3 /* Copyright 1998 by the Massachusetts Institute of Technology.
5 * Permission to use, copy, modify, and distribute this
6 * software and its documentation for any purpose and without
7 * fee is hereby granted, provided that the above copyright
8 * notice appear in all copies and that both that copyright
9 * notice and this permission notice appear in supporting
10 * documentation, and that the name of M.I.T. not be used in
11 * advertising or publicity pertaining to distribution of the
12 * software without specific, written prior permission.
13 * M.I.T. makes no representations about the suitability of
14 * this software for any purpose. It is provided "as is"
15 * without express or implied warranty.
20 #ifdef HAVE_SYS_SOCKET_H
21 # include <sys/socket.h>
23 #ifdef HAVE_NETINET_IN_H
24 # include <netinet/in.h>
26 #ifdef HAVE_ARPA_NAMESER_H
27 # include <arpa/nameser.h>
31 #ifdef HAVE_ARPA_NAMESER_COMPAT_H
32 # include <arpa/nameser_compat.h>
37 #include "ares_private.h" /* for the memdebug */
39 static int name_length(const unsigned char *encoded, const unsigned char *abuf,
42 /* Expand an RFC1035-encoded domain name given by encoded. The
43 * containing message is given by abuf and alen. The result given by
44 * *s, which is set to a NUL-terminated allocated buffer. *enclen is
45 * set to the length of the encoded name (not the length of the
46 * expanded name; the goal is to tell the caller how many bytes to
47 * move forward to get past the encoded name).
49 * In the simple case, an encoded name is a series of labels, each
50 * composed of a one-byte length (limited to values between 0 and 63
51 * inclusive) followed by the label contents. The name is terminated
52 * by a zero-length label.
54 * In the more complicated case, a label may be terminated by an
55 * indirection pointer, specified by two bytes with the high bits of
56 * the first byte (corresponding to INDIR_MASK) set to 11. With the
57 * two high bits of the first byte stripped off, the indirection
58 * pointer gives an offset from the beginning of the containing
59 * message with more labels to decode. Indirection can happen an
60 * arbitrary number of times, so we have to detect loops.
62 * Since the expanded name uses '.' as a label separator, we use
63 * backslashes to escape periods or backslashes in the expanded name.
66 int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
67 int alen, char **s, long *enclen)
71 const unsigned char *p;
73 len = name_length(encoded, abuf, alen);
83 /* RFC2181 says this should be ".": the root of the DNS tree.
84 * Since this function strips trailing dots though, it becomes ""
87 *enclen = 1; /* the caller should move one byte to get past this */
91 /* No error-checking necessary; it was all done by name_length(). */
95 if ((*p & INDIR_MASK) == INDIR_MASK)
99 *enclen = p + 2 - encoded;
102 p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1));
110 if (*p == '.' || *p == '\\')
119 *enclen = p + 1 - encoded;
121 /* Nuke the trailing period if we wrote one. */
125 *q = 0; /* zero terminate */
130 /* Return the length of the expansion of an encoded domain name, or
131 * -1 if the encoding is invalid.
133 static int name_length(const unsigned char *encoded, const unsigned char *abuf,
136 int n = 0, offset, indir = 0;
138 /* Allow the caller to pass us abuf + alen and have us check for it. */
139 if (encoded == abuf + alen)
144 if ((*encoded & INDIR_MASK) == INDIR_MASK)
146 /* Check the offset and go there. */
147 if (encoded + 1 >= abuf + alen)
149 offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1);
152 encoded = abuf + offset;
154 /* If we've seen more indirects than the message length,
155 * then there's a loop.
163 if (encoded + offset + 1 >= abuf + alen)
168 n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
175 /* If there were any labels at all, then the number of dots is one
176 * less than the number of labels, so subtract one.
178 return (n) ? n - 1 : n;