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 ** bufp,int * buflenp)88 int ares_mkquery(const char *name, int dnsclass, int type, unsigned short id,
89 int rd, unsigned char **bufp, int *buflenp)
90 {
91 size_t len;
92 unsigned char *q;
93 const char *p;
94 size_t buflen;
95 unsigned char *buf;
96
97 /* Set our results early, in case we bail out early with an error. */
98 *buflenp = 0;
99 *bufp = NULL;
100
101 /* Allocate a memory area for the maximum size this packet might need. +2
102 * is for the length byte and zero termination if no dots or ecscaping is
103 * used.
104 */
105 len = strlen(name) + 2 + HFIXEDSZ + QFIXEDSZ;
106 buf = malloc(len);
107 if (!buf)
108 return ARES_ENOMEM;
109
110 /* Set up the header. */
111 q = buf;
112 memset(q, 0, HFIXEDSZ);
113 DNS_HEADER_SET_QID(q, id);
114 DNS_HEADER_SET_OPCODE(q, QUERY);
115 if (rd) {
116 DNS_HEADER_SET_RD(q, 1);
117 }
118 else {
119 DNS_HEADER_SET_RD(q, 0);
120 }
121 DNS_HEADER_SET_QDCOUNT(q, 1);
122
123 /* A name of "." is a screw case for the loop below, so adjust it. */
124 if (strcmp(name, ".") == 0)
125 name++;
126
127 /* Start writing out the name after the header. */
128 q += HFIXEDSZ;
129 while (*name)
130 {
131 if (*name == '.') {
132 free(buf);
133 return ARES_EBADNAME;
134 }
135
136 /* Count the number of bytes in this label. */
137 len = 0;
138 for (p = name; *p && *p != '.'; p++)
139 {
140 if (*p == '\\' && *(p + 1) != 0)
141 p++;
142 len++;
143 }
144 if (len > MAXLABEL) {
145 free(buf);
146 return ARES_EBADNAME;
147 }
148
149 /* Encode the length and copy the data. */
150 *q++ = (unsigned char)len;
151 for (p = name; *p && *p != '.'; p++)
152 {
153 if (*p == '\\' && *(p + 1) != 0)
154 p++;
155 *q++ = *p;
156 }
157
158 /* Go to the next label and repeat, unless we hit the end. */
159 if (!*p)
160 break;
161 name = p + 1;
162 }
163
164 /* Add the zero-length label at the end. */
165 *q++ = 0;
166
167 /* Finish off the question with the type and class. */
168 DNS_QUESTION_SET_TYPE(q, type);
169 DNS_QUESTION_SET_CLASS(q, dnsclass);
170
171 q += QFIXEDSZ;
172
173 buflen = (q - buf);
174
175 /* Reject names that are longer than the maximum of 255 bytes that's
176 * specified in RFC 1035 ("To simplify implementations, the total length of
177 * a domain name (i.e., label octets and label length octets) is restricted
178 * to 255 octets or less."). */
179 if (buflen > (MAXCDNAME + HFIXEDSZ + QFIXEDSZ)) {
180 free(buf);
181 return ARES_EBADNAME;
182 }
183
184 /* we know this fits in an int at this point */
185 *buflenp = (int) buflen;
186 *bufp = buf;
187
188 return ARES_SUCCESS;
189 }
190