ESP-MQTT ======== :link_to_translation:`zh_CN:[中文]` Overview -------- ESP-MQTT is an implementation of `MQTT `__ protocol client, which is a lightweight publish/subscribe messaging protocol. Now ESP-MQTT supports `MQTT v5.0 `__. Features -------- * Support MQTT over TCP, SSL with Mbed TLS, MQTT over WebSocket, and MQTT over WebSocket Secure * Easy to setup with URI * Multiple instances (multiple clients in one application) * Support subscribing, publishing, authentication, last will messages, keep alive pings, and all 3 Quality of Service (QoS) levels (it should be a fully functional client) Application Examples --------------------- * :example:`protocols/mqtt/tcp`: MQTT over TCP, default port 1883 * :example:`protocols/mqtt/ssl`: MQTT over TLS, default port 8883 * :example:`protocols/mqtt/ssl_ds`: MQTT over TLS using digital signature peripheral for authentication, default port 8883 * :example:`protocols/mqtt/ssl_mutual_auth`: MQTT over TLS using certificates for authentication, default port 8883 * :example:`protocols/mqtt/ssl_psk`: MQTT over TLS using pre-shared keys for authentication, default port 8883 * :example:`protocols/mqtt/ws`: MQTT over WebSocket, default port 80 * :example:`protocols/mqtt/wss`: MQTT over WebSocket Secure, default port 443 * :example:`protocols/mqtt5`: Uses ESP-MQTT library to connect to broker with MQTT v5.0 MQTT Message Retransmission --------------------------- A new MQTT message is created by calling :cpp:func:`esp_mqtt_client_publish ` or its non blocking counterpart :cpp:func:`esp_mqtt_client_enqueue `. Messages with QoS 0 is sent only once. QoS 1 and 2 have different behaviors since the protocol requires extra steps to complete the process. The ESP-MQTT library opts to always retransmit unacknowledged QoS 1 and 2 publish messages to avoid losses in faulty connections, even though the MQTT specification requires the re-transmission only on reconnect with Clean Session flag been set to 0 (set :cpp:member:`disable_clean_session ` to true for this behavior). QoS 1 and 2 messages that may need retransmission are always enqueued, but first transmission try occurs immediately if :cpp:func:`esp_mqtt_client_publish ` is used. A transmission retry for unacknowledged messages will occur after :cpp:member:`message_retransmit_timeout `. After :ref:`CONFIG_MQTT_OUTBOX_EXPIRED_TIMEOUT_MS` messages will expire and be deleted. If :ref:`CONFIG_MQTT_REPORT_DELETED_MESSAGES` is set, an event will be sent to notify the user. Configuration ------------- The configuration is made by setting fields in :cpp:class:`esp_mqtt_client_config_t` struct. The configuration struct has the following sub structs to configure different aspects of the client operation. * :cpp:class:`esp_mqtt_client_config_t::broker_t` - Allow to set address and security verification. * :cpp:class:`esp_mqtt_client_config_t::credentials_t` - Client credentials for authentication. * :cpp:class:`esp_mqtt_client_config_t::session_t` - Configuration for MQTT session aspects. * :cpp:class:`esp_mqtt_client_config_t::network_t` - Networking related configuration. * :cpp:class:`esp_mqtt_client_config_t::task_t` - Allow to configure FreeRTOS task. * :cpp:class:`esp_mqtt_client_config_t::buffer_t` - Buffer size for input and output. In the following sections, the most common aspects are detailed. Broker ^^^^^^^^^^^ =========== Address =========== Broker address can be set by usage of :cpp:class:`address ` struct. The configuration can be made by usage of :cpp:member:`uri ` field or the combination of :cpp:member:`hostname `, :cpp:member:`transport ` and :cpp:member:`port `. Optionally, :cpp:member:`path ` could be set, this field is useful in WebSocket connections. The :cpp:member:`uri ` field is used in the format ``scheme://hostname:port/path``. - Curently support ``mqtt``, ``mqtts``, ``ws``, ``wss`` schemes - MQTT over TCP samples: - ``mqtt://mqtt.eclipseprojects.io``: MQTT over TCP, default port 1883 - ``mqtt://mqtt.eclipseprojects.io:1884``: MQTT over TCP, port 1884 - ``mqtt://username:password@mqtt.eclipseprojects.io:1884``: MQTT over TCP, port 1884, with username and password - MQTT over SSL samples: - ``mqtts://mqtt.eclipseprojects.io``: MQTT over SSL, port 8883 - ``mqtts://mqtt.eclipseprojects.io:8884``: MQTT over SSL, port 8884 - MQTT over WebSocket samples: - ``ws://mqtt.eclipseprojects.io:80/mqtt`` - MQTT over WebSocket Secure samples: - ``wss://mqtt.eclipseprojects.io:443/mqtt`` - Minimal configurations: .. code-block:: c const esp_mqtt_client_config_t mqtt_cfg = { .broker.address.uri = "mqtt://mqtt.eclipseprojects.io", }; esp_mqtt_client_handle_t client = esp_mqtt_client_init(&mqtt_cfg); esp_mqtt_client_register_event(client, ESP_EVENT_ANY_ID, mqtt_event_handler, client); esp_mqtt_client_start(client); .. note:: By default MQTT client uses event loop library to post related MQTT events (connected, subscribed, published, etc.). ============ Verification ============ For secure connections with TLS used, and to