glibc/resolv/inet_ntop.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 <sys/param.h>
#include <sys/types.h>
#include <sys/socket.h>

#include <netinet/in.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>

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

#ifdef SPRINTF_CHAR
# define SPRINTF(x) strlen (sprintf /**/ x)
#else
# define SPRINTF(x) ((size_t) sprintf x)
#endif

/*
 * 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.
 */

static const char *inet_ntop4 (const u_char *src, char *dst, socklen_t size);
static const char *inet_ntop6 (const u_char *src, char *dst, socklen_t size);

/* 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 *src, char *dst, socklen_t size)
{
  switch (af)
    {
    case AF_INET:
      return (inet_ntop4 (src, dst, size));
    case AF_INET6:
      return (inet_ntop6 (src, dst, size));
    default:
      __set_errno (EAFNOSUPPORT);
      return (NULL);
    }
  /* NOTREACHED */
}
libc_hidden_def (__inet_ntop)
weak_alias (__inet_ntop, inet_ntop)

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

  if (SPRINTF ((tmp, fmt, src[0], src[1], src[2], src[3])) >= size)
    {
      __set_errno (ENOSPC);
      return (NULL);
    }
  return strcpy (dst, tmp);
}

/* 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 u_char *src, char *dst, socklen_t size)
{
  /*
   * 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"], *tp;
  struct
  {
    int base, len;
  } best, cur;
  u_int words[NS_IN6ADDRSZ / NS_INT16SZ];
  int i;

  /*
   * Preprocess:
   *	Copy the input (bytewise) array into a wordwise array.
   *	Find the longest run of 0x00's in src[] for :: shorthanding.
   */
  memset (words, '\0', sizeof words);
  for (i = 0; i < NS_IN6ADDRSZ; i += 2)
    words[i / 2] = (src[i] << 8) | src[i + 1];
  best.base = -1;
  cur.base = -1;
  best.len = 0;
  cur.len = 0;
  for (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.
   */
  tp = tmp;
  for (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 += strlen (tp);
	  break;
	}
      tp += SPRINTF ((tp, "%x", words[i]));
    }
  /* 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)
    {
      __set_errno (ENOSPC);
      return (NULL);
    }
  return strcpy (dst, tmp);
}