/*      $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 <[email protected]>
* 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;
       }
}

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