Mqtt simple nrf9160, send JSON as utf-8

[David]

Hi,

I have configured the MQTT simple sample from nordic to send data to our broker, this works just fine at the moment.

I would like to send Json formated data to the broker ----->

{
"sensor_id": "c5278fbf-c6d5-4c48-b51d-652beb609b34",
"value": 13.0
}

When I subscribe to topic, I only see "{" as incoming data.

How can I make sure that the Json data is correctly formated i code ?

Any assistance would be appreciated.

I am using the <cJSON.h> library.

char field_name[80], value[80], *out;
                cJSON *root,*car;



                //char str1[80] = "{'sensor_id:' 'c5278fbf-c6d5-4c48-b51d-652beb609b34','value:' 13.0}";

                root  = cJSON_CreateObject();
                car=  cJSON_CreateArray();

                cJSON_AddItemToObject(root, "sensor_id", cJSON_CreateString("c5278fbf-c6d5-4c48-b51d-652beb609b34"));
                cJSON_AddItemToObject(root, "value", cJSON_CreateString("12"));
                cJSON_AddItemToArray(car, root);

                out = cJSON_Print(root);
                printk(out);
                //char out1 = {"sensor_id"":""c5278fbf-c6d5-4c48-b51d-652beb609b34","value"":""13.0"};
                k_sleep(K_MSEC(5000));
                data_publish(&client, MQTT_QOS_1_AT_LEAST_ONCE, car, sizeof(car));
                k_sleep(K_MSEC(5000));

David

[David]

I managed to adapt the example, so now I only need to remove the quotes "" from the value1 "13.0".

Do you have an idea how to do this?

David

[Carl Richard]

You do not want the "sensors" array on top. Do interpret it correctly? 

Best regards,
Carl Richard 

[David]

I want it like this --->

{
"sensor_id": "c5278fbf-c6d5-4c48-b51d-652beb609b34",
"value": "13.0"
}

without the quotes around 13.0

David

[Carl Richard]

Hi again, David!

I've rewritten it to your configuration. However, there is an issue with the cJSON library that prevents it from handling doubles from what I could tell. Therefore you need to convert from string (i.e. "13.0") to float (i.e. 13.0) on the cloud end. 

static void transmit()
{
	char *out;
	char *id1 = "c5278fbf-c6d5-4c48-b51d-652beb609b34";

	char value_buf[6];
	double value = 13.0;

	snprintf(value_buf, sizeof(value_buf), "%.1f",
	value);

	printk("Value: %s\n", value_buf);

	cJSON *root;

	/* create root node and array */
	root = cJSON_CreateObject();	

	/* add sensor data */
	cJSON_AddItemToObject(root, "sensor_id", cJSON_CreateString(id1));
	cJSON_AddItemToObject(root, "value", cJSON_CreateString(value_buf));

	/* print everything */
	out = cJSON_Print(root);
	if (out == NULL) {
		printk("Failed print...\n");
	}
    printk("%s\n", out);

	/* Publish with MQTT */
	data_publish(&client, MQTT_QOS_1_AT_LEAST_ONCE,
   			out, strlen(out));

	free(out);

	/* free all objects under root and root itself */
	cJSON_Delete(root);

	return;
}

I hope this works out!

Best regards,
Carl Richard

[Carl Richard]

Hi again, David!

If you want to use numbers with the cJSON library, have a look at my answer here. The important part is to include cJSON_OS.h and call cJSON_Init at the start of main.
Remember that CONFIG_HEAP_MEM_POOL_SIZE and CONFIG_MAIN_STACK_SIZE must be non-zero values.

Best regards,
Carl Richard