size_t cs_dynamic_data_nnbuf_get_required_alloc_size(size_t max_payload_size, size_t records_count);
void* cs_dynamic_data_nnbuf_add_record(void* buf, size_t record_size);
void cs_dynamic_data_nnbuf_finalize(void* buf, Source queue_type);
size_t cs_dynamic_data_get_current_content_size(const void* buf);

payload_size = content_size = alloc_size - header_size
//comment that payload_size contains dynamic record headers (sizes)

size_t s = cs_nnbuf_get_required_alloc_size(1000);
void* buf = nn_alloc(s);

if (cs_dynamic_data_get_current_content_size(buf) + 500 < 1000) { // 0 -> true
    void* rec = cs_dynamic_data_nnbuf_add_record(buf, 500);
    memcpy(rec);
} else {
    cs_dynamic_data_nnbuf_finalize(buf, 0x8);
    nn_send(&buf);
}

if (cs_dynamic_data_get_current_content_size(buf) + 500 < 1000) { // 504 -> false
    void* rec = cs_dynamic_data_nnbuf_add_record(buf, 500);
    memcpy(rec);
} else {
    cs_dynamic_data_nnbuf_finalize(buf, 0x8);
    nn_send(&buf);
}