1
2 /* Copyright 1998 by the Massachusetts Institute of Technology.
3 *
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.
15 */
16
17 #include "ares_setup.h"
18
19 #ifdef HAVE_SYS_SOCKET_H
20 # include <sys/socket.h>
21 #endif
22 #ifdef HAVE_NETINET_IN_H
23 # include <netinet/in.h>
24 #endif
25 #ifdef HAVE_ARPA_NAMESER_H
26 # include <arpa/nameser.h>
27 #else
28 # include "nameser.h"
29 #endif
30 #ifdef HAVE_ARPA_NAMESER_COMPAT_H
31 # include <arpa/nameser_compat.h>
32 #endif
33
34 #include <stdlib.h>
35 #include <string.h>
36 #include "ares.h"
37 #include "ares_dns.h"
38 #include "ares_private.h"
39
40 /* Header format, from RFC 1035:
41 * 1 1 1 1 1 1
42 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
43 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
44 * | ID |
45 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
46 * |QR| Opcode |AA|TC|RD|RA| Z | RCODE |
47 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
48 * | QDCOUNT |
49 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
50 * | ANCOUNT |
51 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
52 * | NSCOUNT |
53 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
54 * | ARCOUNT |
55 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
56 *
57 * AA, TC, RA, and RCODE are only set in responses. Brief description
58 * of the remaining fields:
59 * ID Identifier to match responses with queries
60 * QR Query (0) or response (1)
61 * Opcode For our purposes, always QUERY
62 * RD Recursion desired
63 * Z Reserved (zero)
64 * QDCOUNT Number of queries
65 * ANCOUNT Number of answers
66 * NSCOUNT Number of name server records
67 * ARCOUNT Number of additional records
68 *
69 * Question format, from RFC 1035:
70 * 1 1 1 1 1 1
71 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
72 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
73 * | |
74 * / QNAME /
75 * / /
76 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
77 * | QTYPE |
78 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
79 * | QCLASS |
80 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
81 *
82 * The query name is encoded as a series of labels, each represented
83 * as a one-byte length (maximum 63) followed by the text of the
84 * label. The list is terminated by a label of length zero (which can
85 * be thought of as the root domain).
86 */
87
ares_mkquery(const char * name,int dnsclass,int type,unsigned short id,int rd,unsigned char ** buf,int * buflen)88 int ares_mkquery(const char *name, int dnsclass, int type, unsigned short id,
89 int rd, unsigned char **buf, int *buflen)
90 {
91 int len;
92 unsigned char *q;
93 const char *p;
94
95 /* Set our results early, in case we bail out early with an error. */
96 *buflen = 0;
97 *buf = NULL;
98
99 /* Compute the length of the encoded name so we can check buflen.
100 * Start counting at 1 for the zero-length label at the end. */
101 len = 1;
102 for (p = name; *p; p++)
103 {
104 if (*p == '\\' && *(p + 1) != 0)
105 p++;
106 len++;
107 }
108 /* If there are n periods in the name, there are n + 1 labels, and
109 * thus n + 1 length fields, unless the name is empty or ends with a
110 * period. So add 1 unless name is empty or ends with a period.
111 */
112 if (*name && *(p - 1) != '.')
113 len++;
114
115 /* Immediately reject names that are longer than the maximum of 255
116 * bytes that's specified in RFC 1035 ("To simplify implementations,
117 * the total length of a domain name (i.e., label octets and label
118 * length octets) is restricted to 255 octets or less."). We aren't
119 * doing this just to be a stickler about RFCs. For names that are
120 * too long, 'dnscache' closes its TCP connection to us immediately
121 * (when using TCP) and ignores the request when using UDP, and
122 * BIND's named returns ServFail (TCP or UDP). Sending a request
123 * that we know will cause 'dnscache' to close the TCP connection is
124 * painful, since that makes any other outstanding requests on that
125 * connection fail. And sending a UDP request that we know
126 * 'dnscache' will ignore is bad because resources will be tied up
127 * until we time-out the request.
128 */
129 if (len > MAXCDNAME)
130 return ARES_EBADNAME;
131
132 *buflen = len + HFIXEDSZ + QFIXEDSZ;
133 *buf = malloc(*buflen);
134 if (!*buf)
135 return ARES_ENOMEM;
136
137 /* Set up the header. */
138 q = *buf;
139 memset(q, 0, HFIXEDSZ);
140 DNS_HEADER_SET_QID(q, id);
141 DNS_HEADER_SET_OPCODE(q, QUERY);
142 if (rd) {
143 DNS_HEADER_SET_RD(q, 1);
144 }
145 else {
146 DNS_HEADER_SET_RD(q, 0);
147 }
148 DNS_HEADER_SET_QDCOUNT(q, 1);
149
150 /* A name of "." is a screw case for the loop below, so adjust it. */
151 if (strcmp(name, ".") == 0)
152 name++;
153
154 /* Start writing out the name after the header. */
155 q += HFIXEDSZ;
156 while (*name)
157 {
158 if (*name == '.')
159 return ARES_EBADNAME;
160
161 /* Count the number of bytes in this label. */
162 len = 0;
163 for (p = name; *p && *p != '.'; p++)
164 {
165 if (*p == '\\' && *(p + 1) != 0)
166 p++;
167 len++;
168 }
169 if (len > MAXLABEL)
170 return ARES_EBADNAME;
171
172 /* Encode the length and copy the data. */
173 *q++ = (unsigned char)len;
174 for (p = name; *p && *p != '.'; p++)
175 {
176 if (*p == '\\' && *(p + 1) != 0)
177 p++;
178 *q++ = *p;
179 }
180
181 /* Go to the next label and repeat, unless we hit the end. */
182 if (!*p)
183 break;
184 name = p + 1;
185 }
186
187 /* Add the zero-length label at the end. */
188 *q++ = 0;
189
190 /* Finish off the question with the type and class. */
191 DNS_QUESTION_SET_TYPE(q, type);
192 DNS_QUESTION_SET_CLASS(q, dnsclass);
193
194 return ARES_SUCCESS;
195 }
196