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[glibc.git] / resolv / nss_dns / dns-canon.c
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1 /* Copyright (C) 2004-2014 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3 Contributed by Ulrich Drepper <drepper@redhat.com>, 2004.
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
19 #include <errno.h>
20 #include <netdb.h>
21 #include <resolv.h>
22 #include <stdlib.h>
23 #include <stdint.h>
24 #include <arpa/nameser.h>
25 #include <nsswitch.h>
28 #if PACKETSZ > 65536
29 # define MAXPACKET PACKETSZ
30 #else
31 # define MAXPACKET 65536
32 #endif
35 /* We need this time later. */
36 typedef union querybuf
38 HEADER hdr;
39 unsigned char buf[MAXPACKET];
40 } querybuf;
43 static const short int qtypes[] = { ns_t_a, ns_t_aaaa };
44 #define nqtypes (sizeof (qtypes) / sizeof (qtypes[0]))
47 enum nss_status
48 _nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
49 char **result,int *errnop, int *h_errnop)
51 /* Just an alibi buffer, res_nquery will allocate a real buffer for
52 us. */
53 unsigned char buf[20];
54 union
56 querybuf *buf;
57 unsigned char *ptr;
58 } ansp = { .ptr = buf };
59 enum nss_status status = NSS_STATUS_UNAVAIL;
61 for (int i = 0; i < nqtypes; ++i)
63 int r = __libc_res_nquery (&_res, name, ns_c_in, qtypes[i],
64 buf, sizeof (buf), &ansp.ptr, NULL, NULL,
65 NULL);
66 if (r > 0)
68 /* We need to decode the response. Just one question record.
69 And if we got no answers we bail out, too. */
70 if (ansp.buf->hdr.qdcount != htons (1))
71 continue;
73 /* Number of answers. */
74 unsigned int ancount = ntohs (ansp.buf->hdr.ancount);
76 /* Beginning and end of the buffer with query, answer, and the
77 rest. */
78 unsigned char *ptr = &ansp.buf->buf[sizeof (HEADER)];
79 unsigned char *endptr = ansp.ptr + r;
81 /* Skip over the query. This is the name, type, and class. */
82 int s = __dn_skipname (ptr, endptr);
83 if (s < 0)
85 unavail:
86 status = NSS_STATUS_UNAVAIL;
87 break;
90 /* Skip over the name and the two 16-bit values containing type
91 and class. */
92 ptr += s + 2 * sizeof (uint16_t);
94 while (ancount-- > 0)
96 /* Now the reply. First again the name from the query,
97 then type, class, TTL, and the length of the RDATA.
98 We remember the name start. */
99 unsigned char *namestart = ptr;
100 s = __dn_skipname (ptr, endptr);
101 if (s < 0)
102 goto unavail;
104 ptr += s;
106 /* Check whether type and class match. */
107 uint_fast16_t type;
108 NS_GET16 (type, ptr);
109 if (type == qtypes[i])
111 /* We found the record. */
112 s = __dn_expand (ansp.buf->buf, endptr, namestart,
113 buffer, buflen);
114 if (s < 0)
116 if (errno != EMSGSIZE)
117 goto unavail;
119 /* The buffer is too small. */
120 *errnop = ERANGE;
121 status = NSS_STATUS_TRYAGAIN;
122 h_errno = NETDB_INTERNAL;
124 else
126 /* Success. */
127 *result = buffer;
128 status = NSS_STATUS_SUCCESS;
131 goto out;
134 if (type != ns_t_cname)
135 goto unavail;
137 if (__ns_get16 (ptr) != ns_c_in)
138 goto unavail;
140 /* Also skip over the TTL. */
141 ptr += sizeof (uint16_t) + sizeof (uint32_t);
143 /* Skip over the data length and data. */
144 ptr += sizeof (uint16_t) + __ns_get16 (ptr);
149 out:
150 *h_errnop = h_errno;
152 if (ansp.ptr != buf)
153 free (ansp.ptr);
155 return status;