#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>

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

static void
test_sendto_self(int to_s, int s)
{
        struct msghdr msg;
        struct iovec iov;
        union {
                struct cmsghdr cm;
                uint8_t data[CMSG_SPACE(sizeof(int))];
        } ctrl;
        struct cmsghdr *cm;
        int n, buf;

        iov.iov_base = &buf;
        iov.iov_len = sizeof(buf);

        memset(&msg, 0, sizeof(msg));
        msg.msg_iov = &iov;
        msg.msg_iovlen = 1;
        msg.msg_control = ctrl.data;
        msg.msg_controllen = sizeof(ctrl.data);

        memset(&ctrl, 0, sizeof(ctrl));
        cm = CMSG_FIRSTHDR(&msg);
        cm->cmsg_len = CMSG_LEN(sizeof(int));
        cm->cmsg_level = SOL_SOCKET;
        cm->cmsg_type = SCM_RIGHTS;
        *((int *)CMSG_DATA(cm)) = s;

        n = sendmsg(to_s, &msg, 0);
        if (n < 0)
                err(1, "sendmsg failed");
        else if (n != sizeof(buf))
                errx(1, "sendmsg sent %d", n);
}

static void
usage(const char *cmd)
{
        fprintf(stderr, "%s [-x]\n", cmd);
        exit(1);
}

int
main(int argc, char *argv[])
{
        int s[2], opt, xref;

        xref = 0;
        while ((opt = getopt(argc, argv, "x")) != -1) {
                switch (opt) {
                case 'x':
                        xref = 1;
                        break;

                default:
                        usage(argv[0]);
                }
        }

        if (socketpair(AF_LOCAL, SOCK_STREAM, 0, s) < 0)
                err(1, "socketpair(LOCAL, STREAM) failed");

        if (xref) {
                fprintf(stderr, "cross reference\n");
                /* Send s[0] to s[1].rcvbuf */
                test_sendto_self(s[0], s[0]);
                /* Send s[1] to s[0].rcvbuf */
                test_sendto_self(s[1], s[1]);
        } else {
                fprintf(stderr, "self reference\n");
                /* Send s[0] to s[0].rcvbuf */
                test_sendto_self(s[1], s[0]);
                /* Send s[1] to s[1].rcvbuf */
                test_sendto_self(s[0], s[1]);
        }
        exit(0);
}