ares_dns.h

#ifndef HEADER_CARES_DNS_H
#define HEADER_CARES_DNS_H

/* Copyright 1998, 2011 by the Massachusetts Institute of Technology.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting
 * documentation, and that the name of M.I.T. not be used in
 * advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is"
 * without express or implied warranty.
 */

/*
 * Macro DNS__16BIT reads a network short (16 bit) given in network
 * byte order, and returns its value as an unsigned short.
 */
#define DNS__16BIT(p)  ((unsigned short)((unsigned int) 0xffff & \
                         (((unsigned int)((unsigned char)(p)[0]) << 8U) | \
                          ((unsigned int)((unsigned char)(p)[1])))))

/*
 * Macro DNS__32BIT reads a network long (32 bit) given in network
 * byte order, and returns its value as an unsigned int.
 */
#define DNS__32BIT(p)  ((unsigned int) \
                         (((unsigned int)((unsigned char)(p)[0]) << 24U) | \
                          ((unsigned int)((unsigned char)(p)[1]) << 16U) | \
                          ((unsigned int)((unsigned char)(p)[2]) <<  8U) | \
                          ((unsigned int)((unsigned char)(p)[3]))))

#define DNS__SET16BIT(p, v)  (((p)[0] = (unsigned char)(((v) >> 8) & 0xff)), \
                              ((p)[1] = (unsigned char)((v) & 0xff)))
#define DNS__SET32BIT(p, v)  (((p)[0] = (unsigned char)(((v) >> 24) & 0xff)), \
                              ((p)[1] = (unsigned char)(((v) >> 16) & 0xff)), \
                              ((p)[2] = (unsigned char)(((v) >> 8) & 0xff)), \
                              ((p)[3] = (unsigned char)((v) & 0xff)))

#if 0
/* we cannot use this approach on systems where we can't access 16/32 bit
   data on un-aligned addresses */
#define DNS__16BIT(p)                   ntohs(*(unsigned short*)(p))
#define DNS__32BIT(p)                   ntohl(*(unsigned long*)(p))
#define DNS__SET16BIT(p, v)             *(unsigned short*)(p) = htons(v)
#define DNS__SET32BIT(p, v)             *(unsigned long*)(p) = htonl(v)
#endif

/* Macros for parsing a DNS header */
#define DNS_HEADER_QID(h)               DNS__16BIT(h)
#define DNS_HEADER_QR(h)                (((h)[2] >> 7) & 0x1)
#define DNS_HEADER_OPCODE(h)            (((h)[2] >> 3) & 0xf)
#define DNS_HEADER_AA(h)                (((h)[2] >> 2) & 0x1)
#define DNS_HEADER_TC(h)                (((h)[2] >> 1) & 0x1)
#define DNS_HEADER_RD(h)                ((h)[2] & 0x1)
#define DNS_HEADER_RA(h)                (((h)[3] >> 7) & 0x1)
#define DNS_HEADER_Z(h)                 (((h)[3] >> 4) & 0x7)
#define DNS_HEADER_RCODE(h)             ((h)[3] & 0xf)
#define DNS_HEADER_QDCOUNT(h)           DNS__16BIT((h) + 4)
#define DNS_HEADER_ANCOUNT(h)           DNS__16BIT((h) + 6)
#define DNS_HEADER_NSCOUNT(h)           DNS__16BIT((h) + 8)
#define DNS_HEADER_ARCOUNT(h)           DNS__16BIT((h) + 10)

/* Macros for constructing a DNS header */
#define DNS_HEADER_SET_QID(h, v)      DNS__SET16BIT(h, v)
#define DNS_HEADER_SET_QR(h, v)       ((h)[2] |= (unsigned char)(((v) & 0x1) << 7))
#define DNS_HEADER_SET_OPCODE(h, v)   ((h)[2] |= (unsigned char)(((v) & 0xf) << 3))
#define DNS_HEADER_SET_AA(h, v)       ((h)[2] |= (unsigned char)(((v) & 0x1) << 2))
#define DNS_HEADER_SET_TC(h, v)       ((h)[2] |= (unsigned char)(((v) & 0x1) << 1))
#define DNS_HEADER_SET_RD(h, v)       ((h)[2] |= (unsigned char)((v) & 0x1))
#define DNS_HEADER_SET_RA(h, v)       ((h)[3] |= (unsigned char)(((v) & 0x1) << 7))
#define DNS_HEADER_SET_Z(h, v)        ((h)[3] |= (unsigned char)(((v) & 0x7) << 4))
#define DNS_HEADER_SET_RCODE(h, v)    ((h)[3] |= (unsigned char)((v) & 0xf))
#define DNS_HEADER_SET_QDCOUNT(h, v)  DNS__SET16BIT((h) + 4, v)
#define DNS_HEADER_SET_ANCOUNT(h, v)  DNS__SET16BIT((h) + 6, v)
#define DNS_HEADER_SET_NSCOUNT(h, v)  DNS__SET16BIT((h) + 8, v)
#define DNS_HEADER_SET_ARCOUNT(h, v)  DNS__SET16BIT((h) + 10, v)

/* Macros for parsing the fixed part of a DNS question */
#define DNS_QUESTION_TYPE(q)            DNS__16BIT(q)
#define DNS_QUESTION_CLASS(q)           DNS__16BIT((q) + 2)

/* Macros for constructing the fixed part of a DNS question */
#define DNS_QUESTION_SET_TYPE(q, v)     DNS__SET16BIT(q, v)
#define DNS_QUESTION_SET_CLASS(q, v)    DNS__SET16BIT((q) + 2, v)

/* Macros for parsing the fixed part of a DNS resource record */
#define DNS_RR_TYPE(r)                  DNS__16BIT(r)
#define DNS_RR_CLASS(r)                 DNS__16BIT((r) + 2)
#define DNS_RR_TTL(r)                   DNS__32BIT((r) + 4)
#define DNS_RR_LEN(r)                   DNS__16BIT((r) + 8)

/* Macros for constructing the fixed part of a DNS resource record */
#define DNS_RR_SET_TYPE(r, v)           DNS__SET16BIT(r, v)
#define DNS_RR_SET_CLASS(r, v)          DNS__SET16BIT((r) + 2, v)
#define DNS_RR_SET_TTL(r, v)            DNS__SET32BIT((r) + 4, v)
#define DNS_RR_SET_LEN(r, v)            DNS__SET16BIT((r) + 8, v)

#endif /* HEADER_CARES_DNS_H */