Publishing MQTT data to multiple topics in Thingy91

[Adeel]

Hi Dev Team,

I am running a program that is publishing data over MQTT using a particular topic and broker on the Thingy91.

I wanted to know a way in which I could send different data to different topics and how it could be configured in the mqtt example.

For instance, I need to send different sensor values to different topics : (home/living/temp for temperature), (home/living/humid for humidity value).

I don't see an option of configuring more than 1 topic in the mqtt example. 

For now, I have defined it as : CONFIG_MQTT_PUB_TOPIC "home/living" in the autoconf.h file.

Could you let me know how to configure multiple topics in the program ?

Regards,

Adeel.

[Hakon]

Hello,

 

Could you let me know how to configure multiple topics in the program ?

 What do you mean by configure multiple topics? Do you mean publishing to multiple topics or subscribe to multiple topics?

[Adeel]

Hi Hakon,

I meant publishing to multiple topics .

Regards,

Adeel.

[Hakon]

What sample are you using? Are you using the AWS IoT library?

[Adeel]

Hi Hakon,

No, I am just building up my application on the mqtt_simple example. So basically the sample I am using is mqtt_simple.

Right now, I have 1 topic assigned and I am able to publish the data to that topic. I need to publish another data to a different topic as well. I wanted to know as to how I could do that.

Regards,

Adeel.

[Adeel]

Hi Hakon,

I found a way of doing this, though I am not sure its the most optimized way.

I duplicated the data_publish() function in the mqtt_simple , with a name : data_publish1() and configured it with a different topic : CONFIG_MQTT_PUB_TOPIC_1. I already updated this topic in the autoconf.h file.

I added this new function I created to the MQTT_EVT_PUBLISH event after the data_publish() function.

By doing this, I am able to publish different data to different topics now, although I think there can be an optimized method of doing this instead of creating new functions for different MQTT_topics. 

Could you let me know if there can be another method for doing this ?

Regards,

Adeel.

[Hakon]

Adeel said:

Could you let me know if there can be another method for doing this ?

 You can't use the data_publish() as it is, because the publish topic is hard coded. But you can just change the value of param.message.topic.topic.utf8 to something else.

[Adeel]

Hi Hakon,

Hakon said:

 You can't use the data_publish() as it is, because the publish topic is hard coded.

Yeah I understand this now. 

I added another function : data_publish1() like this : 

/**@brief Function to publish data on the configured topic
 */
static int data_publish(struct mqtt_client *c, enum mqtt_qos qos,
	u8_t *data, size_t len)
{
	struct mqtt_publish_param param;

	param.message.topic.qos = qos;
	param.message.topic.topic.utf8 = CONFIG_MQTT_PUB_TOPIC;
	param.message.topic.topic.size = strlen(CONFIG_MQTT_PUB_TOPIC);
	param.message.payload.data = data;
	param.message.payload.len = len;
	param.message_id = sys_rand32_get();
	param.dup_flag = 0;
	param.retain_flag = 0;

	data_print("Publishing: ", data, len);
	printk("to topic: %s len: %u\n",
		CONFIG_MQTT_PUB_TOPIC,
		(unsigned int)strlen(CONFIG_MQTT_PUB_TOPIC));

	return mqtt_publish(c, &param);
}


/**@brief Function to publish data on the configured topic
 */
static int data_publish1(struct mqtt_client *c, enum mqtt_qos qos,
	u8_t *data, size_t len)
{
	struct mqtt_publish_param param;

	param.message.topic.qos = qos;
	param.message.topic.topic.utf8 = CONFIG_MQTT_PUB_TOPIC_1;
	param.message.topic.topic.size = strlen(CONFIG_MQTT_PUB_TOPIC_1);
	param.message.payload.data = data;
	param.message.payload.len = len;
	param.message_id = sys_rand32_get();
	param.dup_flag = 0;
	param.retain_flag = 0;

	data_print("Publishing: ", data, len);
	printk("to topic: %s len: %u\n",
		CONFIG_MQTT_PUB_TOPIC_1,
		(unsigned int)strlen(CONFIG_MQTT_PUB_TOPIC_1));

	return mqtt_publish(c, &param);
}

In the autoconf.h file, I added : 

#define CONFIG_MQTT_PUB_TOPIC "sensorstest1/nrf352656101119801/pressure"
#define CONFIG_MQTT_PUB_TOPIC_1 "sensorstest1/nrf352656101119801/humidity"

In the MQTT_EVENT_PUBLISH: , i added : 

case MQTT_EVT_PUBLISH: {
		const struct mqtt_publish_param *p = &evt->param.publish;

		printk("[%s:%d] MQTT PUBLISH result=%d len=%d\n", __func__,
		       __LINE__, evt->result, p->message.payload.len);
		err = publish_get_payload(c, p->message.payload.len);
		if (err >= 0) {
			data_print("Received: ", payload_buf,
				p->message.payload.len);
			/* Echo back received data */
			data_publish(&client, MQTT_QOS_1_AT_LEAST_ONCE,
				payload_buf, p->message.payload.len);
                        data_publish1(&client, MQTT_QOS_1_AT_LEAST_ONCE,
				payload_buf, p->message.payload.len);

This made it work as I am able to publish on different topic.

Is it possible to have just one data_publish function wherein I can publish to various topics ? (only if possible, otherwise the above mentioned method is working :) ).

Regards,

Adeel.

[Hakon]

Adeel said:

Is it possible to have just one data_publish function wherein I can publish to various topics ?

 Yes, it should be possible to use the same function if you just change the content of param.message.topic.topic.utf8 between each time you call mqtt_publish(). No need to have two separate functions, just change the publish topic inside the data_publish() function. Does that make sense?