-/* exclude.c -- exclude file names
+/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
- Copyright 2001 Free Software Foundation, Inc.
+ Copyright (C) 2001, 2003, 2004 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
# include <config.h>
#endif
+#include "xreadlink.h"
+
#include <stdio.h>
-#if HAVE_SYS_TYPES_H
-# include <sys/types.h>
-#endif
-#if HAVE_STDLIB_H
-# include <stdlib.h>
-#endif
+#include <errno.h>
+#include <limits.h>
+#include <sys/types.h>
+#include <stdlib.h>
#if HAVE_UNISTD_H
# include <unistd.h>
#endif
+#ifndef SIZE_MAX
+# define SIZE_MAX ((size_t) -1)
+#endif
+#ifndef SSIZE_MAX
+# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
+#endif
+
#include "xalloc.h"
-#include "xreadlink.h"
/* Call readlink to get the symbolic link value of FILENAME.
+ 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, return NULL (use errno to diagnose).
- If realloc fails, or if the link value is longer than SIZE_MAX :-),
+ If readlink fails, return NULL (caller may use errno to diagnose).
+ If malloc fails, or if the link value is longer than SSIZE_MAX :-),
give a diagnostic and exit. */
char *
-xreadlink (char const *filename, size_t *link_length_arg)
+xreadlink (char const *filename, size_t size)
{
- size_t buf_size = 128; /* must be a power of 2 */
- char *buffer = NULL;
+ /* The initial buffer size for the link value. A power of 2
+ detects arithmetic overflow earlier, but is not required. */
+ size_t buf_size = size + 1;
while (1)
{
- int link_length;
- buffer = (char *) xrealloc (buffer, buf_size);
- link_length = readlink (filename, buffer, buf_size);
+ char *buffer = xmalloc (buf_size);
+ ssize_t link_length = readlink (filename, buffer, buf_size);
+
if (link_length < 0)
{
+ int saved_errno = errno;
free (buffer);
+ errno = saved_errno;
return NULL;
}
- if (link_length < buf_size)
+
+ if ((size_t) link_length < buf_size)
{
- *link_length_arg = link_length;
buffer[link_length] = 0;
return buffer;
}
+
+ free (buffer);
buf_size *= 2;
- if (buf_size == 0)
+ if (! (0 < buf_size && buf_size <= SSIZE_MAX))
xalloc_die ();
}
}