CHECKSUM_LEN
if (req->wlen > (BUF_LEN - REQ_HDR_LEN - CHECKSUM_LEN) ||
req->rlen > (BUF_LEN - ACK_HDR_LEN - CHECKSUM_LEN)) {
state->buf[0] = REQ_HDR_LEN + req->wlen + CHECKSUM_LEN - 1;
wlen = REQ_HDR_LEN + req->wlen + CHECKSUM_LEN;
rlen = ACK_HDR_LEN + req->rlen + CHECKSUM_LEN;