Gilad Arnold | 968bf19 | 2015-07-17 00:23:30 -0700 | [diff] [blame] | 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 | } |