OPT_LEN
if (!buffer_available(packet, (OPT_LEN + OPT_RDATA)))
: (OPT_LEN + OPT_RDATA + edns->opt_reserved_space);
unsigned char ok[OPT_LEN];
unsigned char error[OPT_LEN];
buffer_limit(q->packet) >= QHEADERSZ+OPT_LEN+
buffer_write(q->packet, edns->ok, OPT_LEN);
buffer_write(q->packet, edns->error, OPT_LEN);