guarantee Broker's identity, the :cpp:class:`verification ` struct must be set. The broker certificate may be set in PEM or DER format. To select DER, the equivalent :cpp:member:`certificate_len ` field must be set. Otherwise, a null-terminated string in PEM format should be provided to :cpp:member:`certificate ` field. - Get certificate from server, example: ``mqtt.eclipseprojects.io`` .. code:: openssl s_client -showcerts -connect mqtt.eclipseprojects.io:8883 < /dev/null \ 2> /dev/null | openssl x509 -outform PEM > mqtt_eclipse_org.pem - Check the sample application: :example:`protocols/mqtt/ssl` - Configuration: .. code:: c const esp_mqtt_client_config_t mqtt_cfg = { .broker = { .address.uri = "mqtts://mqtt.eclipseprojects.io:8883", .verification.certificate = (const char *)mqtt_eclipse_org_pem_start, }, }; For details about other fields, please check the `API Reference`_ and :ref:`esp_tls_server_verification`. Client Credentials ^^^^^^^^^^^^^^^^^^ All client related credentials are under the :cpp:class:`credentials ` field. * :cpp:member:`username `: pointer to the username used for connecting to the broker, can also be set by URI * :cpp:member:`client_id `: pointer to the client ID, defaults to ``ESP32_%CHIPID%`` where ``%CHIPID%`` are the last 3 bytes of MAC address in hex format ============== Authentication ============== It is possible to set authentication parameters through the :cpp:class:`authentication ` field. The client supports the following authentication methods: * :cpp:member:`password `: use a password by setting * :cpp:member:`certificate ` and :cpp:member:`key `: mutual authentication with TLS, and both can be provided in PEM or DER format * :cpp:member:`use_secure_element `: use secure element available in ESP32-WROOM-32SE * :cpp:member:`ds_data `: use Digital Signature Peripheral available in some Espressif devices Session ^^^^^^^^^^^ For MQTT session related configurations, :cpp:class:`session ` fields should be used. ======================= Last Will and Testament ======================= MQTT allows for a last will and testament (LWT) message to notify other clients when a client ungracefully disconnects. This is configured by the following fields in the :cpp:class:`last_will ` struct. * :cpp:member:`topic `: pointer to the LWT message topic * :cpp:member:`msg `: pointer to the LWT message * :cpp:member:`msg_len `: length of the LWT message, required if :cpp:member:`msg ` is not null-terminated * :cpp:member:`qos `: quality of service for the LWT message * :cpp:member:`retain `: specifies the retain flag of the LWT message Change Settings in Project Configuration Menu ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The settings for MQTT can be found using :code:`idf.py menuconfig`, under ``Component config`` > ``ESP-MQTT Configuration``. The following settings are available: - :ref:`CONFIG_MQTT_PROTOCOL_311`: enable 3.1.1 version of MQTT protocol - :ref:`CONFIG_MQTT_TRANSPORT_SSL` and :ref:`CONFIG_MQTT_TRANSPORT_WEBSOCKET`: enable specific MQTT transport layer, such as SSL, WEBSOCKET, and WEBSOCKET_SECURE - :ref:`CONFIG_MQTT_CUSTOM_OUTBOX`: disable default implementation of mqtt_outbox, so a specific implementation can be supplied Events ------ The following events may be posted by the MQTT client: * ``MQTT_EVENT_BEFORE_CONNECT``: The client is initialized and about to start connecting to the broker. * ``MQTT_EVENT_CONNECTED``: The client has successfully established a connection to the broker. The client is now ready to send and receive data. * ``MQTT_EVENT_DISCONNECTED``: The client has aborted the connection due to being unable to read or write data, e.g., because the server is unavailable. * ``MQTT_EVENT_SUBSCRIBED``: The broker has acknowledged the client's subscribe request. The event data contains the message ID of the subscribe message. * ``MQTT_EVENT_UNSUBSCRIBED``: The broker has acknowledged the client's unsubscribe request. The event data contains the message ID of the unsubscribe message. * ``MQTT_EVENT_PUBLISHED``: The broker has acknowledged the client's publish message. This is only posted for QoS level 1 and 2, as level 0 does not use acknowledgements. The event data contains the message ID of the publish message. * ``MQTT_EVENT_DATA``: The client has received a publish message. The event data contains: message ID, name of the topic it was published to, received data and its length. For data that exceeds the internal buffer, multiple ``MQTT_EVENT_DATA`` events are posted and :cpp:member:`current_data_offset ` and :cpp:member:`total_data_len` from event data updated to keep track of the fragmented message. * ``MQTT_EVENT_ERROR``: The client has encountered an error. The field :cpp:type:`error_handle ` in the event data contains :cpp:type:`error_type ` that can be used to identify the error. The type of error determines which parts of the :cpp:type:`error_handle ` struct is filled. API Reference ------------- .. include-build-file:: inc/mqtt_client.inc