Extracting topic data from JSON topic received from AWS broker (using nRF9160dk)

RE: Extracting topic data from JSON topic received from AWS broker (using nRF9160dk)

garrettb — Thu, 31 Mar 2022 08:06:22 GMT

Thank you Dejan

You are correct - and I got it working.

Below is an example of how it worked for me.

Again, this is rough and ready - just trying to get the concept etc.

	cJSON *objState;
	cJSON *objDesired;
	cJSON *objBatval;
	cJSON *json_parsed = cJSON_Parse(str);

	objState = cJSON_GetObjectItemCaseSensitive(json_parsed, "state");
	if (objState == NULL)
	{
		printk("\n3a objState is null");
	} else {
		str2 = cJSON_Print(objState);
		json_parsed = cJSON_Parse(str2);
		objDesired = cJSON_GetObjectItemCaseSensitive(json_parsed, "desired");
		if (objDesired == NULL)
		{
			printk("\n3b objDesired is null");
		} else {
			str2 = cJSON_Print(objDesired);
			json_parsed = cJSON_Parse(str2);
			objBatval = cJSON_GetObjectItemCaseSensitive(json_parsed, "batv");
			if (objBatval == NULL)
			{
				printk("\n3c objBatval is null");
			} else {
				printk("\n3d objBatval is NOT null");
				str2 = cJSON_Print(objBatval);
				printk("\n3e ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");
				printk("objBatval: %s\n", str2);
				printk("\n3f ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");
			}
		}
	}

Regards

Garrett

RE: Extracting topic data from JSON topic received from AWS broker (using nRF9160dk)

dejans — Wed, 30 Mar 2022 11:01:42 GMT

Hi,

Currently, you are accessing batv at the root level. Based on your structure, batv cannot be read directly (as if it is in the root level) because it is nested inside "state" and "desired".

Best regards,
Dejan

RE: Extracting topic data from JSON topic received from AWS broker (using nRF9160dk)

garrettb — Tue, 29 Mar 2022 15:49:14 GMT

Hi Dejan

Thanks for the suggestion.

I have been going around in circles with this :)

Here is what I have at the moment - it's a bit messy as I have been adding a lot of debug feedback etc.

For some reason, it doesn't seem to extract the "batv" value

Code:

static void print_received_data(const char *buf, const char *topic,
				size_t topic_len)
{
	char *str = NULL;
	cJSON *root_obj = NULL;
		
	printk("\n. . . . . . . . \n");
	printk("print_received_data");
	printk("\n. . . . . . . . \n");
	printk("Received buffer: \n%s\n", buf);
	printk("Received topic: \n%s\n", topic);
	printk("Received topic len: \n%d", topic_len);
	printk("\n. . . . . . . . \n");

	printk("\n1 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");
	root_obj = cJSON_Parse(buf);
	if (root_obj == NULL) {
		printk("cJSON Parse failure");
		return;
	}

	printk("\n2 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");
	str = cJSON_Print(root_obj);
	if (str == NULL) {
		printk("Failed to print JSON object");
		goto clean_exit;
	}
	printk("\n3 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");

	cJSON *batval;
	cJSON *json_parsed = cJSON_Parse(str);
	batval = cJSON_GetObjectItemCaseSensitive(json_parsed, "batv");
	if (batval == NULL)
	{
		printk("\n3a bat_val is null");
	} else {
		char *str2 = cJSON_Print(batval);
		printk("\n3b ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");
		printk("batval: %s\n", str2);
		printk("\n3c ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");

	}
	printk("\n4 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^");

Output on the terminal:

. . . . . . . . 
print_received_data
. . . . . . . . 
Received buffer: 
{"state":{"desired":{"dbg":444,"batv":445,"dbgStr":"apples"},"reported":{"app_version":"v1.0.0","batv":5019,"ts":69521,"dbg":0,"dbgStr":""},"delta":{"dbg":444,"batv":445,"dbgStr":"apples"}},"metadata":{"desired":{"dbg":{"timestamp":1648562859},"batv":{"timestamp":1648562859},"dbgStr":{"timestamp":1648562859}},"reported":{"app_version":{"timestamp":1648567600},"batv":{"timestamp":1648567659},"ts":{"timestamp":1648567659},"dbg":{"timestamp":1648567659},"dbgStr":{"timestamp":1648567659}}},"version":2102,"timestamp":1648567687}
Received topic: 
$aws/things/my-nRF9160dk_thing01/shadow/get/accepted
Received topic len: 
57
. . . . . . . . 

1 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
3a bat_val is null
4 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

RE: Extracting topic data from JSON topic received from AWS broker (using nRF9160dk)

dejans — Tue, 29 Mar 2022 13:36:24 GMT

Hi,

Could you try replacing the line

batVal = cJSON_GetObjectItemCaseSensitive(root_obj, "batv");

with the following 2 lines

cJSON *json_parsed = cJSON_Parse(str);
batVal = cJSON_GetObjectItemCaseSensitive(json_parsed, "batv");

You could then print with

char *str2 = cJSON_Print(batVal);
printk("batVal: %s\n", str2);

Best regards,
Dejan