• Based on: https://github.com/tuanpmt/esp_mqtt
• Support MQTT over TCP, SSL with mbedtls, MQTT over Websocket, MQTT over Websocket Secure
• Easy to setup with URI
• Multiple instances (Multiple clients in one application)
• Support subscribing, publishing, authentication, will messages, keep alive pings and all 3 QoS levels (it should be a fully functional client).

From IDFv3.2 ESP-MQTT is integrated in ESP-IDF as a submodule. Please do not use separately.

For ESP-IDF versions prior to IDFv3.2, please checkout the ESP-MQTT_FOR_IDF_3.1 tag and follow the instructions below:

Clone this component to ESP-IDF project (as submodule):

git submodule add https://github.com/tuanpmt/espmqtt.git components/espmqtt

Or run a sample (make sure you have installed the toolchain):

git clone https://github.com/tuanpmt/espmqtt.git
cd espmqtt/examples/mqtt_tcp
make menuconfig
make flash monitor

• Curently support mqtt, mqtts, ws, wss schemes
• MQTT over TCP samples:
  • mqtt://iot.eclipse.org: MQTT over TCP, default port 1883:
  • mqtt://iot.eclipse.org:1884 MQTT over TCP, port 1884:
  • mqtt://username:[email protected]:1884 MQTT over TCP, port 1884, with username and password
• MQTT over SSL samples:
  • mqtts://iot.eclipse.org: MQTT over SSL, port 8883
  • mqtts://iot.eclipse.org:8884: MQTT over SSL, port 8884
• MQTT over Websocket samples:
  • ws://iot.eclipse.org:80/ws
• MQTT over Websocket Secure samples:
  • wss://iot.eclipse.org:443/ws
• Minimal configurations:

const esp_mqtt_client_config_t mqtt_cfg = {
    .uri = "mqtt://iot.eclipse.org",
    .event_handle = mqtt_event_handler,
    // .user_context = (void *)your_context
};

• If there are any options related to the URI in esp_mqtt_client_config_t, the option defined by the URI will be overridden. Sample:

const esp_mqtt_client_config_t mqtt_cfg = {
    .uri = "mqtt://iot.eclipse.org:1234",
    .event_handle = mqtt_event_handler,
    .port = 4567,
};
//MQTT client will connect to iot.eclipse.org using port 4567

• Get Certification from server, example: iot.eclipse.org openssl s_client -showcerts -connect iot.eclipse.org:8883 </dev/null 2>/dev/null|openssl x509 -outform PEM >iot_eclipse_org.pem
• Check the sample application: examples/mqtt_ssl
• Configuration:

const esp_mqtt_client_config_t mqtt_cfg = {
    .uri = "mqtts://iot.eclipse.org:8883",
    .event_handle = mqtt_event_handler,
    .cert_pem = (const char *)iot_eclipse_org_pem_start,
};

• event_handle for MQTT events
• host: MQTT server domain (ipv4 as string)
• port: MQTT server port
• client_id: default client id is ESP32_%CHIPID%
• username: MQTT username
• password: MQTT password
• lwt_topic, lwt_msg, lwt_qos, lwt_retain, lwt_msg_len: are mqtt lwt options, default NULL
• disable_clean_session: mqtt clean session, default clean_session is true
• keepalive: (value in seconds) mqtt keepalive, default is 120 seconds
• disable_auto_reconnect: this mqtt client will reconnect to server (when errors/disconnect). Set disable_auto_reconnect=true to disable
• user_context pass user context to this option, then can receive that context in event->user_context
• task_prio, task_stack for MQTT task, default priority is 5, and task_stack = 6144 bytes (or default task stack can be set via make menucofig).
• buffer_size for MQTT send/receive buffer, default is 1024
• cert_pem pointer to CERT file for server verify (with SSL), default is NULL, not required to verify the server
• client_cert_pem pointer to CERT file for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed. If it is not NULL, also client_key_pem has to be provided.
• client_key_pem pointer to PEM private key file for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed. If it is not NULL, also client_cert_pem has to be provided.
• transport: override URI transport
  • MQTT_TRANSPORT_OVER_TCP: MQTT over TCP, using scheme: mqtt
  • MQTT_TRANSPORT_OVER_SSL: MQTT over SSL, using scheme: mqtts
  • MQTT_TRANSPORT_OVER_WS: MQTT over Websocket, using scheme: ws
  • MQTT_TRANSPORT_OVER_WSS: MQTT over Websocket Secure, using scheme: wss

make menuconfig 
-> Component config -> ESPMQTT Configuration 

Check examples/mqtt_tcp and examples/mqtt_ssl project. In Short:

static esp_err_t mqtt_event_handler(esp_mqtt_event_handle_t event)
{
    esp_mqtt_client_handle_t client = event->client;
    int msg_id;
    // your_context_t *context = event->context;
    switch (event->event_id) {
        case MQTT_EVENT_CONNECTED:
            ESP_LOGI(TAG, "MQTT_EVENT_CONNECTED");
            msg_id = esp_mqtt_client_subscribe(client, "/topic/qos0", 0);
            ESP_LOGI(TAG, "sent subscribe successful, msg_id=%d", msg_id);

            msg_id = esp_mqtt_client_subscribe(client, "/topic/qos1", 1);
            ESP_LOGI(TAG, "sent subscribe successful, msg_id=%d", msg_id);

            msg_id = esp_mqtt_client_unsubscribe(client, "/topic/qos1");
            ESP_LOGI(TAG, "sent unsubscribe successful, msg_id=%d", msg_id);
            break;
        case MQTT_EVENT_DISCONNECTED:
            ESP_LOGI(TAG, "MQTT_EVENT_DISCONNECTED");
            break;

        case MQTT_EVENT_SUBSCRIBED:
            ESP_LOGI(TAG, "MQTT_EVENT_SUBSCRIBED, msg_id=%d", event->msg_id);
            msg_id = esp_mqtt_client_publish(client, "/topic/qos0", "data", 0, 0, 0);
            ESP_LOGI(TAG, "sent publish successful, msg_id=%d", msg_id);
            break;
        case MQTT_EVENT_UNSUBSCRIBED:
            ESP_LOGI(TAG, "MQTT_EVENT_UNSUBSCRIBED, msg_id=%d", event->msg_id);
            break;
        case MQTT_EVENT_PUBLISHED:
            ESP_LOGI(TAG, "MQTT_EVENT_PUBLISHED, msg_id=%d", event->msg_id);
            break;
        case MQTT_EVENT_DATA:
            ESP_LOGI(TAG, "MQTT_EVENT_DATA");
            printf("TOPIC=%.*s\r\n", event->topic_len, event->topic);
            printf("DATA=%.*s\r\n", event->data_len, event->data);
            break;
        case MQTT_EVENT_ERROR:
            ESP_LOGI(TAG, "MQTT_EVENT_ERROR");
            break;
    }
    return ESP_OK;
}
const esp_mqtt_client_config_t mqtt_cfg = {
    .uri = "mqtt://iot.eclipse.org",
    .event_handle = mqtt_event_handler,
    // .user_context = (void *)your_context
};

esp_mqtt_client_handle_t client = esp_mqtt_client_init(&mqtt_cfg);
esp_mqtt_client_start(client);

• MQTT Package - Stephen Robinson - contiki-mqtt
• Others @tuanpmt Apache License