1 files changed, 149 insertions, 0 deletions
diff --git a/lib/same.c b/lib/same.c
new file mode 100644
index 0000000..cb5e60f
--- /dev/null
+++ b/lib/same.c
@@ -0,0 +1,149 @@
+/* Determine whether two file names refer to the same file.
+
+   Copyright (C) 1997-2000, 2002-2006, 2009-2020 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* written by Jim Meyering */
+
+#include <config.h>
+
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <ctype.h>
+#include <errno.h>
+
+#include <string.h>
+
+#include <limits.h>
+#ifndef _POSIX_NAME_MAX
+# define _POSIX_NAME_MAX 14
+#endif
+
+#include "same.h"
+#include "dirname.h"
+#include "error.h"
+#include "same-inode.h"
+
+#ifndef MIN
+# define MIN(a, b) ((a) < (b) ? (a) : (b))
+#endif
+
+/* Whether file name components are silently truncated (behavior that
+   POSIX stopped allowing in 2008).  This enables checks whether
+   truncated base names are the same, while checking the directories.  */
+#if !_POSIX_NO_TRUNC && HAVE_FPATHCONF && defined _PC_NAME_MAX
+# define CHECK_TRUNCATION true
+#else
+# define CHECK_TRUNCATION false
+#endif
+
+/* Return nonzero if SOURCE and DEST point to the same name in the same
+   directory.  */
+
+bool
+same_name (const char *source, const char *dest)
+{
+  return same_nameat (AT_FDCWD, source, AT_FDCWD, dest);
+}
+
+/* Likewise, but interpret the file names relative to SOURCE_FD and DEST_FD,
+   in the style of openat.  */
+
+bool
+same_nameat (int source_dfd, char const *source,
+             int dest_dfd, char const *dest)
+{
+  /* Compare the basenames.  */
+  char const *source_basename = last_component (source);
+  char const *dest_basename = last_component (dest);
+  size_t source_baselen = base_len (source_basename);
+  size_t dest_baselen = base_len (dest_basename);
+  bool identical_basenames =
+    (source_baselen == dest_baselen
+     && memcmp (source_basename, dest_basename, dest_baselen) == 0);
+  bool compare_dirs = identical_basenames;
+  bool same = false;
+
+#if CHECK_TRUNCATION
+  size_t slen_max = HAVE_LONG_FILE_NAMES ? 255 : _POSIX_NAME_MAX;
+  size_t min_baselen = MIN (source_baselen, dest_baselen);
+  if (slen_max <= min_baselen
+      && memcmp (source_basename, dest_basename, slen_max) == 0)
+    compare_dirs = true;
+#endif
+
+  if (compare_dirs)
+    {
+      struct stat source_dir_stats;
+      struct stat dest_dir_stats;
+
+      /* Compare the parent directories (via the device and inode numbers).  */
+      char *source_dirname = dir_name (source);
+      int flags = AT_SYMLINK_NOFOLLOW;
+      if (fstatat (source_dfd, source_dirname, &source_dir_stats, flags) != 0)
+        {
+          /* Shouldn't happen.  */
+          error (1, errno, "%s", source_dirname);
+        }
+      free (source_dirname);
+
+      char *dest_dirname = dir_name (dest);
+
+#if CHECK_TRUNCATION
+      int destdir_errno = 0;
+      int open_flags = O_SEARCH | O_CLOEXEC | O_DIRECTORY;
+      int destdir_fd = openat (dest_dfd, dest_dirname, open_flags);
+      if (destdir_fd < 0 || fstat (destdir_fd, &dest_dir_stats) != 0)
+        destdir_errno = errno;
+      else if (SAME_INODE (source_dir_stats, dest_dir_stats))
+        {
+          same = identical_basenames;
+          if (! same)
+            {
+              errno = 0;
+              long name_max = fpathconf (destdir_fd, _PC_NAME_MAX);
+              if (name_max < 0)
+                destdir_errno = errno;
+              else
+                same = (name_max <= min_baselen
+                        && (memcmp (source_basename, dest_basename, name_max)
+                            == 0));
+            }
+        }
+      close (destdir_fd);
+      if (destdir_errno != 0)
+        {
+          /* Shouldn't happen.  */
+          error (1, destdir_errno, "%s", dest_dirname);
+        }
+#else
+      if (fstatat (dest_dfd, dest_dirname, &dest_dir_stats, flags) != 0)
+        {
+          /* Shouldn't happen.  */
+          error (1, errno, "%s", dest_dirname);
+        }
+      same = SAME_INODE (source_dir_stats, dest_dir_stats);
+#endif
+
+      free (dest_dirname);
+    }
+
+  return same;
+}