Receiving JSON

Within the wifi-multiplexer.c file , we begin by instantiating a HTTP response handler static esp_err_t get_json_handler(httpd_req_t *req) . After which the function proceeds as follows ..

static esp_err_t get_json_handler(httpd_req_t *req)
{
    cJSON *root = cJSON_CreateObject();

    cJSON_AddStringToObject(root, "device", "ESP32");
    cJSON_AddNumberToObject(root, "uptime", esp_timer_get_time() / 1000000); // seconds
    cJSON_AddBoolToObject(root, "led_state", gpio_get_level(LED_PIN));

    cJSON *measurements = cJSON_CreateArray();
    for (int i = 0; i < 3; i++) {
        cJSON *measurement = cJSON_CreateObject();
        cJSON_AddNumberToObject(measurement, "value", i * 10);
        cJSON_AddNumberToObject(measurement, "timestamp", esp_timer_get_time() + i);
        cJSON_AddItemToArray(measurements, measurement);
    }
    cJSON_AddItemToObject(root, "measurements", measurements);

    char *json_string = cJSON_Print(root);

    httpd_resp_set_type(req, "application/json");
    httpd_resp_send(req, json_string, strlen(json_string));

    free(json_string);
    cJSON_Delete(root);

    return ESP_OK;
}

Here we create a JSON Object with the handle root . After which we assign fields to the JSON Object , namely

• "device" is assigned the string value "ESP32".
• "uptime" is assigned the unsigned integer value of uptime in seconds .
• "led_state" is assigned a boolean value with the state of the LED .