112 lines
3.5 KiB
C
112 lines
3.5 KiB
C
/*
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* Copyright 1994, 1995 Massachusetts Institute of Technology
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*
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* Permission to use, copy, modify, and distribute this software and
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* its documentation for any purpose and without fee is hereby
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* granted, provided that both the above copyright notice and this
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* permission notice appear in all copies, that both the above
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* copyright notice and this permission notice appear in all
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* supporting documentation, and that the name of M.I.T. not be used
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* in advertising or publicity pertaining to distribution of the
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* software without specific, written prior permission. M.I.T. makes
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* no representations about the suitability of this software for any
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* purpose. It is provided "as is" without express or implied
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* warranty.
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*
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* THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
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* ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
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* SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $Id$
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*/
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/*
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* This is a simple program which demonstrates how to query the kernel
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* routing mechanism using only a UDP socket. Pass it a hostname on
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* the command line (sorry, it doesn't parse dotted decimal) and it will
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* print out an IP address which names the interface over which UDP
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* packets intended for that destination would be sent.
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* A more sophisticated program might use the list obtained from SIOCGIFCONF
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* to match the address with an interface name, but applications programmers
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* much more often need to know the address of the interface rather than
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* the name.
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*/
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <unistd.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <netdb.h>
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#include <err.h>
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#include <errno.h>
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#include <string.h>
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#include <sysexits.h>
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int
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main(int argc, char **argv)
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{
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struct sockaddr_in local, remote;
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struct hostent *hp;
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int s, rv, namelen;
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argc--, argv++;
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if (!*argv) {
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errx(EX_USAGE, "must supply a hostname");
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}
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hp = gethostbyname(*argv);
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if (!hp) {
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errx(EX_NOHOST, "cannot resolve hostname: %s", *argv);
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}
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memcpy(&remote.sin_addr, hp->h_addr_list[0], sizeof remote.sin_addr);
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remote.sin_port = htons(60000);
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remote.sin_family = AF_INET;
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remote.sin_len = sizeof remote;
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local.sin_addr.s_addr = htonl(INADDR_ANY);
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local.sin_port = htons(60000);
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local.sin_family = AF_INET;
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local.sin_len = sizeof local;
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s = socket(PF_INET, SOCK_DGRAM, 0);
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if (s < 0)
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err(EX_OSERR, "socket");
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do {
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rv = bind(s, (struct sockaddr *)&local, sizeof local);
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local.sin_port++;
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} while(rv < 0 && errno == EADDRINUSE);
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if (rv < 0)
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err(EX_OSERR, "bind");
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do {
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rv = connect(s, (struct sockaddr *)&remote, sizeof remote);
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remote.sin_port++;
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} while(rv < 0 && errno == EADDRINUSE);
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if (rv < 0)
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err(EX_OSERR, "connect");
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namelen = sizeof local;
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rv = getsockname(s, (struct sockaddr *)&local, &namelen);
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if (rv < 0)
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err(EX_OSERR, "getsockname");
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printf("Route to %s is out %s\n", *argv, inet_ntoa(local.sin_addr));
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return 0;
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}
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