/* Copyright (C) 1995-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C 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 2.1 of the License, or (at your option) any later version.

   The GNU C 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 the GNU C Library; if not, see

   <http://www.gnu.org/licenses/>.  */

#include <alloca.h>

#include <errno.h>

#include <fcntl.h>

#include <unistd.h>

#include <netdb.h>

#include <not-cancel.h>

#include <stdbool.h>

#define HOSTIDFILE "/etc/hostid"

#ifdef SET_PROCEDURE

int

sethostid (long int id)

{

  int fd;

  ssize_t written;

  int32_t id32 = id;

  /* Test for appropriate rights to set host ID.  */

  if (__libc_enable_secure)

    {

      __set_errno (EPERM);

      return -1;

    }

  /* Make sure the ID is not too large.  Needed for bi-arch support.   */

  if (id32 != id)

    {

      __set_errno (EOVERFLOW);

      return -1;

    }

  /* Open file for writing.  Everybody is allowed to read this file.  */

  fd = __open_nocancel (HOSTIDFILE, O_CREAT|O_WRONLY|O_TRUNC, 0644);

  if (fd < 0)

    return -1;

  written = __write_nocancel (fd, &id32, sizeof (id32));

  __close_nocancel_nostatus (fd);

  return written != sizeof (id32) ? -1 : 0;

}

#else

# include <string.h>

# include <sys/param.h>

# include <resolv/netdb.h>

# include <netinet/in.h>

# include <scratch_buffer.h>

long int

gethostid (void)

{

  char hostname[MAXHOSTNAMELEN + 1];

  struct hostent hostbuf, *hp;

  int32_t id;

  struct in_addr in;

  int herr;

  int fd;

  /* First try to get the ID from a former invocation of sethostid.  */

  fd = __open_nocancel (HOSTIDFILE, O_RDONLY|O_LARGEFILE, 0);

  if (fd >= 0)

    {

      ssize_t n = __read_nocancel (fd, &id, sizeof (id));

      __close_nocancel_nostatus (fd);

      if (n == sizeof (id))

	return id;

    }

  /* Getting from the file was not successful.  An intelligent guess

     for a unique number of a host is its IP address.  To get the IP

     address we need to know the host name.  */

  if (__gethostname (hostname, MAXHOSTNAMELEN) < 0 || hostname[0] == '\0')

    /* This also fails.  Return and arbitrary value.  */

    return 0;

  /* Determine the IP address of the host name.  */

  struct scratch_buffer tmpbuf;

  scratch_buffer_init (&tmpbuf);

  while (true)

    {

      int ret = __gethostbyname_r (hostname, &hostbuf,

				   tmpbuf.data, tmpbuf.length, &hp, &herr;;

      if (ret == 0 && hp != NULL)

	break;

      else

	{

	  /* Enlarge the buffer on ERANGE.  */

	  if (ret != 0 && herr == NETDB_INTERNAL && errno == ERANGE)

	    {

	      if (!scratch_buffer_grow (&tmpbuf))

		return 0;

	    }

	  /* Other errors are a failure.  Return an arbitrary value.  */

	  else

	    {

	      scratch_buffer_free (&tmpbuf);

	      return 0;

	    }

	}

    }

  in.s_addr = 0;

  memcpy (&in, hp->h_addr,

	  (int) sizeof (in) < hp->h_length ? (int) sizeof (in) : hp->h_length);

  scratch_buffer_free (&tmpbuf);

  /* For the return value to be not exactly the IP address we do some

     bit fiddling.  */

  return (int32_t) (in.s_addr << 16 | in.s_addr >> 16);

}

#endif