#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/stat.h>

void
sendfd(int sockfd, int fd)
{
	char dummybuf;
	struct iovec iov;
	struct msghdr mh;
	struct cmsghdr *cmp = malloc(CMSG_LEN(sizeof(int)));

	if (cmp == NULL) {
		fprintf(stderr, "can't malloc: %s\n", strerror(errno));
		exit(1);
	}
	iov.iov_base = &dummybuf;
	iov.iov_len = 1;
	mh.msg_iov = &iov;
	mh.msg_iovlen = 1;
	mh.msg_name = NULL;
	mh.msg_namelen = 0;
	mh.msg_control = cmp;
	mh.msg_controllen = CMSG_LEN(sizeof(int));
	cmp->cmsg_level = SOL_SOCKET;
	cmp->cmsg_type = SCM_RIGHTS;
	cmp->cmsg_len = CMSG_LEN(sizeof(int));
	*(int *)CMSG_DATA(cmp) = fd;
	if (sendmsg(sockfd, &mh, 0) < 0) {
		fprintf(stderr, "sendmsg failed: %s\n", strerror(errno));
		exit(1);
	}
	free(cmp);
}

int
recvfd(int sockfd)
{
	struct msghdr mh;
	int nfd;
	char dummybuf;
	struct iovec iov;
	long csz = CMSG_LEN(sizeof(int));
	struct cmsghdr *cmp = malloc(csz);

	if (cmp == NULL) {
		fprintf(stderr, "can't malloc: %s\n", strerror(errno));
		exit(1);
	}
	iov.iov_base = &dummybuf;
	iov.iov_len = 1;
	mh.msg_iov = &iov;
	mh.msg_iovlen = 1;
	mh.msg_name = NULL;
	mh.msg_namelen = 0;
	mh.msg_control = cmp;
	mh.msg_controllen = csz;
	if (recvmsg(sockfd, &mh, 0) < 0) {
		fprintf(stderr, "recvmsg failed: %s\n", strerror(errno));
		exit(1);
	}
	if (mh.msg_controllen == 0) {
		fprintf(stderr, "no control data in message\n");
		exit(1);
	}
	if (mh.msg_controllen != csz)
		fprintf(stderr, "WARNING: controllen %ld, should be %ld\n", mh.msg_controllen, csz);
	nfd = *(int *)CMSG_DATA(cmp);
	free(cmp);
	return(nfd);
}

int
main()
{
	int nfd, nfd2;
	int fd[2];
	struct stat sbuf[2];

	printf("sizeof(int) = %d\n", (int)sizeof(int));
	printf("sizeof(long) = %d\n", (int)sizeof(long));
	printf("sizeof(size_t) = %d\n", (int)sizeof(size_t));
	printf("CMSG_LEN(sizeof(int)) = %d\n", (int)CMSG_LEN(sizeof(int)));
	printf("CMSG_SPACE(sizeof(int)) = %d\n", (int)CMSG_SPACE(sizeof(int)));
	if (socketpair(AF_UNIX, SOCK_STREAM, 0, fd) < 0) {
		fprintf(stderr, "can't create socket pair: %s\n", strerror(errno));
		exit(1);
	}
	if ((nfd = open("/etc/services", O_RDONLY)) < 0) {
		fprintf(stderr, "can't open /etc/services: %s", strerror(errno));
		exit(1);
	}
	sendfd(fd[0], nfd);
	nfd2 = recvfd(fd[1]);
	if (fstat(nfd, &sbuf[0]) < 0 || fstat(nfd2, &sbuf[1]) < 0) {
		fprintf(stderr, "fstat failed: %s\n", strerror(errno));
		exit(1);
	}
	if (sbuf[0].st_dev == sbuf[1].st_dev && sbuf[0].st_ino == sbuf[1].st_ino)
		printf("the files are the same\n");
	else
		printf("the files are different\n");
	exit(0);
}