Hi,
Here is the variant of readlink that allocates memory for the result but
does not exit in case of "out of memory" situation. Suggested by Jim.
This is mostly code duplication with 'xreadlink' for now; the next patch
will change xreadlink to use areadlink.
Comments, objections?
Bruno
2007-09-15 Bruno Haible <[EMAIL PROTECTED]>
* modules/areadlink: New file.
* lib/areadlink.h (areadlink): New declaration.
* lib/areadlink.c: New file, based on lib/xreadlink.c.
=============================== modules/areadlink ==========================
Description:
Reading symbolic links without size limitation.
Files:
lib/areadlink.h
lib/areadlink.c
Depends-on:
readlink
ssize_t
unistd
malloc-posix
configure.ac:
Makefile.am:
lib_SOURCES += areadlink.c
Include:
"areadlink.h"
License:
GPL
Maintainer:
Bruno Haible, Jim Meyering
================================ lib/areadlink.c ===========================
/* areadlink.c -- 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 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 2, 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; see the file COPYING.
If not, write to the Free Software Foundation,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
/* Written by Jim Meyering <[EMAIL PROTECTED]>
and Bruno Haible <[EMAIL PROTECTED]>. */
#include <config.h>
/* Specification. */
#include "areadlink.h"
#include <string.h>
#include <errno.h>
#include <limits.h>
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#ifndef SIZE_MAX
# define SIZE_MAX ((size_t) -1)
#endif
#ifndef SSIZE_MAX
# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
#endif
/* Call readlink to get the symbolic link value of FILENAME.
Return a pointer to that NUL-terminated string in malloc'd storage.
If readlink fails, return NULL and set errno.
If realloc fails, or if the link value is longer than SIZE_MAX :-),
return NULL and set errno to ENOMEM. */
char *
areadlink (char const *filename)
{
/* The initial buffer size for the link value. A power of 2
detects arithmetic overflow earlier, but is not required. */
#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)
{
/* 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 (link_length < 0 && errno != ERANGE)
{
if (buffer != initial_buf)
{
int saved_errno = errno;
free (buffer);
errno = saved_errno;
}
return NULL;
}
if ((size_t) link_length < buf_size)
{
buffer[link_length++] = '\0';
/* Return it in a chunk of memory as small as possible. */
if (buffer == initial_buf)
{
buffer = (char *) malloc (link_length);
if (buffer == NULL)
/* errno is ENOMEM. */
return NULL;
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;
}
if (buffer != initial_buf)
free (buffer);
buf_size *= 2;
if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
{
errno = ENOMEM;
return NULL;
}
buffer = (char *) malloc (buf_size);
if (buffer == NULL)
/* errno is ENOMEM. */
return NULL;
}
}
============================================================================
*** lib/areadlink.h 28 Aug 2007 09:13:05 -0000 1.1
--- lib/areadlink.h 15 Sep 2007 23:34:43 -0000
***************
*** 21,24 ****
--- 21,25 ----
#include <stddef.h>
+ extern char *areadlink (char const *filename);
extern char *areadlink_with_size (char const *filename, size_t size_hint);
