fdpass.c

/*
 * Copyright © 2012 Keith Packard <keithp@keithp.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
 */

#include "fdpass.h"

ssize_t
sock_fd_read(int sock, void *buf, ssize_t bufsize, int *fd)
{
	ssize_t		size;

	if (fd) {
		struct msghdr	msg;
		struct iovec	iov;
		union {
			struct cmsghdr	cmsghdr;
			char		control[CMSG_SPACE(sizeof (int))];
		} cmsgu;
		struct cmsghdr	*cmsg;

		iov.iov_base = buf;
		iov.iov_len = bufsize;

		msg.msg_name = NULL;
		msg.msg_namelen = 0;
		msg.msg_iov = &iov;
		msg.msg_iovlen = 1;
		msg.msg_control = cmsgu.control;
		msg.msg_controllen = sizeof(cmsgu.control);
		size = recvmsg (sock, &msg, 0);
		if (size < 0) {
			perror ("recvmsg");
			exit(1);
		}
		if ((msg.msg_flags & MSG_TRUNC) ||
		    (msg.msg_flags & MSG_CTRUNC)) {
			fprintf (stderr, "control message truncated");
			exit(1);
		}
		cmsg = CMSG_FIRSTHDR(&msg);
		if (cmsg && cmsg->cmsg_len == CMSG_LEN(sizeof(int))) {
			if (cmsg->cmsg_level != SOL_SOCKET) {
				fprintf (stderr, "invalid cmsg_level %d\n",
					 cmsg->cmsg_level);
				exit(1);
			}
			if (cmsg->cmsg_type != SCM_RIGHTS) {
				fprintf (stderr, "invalid cmsg_type %d\n",
					 cmsg->cmsg_type);
				exit(1);
			}

			*fd = *((int *) CMSG_DATA(cmsg));
		} else
			*fd = -1;
	} else {
		size = read (sock, buf, bufsize);
		if (size < 0) {
			perror("read");
			exit(1);
		}
	}
	return size;
}

ssize_t
sock_fd_write(int sock, void *buf, ssize_t buflen, int fd)
{
	ssize_t		size;
	struct msghdr	msg;
	struct iovec	iov;
	union {
		struct cmsghdr	cmsghdr;
		char		control[CMSG_SPACE(sizeof (int))];
	} cmsgu;
	struct cmsghdr	*cmsg;

	iov.iov_base = buf;
	iov.iov_len = buflen;

	msg.msg_name = NULL;
	msg.msg_namelen = 0;
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;

	if (fd != -1) {
		msg.msg_control = cmsgu.control;
		msg.msg_controllen = sizeof(cmsgu.control);

		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;
	} else {
		msg.msg_control = NULL;
		msg.msg_controllen = 0;
		printf ("not passing fd\n");
	}

	size = sendmsg(sock, &msg, 0);

	if (size < 0)
		perror ("sendmsg");
	return size;
}