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 * $FreeBSD: src/share/examples/find_interface/find_interface.c,v 1.5 1999/08/28 00:19:18 peter Exp $ 30 * $DragonFly: src/share/examples/find_interface/find_interface.c,v 1.2 2003/06/17 04:36:57 dillon Exp $ 31 */ 32 33 /* 34 * This is a simple program which demonstrates how to query the kernel 35 * routing mechanism using only a UDP socket. Pass it a hostname on 36 * the command line (sorry, it doesn't parse dotted decimal) and it will 37 * print out an IP address which names the interface over which UDP 38 * packets intended for that destination would be sent. 39 * A more sophisticated program might use the list obtained from SIOCGIFCONF 40 * to match the address with an interface name, but applications programmers 41 * much more often need to know the address of the interface rather than 42 * the name. 43 */ 44 #include <sys/types.h> 45 #include <sys/socket.h> 46 #include <unistd.h> 47 #include <netinet/in.h> 48 #include <arpa/inet.h> 49 #include <stdlib.h> 50 #include <stdio.h> 51 #include <netdb.h> 52 #include <err.h> 53 #include <errno.h> 54 #include <string.h> 55 #include <sysexits.h> 56 57 int 58 main(int argc, char **argv) 59 { 60 struct sockaddr_in local, remote; 61 struct hostent *hp; 62 int s, rv, namelen; 63 64 argc--, argv++; 65 66 if (!*argv) { 67 errx(EX_USAGE, "must supply a hostname"); 68 } 69 70 hp = gethostbyname(*argv); 71 if (!hp) { 72 errx(EX_NOHOST, "cannot resolve hostname: %s", *argv); 73 } 74 75 memcpy(&remote.sin_addr, hp->h_addr_list[0], sizeof remote.sin_addr); 76 remote.sin_port = htons(60000); 77 remote.sin_family = AF_INET; 78 remote.sin_len = sizeof remote; 79 80 local.sin_addr.s_addr = htonl(INADDR_ANY); 81 local.sin_port = htons(60000); 82 local.sin_family = AF_INET; 83 local.sin_len = sizeof local; 84 85 s = socket(PF_INET, SOCK_DGRAM, 0); 86 if (s < 0) 87 err(EX_OSERR, "socket"); 88 89 do { 90 rv = bind(s, (struct sockaddr *)&local, sizeof local); 91 local.sin_port = htons(ntohs(local.sin_port) + 1); 92 } while(rv < 0 && errno == EADDRINUSE); 93 94 if (rv < 0) 95 err(EX_OSERR, "bind"); 96 97 do { 98 rv = connect(s, (struct sockaddr *)&remote, sizeof remote); 99 remote.sin_port = htons(ntohs(remote.sin_port) + 1); 100 } while(rv < 0 && errno == EADDRINUSE); 101 102 if (rv < 0) 103 err(EX_OSERR, "connect"); 104 105 namelen = sizeof local; 106 rv = getsockname(s, (struct sockaddr *)&local, &namelen); 107 if (rv < 0) 108 err(EX_OSERR, "getsockname"); 109 110 printf("Route to %s is out %s\n", *argv, inet_ntoa(local.sin_addr)); 111 return 0; 112 } 113