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/* Read the contents of a symbolic link.
Copyright (C) 2003-2007, 2009-2023 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/>. */
#include <config.h>
/* Specification. */
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/stat.h>
#if !HAVE_READLINK
/* readlink() substitute for systems that don't have a readlink() function,
such as DJGPP 2.03 and mingw32. */
ssize_t
readlink (char const *file, _GL_UNUSED char *buf,
_GL_UNUSED size_t bufsize)
{
struct stat statbuf;
/* In general we should use lstat() here, not stat(). But on platforms
without symbolic links, lstat() - if it exists - would be equivalent to
stat(), therefore we can use stat(). This saves us a configure check. */
if (stat (file, &statbuf) >= 0)
errno = EINVAL;
return -1;
}
#else /* HAVE_READLINK */
# undef readlink
/* readlink() wrapper that uses correct types, for systems like cygwin
1.5.x where readlink returns int, and which rejects trailing slash,
for Solaris 9. */
ssize_t
rpl_readlink (char const *file, char *buf, size_t bufsize)
{
# if READLINK_TRAILING_SLASH_BUG
size_t file_len = strlen (file);
if (file_len && file[file_len - 1] == '/')
{
/* Even if FILE without the slash is a symlink to a directory,
both lstat() and stat() must resolve the trailing slash to
the directory rather than the symlink. We can therefore
safely use stat() to distinguish between EINVAL and
ENOTDIR/ENOENT, avoiding extra overhead of rpl_lstat(). */
struct stat st;
if (stat (file, &st) == 0 || errno == EOVERFLOW)
errno = EINVAL;
return -1;
}
# endif /* READLINK_TRAILING_SLASH_BUG */
ssize_t r = readlink (file, buf, bufsize);
# if READLINK_TRUNCATE_BUG
if (r < 0 && errno == ERANGE)
{
/* Try again with a bigger buffer. This is just for test cases;
real code invariably discards short reads. */
char stackbuf[4032];
r = readlink (file, stackbuf, sizeof stackbuf);
if (r < 0)
{
if (errno == ERANGE)
{
/* Clear the buffer, which is good enough for real code.
Thankfully, no test cases try short reads of enormous
symlinks and what would be the point anyway? */
r = bufsize;
memset (buf, 0, r);
}
}
else
{
if (bufsize < r)
r = bufsize;
memcpy (buf, stackbuf, r);
}
}
# endif
return r;
}
#endif /* HAVE_READLINK */
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