roboflex.transport.mqtt

Rooboflex support for the MQTT transport.

See https://mqtt.org/ for details.

Using MQTT, nodes can connect to other nodes, even running on different computers. You must run your own MQTT broker - broker functionality is not wrapped in any way.

any node -> MQTTPublisher ==MQTT BROKER==> MQTTSubscriber -> any node

Contents

• Install
• Import
• Classes
  • MQTTContext
  • MQTTNodeBase
  • MQTTPublisher
  • MQTTSubscriber

System Dependencies

apt-get install mosquitto
apt-get install libmosquitto-dev

... or on mac ...
brew install mosquitto

Build

mkdir build && cd build
cmake ..
make

Run Examples (see examples)

pub_sub_0_cpp
python pub_sub_0_py

Import

import roboflex.transport.mqtt as rtm

Classes

Roboflex's support for MQTT is embodied in four classes:

1. MQTTContext, which you just have to instantiate somewhere
2. MQTTNodeBase, a base class which you don't use
3. MQTTPublisher, which can publish to an mqtt topic somewhere
4. MQTTSubscriber, which can subscribe to an mqtt topic somewhere

MQTTContext

In order to use the other MQTT classes, you must instantiate an MQTTContext, and its lifetime must be >= the lifetime of all other MQTT node classes. You must pass an instance of this class to the constructors of both MQTTPublisher and MQTTSubscriber.

# instantiate like so:
mqtt_context = rtm.MQTTContext()

MQTTNodeBase

Do not instantiate directly. This is the base class for MQTTPublisher and MQTTSubscriber, and holds common functionality and properties.

# the address of the broker
mqtt_node.broker_address -> str

# the port number of the broker
mqtt_node.broker_port -> int

# the number of seconds between keepalive messages
mqtt_node.keepalive_seconds -> int

# the topic to publish or subscribe to
mqtt_node.topic_name -> str

# the mqtt quality-of-service
mqtt_node.qos -> int

# whether to print out debug messages
mqtt_node.debug -> bool

MQTTPublisher

(inherits MQTTNodeBase)

Publishes any messages it receives to some topic, on some broker. When it receives an message, it publishes the binary representation on the given topic, and then propagages the message verbatim.

mqtt_publisher = rtm.MQTTPublisher(
    mqtt_context: rtm.MQTTContext,
    broker_address: str,
    broker_port: int,
    keepalive_seconds: int,
    topic_name: str,

    # optional...
    name: str = "MQTTPublisher",
    qos: int = 0,
    retained: bool = false,
    debug: bool = false,
)

# additional properties:

# See the MQTT documentation for what the retained feature does:
# https://www.hivemq.com/blog/mqtt-essentials-part-8-retained-messages/
mqtt_publisher.retained -> bool

# If you have some message 'in hand' in some other function,
# you can just use an MQTTPublisher to publish the message
# directly. This is just an alias for 'signal_self' on core::Node.
mqtt_publisher.publish({"key1": 32})

MQTTSubscriber

(inherits MQTTNodeBase)

Suscribes to some topic from some broker. Expects only Roboflex encoded messages.

mqtt_subscriber = rtm.MQTTSubscriber(
    mqtt_context: rtm.MQTTContext,
    broker_address: str,
    broker_port: int,
    keepalive_seconds: int,
    topic_name: str,

    # optional...
    name: str = "MQTTSubscriber",
    qos: int = 0,
    loop_timeout_milliseconds: int = 100,
    debug: bool = false,
)

# additional properties:

# number of milliseconds, max, to wait in the mqtt message loop,
# before checking whether to continue or not.
mqtt_subscriber.loop_timeout_milliseconds -> int