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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"
- #ifdef HAVE_SYS_SOCKET_H
- # include <sys/socket.h>
- #endif
- #ifdef HAVE_NETINET_IN_H
- # include <netinet/in.h>
- #endif
- #ifdef HAVE_ARPA_NAMESER_H
- # include <arpa/nameser.h>
- #else
- # include "nameser.h"
- #endif
- #ifdef HAVE_ARPA_NAMESER_COMPAT_H
- # include <arpa/nameser_compat.h>
- #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;
- }
- /* Like ares_expand_name but returns EBADRESP in case of invalid input. */
- int ares__expand_name_for_response(const unsigned char *encoded,
- const unsigned char *abuf, int alen,
- char **s, long *enclen)
- {
- int status = ares_expand_name(encoded, abuf, alen, s, enclen);
- if (status == ARES_EBADNAME)
- status = ARES_EBADRESP;
- return status;
- }
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