/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
- Copyright (C) 2001, 2003, 2004 Free Software Foundation, Inc.
+ Copyright (C) 2001, 2003-2007 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
If not, write to the Free Software Foundation,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
-/* Written by Jim Meyering <jim@meyering.net> */
+/* Written by Jim Meyering <jim@meyering.net>
+ and Bruno Haible <bruno@clisp.org>. */
-#if HAVE_CONFIG_H
-# include <config.h>
-#endif
+#include <config.h>
+/* Specification. */
#include "xreadlink.h"
#include <stdio.h>
+#include <string.h>
#include <errno.h>
#include <limits.h>
#include <sys/types.h>
#include <stdlib.h>
-#if HAVE_UNISTD_H
-# include <unistd.h>
-#endif
+#include <unistd.h>
#ifndef SIZE_MAX
# define SIZE_MAX ((size_t) -1)
# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
#endif
-#define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
-
-#include "xalloc.h"
+#ifdef NO_XMALLOC
+# define xmalloc malloc
+#else
+# include "xalloc.h"
+#endif
/* 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 (caller may use errno to diagnose).
- If malloc fails, or if the link value is longer than SSIZE_MAX :-),
+ If realloc fails, or if the link value is longer than SIZE_MAX :-),
give a diagnostic and exit. */
char *
-xreadlink (char const *filename, size_t size)
+xreadlink (char const *filename)
{
/* 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 < MAXSIZE ? size + 1 : MAXSIZE;
+#define INITIAL_BUF_SIZE 1024
+
+ /* Allocate the initial buffer on the stack. This way, in the common
+ case of a symlink of small size, we get away with a single small malloc()
+ instead of a big malloc() followed by a shrinking realloc(). */
+ char initial_buf[INITIAL_BUF_SIZE];
+
+ char *buffer = initial_buf;
+ size_t buf_size = sizeof (initial_buf);
while (1)
{
- char *buffer = xmalloc (buf_size);
- ssize_t r = readlink (filename, buffer, buf_size);
- size_t link_length = r;
+ /* Attempt to read the link into the current buffer. */
+ ssize_t link_length = readlink (filename, buffer, buf_size);
/* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
with errno == ERANGE if the buffer is too small. */
- if (r < 0 && errno != ERANGE)
+ if (link_length < 0 && errno != ERANGE)
{
- int saved_errno = errno;
- free (buffer);
- errno = saved_errno;
+ if (buffer != initial_buf)
+ {
+ int saved_errno = errno;
+ free (buffer);
+ errno = saved_errno;
+ }
return NULL;
}
- if (link_length < buf_size)
+ if ((size_t) link_length < buf_size)
{
- buffer[link_length] = 0;
+ buffer[link_length++] = '\0';
+
+ /* Return it in a chunk of memory as small as possible. */
+ if (buffer == initial_buf)
+ {
+ buffer = (char *) xmalloc (link_length);
+#ifdef NO_XMALLOC
+ if (buffer == NULL)
+ return NULL;
+#endif
+ memcpy (buffer, initial_buf, link_length);
+ }
+ else
+ {
+ /* Shrink buffer before returning it. */
+ if ((size_t) link_length < buf_size)
+ {
+ char *smaller_buffer = (char *) realloc (buffer, link_length);
+
+ if (smaller_buffer != NULL)
+ buffer = smaller_buffer;
+ }
+ }
return buffer;
}
- free (buffer);
- if (buf_size <= MAXSIZE / 2)
- buf_size *= 2;
- else if (buf_size < MAXSIZE)
- buf_size = MAXSIZE;
- else
+ if (buffer != initial_buf)
+ free (buffer);
+ buf_size *= 2;
+ if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
+#ifdef NO_XMALLOC
+ return NULL;
+#else
xalloc_die ();
+#endif
+ buffer = (char *) xmalloc (buf_size);
+#ifdef NO_XMALLOC
+ if (buffer == NULL)
+ return NULL;
+#endif
}
}