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

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.

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

$ pip3 install -r requirements.txt

$ ros2 launch mqtt_bridge demo.launch.py

Publish to /ping,

$ ros2 topic pub /ping std_msgs/Bool "data: true"

and see response to /pong.

$ ros2 topic echo /pong
data: True
---

Publish "hello" to /echo,

$ ros2 topic pub /echo std_msgs/String "data: 'hello'"

and see response to /back.

$ ros2 topic echo /back
data: hello
---

You can also see MQTT messages using mosquitto_sub

$ mosquitto_sub -t '#'

parameter file (config.yaml):

mqtt:
  client:
    protocol: 4      # MQTTv311
  connection:
    host: localhost
    port: 1883
    keepalive: 60
n_bridge: 2 # specifying number of bridges required
bridge:
            # factory, msg_type, topic_from, topic_to
  bridge1: ["mqtt_bridge.bridge:RosToMqttBridge","std_msgs.msg:Bool","/ping","ping"]
  bridge2: ["mqtt_bridge.bridge:MqttToRosBridge","std_msgs.msg:Bool","ping","/pong"]
  # ros2 parser cannot parse the earlier config type and therefore it has to be changed as above

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

launch file:

# to configure node configs
config = os.path.join(
        get_package_share_directory('mqtt_bridge'),
        'config',
        'demo_params.yaml'
        )

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

• 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.

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".

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

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

n_bridge: 2 # specifying number of bridges required
bridge:
            # factory, msg_type, topic_from, topic_to
  bridge1: ["mqtt_bridge.bridge:RosToMqttBridge","std_msgs.msg:Bool","/ping","ping"]
  bridge2: ["mqtt_bridge.bridge:MqttToRosBridge","std_msgs.msg:Bool","ping","/pong"]
  # ros2 parser cannot parse the earlier config type and therefore it has to be changed as above

• 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.

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