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94 lines
2.6 KiB
C
94 lines
2.6 KiB
C
/* xreadlink.c -- readlink wrapper to return the link name in malloc'd storage
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Copyright (C) 2001, 2003, 2004, 2005 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; see the file COPYING.
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If not, write to the Free Software Foundation,
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51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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/* Written by Jim Meyering <jim@meyering.net> */
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#if HAVE_CONFIG_H
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# include <config.h>
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#endif
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#include "xreadlink.h"
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#include <stdio.h>
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#include <errno.h>
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#include <limits.h>
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#include <sys/types.h>
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#include <stdlib.h>
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#if HAVE_UNISTD_H
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# include <unistd.h>
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#endif
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#ifndef SIZE_MAX
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# define SIZE_MAX ((size_t) -1)
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#endif
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#ifndef SSIZE_MAX
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# define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2))
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#endif
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#define MAXSIZE (SIZE_MAX < SSIZE_MAX ? SIZE_MAX : SSIZE_MAX)
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#include "xalloc.h"
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/* Call readlink to get the symbolic link value of FILE.
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SIZE is a hint as to how long the link is expected to be;
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typically it is taken from st_size. It need not be correct.
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Return a pointer to that NUL-terminated string in malloc'd storage.
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If readlink fails, return NULL (caller may use errno to diagnose).
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If malloc fails, or if the link value is longer than SSIZE_MAX :-),
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give a diagnostic and exit. */
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char *
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xreadlink (char const *file, size_t size)
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{
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/* The initial buffer size for the link value. A power of 2
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detects arithmetic overflow earlier, but is not required. */
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size_t buf_size = size < MAXSIZE ? size + 1 : MAXSIZE;
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while (1)
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{
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char *buffer = xmalloc (buf_size);
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ssize_t r = readlink (file, buffer, buf_size);
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size_t link_length = r;
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/* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1
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with errno == ERANGE if the buffer is too small. */
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if (r < 0 && errno != ERANGE)
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{
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int saved_errno = errno;
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free (buffer);
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errno = saved_errno;
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return NULL;
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}
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if (link_length < buf_size)
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{
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buffer[link_length] = 0;
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return buffer;
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}
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free (buffer);
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if (buf_size <= MAXSIZE / 2)
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buf_size *= 2;
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else if (buf_size < MAXSIZE)
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buf_size = MAXSIZE;
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else
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xalloc_die ();
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}
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}
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