rclpy_message_converter

rclpy_message_converter is a lightweight ROS2 package and Python library to convert from Python dictionaries and JSON messages to rclpy messages, and vice versa.

ROS 1 and ROS 2 branches

ROS 1 users should use the master branch. ROS 2 users should use the appropriate branch for their distro (foxy/galactic/humble/rolling/…).

Note to ROS 2 users

Most ROS 2 users probably do not need this package. This package was originally developed for ROS 1. In ROS 2, most of the functionality is already built in. Specifically, check out

• rosidl_runtime_py.set_message.set_message_fields() for converting a Python dictionary to a ROS message, and
• rosidl_runtime_py.convert.message_to_orderreddict for converting a ROS message to a Python dictionary.

The rclpy_message_converter mainly adds the functionality to encode all variable-size uint8[] or fixed-size uint8[n] fields using Base64 encoding when the parameter base64_encoding is set. This saves a lot of space when converting large messages (such as sensor_msgs/Image) to JSON format. Also, encoding/decoding of Base64 strings is required by some packages (such as mir_robot) that were originally developed in ROS1.

Usage

Convert a dictionary to a ROS message

from rclpy_message_converter import message_converter
from std_msgs.msg import String
dictionary = { 'data': 'Howdy' }
message = message_converter.convert_dictionary_to_ros_message('std_msgs/msg/String', dictionary)

Convert a ROS message to a dictionary

from rclpy_message_converter import message_converter
from std_msgs.msg import String
message = String(data = 'Howdy')
dictionary = message_converter.convert_ros_message_to_dictionary(message)

Convert JSON to a ROS message

from rclpy_message_converter import json_message_converter
from std_msgs.msg import String
json_str = '{"data": "Hello"}'
message = json_message_converter.convert_json_to_ros_message('std_msgs/msg/String', json_str)

Convert a ROS message to JSON

from rclpy_message_converter import json_message_converter
from std_msgs.msg import String
message = String(data = 'Hello')
json_str = json_message_converter.convert_ros_message_to_json(message)

Test

To run the tests:

colcon test

pre-commit Formatting Checks

This repo has a pre-commit check that runs in CI. You can use this locally and set it up to run automatically before you commit something. To install, use pip:

pip3 install --user pre-commit

To run over all the files in the repo manually:

pre-commit run -a

To run pre-commit automatically before committing in the local repo, install the git hooks:

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