+static const socklen_t controllen = CMSG_LEN (sizeof (int));
+
+static void
+receive_stdout (int s)
+{
+ static struct cmsghdr *cmptr = NULL, *h;
+ struct msghdr msg;
+ struct iovec iov[1];
+
+ /* Our 1 byte buffer */
+ char buf[1];
+
+ if (NULL == cmptr) {
+ cmptr = malloc (controllen);
+ if (NULL == cmptr) {
+ perror ("malloc");
+ exit (EXIT_FAILURE);
+ }
+ }
+
+ /* Don't specify a source */
+ msg.msg_name = NULL;
+ msg.msg_namelen = 0;
+
+ /* Initialise the msghdr to receive zero byte */
+ iov[0].iov_base = buf;
+ iov[0].iov_len = 1;
+ msg.msg_iov = iov;
+ msg.msg_iovlen = 1;
+
+ /* Initialise the control data */
+ msg.msg_control = cmptr;
+ msg.msg_controllen = controllen;
+
+ /* Read a message from the socket */
+ ssize_t n = recvmsg (s, &msg, 0);
+ if (n < 0) {
+ perror ("recvmsg stdout fd");
+ exit (EXIT_FAILURE);
+ }
+
+ h = CMSG_FIRSTHDR(&msg);
+ if (NULL == h) {
+ fprintf (stderr, "didn't receive a stdout file descriptor\n");
+ }
+
+ else {
+ /* Extract the transferred file descriptor from the control data */
+ unsigned char *data = CMSG_DATA (h);
+ int fd = *(int *)data;
+
+ /* Duplicate the received file descriptor to stdout */
+ dup2 (fd, STDOUT_FILENO);
+ close (fd);
+ }
+}
+
+static void
+send_stdout (int s)
+{
+ static struct cmsghdr *cmptr = NULL;
+ struct msghdr msg;
+ struct iovec iov[1];
+
+ /* Our 1 byte dummy buffer */
+ char buf[1];
+
+ /* Don't specify a destination */
+ msg.msg_name = NULL;
+ msg.msg_namelen = 0;
+
+ /* Initialise the msghdr to send zero byte */
+ iov[0].iov_base = buf;
+ iov[0].iov_len = 1;
+ msg.msg_iov = iov;
+ msg.msg_iovlen = 1;
+
+ /* Initialize the zero byte */
+ buf[0] = 0;
+
+ /* Initialize the control data */
+ if (NULL == cmptr) {
+ cmptr = malloc (controllen);
+ if (NULL == cmptr) {
+ perror ("malloc");
+ exit (EXIT_FAILURE);
+ }
+ }
+ cmptr->cmsg_level = SOL_SOCKET;
+ cmptr->cmsg_type = SCM_RIGHTS;
+ cmptr->cmsg_len = controllen;
+
+ /* Add control header to the message */
+ msg.msg_control = cmptr;
+ msg.msg_controllen = controllen;
+
+ /* Add STDOUT to the control data */
+ unsigned char *data = CMSG_DATA (cmptr);
+ *(int *)data = STDOUT_FILENO;
+
+ if (sendmsg (s, &msg, 0) != 1) {
+ perror ("sendmsg stdout fd");
+ exit (EXIT_FAILURE);
+ }
+}
+
+static void
+close_stdout (void)
+{
+ int fd;
+
+ fd = open ("/dev/null", O_WRONLY);
+ if (fd == -1)
+ perror ("/dev/null");
+ else {
+ dup2 (fd, STDOUT_FILENO);
+ close (fd);
+ }
+}
+