#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>

int
main (int argc, char **argv)
{
  struct msghdr msg1  = { 0 }, msg2 = { 0 };
  struct cmsghdr *cmsg;
  struct iovec iov;
  int sv1[2], sv2[2], *fds, dummy;
  char buf[CMSG_SPACE(sizeof sv2)], buf2[2048];

  if (socketpair (PF_UNIX, SOCK_STREAM, 0, sv1) == -1)
    {
      perror ("socketpair");
      return 1;
    }
#if 1
  if (socketpair (PF_UNIX, SOCK_STREAM, 0, sv2) == -1)
    {
      perror ("socketpair");
      return 1;
    }
#else
  if ((sv2[0] = open ("/tmp/file1", O_RDONLY)) == -1)
    {
      perror ("open");
      return 1;
    }
  if ((sv2[1] = open ("/tmp/file2", O_RDONLY)) == -1)
    {
      perror ("open");
      return 1;
    }
#endif

  iov.iov_base = &dummy;
  iov.iov_len = 1;

  msg1.msg_iov = &iov;
  msg1.msg_iovlen = 1;
  msg1.msg_control = buf;
  msg1.msg_controllen = sizeof (buf);

  cmsg = CMSG_FIRSTHDR (&msg1);
  cmsg->cmsg_level = SOL_SOCKET;
  cmsg->cmsg_type = SCM_RIGHTS;
  cmsg->cmsg_len = CMSG_LEN (sizeof (sv2));
  memcpy (CMSG_DATA (cmsg), sv2, sizeof (sv2));

  if (sendmsg (sv1[0], &msg1, 0) < 0)
    {
      perror ("sendmsg");
      return 1;
    }

  assert (close (sv2[0]) == 0);
  assert (close (sv2[1]) == 0);

  msg2.msg_name = NULL;
  msg2.msg_namelen = 0;
  msg2.msg_iov = &iov;
  msg2.msg_iovlen = 1;
  msg2.msg_controllen = sizeof (buf2);
  msg2.msg_control = buf2;

  if (recvmsg (sv1[1], &msg2, msg2.msg_flags) < 0)
    {
      perror ("recvmsg");
      return 1;
    }

  cmsg = CMSG_FIRSTHDR (&msg2);
  assert (cmsg->cmsg_level == SOL_SOCKET);
  assert (cmsg->cmsg_type == SCM_RIGHTS);
  assert (sizeof (sv2) == (cmsg->cmsg_len - ((char *)CMSG_DATA (cmsg) - (char *)cmsg)));

  fds = (int*) CMSG_DATA (cmsg);

  assert (close (fds[0]) == 0);
  assert (close (fds[1]) == 0);

  return 0;
}