2 /* Copyright 1998 by the Massachusetts Institute of Technology.
4 * Permission to use, copy, modify, and distribute this
5 * software and its documentation for any purpose and without
6 * fee is hereby granted, provided that the above copyright
7 * notice appear in all copies and that both that copyright
8 * notice and this permission notice appear in supporting
9 * documentation, and that the name of M.I.T. not be used in
10 * advertising or publicity pertaining to distribution of the
11 * software without specific, written prior permission.
12 * M.I.T. makes no representations about the suitability of
13 * this software for any purpose. It is provided "as is"
14 * without express or implied warranty.
17 #include "ares_setup.h"
19 #ifdef HAVE_NETINET_IN_H
20 # include <netinet/in.h>
23 #include "ares_nameser.h"
27 #include "ares_private.h"
30 /* Header format, from RFC 1035:
32 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
33 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
35 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
36 * |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
37 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
39 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
41 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
43 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
45 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
47 * AA, TC, RA, and RCODE are only set in responses. Brief description
48 * of the remaining fields:
49 * ID Identifier to match responses with queries
50 * QR Query (0) or response (1)
51 * Opcode For our purposes, always O_QUERY
52 * RD Recursion desired
54 * QDCOUNT Number of queries
55 * ANCOUNT Number of answers
56 * NSCOUNT Number of name server records
57 * ARCOUNT Number of additional records
59 * Question format, from RFC 1035:
61 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
62 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
66 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
68 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
70 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
72 * The query name is encoded as a series of labels, each represented
73 * as a one-byte length (maximum 63) followed by the text of the
74 * label. The list is terminated by a label of length zero (which can
75 * be thought of as the root domain).
78 int ares_create_query(const char *name, int dnsclass, int type,
79 unsigned short id, int rd, unsigned char **bufp,
80 int *buflenp, int max_udp_size)
88 /* Set our results early, in case we bail out early with an error. */
92 /* Per RFC 7686, reject queries for ".onion" domain names with NXDOMAIN. */
93 if (ares__is_onion_domain(name))
94 return ARES_ENOTFOUND;
96 /* Allocate a memory area for the maximum size this packet might need. +2
97 * is for the length byte and zero termination if no dots or ecscaping is
100 len = strlen(name) + 2 + HFIXEDSZ + QFIXEDSZ +
101 (max_udp_size ? EDNSFIXEDSZ : 0);
102 buf = ares_malloc(len);
106 /* Set up the header. */
108 memset(q, 0, HFIXEDSZ);
109 DNS_HEADER_SET_QID(q, id);
110 DNS_HEADER_SET_OPCODE(q, O_QUERY);
112 DNS_HEADER_SET_RD(q, 1);
115 DNS_HEADER_SET_RD(q, 0);
117 DNS_HEADER_SET_QDCOUNT(q, 1);
120 DNS_HEADER_SET_ARCOUNT(q, 1);
123 /* A name of "." is a screw case for the loop below, so adjust it. */
124 if (strcmp(name, ".") == 0)
127 /* Start writing out the name after the header. */
133 return ARES_EBADNAME;
136 /* Count the number of bytes in this label. */
138 for (p = name; *p && *p != '.'; p++)
140 if (*p == '\\' && *(p + 1) != 0)
144 if (len > MAXLABEL) {
146 return ARES_EBADNAME;
149 /* Encode the length and copy the data. */
150 *q++ = (unsigned char)len;
151 for (p = name; *p && *p != '.'; p++)
153 if (*p == '\\' && *(p + 1) != 0)
158 /* Go to the next label and repeat, unless we hit the end. */
164 /* Add the zero-length label at the end. */
167 /* Finish off the question with the type and class. */
168 DNS_QUESTION_SET_TYPE(q, type);
169 DNS_QUESTION_SET_CLASS(q, dnsclass);
174 memset(q, 0, EDNSFIXEDSZ);
176 DNS_RR_SET_TYPE(q, T_OPT);
177 DNS_RR_SET_CLASS(q, max_udp_size);
178 q += (EDNSFIXEDSZ-1);
182 /* Reject names that are longer than the maximum of 255 bytes that's
183 * specified in RFC 1035 ("To simplify implementations, the total length of
184 * a domain name (i.e., label octets and label length octets) is restricted
185 * to 255 octets or less."). */
186 if (buflen > (size_t)(MAXCDNAME + HFIXEDSZ + QFIXEDSZ +
187 (max_udp_size ? EDNSFIXEDSZ : 0))) {
189 return ARES_EBADNAME;
192 /* we know this fits in an int at this point */
193 *buflenp = (int) buflen;