int download_callback(request_t *req, char *data, int len)
{
    list_t *found = req->response->header;
    while(found->next != NULL) {
        found = found->next;
        ESP_LOGI(TAG,"Response header %s:%s", (char*)found->key, (char*)found->value);
    }
    //or 
    found = list_get_key(req->response->header, "Content-Length");
    if(found) {
        ESP_LOGI(TAG,"Get header %s:%s", (char*)found->key, (char*)found->value);
    }
    ESP_LOGI(TAG,"%s", data);
    return 0;
}
static void request_task(void *pvParameters)
{
    request_t *req;
    int status;
    xEventGroupWaitBits(wifi_event_group, CONNECTED_BIT, false, true, portMAX_DELAY);
    ESP_LOGI(TAG, "Connected to AP, freemem=%d",esp_get_free_heap_size());
    // vTaskDelay(1000/portTICK_RATE_MS);
    req = req_new("http:https://httpbin.org/post"); 
    //or
    //request *req = req_new("https://google.com"); //for SSL
    req_setopt(req, REQ_SET_METHOD, "POST");
    req_setopt(req, REQ_SET_POSTFIELDS, "test=data&test2=data2");
    req_setopt(req, REQ_FUNC_DOWNLOAD_CB, download_callback);
    status = req_perform(req);
    req_clean(req);
    vTaskDelete(NULL);
}