README

ros2_medkit_serialization

Runtime JSON ↔ ROS 2 message serialization library for the ros2_medkit gateway.

Overview

This package provides dynamic message serialization using dynmsg, enabling JSON ↔ ROS 2 message conversion at runtime without compile-time type dependencies. It eliminates CLI fallbacks in the gateway by providing native C++ APIs for all message operations.

Features

JSON Serialization: Convert ROS 2 messages to/from JSON (via YAML bridge)
CDR Serialization: Serialize JSON to CDR format for GenericPublisher and GenericClient
CDR Deserialization: Deserialize CDR data from GenericSubscription to JSON
Type Caching: Thread-safe caching of type introspection data with LRU eviction
Service/Action Types: Helper functions for request/response/goal type derivation
Schema Generation: Generate JSON schemas for ROS 2 message types

Dependencies

dynmsg - OSRF dynamic message introspection library
nlohmann_json - JSON library
yaml_cpp_vendor - YAML library (for dynmsg compatibility)
rclcpp - ROS 2 client library (for SerializedMessage)

Usage

#include "ros2_medkit_serialization/json_serializer.hpp"
#include "ros2_medkit_serialization/type_cache.hpp"

// Get type info (cached)
auto& cache = ros2_medkit_serialization::TypeCache::instance();
auto type_info = cache.get("std_msgs", "String");

// Create serializer
ros2_medkit_serialization::JsonSerializer serializer;

// Serialize JSON to CDR for GenericPublisher
nlohmann::json msg_json = {{"data", "Hello World"}};
auto serialized = serializer.serialize("std_msgs/msg/String", msg_json);
// Use with: generic_publisher->publish(serialized);

// Deserialize CDR to JSON from GenericSubscription
nlohmann::json result = serializer.deserialize("std_msgs/msg/String", serialized_msg);

// Convert in-memory message to JSON
nlohmann::json json = serializer.to_json(type_info, message_ptr);

// Generate schema for a type
nlohmann::json schema = serializer.get_schema("geometry_msgs/msg/Twist");

API Reference

JsonSerializer

Method	Description
`serialize(type, json)`	Serialize JSON to CDR `SerializedMessage`
`deserialize(type, msg)`	Deserialize CDR to JSON
`to_json(type_info, ptr)`	Convert in-memory message to JSON
`from_json(type, json)`	Create message from JSON
`get_schema(type)`	Get JSON schema for type
`get_defaults(type)`	Get default values as JSON
`yaml_to_json(yaml)`	Convert YAML node to JSON (static)

TypeCache

Method	Description
`instance()`	Get singleton instance
`get(pkg, name)`	Get cached type info
`get(type_string)`	Get cached type info from full type string
`clear()`	Clear all cached entries

Building

cd /path/to/ros2_medkit
colcon build --packages-select ros2_medkit_serialization

Testing

colcon test --packages-select ros2_medkit_serialization
colcon test-result --verbose

Design Documentation

See the design documentation for architecture details.

License

Apache-2.0