistently with the package type.
- Keep launch files under `launch/`, configs under `config/`, messages under `msg/`, services under `srv/`, and actions under `action/`.
- Use namespaces and remapping instead of hardcoded topic names when nodes may be reused.

## Nodes and Interfaces

- Keep nodes small and composable.
- Use parameters for tunable behavior; declare ROS2 parameters explicitly.
- Prefer messages for state streams, services for quick request/response operations, and actions for long-running goals with feedback.
- Use standard message types before creating custom interfaces.
- Document topic, service, action, frame, and parameter contracts.

## Timing and Frames

- Use ROS time when simulation or bag replay matters.
- Use `tf2` for frame transforms and document frame names.
- Avoid blocking callbacks; move long work to timers, worker threads, or actions.
- Set QoS profiles intentionally for sensor data, latched-like config, and reliable command paths.

## Build and Test

- Use `colcon build` and keep package dependencies explicit.
- Run linters and formatters used by the workspace.
- Add launch tests or integration tests for multi-node behavior.
- Use simulation, bags, or recorded fixtures for repeatable sensor scenarios.
- Test failure cases such as missing transforms, stale sensor data, and unavailable services.

## Common Mistakes

- Do not hardcode absolute paths; use package share directories.
- Do not publish commands without validating frame, units, and timestamp assumptions.
- Do not create custom messages when a standard message fits.
- Do not ignore QoS mismatches between publishers and subscribers.