CTAP_INIT_HEADER_LEN
#define CTAP_MIN_REPORT_LEN (CTAP_INIT_HEADER_LEN + 1)
uint8_t data[CTAP_MAX_REPORT_LEN - CTAP_INIT_HEADER_LEN];
if (d->rx_len <= CTAP_INIT_HEADER_LEN ||
init_data_len = d->rx_len - CTAP_INIT_HEADER_LEN;
if (d->tx_len - CTAP_INIT_HEADER_LEN > sizeof(fp->body.init.data))
count = MIN(count, d->tx_len - CTAP_INIT_HEADER_LEN);