1 /* Copyright 1998 by the Massachusetts Institute of Technology.
3 * Permission to use, copy, modify, and distribute this
4 * software and its documentation for any purpose and without
5 * fee is hereby granted, provided that the above copyright
6 * notice appear in all copies and that both that copyright
7 * notice and this permission notice appear in supporting
8 * documentation, and that the name of M.I.T. not be used in
9 * advertising or publicity pertaining to distribution of the
10 * software without specific, written prior permission.
11 * M.I.T. makes no representations about the suitability of
12 * this software for any purpose. It is provided "as is"
13 * without express or implied warranty.
17 #include <sys/types.h>
19 #if defined(WIN32) && !defined(WATT32)
22 #include <netinet/in.h>
23 #include <arpa/nameser.h>
24 #ifdef HAVE_ARPA_NAMESER_COMPAT_H
25 #include <arpa/nameser_compat.h>
31 #include "ares_private.h" /* for the memdebug */
33 static int name_length(const unsigned char *encoded, const unsigned char *abuf,
36 /* Expand an RFC1035-encoded domain name given by encoded. The
37 * containing message is given by abuf and alen. The result given by
38 * *s, which is set to a NUL-terminated allocated buffer. *enclen is
39 * set to the length of the encoded name (not the length of the
40 * expanded name; the goal is to tell the caller how many bytes to
41 * move forward to get past the encoded name).
43 * In the simple case, an encoded name is a series of labels, each
44 * composed of a one-byte length (limited to values between 0 and 63
45 * inclusive) followed by the label contents. The name is terminated
46 * by a zero-length label.
48 * In the more complicated case, a label may be terminated by an
49 * indirection pointer, specified by two bytes with the high bits of
50 * the first byte (corresponding to INDIR_MASK) set to 11. With the
51 * two high bits of the first byte stripped off, the indirection
52 * pointer gives an offset from the beginning of the containing
53 * message with more labels to decode. Indirection can happen an
54 * arbitrary number of times, so we have to detect loops.
56 * Since the expanded name uses '.' as a label separator, we use
57 * backslashes to escape periods or backslashes in the expanded name.
60 int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
61 int alen, char **s, long *enclen)
65 const unsigned char *p;
67 len = name_length(encoded, abuf, alen);
76 /* No error-checking necessary; it was all done by name_length(). */
80 if ((*p & INDIR_MASK) == INDIR_MASK)
84 *enclen = p + 2 - encoded;
87 p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1));
95 if (*p == '.' || *p == '\\')
104 *enclen = p + 1 - encoded;
106 /* Nuke the trailing period if we wrote one. */
113 /* Return the length of the expansion of an encoded domain name, or
114 * -1 if the encoding is invalid.
116 static int name_length(const unsigned char *encoded, const unsigned char *abuf,
119 int n = 0, offset, indir = 0;
121 /* Allow the caller to pass us abuf + alen and have us check for it. */
122 if (encoded == abuf + alen)
127 if ((*encoded & INDIR_MASK) == INDIR_MASK)
129 /* Check the offset and go there. */
130 if (encoded + 1 >= abuf + alen)
132 offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1);
135 encoded = abuf + offset;
137 /* If we've seen more indirects than the message length,
138 * then there's a loop.
146 if (encoded + offset + 1 >= abuf + alen)
151 n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
158 /* If there were any labels at all, then the number of dots is one
159 * less than the number of labels, so subtract one.
161 return (n) ? n - 1 : n;