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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 */