Data Logger: MQTT Sink

Requirements

See also

• Predecessor task: (DONE) Data Logger

• An MQTT implementation of the SinkLogger interface, using mosquitto (see below)

• A wrapper class around the plain C struct mosquitto that can take a SensorValues instance, like

  SensorValues v = sensor_config.getAllMeasurements();
  // ...
  Mosquitto client("localhost", 1883 /*default MQTT port*/);
  client.publish(v);
  

• A definition of the MQTT transport format in JSON, like

  { "sensor1": 37.5,
    "sensor2": 42.666
  }
  

  Write unit tests to define the format

Implementation

See also

• Mosquitto API

• Sample client implementation using Mosquitto API: bin/mosquitto-publish-demo.cpp

MQTT Implementation: mosquitto

Cross development is a burden, especially when you do C++ with a handmade Raspberry toolchain. mosquitto is written in pure C.

Installation

Ubuntu

$ sudo apt install mosquitto-dev

Fedora

$ sudo dnf install mosquitto-devel

Wrapper

• Constructor: allocate client using mosquitto_new(), and use mosquitto_connect() on it

• Destructor: mosquitto_destroy()

• Prohibit copy

Testing

• Unit test for JSON format

• Sample publish program using the wrapper class, in bin/

Future (Not Part Of This Development Cycle)

• The wrapper class will become more widely available when the boiling pot ((DONE) Boiling Pot (The Beginning)) goes IoT. The pot will broadcast “switch-on”/”switch-off” events and temperature measurements (it only has a single sensor, the temperature of the pot itself) - will need a more flexible input than just SensorValues