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 31 /* 32 * From: 33 * Id: find_interface.c,v 1.1 1995/08/14 16:08:39 wollman Exp 34 */ 35 36 #include <errno.h> 37 #include <string.h> 38 #include <unistd.h> 39 40 #include "talk.h" 41 42 /* 43 * Try to find the interface address that is used to route an IP 44 * packet to a remote peer. 45 */ 46 47 int 48 get_iface(struct in_addr *dst, struct in_addr *iface) 49 { 50 static struct sockaddr_in local; 51 struct sockaddr_in remote; 52 socklen_t namelen; 53 int s, rv; 54 55 memcpy(&remote.sin_addr, dst, sizeof remote.sin_addr); 56 remote.sin_port = htons(60000); 57 remote.sin_family = AF_INET; 58 remote.sin_len = sizeof remote; 59 60 local.sin_addr.s_addr = htonl(INADDR_ANY); 61 local.sin_port = htons(60000); 62 local.sin_family = AF_INET; 63 local.sin_len = sizeof local; 64 65 s = socket(PF_INET, SOCK_DGRAM, 0); 66 if (s < 0) 67 return -1; 68 69 do { 70 rv = bind(s, (struct sockaddr *)&local, sizeof local); 71 local.sin_port = htons(ntohs(local.sin_port) + 1); 72 } while(rv < 0 && errno == EADDRINUSE); 73 74 if (rv < 0) { 75 close(s); 76 return -1; 77 } 78 79 do { 80 rv = connect(s, (struct sockaddr *)&remote, sizeof remote); 81 remote.sin_port = htons(ntohs(remote.sin_port) + 1); 82 } while(rv < 0 && errno == EADDRINUSE); 83 84 if (rv < 0) { 85 close(s); 86 return -1; 87 } 88 89 namelen = sizeof local; 90 rv = getsockname(s, (struct sockaddr *)&local, &namelen); 91 close(s); 92 if (rv < 0) 93 return -1; 94 95 memcpy(iface, &local.sin_addr, sizeof local.sin_addr); 96 return 0; 97 } 98