Mongoose OS + private MQTT server

The mqtt library provides MQTT protocol API that allows devices to talk to MQTT servers.

Mongoose OS implements MQTT 3.1.1 client functionality, and works with all popular MQTT server implementations, like AWS IoT, Google IoT Core, Microsoft Azure, IBM Watson, HiveMQ, Mosquitto, etc.

Usage

In order to use MQTT functionality,

  • Include mqtt library in the libs section of the mos.yml file of your app:
    libs:
    ...
    - origin: https://github.com/mongoose-os-libs/mqtt # <-- Add this!
  • Rebuild and reflash your app:
    mos build --platform YOUR_PLATFORM # e.g. stm32, esp32, cc3220, esp8266, cc3200, etc
    mos flash

NOTE: if you're using a pre-built Mongoose OS demo-js app, that step is not required, since mqtt library is already included in the demo-js.

In order to talk to an MQTT server, configure MQTT server settings - see Configuration section below. Once configured, Mongoose OS keeps that connection alive by reconnecting and re-subscribing to all topics after disconnections - you do not need to implement the reconnection logic.

$ mos config-set mqtt.enable=true mqtt.server=my_server:1883

If you want to use TLS, set mqtt.ssl_ca_cert=ca.pem. Make sure that ca.pem file has required CA certificates. If you want to use mutual TLS, set mqtt.ssl_cert=CLIENT_CERT.pem and mqtt.ssl_key=PRIVATE_KEY.pem.

See example video (don't forget to set mqtt.enable=true before you try it):

MQTT publish and subscribe - JavaScript

load('api_mqtt.js');
load('api_gpio.js');

let pin = 0, topic = 'my/topic';

GPIO.set_button_handler(pin, GPIO.PULL_UP, GPIO.INT_EDGE_NEG, 200, function() {
  MQTT.pub('my/topic', JSON.stringify({ a: 1, b: 2 }));
}, null);

MQTT.sub('my/topic/#', function(conn, topic, msg) {
  print('Topic:', topic, 'message:', msg);
}, null);

MQTT publish and subscribe - C/C++

#include "mgos_mqtt.h"

static void handler(struct mg_connection *c, const char *topic, int topic_len,
                    const char *msg, int msg_len, void *userdata) {
  LOG(LL_INFO, ("Got message on topic %.*s", topic_len, topic));
  ...
}

mgos_mqtt_sub("my/#", handler, NULL);       /* Subscribe */
mgos_mqtt_pub("my/topic", "hi", 2, 1, 0);   /* Publish */

Configuration Reference

The MQTT library adds mqtt section to the device configuration:

{
  "clean_session": true,        // Clean session info stored on server 
  "client_id": "",              // If not set, device.id is used
  "enable": false,              // Enable MQTT functionality
  "keep_alive": 60,             // How often to send PING messages in seconds
  "pass": "",                   // User password
  "reconnect_timeout_max": 60,  // Maximum reconnection timeout in seconds
  "reconnect_timeout_min": 2,   // Minimum reconnection timeout in seconds
  "server": "iot.eclipse.org:1883",    // SERVER:PORT to connect to
  "ssl_ca_cert": "",            // Set this to file name with CA certs to enable TLS
  "ssl_cert": "",               // Client certificate for mutual TLS
  "ssl_cipher_suites": "",      // TLS cipher suites
  "ssl_key": "",                // Private key for the client certificate
  "ssl_psk_identity": "",       // If set, a preshared key auth is used
  "ssl_psk_key": "",            // Preshared key
  "user": "",                   // MQTT user name, if MQTT auth is used
  "will_message": "",           // MQTT last will message
  "will_topic": ""              // MQTT last will topic
}
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