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samples: net: mqtt_publisher: Enable MQTT 5.0 support

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Enable MQTT 5.0 support in the mqtt_publisher sample and make use
of the topic aliasing feature.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
This commit is contained in:
Robert Lubos 2025-04-24 14:46:16 +02:00 committed by Benjamin Cabé
parent a831122029
commit 6a672bc5ba
3 changed files with 68 additions and 9 deletions
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29
samples/net/mqtt_publisher/README.rst
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@ -11,11 +11,15 @@ Overview
publish/subscribe messaging protocol optimized for small sensors and
mobile devices.
The Zephyr MQTT Publisher sample application is a MQTT v3.1.1
client that sends MQTT PUBLISH messages to a MQTT broker.
See the `MQTT V3.1.1 spec`_ for more information.
The Zephyr MQTT Publisher sample application is a MQTT client that sends
MQTT PUBLISH messages to a MQTT broker. The sample supports MQTT client in
version v3.1.1 (default) and v5.0.
.. _MQTT V3.1.1 spec: http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html
See the `MQTT v3.1.1 spec`_ and `MQTT v5.0 spec`_ for more information about
MQTT v3.1.1 and v5.0, respectively.
.. _MQTT v3.1.1 spec: https://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html
.. _MQTT v5.0 spec: https://docs.oasis-open.org/mqtt/mqtt/v5.0/mqtt-v5.0.html
The source code of this sample application can be found at:
:zephyr_file:`samples/net/mqtt_publisher`.
@ -136,6 +140,23 @@ Open another terminal window and type:
$ mosquitto_sub -t sensors
MQTT v5.0 support
=================
The sample can be configured to use MQTT v5.0 instead of MQTT v3.1.1. To enable
MQTT v5.0 in the sample, build it with ``-DEXTRA_CONF_FILE=overlay-mqtt-5.conf``
parameter. The sample should work with any broker supporting MQTT v5.0, however
it was specifically tested with mosquitto version 2.0.21. Server side
configuration in this particular case is the same as for MQTT v3.1.1.
When the sample is configured in the MQTT v5.0 mode, it makes use of the topic
aliasing feature. i.e. if the broker reports it supports topic aliases, the
client will register a topic alias for the default ``sensors`` topic, and use it
for consecutive MQTT Publish messages. It can be observed (for example using
Wireshark) how the actual topic is only present in the first Publish message, and
all subsequent Publish messages are smaller, as they include topic alias
property only.
Connecting securely using TLS
=============================

1
samples/net/mqtt_publisher/overlay-mqtt-5.conf Normal file
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@ -0,0 +1 @@
CONFIG_MQTT_VERSION_5_0=y

47
samples/net/mqtt_publisher/src/main.c
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@ -53,9 +53,14 @@ static APP_BMEM struct sockaddr socks5_proxy;
static APP_BMEM struct pollfd fds[1];
static APP_BMEM int nfds;
static APP_BMEM bool connected;
/* Whether to include full topic in the publish message, or alias only (MQTT 5). */
static APP_BMEM bool include_topic;
static APP_BMEM bool aliases_enabled;
#define APP_TOPIC_ALIAS 1
#if defined(CONFIG_MQTT_LIB_TLS)
#include "test_certs.h"
@ -155,6 +160,18 @@ void mqtt_evt_handler(struct mqtt_client *const client,
connected = true;
LOG_INF("MQTT client connected!");
#if defined(CONFIG_MQTT_VERSION_5_0)
if (evt->param.connack.prop.rx.has_topic_alias_maximum &&
evt->param.connack.prop.topic_alias_maximum > 0) {
LOG_INF("Topic aliases allowed by the broker, max %u.",
evt->param.connack.prop.topic_alias_maximum);
aliases_enabled = true;
} else {
LOG_INF("Topic aliases disallowed by the broker.");
}
#endif
break;
case MQTT_EVT_DISCONNECT:
@ -242,12 +259,18 @@ static char *get_mqtt_topic(void)
static int publish(struct mqtt_client *client, enum mqtt_qos qos)
{
struct mqtt_publish_param param;
struct mqtt_publish_param param = { 0 };
/* Always true for MQTT 3.1.1.
* True only on first publish message for MQTT 5.0 if broker allows aliases.
*/
if (include_topic) {
param.message.topic.topic.utf8 = (uint8_t *)get_mqtt_topic();
param.message.topic.topic.size =
strlen(param.message.topic.topic.utf8);
}
param.message.topic.qos = qos;
param.message.topic.topic.utf8 = (uint8_t *)get_mqtt_topic();
param.message.topic.topic.size =
strlen(param.message.topic.topic.utf8);
param.message.payload.data = get_mqtt_payload(qos);
param.message.payload.len =
strlen(param.message.payload.data);
@ -255,6 +278,13 @@ static int publish(struct mqtt_client *client, enum mqtt_qos qos)
param.dup_flag = 0U;
param.retain_flag = 0U;
#if defined(CONFIG_MQTT_VERSION_5_0)
if (aliases_enabled) {
param.prop.topic_alias = APP_TOPIC_ALIAS;
include_topic = false;
}
#endif
return mqtt_publish(client, &param);
}
@ -308,7 +338,11 @@ static void client_init(struct mqtt_client *client)
client->client_id.size = strlen(MQTT_CLIENTID);
client->password = NULL;
client->user_name = NULL;
#if defined(CONFIG_MQTT_VERSION_5_0)
client->protocol_version = MQTT_VERSION_5_0;
#else
client->protocol_version = MQTT_VERSION_3_1_1;
#endif
/* MQTT buffers configuration */
client->rx_buf = rx_buffer;
@ -435,6 +469,9 @@ static int publisher(void)
{
int i, rc, r = 0;
include_topic = true;
aliases_enabled = false;
LOG_INF("attempting to connect: ");
rc = try_to_connect(&client_ctx);
PRINT_RESULT("try_to_connect", rc);