mqtt_bridge

mqtt_bridge provides a functionality to bridge between ROS and MQTT in bidirectional.

Principle

mqtt_bridge uses ROS message as its protocol. Messages from ROS are serialized by json (or messagepack) for MQTT, and messages from MQTT are deserialized for ROS topic. So MQTT messages should be ROS message compatible. (We use rosbridge_library.internal.message_conversion for message conversion.)

This limitation can be overcome by defining custom bridge class, though.

Demo

Prerequisites

$ sudo apt install python3-pip
$ sudo apt install ros-noetic-rosbridge-library
$ sudo apt install mosquitto mosquitto-clients

Install python modules

$ pip3 install -r requirements.txt

launch node

$ roslaunch mqtt_bridge demo.launch

Publish to /ping,

$ rostopic pub /ping std_msgs/Bool "data: true"

and see response to /pong.

$ rostopic echo /pong
data: True
---

Publish "hello" to /echo,

$ rostopic pub /echo std_msgs/String "data: 'hello'"

and see response to /back.

$ rostopic echo /back
data: hello
---

You can also see MQTT messages using mosquitto_sub

$ mosquitto_sub -t '#'

Usage

parameter file (config.yaml):

mqtt:
  client:
    protocol: 4      # MQTTv311
  connection:
    host: localhost
    port: 1883
    keepalive: 60
bridge:
  # ping pong
  - factory: mqtt_bridge.bridge:RosToMqttBridge
    msg_type: std_msgs.msg:Bool
    topic_from: /ping
    topic_to: ping
  - factory: mqtt_bridge.bridge:MqttToRosBridge
    msg_type: std_msgs.msg:Bool
    topic_from: ping
    topic_to: /pong

you can use any msg types like sensor_msgs.msg:Imu.

launch file:

<launch>
  <node name="mqtt_bridge" pkg="mqtt_bridge" type="mqtt_bridge_node.py" output="screen">
    <rosparam file="/path/to/config.yaml" command="load" />
  </node>
</launch>

Configuration

mqtt

Parameters under mqtt section are used for creating paho's mqtt.Client and its configuration.

subsections

client: used for mqtt.Client constructor
tls: used for tls configuration
account: used for username and password configuration
message: used for MQTT message configuration
userdata: used for MQTT userdata configuration
will: used for MQTT's will configuration

See mqtt_bridge.mqtt_client for detail.

mqtt private path

If mqtt/private_path parameter is set, leading ~/ in MQTT topic path will be replaced by this value. For example, if mqtt/pivate_path is set as "device/001", MQTT path "~/value" will be converted to "device/001/value".

serializer and deserializer

mqtt_bridge uses msgpack as a serializer by default. But you can also configure other serializers. For example, if you want to use json for serialization, add following configuration.

serializer: json:dumps
deserializer: json:loads

bridges

You can list ROS <--> MQTT tranfer specifications in following format.

bridge:
  # ping pong
  - factory: mqtt_bridge.bridge:RosToMqttBridge
    msg_type: std_msgs.msg:Bool
    topic_from: /ping
    topic_to: ping
  - factory: mqtt_bridge.bridge:MqttToRosBridge
    msg_type: std_msgs.msg:Bool
    topic_from: ping
    topic_to: /pong

factory: bridge class for transfering message from ROS to MQTT, and vise versa.
msg_type: ROS Message type transfering through the bridge.
topic_from: topic incoming from (ROS or MQTT)
topic_to: topic outgoing to (ROS or MQTT)

Also, you can create custom bridge class by inheriting mqtt_brige.bridge.Bridge.

License

This software is released under the MIT License, see LICENSE.txt.

freshrobotics/mqtt_bridge