// $Id: unify-unify.c 1973 2005-03-24 00:12:23Z ensc $    --*- c -*--

// Copyright (C) 2004 Enrico Scholz <enrico.scholz@informatik.tu-chemnitz.de>
//  
// 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; version 2 of the License.
//  
// 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; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.


#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include "unify.h"
#include "vserver.h"

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>

bool
Unify_unify(char const *src, struct stat const UNUSED *src_stat,
	    char const *dst, bool ignore_zero)
{
  size_t	l = strlen(dst);
  char		tmpfile[l + sizeof(";XXXXXX")];
  int		fd;
  bool		res = false;
  struct stat	st;
  bool		lstat_succeeded;
  sigset_t	mask_new, mask_old;
  int		old_errno;

  // at first, set the ILI flags on 'src'
  if (vc_set_iattr(src,
		   0,
		   VC_IATTR_IUNLINK|VC_IATTR_IMMUTABLE,
		   VC_IATTR_IUNLINK|VC_IATTR_IMMUTABLE)==-1) {
    perror("vc_set_iattr()");
    return false;
  }

  lstat_succeeded = lstat(dst, &st)==0;

  sigfillset(&mask_new);
  if (sigprocmask(SIG_SETMASK, &mask_new, &mask_old)==-1) {
    perror("sigprocmask()");
    return false;
  }
    
  
  // check if 'dst' already exists
  // when ignore_zero is true, do not make backups of empty destinations
  if (lstat_succeeded && (st.st_size>0 || !ignore_zero)) {
      // now, create a temporary filename
    memcpy(tmpfile,   dst, l);
    memcpy(tmpfile+l, ";XXXXXX", 8);
    fd = mkstemp(tmpfile);
    close(fd);

    if (fd==-1) {
      perror("mkstemp()");
      tmpfile[0] = '\0';
      goto err;
    }

      // and rename the old file to this name

      // NOTE: this rename() is race-free; when an attacker makes 'tmpfile' a
      // directory, the operation would fail; when making it a symlink to a file
      // or directory, the symlink but not the file/directory would be overridden
    if (rename(dst, tmpfile)==-1) {
      perror("rename()");
      goto err;
    }
  }
  else {
    if (lstat_succeeded) unlink(dst);	
    tmpfile[0] = '\0';
  }

  // now, link the src-file to dst
  if (link(src, dst)==-1) {
    perror("link()");

    unlink(dst);
    if (tmpfile[0]!='\0' &&
	rename(tmpfile, dst)==-1) {
      perror("FATAL error in rename()");
      _exit(1);
    }
    goto err;
  }

  res = true;

  err:
  old_errno = errno;

  if (tmpfile[0]!='\0')
    unlink(tmpfile);

  if (sigprocmask(SIG_SETMASK, &mask_old, 0)==-1)
    perror("sigprocmask()");

  errno     = old_errno;
  return res;
}