#include <sys/ioctl.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main(void)
{
	int nspace;
	int hostfd, appfd;
	char *pts;
	int flags;
	char buf[BUFSIZ] = {0};
	size_t n;
	ssize_t nwrit;

	if ((hostfd = posix_openpt(O_RDWR|O_NOCTTY)) == -1)
		err(1, "posix_openpt");
	if (grantpt(hostfd) == -1)
		err(1, "grantpt");
	if (unlockpt(hostfd) == -1)
		err(1, "unlockpt");
	if ((pts = ptsname(hostfd)) == NULL)
		err(1, "ptsname");
	if ((appfd = open(pts, O_RDWR|O_NOCTTY)) == -1)
		err(1, "open app side");
	if (ioctl(hostfd, FIONSPACE, &nspace) == -1)
		err(1, "ioctl(FIONSPACE)");
	fprintf(stderr, "nspace=%d\n", nspace);
	if ((flags = fcntl(hostfd, F_GETFL)) == -1)
		err(1, "fcntl(F_GETFL)");
	if (fcntl(hostfd, F_SETFL, flags|O_NONBLOCK) == -1)
		err(1, "fcntl(F_SETFL)");
	for (n = 0;
	     (nwrit = write(hostfd, buf, sizeof(buf))) != -1;
	     n += (size_t)nwrit)
		fprintf(stderr, "%zu bytes so far\n", n);
	warn("write failed -- is this ever reached?");
	fflush(stdout);
	return ferror(stdout);
}