Using JSON with nRF5340 and nRF Connect

[garrettb]

Hi

Are there any examples of how to use JSON with nRF5340 DK (or similar) and nRF Connect?

I am using SDK v2.4.1.

I found these files:

c:\ncs\v2.4.1\nrf\ext\iperf3\cjson.c and cjson.h

I wasn't able to include them, so I just copied them to my project folder.\I had to comment out the " iperf_config.h" include in  cjson.h.

I was able to write some basic code:

	cJSON *json_obj;
	cJSON *json_item;
	bool b_result;
	const char *key_str = "key_1";
	char *val_str = "value_1";
	char *json_str = NULL;


	// Create empty JSON object
	json_obj = cJSON_CreateObject();
	// Create a JSON item
	json_item = cJSON_CreateString(val_str);
	// Add an item to this object
	b_result = cJSON_AddItemToObject(json_obj, key_str, json_item);
	// Print the full string
	json_str = cJSON_Print(json_obj);
	// Finished with object, so delete it!
	cJSON_Delete(json_obj);

Initially I got some error about CONFIG_MINIMAL_LIBC_MALLOC_ARENA_SIZE being 0, so in the prj.conf file I set:

CONFIG_MINIMAL_LIBC_MALLOC=y
CONFIG_MINIMAL_LIBC_MALLOC_ARENA_SIZE=1000

This builds if I comment out the call to cJSON_Print().

I can continue to work with this - although I don't understand how I would eventually "release" the json_str created by cJSON_Print() etc.

So I was hoping there was sample code out there, with the correct includes etc.

[JamesDougherty]

FYI - I mocked up quick samples to show how I parse JSON and create the JSON strings. I didn't test these, but it should get you started.

Create JSON String

static bool sample_create_json(void)
{
    // 1 - Create the root object
    cJSON *root = cJSON_CreateObject();

    if (!root)
    {
        printk("Unable to create root CJSON object.\n");
        return false;
    }

    // 2 - Add items
    cJSON *numberItem = cJSON_AddNumberToObjectCS(root, "name", 123);

    if (!numberItem)
    {
        printk("Unable to create JSON object.\n");
        cJSON_Delete(root);
        return false;
    }

    // Add other values as needed

    // 3 - Create the JSON string
    char *json = cJSON_PrintUnformatted(root);

    if (!json)
    {
        printk("Unable to create JSON string.\n");
        cJSON_Delete(root);
        return false;
    }

    // 4 - Do something with the JSON that was created

    // 5 - Always free the memory that was allocated.
    cJSON_Delete(root);
    return true;
}

Parse JSON String

static bool sample_parse_json(const char *json)
{
    __ASSERT_NO_MSG(json);

    // 1 - Parse the JSON
    cJSON *root = cJSON_Parse(json);

    // 2 - Verify it was parsed correctly
    if (!root)
    {
        const char *error = cJSON_GetErrorPtr();

        if (error)
        {
            printk("JSON Parse Error: %s\n", error);
        }

        return false;
    }

    // 3 - Do something with the parsed data
    for (cJSON *item = root; item; item = item->next)
    {
        const cJSON *child = item->child;

        while (child)
        {
            if (cJSON_IsNumber(child))
            {
                // Process number
            }
            else if (cJSON_IsString(child))
            {
                // Process string
            }
            else if (cJSON_IsArray(child))
            {
                // Process array
            }
            else
            {
                // Etc...
            }

            child = child->next;
        }
    }

    // 5 - Always free the memory that was allocated.
    cJSON_Delete(root);
    return true;
}

[garrettb]

This looks like really good info thanks - it'll be a few days before I get to work with - will let you know