#pragma once
struct dnsheader {
        unsigned        id :16;         /* query identification number */
#if BYTE_ORDER == BIG_ENDIAN
                        /* fields in third byte */
        unsigned        qr: 1;          /* response flag */
        unsigned        opcode: 4;      /* purpose of message */
        unsigned        aa: 1;          /* authoritative answer */
        unsigned        tc: 1;          /* truncated message */
        unsigned        rd: 1;          /* recursion desired */
                        /* fields in fourth byte */
        unsigned        ra: 1;          /* recursion available */
        unsigned        unused :1;      /* unused bits (MBZ as of 4.9.3a3) */
        unsigned        ad: 1;          /* authentic data from named */
        unsigned        cd: 1;          /* checking disabled by resolver */
        unsigned        rcode :4;       /* response code */
#elif BYTE_ORDER == LITTLE_ENDIAN || BYTE_ORDER == PDP_ENDIAN
                        /* fields in third byte */
        unsigned        rd :1;          /* recursion desired */
        unsigned        tc :1;          /* truncated message */
        unsigned        aa :1;          /* authoritative answer */
        unsigned        opcode :4;      /* purpose of message */
        unsigned        qr :1;          /* response flag */
                        /* fields in fourth byte */
        unsigned        rcode :4;       /* response code */
        unsigned        cd: 1;          /* checking disabled by resolver */
        unsigned        ad: 1;          /* authentic data from named */
        unsigned        unused :1;      /* unused bits (MBZ as of 4.9.3a3) */
        unsigned        ra :1;          /* recursion available */
#endif
                        /* remaining bytes */
        unsigned        qdcount :16;    /* number of question entries */
        unsigned        ancount :16;    /* number of answer entries */
        unsigned        nscount :16;    /* number of authority entries */
        unsigned        arcount :16;    /* number of resource entries */
};

static_assert(sizeof(dnsheader) == 12, "dnsheader size must be 12");