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 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
