man.bsd.lv manual page server

#include <sys/socket.h>

#include <err.h>
#include <stdio.h>
#include <string.h>
#include <sysexits.h>
#include <unistd.h>

#define	HELLOLEN    sizeof("hello")

int
main()
{
	struct msghdr msg;
	union {
		struct cmsghdr hdr;
		unsigned char	 buf[CMSG_SPACE(sizeof(int))];
	} cmsgbuf;
	char buf[HELLOLEN];
	int hellofd[2];
	int presharedfd[2];
	struct cmsghdr *cmsg;

	if (socketpair(PF_LOCAL, SOCK_STREAM, 0, presharedfd) == -1)
		err(EX_OSERR, "failed to create a pre-shared socket pair");

	memset(&msg, 0, sizeof(msg));
	msg.msg_control = &cmsgbuf.buf;
	msg.msg_controllen = sizeof(cmsgbuf.buf);
	msg.msg_iov = NULL;
	msg.msg_iovlen = 0;

	switch (fork()) {
	case -1:
		err(EX_OSERR, "fork");
	case 0:
		close(presharedfd[0]);
		strlcpy(buf, "hello", HELLOLEN);

		if (recvmsg(presharedfd[1], &msg, 0) == -1)
			err(EX_IOERR, "failed to receive a message");
		if (msg.msg_flags & (MSG_CTRUNC | MSG_TRUNC))
			errx(EX_IOERR, "control message truncated");
		for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL;
		    cmsg = CMSG_NXTHDR(&msg, cmsg)) {
			if (cmsg->cmsg_len == CMSG_LEN(sizeof(int)) &&
			    cmsg->cmsg_level == SOL_SOCKET &&
			    cmsg->cmsg_type == SCM_RIGHTS) {
				hellofd[1] = *(int *)CMSG_DATA(cmsg);
				printf("child: sending '%s'0, buf);
				if (write(hellofd[1], buf, HELLOLEN) == -1)
				    err(EX_IOERR, "failed to send 'hello'");
			}
		}
		break;
	default:
		close(presharedfd[1]);

		if (socketpair(PF_LOCAL, SOCK_STREAM, 0, hellofd) == -1)
			err(EX_OSERR, "failed to create a 'hello' socket pair");

		cmsg = CMSG_FIRSTHDR(&msg);
		cmsg->cmsg_len = CMSG_LEN(sizeof(int));
		cmsg->cmsg_level = SOL_SOCKET;
		cmsg->cmsg_type = SCM_RIGHTS;
		*(int *)CMSG_DATA(cmsg) = hellofd[1];

		if (sendmsg(presharedfd[0], &msg, 0) == -1)
			err(EX_IOERR, "sendmsg");
		close(hellofd[1]);

		if (read(hellofd[0], buf, HELLOLEN) == -1)
			err(EX_IOERR, "faild to receive 'hello'");
		printf("parent: received '%s'0, buf);
		break;
	}

	return (0);
}