2 raw DNS packet parsing routines
4 Copyright (C) 2005 Michael Tokarev <mjt@corpit.ru>
5 This file is part of UDNS library, an async DNS stub resolver.
7 This library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
12 This library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
17 You should have received a copy of the GNU Lesser General Public
18 License along with this library, in file named COPYING.LGPL; if not,
19 write to the Free Software Foundation, Inc., 59 Temple Place,
20 Suite 330, Boston, MA 02111-1307 USA
28 dnscc_t *dns_skipdn(dnscc_t *cur, dnscc_t *end) {
36 if (c & 192) /* jump */
37 return cur + 1 >= end ? NULL : cur + 1;
43 dns_getdn(dnscc_t *pkt, dnscc_t **cur, dnscc_t *end,
44 register dnsc_t *dn, unsigned dnsiz) {
46 dnscc_t *pp = *cur; /* current packet pointer */
47 dnsc_t *dp = dn; /* current dn pointer */
48 dnsc_t *const de /* end of the DN dest */
49 = dn + (dnsiz < DNS_MAXDN ? dnsiz : DNS_MAXDN);
50 dnscc_t *jump = NULL; /* ptr after first jump if any */
51 unsigned loop = 100; /* jump loop counter */
53 for(;;) { /* loop by labels */
54 if (pp >= end) /* reached end of packet? */
56 c = *pp++; /* length of the label */
57 if (!c) { /* empty label: terminate */
58 if (dn >= de) /* can't fit terminator */
61 /* return next pos: either after the first jump or current */
62 *cur = jump ? jump : pp;
65 if (c & 192) { /* jump */
66 if (pp >= end) /* eop instead of jump pos */
68 if (!jump) jump = pp + 1; /* remember first jump */
69 else if (!--loop) return -1; /* too many jumps */
70 c = ((c & ~192) << 8) | *pp; /* new pos */
71 if (c < DNS_HSIZE) /* don't allow jump into the header */
76 if (c > DNS_MAXLABEL) /* too long label? */
78 if (pp + c > end) /* label does not fit in packet? */
80 if (dp + c + 1 > de) /* if enouth room for the label */
82 *dp++ = c; /* label length */
83 memcpy(dp, pp, c); /* and the label itself */
85 pp += c; /* advance to the next label */
88 return dnsiz < DNS_MAXDN ? 0 : -1;
91 void dns_rewind(struct dns_parse *p, dnscc_t *qdn) {
93 p->dnsp_cur = p->dnsp_ans;
94 p->dnsp_rrl = dns_numan(p->dnsp_pkt);
95 p->dnsp_ttl = 0xffffffffu;
100 dns_initparse(struct dns_parse *p, dnscc_t *qdn,
101 dnscc_t *pkt, dnscc_t *cur, dnscc_t *end) {
104 p->dnsp_rrl = dns_numan(pkt);
106 assert(cur + 4 <= end);
107 if ((p->dnsp_qtyp = dns_get16(cur+0)) == DNS_T_ANY) p->dnsp_qtyp = 0;
108 if ((p->dnsp_qcls = dns_get16(cur+2)) == DNS_C_ANY) p->dnsp_qcls = 0;
109 p->dnsp_cur = p->dnsp_ans = cur + 4;
110 p->dnsp_ttl = 0xffffffffu;
114 int dns_nextrr(struct dns_parse *p, struct dns_rr *rr) {
115 dnscc_t *cur = p->dnsp_cur;
116 while(p->dnsp_rrl > 0) {
118 if (dns_getdn(p->dnsp_pkt, &cur, p->dnsp_end,
119 rr->dnsrr_dn, sizeof(rr->dnsrr_dn)) <= 0)
121 if (cur + 10 > p->dnsp_end)
123 rr->dnsrr_typ = dns_get16(cur);
124 rr->dnsrr_cls = dns_get16(cur+2);
125 rr->dnsrr_ttl = dns_get32(cur+4);
126 rr->dnsrr_dsz = dns_get16(cur+8);
127 rr->dnsrr_dptr = cur = cur + 10;
128 rr->dnsrr_dend = cur = cur + rr->dnsrr_dsz;
129 if (cur > p->dnsp_end)
131 if (p->dnsp_qdn && !dns_dnequal(p->dnsp_qdn, rr->dnsrr_dn))
133 if ((!p->dnsp_qcls || p->dnsp_qcls == rr->dnsrr_cls) &&
134 (!p->dnsp_qtyp || p->dnsp_qtyp == rr->dnsrr_typ)) {
137 if (p->dnsp_ttl > rr->dnsrr_ttl) p->dnsp_ttl = rr->dnsrr_ttl;
140 if (p->dnsp_qdn && rr->dnsrr_typ == DNS_T_CNAME && !p->dnsp_nrr) {
141 if (dns_getdn(p->dnsp_pkt, &rr->dnsrr_dptr, p->dnsp_end,
142 p->dnsp_dnbuf, sizeof(p->dnsp_dnbuf)) <= 0 ||
143 rr->dnsrr_dptr != rr->dnsrr_dend)
145 p->dnsp_qdn = p->dnsp_dnbuf;
146 if (p->dnsp_ttl > rr->dnsrr_ttl) p->dnsp_ttl = rr->dnsrr_ttl;
153 int dns_stdrr_size(const struct dns_parse *p) {
155 dns_dntop_size(p->dnsp_qdn) +
156 (p->dnsp_qdn == dns_payload(p->dnsp_pkt) ? 0 :
157 dns_dntop_size(dns_payload(p->dnsp_pkt)));
160 void *dns_stdrr_finish(struct dns_rr_null *ret, char *cp,
161 const struct dns_parse *p) {
162 cp += dns_dntop(p->dnsp_qdn, (ret->dnsn_cname = cp), DNS_MAXNAME);
163 if (p->dnsp_qdn == dns_payload(p->dnsp_pkt))
164 ret->dnsn_qname = ret->dnsn_cname;
166 dns_dntop(dns_payload(p->dnsp_pkt), (ret->dnsn_qname = cp), DNS_MAXNAME);
167 ret->dnsn_ttl = p->dnsp_ttl;