1 files changed, 123 insertions, 0 deletions
diff --git a/lib/areadlink-with-size.c b/lib/areadlink-with-size.c
new file mode 100644
index 0000000..7af97c2
--- /dev/null
+++ b/lib/areadlink-with-size.c
@@ -0,0 +1,123 @@
+/* readlink wrapper to return the link name in malloc'd storage.
+   Unlike xreadlink and xreadlink_with_size, don't ever call exit.
+
+   Copyright (C) 2001, 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/>.  */
+
+/* Written by Jim Meyering <jim@meyering.net>  */
+
+#include <config.h>
+
+#include "areadlink.h"
+
+#include <errno.h>
+#include <limits.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+/* SYMLINK_MAX is used only for an initial memory-allocation sanity
+   check, so it's OK to guess too small on hosts where there is no
+   arbitrary limit to symbolic link length.  */
+#ifndef SYMLINK_MAX
+# define SYMLINK_MAX 1024
+#endif
+
+#define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
+
+/* Call readlink to get the symbolic link value of FILE.
+   SIZE is a hint as to how long the link is expected to be;
+   typically it is taken from st_size.  It need not be correct.
+   Return a pointer to that NUL-terminated string in malloc'd storage.
+   If readlink fails, malloc fails, or if the link value is longer
+   than SSIZE_MAX, return NULL (caller may use errno to diagnose).  */
+
+char *
+areadlink_with_size (char const *file, size_t size)
+{
+  /* Some buggy file systems report garbage in st_size.  Defend
+     against them by ignoring outlandish st_size values in the initial
+     memory allocation.  */
+  size_t symlink_max = SYMLINK_MAX;
+  size_t INITIAL_LIMIT_BOUND = 8 * 1024;
+  size_t initial_limit = (symlink_max < INITIAL_LIMIT_BOUND
+                          ? symlink_max + 1
+                          : INITIAL_LIMIT_BOUND);
+
+  enum { stackbuf_size = 128 };
+
+  /* The initial buffer size for the link value.  */
+  size_t buf_size = (size == 0 ? stackbuf_size
+                     : size < initial_limit ? size + 1 : initial_limit);
+
+  while (1)
+    {
+      ssize_t r;
+      size_t link_length;
+      char stackbuf[stackbuf_size];
+      char *buf = stackbuf;
+      char *buffer = NULL;
+
+      if (! (size == 0 && buf_size == stackbuf_size))
+        {
+          buf = buffer = malloc (buf_size);
+          if (!buffer)
+            {
+              errno = ENOMEM;
+              return NULL;
+            }
+        }
+
+      r = readlink (file, buf, buf_size);
+      link_length = r;
+
+      if (r < 0)
+        {
+          free (buffer);
+          return NULL;
+        }
+
+      if (link_length < buf_size)
+        {
+          buf[link_length] = 0;
+          if (!buffer)
+            {
+              buffer = malloc (link_length + 1);
+              if (buffer)
+                return memcpy (buffer, buf, link_length + 1);
+            }
+          else if (link_length + 1 < buf_size)
+            {
+              /* Shrink BUFFER before returning it.  */
+              char *shrinked_buffer = realloc (buffer, link_length + 1);
+              if (shrinked_buffer != NULL)
+                buffer = shrinked_buffer;
+            }
+          return buffer;
+        }
+
+      free (buffer);
+      if (buf_size <= MAXSIZE / 2)
+        buf_size *= 2;
+      else if (buf_size < MAXSIZE)
+        buf_size = MAXSIZE;
+      else
+        {
+          errno = ENOMEM;
+          return NULL;
+        }
+    }
+}