/*      $NetBSD: fdpass.c,v 1.1 2012/08/13 11:15:05 christos Exp $      */
/* $OpenBSD: monitor_fdpass.c,v 1.19 2010/01/12 00:58:25 djm Exp $ */
/*
 * Copyright 2001 Niels Provos <provos@citi.umich.edu>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: fdpass.c,v 1.1 2012/08/13 11:15:05 christos Exp $");
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/wait.h>

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

static int debug;

static int
send_fd(int sock, int fd)
{
        struct msghdr msg;
        union {
                struct cmsghdr hdr;
                char buf[1024];
        } cmsgbuf;
        struct cmsghdr *cmsg;
        struct iovec vec;
        char ch = '\0';
        ssize_t n;
        struct pollfd pfd;

        if (sizeof(cmsgbuf.buf) < CMSG_SPACE(sizeof(int)))
                errx(1, "%s: %zu < %zu, recompile", __func__, 
                    sizeof(cmsgbuf.buf), CMSG_SPACE(sizeof(int)));

        memset(&msg, 0, sizeof(msg));
        msg.msg_control = &cmsgbuf.buf;
        msg.msg_controllen = CMSG_SPACE(sizeof(int));
        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) = fd;
        msg.msg_controllen = cmsg->cmsg_len;

        vec.iov_base = &ch;
        vec.iov_len = 1;
        msg.msg_iov = &vec;
        msg.msg_iovlen = 1;

        pfd.fd = sock;
        pfd.events = POLLOUT;
        while ((n = sendmsg(sock, &msg, 0)) == -1 &&
            (errno == EAGAIN || errno == EINTR)) {
                (void)poll(&pfd, 1, -1);
        }
        switch (n) {
        case -1:
                err(1, "%s: sendmsg(%d)", __func__, fd);
        case 1:
                if (debug)
                        fprintf(stderr, "%d: send fd %d\n", getpid(), fd);
                return 0;
        default:
                errx(1, "%s: sendmsg: expected sent 1 got %ld",
                    __func__, (long)n);
        }
}

static int
recv_fd(int sock)
{
        struct msghdr msg;
        union {
                struct cmsghdr hdr;
                char buf[1024];
        } cmsgbuf;
        struct cmsghdr *cmsg;
        struct iovec vec;
        ssize_t n;
        char ch;
        int fd;
        struct pollfd pfd;

        if (sizeof(cmsgbuf.buf) < CMSG_SPACE(sizeof(int)))
                errx(1, "%s: %zu < %zu, recompile", __func__, 
                    sizeof(cmsgbuf.buf), CMSG_SPACE(sizeof(int)));

        memset(&msg, 0, sizeof(msg));
        vec.iov_base = &ch;
        vec.iov_len = 1;
        msg.msg_iov = &vec;
        msg.msg_iovlen = 1;
        msg.msg_control = &cmsgbuf.buf;
        msg.msg_controllen = CMSG_SPACE(sizeof(int));

        pfd.fd = sock;
        pfd.events = POLLIN;
        while ((n = recvmsg(sock, &msg, 0)) == -1 &&
            (errno == EAGAIN || errno == EINTR)) {
                (void)poll(&pfd, 1, -1);
        }
        switch (n) {
        case -1:
                err(1, "%s: recvmsg", __func__);
        case 1:
                break;
        default:
                errx(1, "%s: recvmsg: expected received 1 got %ld",
                    __func__, (long)n);
        }

        cmsg = CMSG_FIRSTHDR(&msg);
        if (cmsg == NULL)
                errx(1, "%s: no message header", __func__);

        if (cmsg->cmsg_type != SCM_RIGHTS)
                err(1, "%s: expected type %d got %d", __func__,
                    SCM_RIGHTS, cmsg->cmsg_type);
        fd = (*(int *)CMSG_DATA(cmsg));
        if (debug)
                fprintf(stderr, "%d: recv fd %d\n", getpid(), fd);
        return fd;
}

static void usage(void) __attribute__((__noreturn__));

static void
usage(void)
{
        fprintf(stderr, "Usage: %s [-vd] -i <input> -o <output>\n"
            "\t %s [-v] -p <progname>\n", getprogname(), getprogname());
        exit(EXIT_FAILURE);
}

int
main(int argc, char *argv[])
{
        int s[2], fd, status, c, verbose;
        char buf[1024], *prog;

        prog = NULL;
        s[0] = s[1] = -1;
        verbose = 0;

        while ((c = getopt(argc, argv, "di:o:p:")) != -1)
                switch (c) {
                case 'd':
                        debug++;
                        break;
                case 'i':
                        s[0] = atoi(optarg);
                        break;
                case 'o':
                        s[1] = atoi(optarg);
                        break;
                case 'p':
                        prog = optarg;
                        break;
                default:
                        usage();
                }

        if ((s[0] == -1 && s[1] != -1) || (s[0] != -1 && s[1] == -1))
                usage();

        if (s[0] == -1) {
                if (socketpair(AF_LOCAL, SOCK_DGRAM, 0, s) == -1)
                        err(1, "socketpair");
        } else
                goto recv;

        switch (fork()) {
        case -1:
                err(1, "fork");
        default:
                fd = open("foo", O_RDWR|O_CREAT|O_TRUNC, 0666);
                if (fd == -1)
                        err(1, "open");
                send_fd(s[0], fd);
                wait(&status);
                return 0;
        case 0:
                if (prog != NULL) {
                        char i[64], o[64];
                        snprintf(i, sizeof(i), "%d", s[0]);
                        snprintf(o, sizeof(o), "%d", s[1]);
                        execlp(prog, prog, "-i", i, "-o", o, NULL);
                        err(1, "execlp");
                }
        recv:
                fd = recv_fd(s[1]);
                if (verbose) {
                        snprintf(buf, sizeof(buf), "ls -l /proc/%d/fd",
                            getpid());
                        system(buf);
                }
                if (write(fd, "foo\n", 4) == -1)
                        err(1, "write");
                close(fd);
                return 0;
        }
}