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diff --git a/ares/ares_dns.h b/ares/ares_dns.h
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+/* $Id$ */
+
+/* Copyright 1998 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.
+ */
+
+#ifndef ARES__DNS_H
+#define ARES__DNS_H
+
+#define DNS__16BIT(p) (((p)[0] << 8) | (p)[1])
+#define DNS__32BIT(p) (((p)[0] << 24) | ((p)[1] << 16) | \
+ ((p)[2] << 8) | (p)[3])
+#define DNS__SET16BIT(p, v) (((p)[0] = ((v) >> 8) & 0xff), \
+ ((p)[1] = (v) & 0xff))
+#define DNS__SET32BIT(p, v) (((p)[0] = ((v) >> 24) & 0xff), \
+ ((p)[1] = ((v) >> 16) & 0xff), \
+ ((p)[2] = ((v) >> 8) & 0xff), \
+ ((p)[3] = (v) & 0xff))
+
+/* 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] |= (((v) & 0x1) << 7))
+#define DNS_HEADER_SET_OPCODE(h, v) ((h)[2] |= (((v) & 0xf) << 3))
+#define DNS_HEADER_SET_AA(h, v) ((h)[2] |= (((v) & 0x1) << 2))
+#define DNS_HEADER_SET_TC(h, v) ((h)[2] |= (((v) & 0x1) << 1))
+#define DNS_HEADER_SET_RD(h, v) ((h)[2] |= (((v) & 0x1)))
+#define DNS_HEADER_SET_RA(h, v) ((h)[3] |= (((v) & 0x1) << 7))
+#define DNS_HEADER_SET_Z(h, v) ((h)[3] |= (((v) & 0x7) << 4))
+#define DNS_HEADER_SET_RCODE(h, v) ((h)[3] |= (((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) DNS__SET16BIT(r, v)
+#define DNS_RR_SET_CLASS(r) DNS__SET16BIT((r) + 2, v)
+#define DNS_RR_SET_TTL(r) DNS__SET32BIT((r) + 4, v)
+#define DNS_RR_SET_LEN(r) DNS__SET16BIT((r) + 8, v)
+
+#endif /* ARES__DNS_H */