doc/mqtt: add event description and more details about configuration to API reference

docs/en/api-reference/protocols/mqtt.rst

@@ -9,10 +9,10 @@ ESP-MQTT is an implementation of MQTT protocol client (MQTT is a lightweight pub
 
 Features
 --------
-   * supports MQTT over TCP, SSL with mbedtls, MQTT over Websocket, MQTT over Websocket Secure.
+   * Supports 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).
+   * Support subscribing, publishing, authentication, last will messages, keep alive pings and all 3 QoS levels (it should be a fully functional client).
 
 
 Application Example
@@ -20,6 +20,7 @@ Application Example
 
     * :example:`protocols/mqtt/tcp`: MQTT over tcp, default port 1883
     * :example:`protocols/mqtt/ssl`:  MQTT over tcp, default port 8883
+    * :example:`protocols/mqtt/ssl_psk`: MQTT over tcp 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
 
@@ -62,19 +63,8 @@ URI
     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, subsribed, published, etc.)
+-  Note: By default mqtt client uses event loop library to post related mqtt events (connected, subscribed, published, etc.)
 
--  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:
-
-.. code:: c
-
-    const esp_mqtt_client_config_t mqtt_cfg = {
-        .uri = "mqtt://mqtt.eclipse.org:1234",
-        .port = 4567,
-    };
-    //MQTT client will connect to mqtt.eclipse.org using port 4567
 
 SSL
 ^^^
@@ -84,7 +74,7 @@ SSL
 -  Check the sample application: ``examples/mqtt_ssl``
 -  Configuration:
 
-.. code:: cpp
+.. code:: c
 
     const esp_mqtt_client_config_t mqtt_cfg = {
         .uri = "mqtts://mqtt.eclipse.org:8883",
@@ -92,15 +82,56 @@ SSL
         .cert_pem = (const char *)mqtt_eclipse_org_pem_start,
     };
 
+If the certificate is not null-terminated then ``cert_len`` should also be set.
+Other SSL related configuration parameters are:
+
+ * ``use_global_ca_store``: use the global certificate store to verify server certificate, see ``esp-tls.h`` for more information
+ * ``client_cert_pem``: pointer to certificate data in PEM or DER format for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed.
+ * ``client_cert_len``: length of the buffer pointed to by client_cert_pem. May be 0 for null-terminated pem.
+ * ``client_key_pem``: pointer to private key data in PEM or DER format for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed.
+ * ``client_key_len``: length of the buffer pointed to by client_key_pem. May be 0 for null-terminated pem.
+ * ``psk_hint_key``: pointer to PSK struct defined in esp_tls.h to enable PSK authentication (as alternative to certificate verification). If not NULL and server/client certificates are NULL, PSK is enabled
+ * ``alpn_protos``: NULL-terminated list of protocols to be used for ALPN.
+
+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 ``esp_mqtt_client_config_t``-struct.
+
+ * ``lwt_topic``: pointer to the LWT message topic
+ * ``lwt_msg``: pointer to the LWT message
+ * ``lwt_msg_len``: length of the LWT message, required if ``lwt_msg`` is not null-terminated
+ * ``lwt_qos``: quality of service for the LWT message
+ * ``lwt_retain``: specifies the retain flag of the LWT message
+
+Other Configuration Parameters
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ * ``disable_clean_session``: determines the clean session flag for the connect message, defaults to a clean session
+ * ``keepalive``: determines how many seconds the client will wait for a ping response before disconnecting, default is 120 seconds.
+ * ``disable_auto_reconnect``: enable to stop the client from reconnecting to server after errors or disconnects
+ * ``user_context``: custom context that will be passed to the event handler
+ * ``task_prio``: MQTT task priority, defaults to 5
+ * ``task_stack``: MQTT task stack size, defaults to 6144 bytes, setting this will override setting from menuconfig
+ * ``buffer_size``: size of MQTT send/receive buffer, default is 1024 bytes
+ * ``username``: pointer to the username used for connecting to the broker
+ * ``password``: pointer to the password used for connecting to the broker
+ * ``client_id``: pointer to the client id, defaults to ``ESP32_%CHIPID%`` where %CHIPID% are the last 3 bytes of MAC address in hex format
+ * ``host``: MQTT broker domain (ipv4 as string), setting the uri will override this
+ * ``port``: MQTT broker port, specifying the port in the uri will override this
+ * ``transport``: sets the transport protocol, setting the uri will override this
+ * ``refresh_connection_after_ms``: refresh connection after this value (in milliseconds)
+ * ``event_handle``: handle for MQTT events as a callback in legacy mode
+ * ``event_loop_handle``: handle for MQTT event loop library
+
+
+
 For more options on ``esp_mqtt_client_config_t``, please refer to API reference below
 
 Change settings in Project Configuration Menu
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+The settings for MQTT can be found using ``idf.py menuconfig``, under Component config -> ESP-MQTT Configuration
 
-::
-    idf.py menuconfig
-    -> Component config -> ESP-MQTT Configuration
-
+The following settings are available:
 
 - :ref:`CONFIG_MQTT_PROTOCOL_311`: Enables 3.1.1 version of MQTT protocol
 
@@ -109,6 +140,21 @@ Change settings in Project Configuration Menu
 - :ref:`CONFIG_MQTT_CUSTOM_OUTBOX`: Disables default implementation of mqtt_outbox, so a specific implementaion 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 will contain the message ID of the subscribe message.
+* ``MQTT_EVENT_UNSUBSCRIBED``: The broker has acknowledged the client's unsubscribe request. The event data will contain the message ID of the unsubscribe message.
+* ``MQTT_EVENT_PUBLISHED``: The broker has acknowledged the client's publish message. This will only be posted for Quality of Service level 1 and 2, as level 0 does not use acknowledgements. The event data will contain 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` will be posted and `current_data_offset` and `total_data_len` from event data updated to keep track of the fragmented message.
+* ``MQTT_EVENT_ERROR``: The client has encountered an error. `esp_mqtt_error_type_t` from `error_handle` in the event data can be used to further determine the type of the error. The type of error will determine which parts of the `error_handle` struct is filled.
+
+
+
 API Reference
 -------------