/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
- Copyright (C) 2001, 2003 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>
#include <errno.h>
-#ifndef errno
-extern int errno;
-#endif
-
#include <limits.h>
#include <sys/types.h>
#include <stdlib.h>
# include <unistd.h>
#endif
-#include "xalloc.h"
-#include "xreadlink.h"
-
#ifndef SIZE_MAX
# define SIZE_MAX ((size_t) -1)
#endif
# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
#endif
+#define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
+
+#include "xalloc.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 (caller may use errno to diagnose).
- If realloc fails, or if the link value is longer than SIZE_MAX :-),
+ If malloc fails, or if the link value is longer than SSIZE_MAX :-),
give a diagnostic and exit. */
char *
-xreadlink (char const *filename)
+xreadlink (char const *filename, size_t size)
{
/* The initial buffer size for the link value. A power of 2
detects arithmetic overflow earlier, but is not required. */
- size_t buf_size = 128;
+ size_t buf_size = size < MAXSIZE ? size + 1 : MAXSIZE;
while (1)
{
char *buffer = xmalloc (buf_size);
- ssize_t link_length = readlink (filename, buffer, buf_size);
+ ssize_t r = readlink (filename, buffer, buf_size);
+ size_t link_length = r;
- if (link_length < 0)
+ /* 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)
{
int saved_errno = errno;
free (buffer);
return NULL;
}
- if ((size_t) link_length < buf_size)
+ if (link_length < buf_size)
{
buffer[link_length] = 0;
return buffer;
}
free (buffer);
- buf_size *= 2;
- if (SSIZE_MAX < buf_size || (SIZE_MAX / 2 < SSIZE_MAX && buf_size == 0))
+ if (buf_size <= MAXSIZE / 2)
+ buf_size *= 2;
+ else if (buf_size < MAXSIZE)
+ buf_size = MAXSIZE;
+ else
xalloc_die ();
}
}