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ns_name.c

/*
 * Copyright (c) 1996,1999 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

#include "config.h"

#ifdef HAVE_RESOLV

#include <sys/types.h>

#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
# include <arpa/nameser.h>
#endif

#include <ctype.h>
#include <errno.h>
#ifdef HAVE_RESOLV_H
# include <resolv.h>
#endif
#include <string.h>

/* Data. */

static const char digits[] = "0123456789";

/* Private. */

/*
 * special(ch)
 *    Thinking in noninternationalized USASCII (per the DNS spec),
 *    is this character special ("in need of quoting") ?
 * return:
 *    boolean.
 */
static int
special(int ch) {
      switch (ch) {
      case 0x22: /* '"' */
      case 0x2E: /* '.' */
      case 0x3B: /* ';' */
      case 0x5C: /* '\\' */
      /* Special modifiers in zone files. */
      case 0x40: /* '@' */
      case 0x24: /* '$' */
            return (1);
      default:
            return (0);
      }
}

/*
 * printable(ch)
 *    Thinking in noninternationalized USASCII (per the DNS spec),
 *    is this character visible and not a space when printed ?
 * return:
 *    boolean.
 */
static int
printable(int ch) {
      return (ch > 0x20 && ch < 0x7f);
}

/* Public. */

/*
 * dns_ns_name_ntop(src, dst, dstsiz)
 *    Convert an encoded domain name to printable ascii as per RFC1035.
 * return:
 *    Number of bytes written to buffer, or -1 (with errno set)
 * notes:
 *    The root is returned as "."
 *    All other domains are returned in non absolute form
 */
static int
dns_ns_name_ntop(const u_char *src, char *dst, size_t dstsiz) {
      const u_char *cp;
      char *dn, *eom;
      u_char c;
      u_int n;

      cp = src;
      dn = dst;
      eom = dst + dstsiz;

      while ((n = *cp++) != 0) {
            if ((n & NS_CMPRSFLGS) != 0 && n != 0x41) {
                  /* Some kind of compression pointer. */
                  return (-1);
            }
            if (dn != dst) {
                  if (dn >= eom) {
                        return (-1);
                  }
                  *dn++ = '.';
            }

            if (n == 0x41) {
                  n = *cp++ / 8;
                  if (dn + n * 2 + 4 >= eom) {
                        return (-1);
                  }
                  *dn++ = '\\';
                  *dn++ = '[';
                  *dn++ = 'x';

                  while (n-- > 0) {
                unsigned u;
                        c = *cp++;
                        u = c >> 4;
                        *dn++ = u > 9 ? 'a' + u - 10 : '0' + u;
                        u = c & 0xf;
                        *dn++ = u > 9 ? 'a' + u - 10 : '0' + u;
                  }

                  *dn++ = ']';
                  continue;
            }

            if (dn + n >= eom) {
                  return (-1);
            }
            while (n-- > 0) {
                  c = *cp++;
                  if (special(c)) {
                        if (dn + 1 >= eom) {
                              return (-1);
                        }
                        *dn++ = '\\';
                        *dn++ = (char)c;
                  } else if (!printable(c)) {
                        if (dn + 3 >= eom) {
                              return (-1);
                        }
                        *dn++ = '\\';
                        *dn++ = digits[c / 100];
                        *dn++ = digits[(c % 100) / 10];
                        *dn++ = digits[c % 10];
                  } else {
                        if (dn >= eom) {
                              return (-1);
                        }
                        *dn++ = (char)c;
                  }
            }
      }
      if (dn == dst) {
            if (dn >= eom) {
                  return (-1);
            }
            *dn++ = '.';
      }
      if (dn >= eom) {
            return (-1);
      }
      *dn++ = '\0';
      return (dn - dst);
}


/*
 * dns_ns_name_unpack(msg, eom, src, dst, dstsiz)
 *    Unpack a domain name from a message, source may be compressed.
 * return:
 *    -1 if it fails, or consumed octets if it succeeds.
 */
static int
dns_ns_name_unpack(const u_char *msg, const u_char *eom, const u_char *src,
             u_char *dst, size_t dstsiz)
{
      const u_char *srcp, *dstlim;
      u_char *dstp;
      int n, len, checked;

      len = -1;
      checked = 0;
      dstp = dst;
      srcp = src;
      dstlim = dst + dstsiz;
      if (srcp < msg || srcp >= eom) {
            return (-1);
      }
      /* Fetch next label in domain name. */
      while ((n = *srcp++) != 0) {
            /* Check for indirection. */
            switch (n & NS_CMPRSFLGS) {
            case 0x40:
                  if (n == 0x41) {
                        if (dstp + 1 >= dstlim) {
                              return (-1);
                        }
                        *dstp++ = 0x41;
                        n = *srcp++ / 8;
                        ++checked;
                  } else {
                        return (-1);            /* flag error */
                  }
                  /* FALLTHROUGH */
            case 0:
                  /* Limit checks. */
                  if (dstp + n + 1 >= dstlim || srcp + n >= eom) {
                        return (-1);
                  }
                  checked += n + 1;
                  dstp = memcpy(dstp, srcp - 1, n + 1);
                  dstp += n + 1;
                  srcp += n;
                  break;

            case NS_CMPRSFLGS:
                  if (srcp >= eom) {
                        return (-1);
                  }
                  if (len < 0)
                        len = srcp - src + 1;
                  srcp = msg + (((n & 0x3f) << 8) | (*srcp & 0xff));
                  if (srcp < msg || srcp >= eom) {  /* Out of range. */
                        return (-1);
                  }
                  checked += 2;
                  /*
                   * Check for loops in the compressed name;
                   * if we've looked at the whole message,
                   * there must be a loop.
                   */
                  if (checked >= eom - msg) {
                        return (-1);
                  }
                  break;

            default:
                  return (-1);                  /* flag error */
            }
      }
      *dstp = '\0';
      if (len < 0)
            len = srcp - src;
      return (len);
}


/*
 * dns_ns_name_uncompress(msg, eom, src, dst, dstsiz)
 *    Expand compressed domain name to presentation format.
 * return:
 *    Number of bytes read out of `src', or -1 (with errno set).
 * note:
 *    Root domain returns as "." not "".
 */
int
dns_ns_name_uncompress(const u_char *msg, const u_char *eom, const u_char *src,
               char *dst, size_t dstsiz)
{
      u_char tmp[NS_MAXCDNAME];
      int n;

      if ((n = dns_ns_name_unpack(msg, eom, src, tmp, sizeof tmp)) == -1)
            return (-1);
      if (dns_ns_name_ntop(tmp, dst, dstsiz) == -1)
            return (-1);
      return (n);
}


/*
 * dns_ns_name_skip(ptrptr, eom)
 *    Advance *ptrptr to skip over the compressed name it points at.
 * return:
 *    0 on success, -1 (with errno set) on failure.
 */
int
dns_ns_name_skip(const u_char **ptrptr, const u_char *eom) {
      const u_char *cp;
      u_int n;

      cp = *ptrptr;
      while (cp < eom && (n = *cp++) != 0) {
            /* Check for indirection. */
            switch (n & NS_CMPRSFLGS) {
            case 0:                 /* normal case, n == len */
                  cp += n;
                  continue;
            case NS_CMPRSFLGS:      /* indirection */
                  cp++;
                  break;
            default:          /* illegal type */
                  return (-1);
            }
            break;
      }
      if (cp > eom) {
            return (-1);
      }
      *ptrptr = cp;
      return (0);
}

#endif  /* HAVE_RESOLV */

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