/usr.bin/talk/get_iface.c

  1/*
  2 * Copyright 1994, 1995 Massachusetts Institute of Technology
  3 *
  4 * Permission to use, copy, modify, and distribute this software and
  5 * its documentation for any purpose and without fee is hereby
  6 * granted, provided that both the above copyright notice and this
  7 * permission notice appear in all copies, that both the above
  8 * copyright notice and this permission notice appear in all
  9 * supporting documentation, and that the name of M.I.T. not be used
 10 * in advertising or publicity pertaining to distribution of the
 11 * software without specific, written prior permission.  M.I.T. makes
 12 * no representations about the suitability of this software for any
 13 * purpose.  It is provided "as is" without express or implied
 14 * warranty.
 15 *
 16 * THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''.  M.I.T. DISCLAIMS
 17 * ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
 18 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
 20 * SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 23 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 24 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 25 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 26 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 27 * SUCH DAMAGE.
 28 */
 29
 30#include <sys/cdefs.h>
 31
 32__FBSDID("$FreeBSD$");
 33
 34/*
 35 * From:
 36 *  Id: find_interface.c,v 1.1 1995/08/14 16:08:39 wollman Exp
 37 */
 38
 39#include <errno.h>
 40#include <string.h>
 41#include <unistd.h>
 42
 43#include "talk.h"
 44
 45/*
 46 * Try to find the interface address that is used to route an IP
 47 * packet to a remote peer.
 48 */
 49
 50int
 51get_iface(struct in_addr *dst, struct in_addr *iface)
 52{
 53	static struct sockaddr_in local;
 54	struct sockaddr_in remote;
 55	socklen_t namelen;
 56	int s, rv;
 57
 58	memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr);
 59	remote.sin_port = htons(60000);
 60	remote.sin_family = AF_INET;
 61	remote.sin_len = sizeof remote;
 62
 63	local.sin_addr.s_addr = htonl(INADDR_ANY);
 64	local.sin_port = htons(60000);
 65	local.sin_family = AF_INET;
 66	local.sin_len = sizeof local;
 67
 68	s = socket(PF_INET, SOCK_DGRAM, 0);
 69	if (s < 0)
 70		return -1;
 71
 72	do {
 73		rv = bind(s, (struct sockaddr *)&local, sizeof local);
 74		local.sin_port = htons(ntohs(local.sin_port) + 1);
 75	} while(rv < 0 && errno == EADDRINUSE);
 76
 77	if (rv < 0) {
 78		close(s);
 79		return -1;
 80	}
 81
 82	do {
 83		rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
 84		remote.sin_port = htons(ntohs(remote.sin_port) + 1);
 85	} while(rv < 0 && errno == EADDRINUSE);
 86
 87	if (rv < 0) {
 88		close(s);
 89		return -1;
 90	}
 91
 92	namelen = sizeof local;
 93	rv = getsockname(s, (struct sockaddr *)&local, &namelen);
 94	close(s);
 95	if (rv < 0)
 96		return -1;
 97
 98	memcpy(iface, &local.sin_addr, sizeof local.sin_addr);
 99	return 0;
100}