lib/inet_ntop.c

/* inet_ntop.c -- convert IPv4 and IPv6 addresses from binary to text form

   Copyright (C) 2005-2006, 2008-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/*
 * 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>

/* Specification.  */
#include <arpa/inet.h>

/* Use this to suppress gcc's "...may be used before initialized" warnings.
   Beware: The Code argument must not contain commas.  */
#ifndef IF_LINT
# if defined GCC_LINT || defined lint
#  define IF_LINT(Code) Code
# else
#  define IF_LINT(Code) /* empty */
# endif
#endif

#if HAVE_DECL_INET_NTOP

# undef inet_ntop

const char *
rpl_inet_ntop (int af, const void *restrict src,
               char *restrict dst, socklen_t cnt)
{
  return inet_ntop (af, src, dst, cnt);
}

#else

# include <stdio.h>
# include <string.h>
# include <errno.h>

# define NS_IN6ADDRSZ 16
# define NS_INT16SZ 2

/*
 * WARNING: Don't even consider trying to compile this on a system where
 * sizeof(int) < 4.  sizeof(int) > 4 is fine; all the world's not a VAX.
 */
typedef int verify_int_size[4 <= sizeof (int) ? 1 : -1];

static const char *inet_ntop4 (const unsigned char *src, char *dst, socklen_t size);
# if HAVE_IPV6
static const char *inet_ntop6 (const unsigned char *src, char *dst, socklen_t size);
# endif


/* char *
 * inet_ntop(af, src, dst, size)
 *      convert a network format address to presentation format.
 * return:
 *      pointer to presentation format address ('dst'), or NULL (see errno).
 * author:
 *      Paul Vixie, 1996.
 */
const char *
inet_ntop (int af, const void *restrict src,
           char *restrict dst, socklen_t cnt)
{
  switch (af)
    {
# if HAVE_IPV4
    case AF_INET:
      return (inet_ntop4 (src, dst, cnt));
# endif

# if HAVE_IPV6
    case AF_INET6:
      return (inet_ntop6 (src, dst, cnt));
# endif

    default:
      errno = EAFNOSUPPORT;
      return (NULL);
    }
  /* NOTREACHED */
}

/* const char *
 * inet_ntop4(src, dst, size)
 *      format an IPv4 address
 * return:
 *      'dst' (as a const)
 * notes:
 *      (1) uses no statics
 *      (2) takes a 'unsigned char *' not an in_addr as input
 * author:
 *      Paul Vixie, 1996.
 */
static const char *
inet_ntop4 (const unsigned char *src, char *dst, socklen_t size)
{
  char tmp[sizeof "255.255.255.255"];
  int len = sprintf (tmp, "%u.%u.%u.%u", src[0], src[1], src[2], src[3]);
  if (len < 0)
    return NULL;

  if (len > size)
    {
      errno = ENOSPC;
      return NULL;
    }

  return strcpy (dst, tmp);
}

# if HAVE_IPV6

/* const char *
 * inet_ntop6(src, dst, size)
 *      convert IPv6 binary address into presentation (printable) format
 * author:
 *      Paul Vixie, 1996.
 */
static const char *
inet_ntop6 (const unsigned char *src, char *dst, socklen_t size)
{
  /*
   * Preprocess:
   *      Copy the input (bytewise) array into a wordwise array.
   *      Find the longest run of 0x00's in src[] for :: shorthanding.
   */
  unsigned int words[NS_IN6ADDRSZ / NS_INT16SZ];
  memset (words, '\0', sizeof words);
  for (int i = 0; i < NS_IN6ADDRSZ; i += 2)
    words[i / 2] = (src[i] << 8) | src[i + 1];

  struct
  {
    int base, len;
  } best, cur;
  best.base = -1;
  cur.base = -1;
  IF_LINT(best.len = 0);
  IF_LINT(cur.len = 0);

  for (int i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++)
    {
      if (words[i] == 0)
        {
          if (cur.base == -1)
            cur.base = i, cur.len = 1;
          else
            cur.len++;
        }
      else
        {
          if (cur.base != -1)
            {
              if (best.base == -1 || cur.len > best.len)
                best = cur;
              cur.base = -1;
            }
        }
    }
  if (cur.base != -1)
    {
      if (best.base == -1 || cur.len > best.len)
        best = cur;
    }
  if (best.base != -1 && best.len < 2)
    best.base = -1;

  /*
   * Format the result.
   */
  /*
   * Note that int32_t and int16_t need only be "at least" large enough
   * to contain a value of the specified size.  On some systems, like
   * Crays, there is no such thing as an integer variable with 16 bits.
   * Keep this in mind if you think this function should have been coded
   * to use pointer overlays.  All the world's not a VAX.
   */
  char tmp[sizeof "ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255"];
  char *tp = tmp;
  for (int i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++)
    {
      /* Are we inside the best run of 0x00's? */
      if (best.base != -1 && i >= best.base && i < (best.base + best.len))
        {
          if (i == best.base)
            *tp++ = ':';
          continue;
        }
      /* Are we following an initial run of 0x00s or any real hex? */
      if (i != 0)
        *tp++ = ':';
      /* Is this address an encapsulated IPv4? */
      if (i == 6 && best.base == 0 &&
          (best.len == 6 || (best.len == 5 && words[5] == 0xffff)))
        {
          if (!inet_ntop4 (src + 12, tp, sizeof tmp - (tp - tmp)))
            return (NULL);
          tp = strnul (tp);
          break;
        }
      {
        int len = sprintf (tp, "%x", words[i]);
        if (len < 0)
          return NULL;
        tp += len;
      }
    }
  /* Was it a trailing run of 0x00's? */
  if (best.base != -1 && (best.base + best.len) ==
      (NS_IN6ADDRSZ / NS_INT16SZ))
    *tp++ = ':';
  *tp++ = '\0';

  /*
   * Check for overflow, copy, and we're done.
   */
  if ((socklen_t) (tp - tmp) > size)
    {
      errno = ENOSPC;
      return NULL;
    }

  return strcpy (dst, tmp);
}

# endif

#endif