nodl_conformance¶

nodl_conformance is a small Python library that compares two loaded NoDL documents. It does not load files, inspect running ROS nodes, or provide launch integration.

from nodl_conformance import diff

differences = diff(expected, actual, node_fqn='/robot/my_node')

expected and actual are nodl_schema.NodlDocument objects. An empty list means conformance. Each Difference contains kind, section, name, and detail. Supported kinds are missing, extra, type_mismatch, qos_mismatch, property_mismatch, and unverifiable.

Comparison rules¶

Interfaces¶

Interfaces are the public communication endpoints exposed or consumed by a node.

Check	Rule
Membership	Missing declared interfaces and extra actual interfaces are differences.
Collections	Publishers, subscriptions, service servers, service clients, action servers, and action clients remain separate.
Names	`/status` stays absolute, `status` resolves in the node namespace, and `~/status` resolves below the full node name.
Types	A short type equals its kind-specific fully qualified form. For example, `std_msgs/String` equals `std_msgs/msg/String` for a topic.
Representation	Collection order and empty collections do not affect the result.
Ignored metadata	Description fields and top-level `codegen` metadata do not affect the result.

QoS¶

Quality of Service (QoS) policies define how an endpoint communicates.

Check	Rule
Observability	Declared QoS that is not observable produces an `unverifiable` difference.
Optional policies	An omitted expected policy places no requirement on the actual endpoint. `SYSTEM_DEFAULT` and `BEST_AVAILABLE` accept a concrete actual policy.
Concrete policies	An unknown actual policy is `unverifiable`. Otherwise, the actual policy must match.
History and depth	`KEEP_LAST` requires a matching depth. Other history policies ignore depth.
Durations	Omitted and zero durations both mean unlimited. Finite nonzero durations must match exactly.

Parameters¶

Parameters are named configuration entries exposed by a node.

Check	Rule
Membership	Missing declared parameters and extra actual parameters are differences.
Type	Types must match. A generic actual type cannot prove a declared fixed-size type and produces `unverifiable`.
Read-only	A declared `read_only` value must match. An unknown actual value is `unverifiable`.
Ignored fields	Description, default value, additional constraints, validation rules, and the actual current value do not affect the result.

Runtime integration¶

ros2nodl loads and composes the expected document, describes a live node, and calls this comparator through ros2 nodl conform.