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/* Convert IPv4/IPv6 addresses from binary to text form.
Copyright (C) 1996-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library 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.
The GNU C Library 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 the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <errno.h>
#include <string.h>
#include <_itoa.h>
static inline char *
put_uint8 (uint8_t word, char *tp)
{
int s = 1;
if (word >= 10)
{
if (word >= 100)
{
tp[2] = '0' + word % 10;
word /= 10;
s += 1;
}
tp[1] = '0' + word % 10;
word /= 10;
s += 1;
}
*tp = '0' + word;
return tp + s;
}
static inline char *
put_uint16 (uint16_t word, char *tp)
{
if (word >= 0x1000)
*tp++ = _itoa_lower_digits[(word >> 12) & 0xf];
if (word >= 0x100)
*tp++ = _itoa_lower_digits[(word >> 8) & 0xf];
if (word >= 0x10)
*tp++ = _itoa_lower_digits[(word >> 4) & 0xf];
*tp++ = _itoa_lower_digits[word & 0xf];
return tp;
}
static __always_inline char *
inet_ntop4_format (const uint8_t *src, char *dst)
{
dst = put_uint8 (src[0], dst);
*(dst++) = '.';
dst = put_uint8 (src[1], dst);
*(dst++) = '.';
dst = put_uint8 (src[2], dst);
*(dst++) = '.';
dst = put_uint8 (src[3], dst);
*dst++ = '\0';
return dst;
}
static __always_inline const char *
inet_ntop4 (const uint8_t *src, char *dst, socklen_t size)
{
if (size >= INET_ADDRSTRLEN)
{
inet_ntop4_format (src, dst);
return dst;
}
char tmp[INET_ADDRSTRLEN];
char *tp = inet_ntop4_format (src, tmp);
socklen_t tmp_s = tp - tmp;
if (tmp_s > size)
{
__set_errno (ENOSPC);
return NULL;
}
return memcpy (dst, tmp, tmp_s);
}
struct best_t
{
int base;
int len;
};
static inline uint16_t
in6_addr_addr16 (const struct in6_addr *src, int idx)
{
const struct { uint16_t x; } __attribute__((__packed__)) *pptr =
(typeof(pptr))(&src->s6_addr16[idx]);
return ntohs (pptr->x);
}
static __always_inline char *
inet_ntop6_format (const struct in6_addr *src, struct best_t best, char *dst)
{
char *tp = dst;
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
&& in6_addr_addr16 (src, 5) == 0xffff)))
{
if (!inet_ntop4 (src->s6_addr + 12, tp,
INET6_ADDRSTRLEN - (tp - dst)))
return NULL;
tp += strlen (tp);
break;
}
tp = put_uint16 (in6_addr_addr16 (src, i), tp);
}
/* Was it a trailing run of 0x00's? */
if (best.base != -1 && (best.base + best.len) == (NS_IN6ADDRSZ / NS_INT16SZ))
*tp++ = ':';
*tp++ = '\0';
return tp;
}
static inline const char *
inet_ntop6 (const struct in6_addr *src, char *dst, socklen_t size)
{
struct best_t best = { -1, 0 }, cur = { -1, 0 };
/* ind the longest run of 0x00's in src[] for :: shorthanding. */
for (int i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++)
{
if (in6_addr_addr16 (src, 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;
if (size >= INET6_ADDRSTRLEN)
{
inet_ntop6_format (src, best, dst);
return dst;
}
char tmp[INET6_ADDRSTRLEN];
char *tp = inet_ntop6_format (src, best, tmp);
socklen_t tmp_s = tp - tmp;
if (tmp_s > size)
{
__set_errno (ENOSPC);
return (NULL);
}
return memcpy (dst, tmp, tmp_s);
}
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);
}
}
libc_hidden_def (__inet_ntop)
weak_alias (__inet_ntop, inet_ntop)
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