/* $NetBSD: ntp_realpath.c,v 1.2 2024/08/18 20:47:13 christos Exp $ */

/* $NetBSD: ntp_realpath.c,v 1.2 2024/08/18 20:47:13 christos Exp $ */

/*
* ntp_realpath.c - get real path for a file
* Juergen Perlinger ([email protected]) for the NTP project.
* Feb 11, 2014 for the NTP project.
*
* This is a butchered version of FreeBSD's implementation of 'realpath()',
* and the following copyright applies:
*----------------------------------------------------------------------
*/

/*-
* SPDX-License-Identifier: BSD-3-Clause
*
* Copyright (c) 2003 Constantin S. Svintsoff <[email protected]>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The names of the authors may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#include "ntp_stdlib.h"

/* ================================================================== */
#if defined(SYS_WINNT)
/* ================================================================== */

#include <stdlib.h>

/* On Windows, we assume 2k for a file path is enough. */
#define NTP_PATH_MAX 2048

static char *
realpath1(const char *path, char *resolved)
{
/* Items in the device name space get passed back AS IS. Everything
* else is fed through '_fullpath()', which is probably the closest
* counterpart to what 'realpath()' is expected to do on Windows...
*/
char * retval = NULL;

if (!strncmp(path, "\\\\.\\", 4)) {
if (strlcpy(resolved, path, NTP_PATH_MAX) >= NTP_PATH_MAX)
errno = ENAMETOOLONG;
else
retval = resolved;
} else if ((retval = _fullpath(resolved, path, NTP_PATH_MAX)) == NULL) {
errno = ENAMETOOLONG;
}
return retval;
}

/* ================================================================== */
#elif !defined(HAVE_FUNC_POSIX_REALPATH)
/* ================================================================== */

#include <sys/stat.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>

/* The following definitions are to avoid system settings with excessive
* values for maxmimum path length and symlink chains/loops. Adjust with
* care, if that's ever needed: some buffers are on the stack!
*/
#define NTP_PATH_MAX 1024
#define NTP_MAXSYMLINKS 16

/*
* Find the real name of path, by removing all ".", ".." and symlink
* components. Returns (resolved) on success, or (NULL) on failure,
* in which case the path which caused trouble is left in (resolved).
*/
static char *
realpath1(const char *path, char *resolved)
{
struct stat sb;
char *p, *q;
size_t left_len, resolved_len, next_token_len;
unsigned symlinks;
ssize_t slen;
char left[NTP_PATH_MAX], next_token[NTP_PATH_MAX], link_tgt[NTP_PATH_MAX];

symlinks = 0;
if (path[0] == '/') {
resolved[0] = '/';
resolved[1] = '\0';
if (path[1] == '\0')
return (resolved);
resolved_len = 1;
left_len = strlcpy(left, path + 1, sizeof(left));
} else {
if (getcwd(resolved, NTP_PATH_MAX) == NULL) {
resolved[0] = '.';
resolved[1] = '\0';
return (NULL);
}
resolved_len = strlen(resolved);
left_len = strlcpy(left, path, sizeof(left));
}
if (left_len >= sizeof(left) || resolved_len >= NTP_PATH_MAX) {
errno = ENAMETOOLONG;
return (NULL);
}

/*
* Iterate over path components in `left'.
*/
while (left_len != 0) {
/*
* Extract the next path component and adjust `left'
* and its length.
*/
p = strchr(left, '/');

next_token_len = p != NULL ? (size_t)(p - left) : left_len;
memcpy(next_token, left, next_token_len);
next_token[next_token_len] = '\0';

if (p != NULL) {
left_len -= next_token_len + 1;
memmove(left, p + 1, left_len + 1);
} else {
left[0] = '\0';
left_len = 0;
}

if (resolved[resolved_len - 1] != '/') {
if (resolved_len + 1 >= NTP_PATH_MAX) {
errno = ENAMETOOLONG;
return (NULL);
}
resolved[resolved_len++] = '/';
resolved[resolved_len] = '\0';
}
if ('\0' == next_token[0]) {
/* Handle consequential slashes. */
continue;
} else if (strcmp(next_token, ".") == 0) {
continue;
} else if (strcmp(next_token, "..") == 0) {
/*
* Strip the last path component except when we have
* single "/"
*/
if (resolved_len > 1) {
resolved[resolved_len - 1] = '\0';
q = strrchr(resolved, '/') + 1;
*q = '\0';
resolved_len = q - resolved;
}
continue;
}

/*
* Append the next path component and lstat() it.
*/
resolved_len = strlcat(resolved, next_token, NTP_PATH_MAX);
if (resolved_len >= NTP_PATH_MAX) {
errno = ENAMETOOLONG;
return (NULL);
}
if (lstat(resolved, &sb) != 0)
return (NULL);
if (S_ISLNK(sb.st_mode)) {
if (++symlinks > NTP_MAXSYMLINKS) {
errno = ELOOP;
return (NULL);
}
slen = readlink(resolved, link_tgt, sizeof(link_tgt));
if (slen <= 0 || slen >= (ssize_t)sizeof(link_tgt)) {
if (slen < 0) {
/* keep errno from readlink(2) call */
} else if (slen == 0) {
errno = ENOENT;
} else {
errno = ENAMETOOLONG;
}
return (NULL);
}
link_tgt[slen] = '\0';
if (link_tgt[0] == '/') {
resolved[1] = '\0';
resolved_len = 1;
} else {
/* Strip the last path component. */
q = strrchr(resolved, '/') + 1;
*q = '\0';
resolved_len = q - resolved;
}

/*
* If there are any path components left, then
* append them to link_tgt. The result is placed
* in `left'.
*/
if (p != NULL) {
if (link_tgt[slen - 1] != '/') {
if (slen + 1 >= (ssize_t)sizeof(link_tgt)) {
errno = ENAMETOOLONG;
return (NULL);
}
link_tgt[slen] = '/';
link_tgt[slen + 1] = 0;
}
left_len = strlcat(link_tgt, left,
sizeof(link_tgt));
if (left_len >= sizeof(link_tgt)) {
errno = ENAMETOOLONG;
return (NULL);
}
}
left_len = strlcpy(left, link_tgt, sizeof(left));
} else if (!S_ISDIR(sb.st_mode) && p != NULL) {
errno = ENOTDIR;
return (NULL);
}
}

/*
* Remove trailing slash except when the resolved pathname
* is a single "/".
*/
if (resolved_len > 1 && resolved[resolved_len - 1] == '/')
resolved[resolved_len - 1] = '\0';
return (resolved);
}

/* ================================================================== */
#endif /* !defined(SYS_WINNT) && !defined(HAVE_POSIX_REALPATH) */
/* ================================================================== */

char *
ntp_realpath(const char * path)
{
# if defined(HAVE_FUNC_POSIX_REALPATH)

return realpath(path, NULL);

# else

char *res = NULL, *m = NULL;
if (path == NULL)
errno = EINVAL;
else if (path[0] == '\0')
errno = ENOENT;
else if ((m = malloc(NTP_PATH_MAX)) == NULL)
errno = ENOMEM; /* MSVCRT malloc does not set this... */
else if ((res = realpath1(path, m)) == NULL)
free(m);
else
res = realloc(res, strlen(res) + 1);
return (res);

# endif
}