config root man

/*
 * Copyright 1994, 1995 Massachusetts Institute of Technology
 *
 * Permission to use, copy, modify, and distribute this software and
 * its documentation for any purpose and without fee is hereby
 * granted, provided that both the above copyright notice and this
 * permission notice appear in all copies, that both the above
 * copyright notice and this permission notice appear in all
 * supporting documentation, and that the name of M.I.T. not be used
 * in advertising or publicity pertaining to distribution of the
 * software without specific, written prior permission.  M.I.T. makes
 * no representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied
 * warranty.
 *
 * THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''.  M.I.T. DISCLAIMS
 * ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
 * SHALL M.I.T. 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>

__FBSDID("$FreeBSD: release/9.1.0/usr.bin/talk/get_iface.c 200418 2009-12-11 23:23:57Z delphij $");

/*
 * From:
 *  Id: find_interface.c,v 1.1 1995/08/14 16:08:39 wollman Exp
 */

#include <errno.h>
#include <string.h>
#include <unistd.h>

#include "talk.h"

/*
 * Try to find the interface address that is used to route an IP
 * packet to a remote peer.
 */

int
get_iface(struct in_addr *dst, struct in_addr *iface)
{
	static struct sockaddr_in local;
	struct sockaddr_in remote;
	socklen_t namelen;
	int s, rv;

	memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr);
	remote.sin_port = htons(60000);
	remote.sin_family = AF_INET;
	remote.sin_len = sizeof remote;

	local.sin_addr.s_addr = htonl(INADDR_ANY);
	local.sin_port = htons(60000);
	local.sin_family = AF_INET;
	local.sin_len = sizeof local;

	s = socket(PF_INET, SOCK_DGRAM, 0);
	if (s < 0)
		return -1;

	do {
		rv = bind(s, (struct sockaddr *)&local, sizeof local);
		local.sin_port = htons(ntohs(local.sin_port) + 1);
	} while(rv < 0 && errno == EADDRINUSE);

	if (rv < 0) {
		close(s);
		return -1;
	}

	do {
		rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
		remote.sin_port = htons(ntohs(remote.sin_port) + 1);
	} while(rv < 0 && errno == EADDRINUSE);

	if (rv < 0) {
		close(s);
		return -1;
	}

	namelen = sizeof local;
	rv = getsockname(s, (struct sockaddr *)&local, &namelen);
	close(s);
	if (rv < 0)
		return -1;

	memcpy(iface, &local.sin_addr, sizeof local.sin_addr);
	return 0;
}