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/* $Id$ */
/* Copyright 1998 by the Massachusetts Institute of Technology.
*
* Permission to use, copy, modify, and distribute this
* software and its documentation for any purpose and without
* fee is hereby granted, provided that the above copyright
* notice appear in all copies and that both that copyright
* notice and this permission notice appear in supporting
* documentation, and that the name of M.I.T. not be used in
* advertising or publicity pertaining to distribution of the
* software without specific, written prior permission.
* M.I.T. makes no representations about the suitability of
* this software for any purpose. It is provided "as is"
* without express or implied warranty.
*/
#include "setup.h"
#if defined(WIN32) && !defined(WATT32)
#include "nameser.h"
#else
#include <netinet/in.h>
#include <arpa/nameser.h>
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif
#endif
#include <stdlib.h>
#include "ares.h"
#include "ares_private.h" /* for the memdebug */
static int name_length(const unsigned char *encoded, const unsigned char *abuf,
int alen);
/* Expand an RFC1035-encoded domain name given by encoded. The
* containing message is given by abuf and alen. The result given by
* *s, which is set to a NUL-terminated allocated buffer. *enclen is
* set to the length of the encoded name (not the length of the
* expanded name; the goal is to tell the caller how many bytes to
* move forward to get past the encoded name).
*
* In the simple case, an encoded name is a series of labels, each
* composed of a one-byte length (limited to values between 0 and 63
* inclusive) followed by the label contents. The name is terminated
* by a zero-length label.
*
* In the more complicated case, a label may be terminated by an
* indirection pointer, specified by two bytes with the high bits of
* the first byte (corresponding to INDIR_MASK) set to 11. With the
* two high bits of the first byte stripped off, the indirection
* pointer gives an offset from the beginning of the containing
* message with more labels to decode. Indirection can happen an
* arbitrary number of times, so we have to detect loops.
*
* Since the expanded name uses '.' as a label separator, we use
* backslashes to escape periods or backslashes in the expanded name.
*/
int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
int alen, char **s, long *enclen)
{
int len, indir = 0;
char *q;
const unsigned char *p;
len = name_length(encoded, abuf, alen);
if (len == -1)
return ARES_EBADNAME;
*s = malloc(len + 1);
if (!*s)
return ARES_ENOMEM;
q = *s;
if (len == 0) {
// RFC2181 says this should be ".": the root of the DNS tree.
// Since this function strips trailing dots though, it becomes ""
q[0] = '\0';
*enclen = 1; // the caller should move one byte to get past this
return ARES_SUCCESS;
}
/* No error-checking necessary; it was all done by name_length(). */
p = encoded;
while (*p)
{
if ((*p & INDIR_MASK) == INDIR_MASK)
{
if (!indir)
{
*enclen = p + 2 - encoded;
indir = 1;
}
p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1));
}
else
{
len = *p;
p++;
while (len--)
{
if (*p == '.' || *p == '\\')
*q++ = '\\';
*q++ = *p;
p++;
}
*q++ = '.';
}
}
if (!indir)
*enclen = p + 1 - encoded;
/* Nuke the trailing period if we wrote one. */
if (q > *s)
*(q - 1) = 0;
else
*q = 0; /* zero terminate */
return ARES_SUCCESS;
}
/* Return the length of the expansion of an encoded domain name, or
* -1 if the encoding is invalid.
*/
static int name_length(const unsigned char *encoded, const unsigned char *abuf,
int alen)
{
int n = 0, offset, indir = 0;
/* Allow the caller to pass us abuf + alen and have us check for it. */
if (encoded == abuf + alen)
return -1;
while (*encoded)
{
if ((*encoded & INDIR_MASK) == INDIR_MASK)
{
/* Check the offset and go there. */
if (encoded + 1 >= abuf + alen)
return -1;
offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1);
if (offset >= alen)
return -1;
encoded = abuf + offset;
/* If we've seen more indirects than the message length,
* then there's a loop.
*/
if (++indir > alen)
return -1;
}
else
{
offset = *encoded;
if (encoded + offset + 1 >= abuf + alen)
return -1;
encoded++;
while (offset--)
{
n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
encoded++;
}
n++;
}
}
/* If there were any labels at all, then the number of dots is one
* less than the number of labels, so subtract one.
*/
return (n) ? n - 1 : n;
}
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