glibc/inet/ether_ntoh.c

/* Copyright (C) 1996-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996.

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

#include <errno.h>
#include <netinet/ether.h>
#include <netinet/if_ether.h>
#include <string.h>

#include <nss/nsswitch.h>


/* Type of the lookup function we need here.  */
typedef int (*lookup_function) (const struct ether_addr *, struct etherent *,
				char *, size_t, int *);

int
ether_ntohost (char *hostname, const struct ether_addr *addr)
{
  static service_user *startp;
  static lookup_function start_fct;
  service_user *nip;
  union
  {
    lookup_function f;
    void *ptr;
  } fct;
  int no_more;
  enum nss_status status = NSS_STATUS_UNAVAIL;
  struct etherent etherent;

  if (startp == NULL)
    {
      no_more = __nss_ethers_lookup2 (&nip, "getntohost_r", NULL, &fct.ptr);
      if (no_more)
	startp = (service_user *) -1;
      else
	{
	  startp = nip;
	  start_fct = fct.f;
	}
    }
  else
    {
      fct.f = start_fct;
      no_more = (nip = startp) == (service_user *) -1;
    }

  while (no_more == 0)
    {
      char buffer[1024];

      status = (*fct.f) (addr, &etherent, buffer, sizeof buffer, &errno);

      no_more = __nss_next2 (&nip, "getntohost_r", NULL, &fct.ptr, status, 0);
    }

  if (status == NSS_STATUS_SUCCESS)
    /* XXX This is a potential cause of trouble because the size of
       the HOSTNAME buffer is not known but the interface does not
       provide this information.  */
    strcpy (hostname, etherent.e_name);

  return status == NSS_STATUS_SUCCESS ? 0 : -1;
}