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