#include <sys/types.h>
#include <sys/errno.h>
#include <sys/fcntl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/uio.h>
#include <sys/wait.h>

#include <err.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

static void
usage(void)
{
	fprintf(stderr, "Usage: sf_copy <src>\n");
	exit(1);
}

static int
parent(int sockfd, int filefd)
{
	off_t sent;
	int rc;

	rc = sendfile(filefd, sockfd, 0, 0, NULL, &sent, SF_NOCACHE);
	if (rc < 0)
		warn("sendfile");
	return (rc);
}

static int
child_null(int sockfd)
{
	static unsigned char junk[1 << 20];
	off_t off = 0;
	int ret;

	for (;;) {
		ret = read(sockfd, junk, sizeof(junk));
		if (ret < 0) {
			if (errno == ECONNRESET)
				break;
			err(1, "read, off=%jd", off);
		}
		off += ret;
		if (ret == 0)
			break;
	}
	return 0;
}

int
main(int argc, const char **argv)
{
	int error, ifd, sockfds[2], status;
	pid_t child;

	if (argc != 2)
		usage();

	ifd = open(argv[1], O_RDONLY);
	if (ifd == -1)
		err(errno, "open(%s)", argv[1]);
	
	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sockfds) == -1)
		err(errno, "socketpair");

	child = fork();
	if (child == -1)
		err(1, "fork");
	if (child > 0) {
		close(sockfds[0]);
		error = parent(sockfds[1], ifd);
		if (error)
			err(errno, "parent");
		/* close writer socket now */
		close(sockfds[1]);
		close(ifd);
		waitpid(child, &status, 0);
		if (error == -1)
			err(errno, "waitpid");
		error = WEXITSTATUS(status);
	} else {
		close(ifd);
		close(sockfds[1]);
		child_null(sockfds[0]);
		close(sockfds[0]);
	}

	return (error);
}