/* Copyright 1998, 2011 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 "ares_setup.h"

#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 "ares.h"

#include "ares_nowarn.h"

#include "ares_private.h" /* for the memdebug */

/* Maximum number of indirections allowed for a name */

#define MAX_INDIRS 50

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;

  union {

    ares_ssize_t sig;

     size_t uns;

  } nlen;

  nlen.sig = name_length(encoded, abuf, alen);

  if (nlen.sig < 0)

    return ARES_EBADNAME;

  *s = ares_malloc(nlen.uns + 1);

  if (!*s)

    return ARES_ENOMEM;

  q = *s;

  if (nlen.uns == 0) {

    /* RFC2181 says this should be ".": the root of the DNS tree.

     * Since this function strips trailing dots though, it becomes ""

     */

    q[0] = '\0';

    /* indirect root label (like 0xc0 0x0c) is 2 bytes long (stupid, but

       valid) */

    if ((*encoded & INDIR_MASK) == INDIR_MASK)

      *enclen = 2L;

    else

      *enclen = 1L;  /* 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 = aresx_uztosl(p + 2U - 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 = aresx_uztosl(p + 1U - encoded);

  /* Nuke the trailing period if we wrote one. */

  if (q > *s)

    *(q - 1) = 0;

  else

    *q = 0; /* zero terminate; LCOV_EXCL_LINE: empty names exit above */

  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, top;

  /* Allow the caller to pass us abuf + alen and have us check for it. */

  if (encoded >= abuf + alen)

    return -1;

  while (*encoded)

    {

      top = (*encoded & INDIR_MASK);

      if (top == 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.

           */

          ++indir;

          if (indir > alen || indir > MAX_INDIRS)

            return -1;

        }

      else if (top == 0x00)

        {

          offset = *encoded;

          if (encoded + offset + 1 >= abuf + alen)

            return -1;

          encoded++;

          while (offset--)

            {

              n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;

              encoded++;

            }

          n++;

        }

      else

        {

          /* RFC 1035 4.1.4 says other options (01, 10) for top 2

           * bits are reserved.

           */

          return -1;

        }

    }

  /* 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;

}