symlink.c
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/* GNU Mailutils -- a suite of utilities for electronic mail
Copyright (C) 1999-2003, 2005-2007, 2009-2012, 2014-2017 Free
Software Foundation, Inc.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 3 of the License, or (at your option) any later version.
This library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General
Public License along with this library. If not, see
<http://www.gnu.org/licenses/>. */
#if HAVE_CONFIG_H
# include <config.h>
#endif
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <mailutils/types.h>
#include <mailutils/util.h>
#define INITIAL_READLINK_SIZE 128
int
mu_readlink (const char *name, char **pbuf, size_t *psize, size_t *plen)
{
size_t status = 0;
char *buf = *pbuf;
size_t size = *psize;
ssize_t linklen;
while (1)
{
if (!buf)
{
size = INITIAL_READLINK_SIZE;
buf = malloc (size);
}
else
{
char *p;
size_t newsize = size << 1;
if (newsize < size)
{
status = ENAMETOOLONG;
break;
}
size = newsize;
p = realloc (buf, size);
if (!p)
free (buf);
buf = p;
}
if (!buf)
{
status = ENOMEM;
break;
}
linklen = readlink (name, buf, size);
if (linklen < 0 && errno != ERANGE)
{
status = errno;
break;
}
if ((size_t) linklen < size)
{
buf[linklen++] = '\0';
status = 0;
break;
}
}
if (status)
{
if (buf)
{
free (buf);
buf = NULL;
}
size = 0;
}
*pbuf = buf;
*psize = size;
if (plen)
*plen = linklen;
return status;
}
#ifndef _POSIX_SYMLOOP_MAX
# define _POSIX_SYMLOOP_MAX 255
#endif
int
mu_unroll_symlink (const char *name, char **pout)
{
size_t symloops = 0;
struct slbuf { char *base; size_t size; } buf[2];
int idx = 0;
int status;
buf[0].base = buf[1].base = NULL;
buf[0].size = buf[1].size = 0;
while (symloops++ < _POSIX_SYMLOOP_MAX)
{
struct stat st;
size_t len;
if (lstat (name, &st) == -1)
return errno;
if (!S_ISLNK (st.st_mode))
{
if (!buf[idx].base)
{
buf[idx].base = strdup (name);
if (!buf[idx].base)
return ENOMEM;
}
status = 0;
break;
}
idx = !idx;
status = mu_readlink (name, &buf[idx].base, &buf[idx].size, &len);
if (status)
break;
name = mu_normalize_path (buf[idx].base);
}
if (status)
{
free (buf[0].base);
free (buf[1].base);
}
else
{
*pout = buf[idx].base;
free (buf[!idx].base);
}
return status;
}