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/*
 * Datapipe - Create a listen socket to pipe connections to another
 * machine/port. 'localport' accepts connections on the machine running    
 * datapipe, which will connect to 'remoteport' on 'remotehost'.
 * It will fork itself into the background on non-Windows machines.
 *
 * This implementation of the traditional "datapipe" does not depend on
 * forking to handle multiple simultaneous clients, and instead is able
 * to do all processing from within a single process, making it ideal
 * for low-memory environments.  The elimination of the fork also
 * allows it to be used in environments without fork, such as Win32.
 *
 * This implementation also differs from most others in that it allows
 * the specific IP address of the interface to listen on to be specified.
 * This is useful for machines that have multiple IP addresses.  The
 * specified listening address will also be used for making the outgoing
 * connections on.
 *
 * Note that select() is not used to perform writability testing on the
 * outgoing sockets, so conceivably other connections might have delayed
 * responses if any of the connected clients or the connection to the
 * target machine is slow enough to allow its outgoing buffer to fill
 * to capacity.
 *
 * Compile with:
 *     cc -O -o datapipe datapipe.c
 * On Solaris/SunOS, compile with:
 *     gcc -Wall datapipe.c -lsocket -lnsl -o datapipe
 * On Windows compile with:
 *     bcc32 /w datapipe.c                (Borland C++)
 *     cl /W3 datapipe.c wsock32.lib      (Microsoft Visual C++)
 *
 * Run as:
 *   datapipe localhost localport remoteport remotehost
 *
 *
 * written by Jeff Lawson <jlawson@bovine.net>
 * inspired by code originally by Todd Vierling, 1995.
 */


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <time.h>
#if defined(__WIN32__) || defined(WIN32) || defined(_WIN32)
#include <winsock.h>
#define bzero(p, l) memset(p, 0, l)
#define bcopy(s, t, l) memmove(t, s, l)
#else
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <strings.h>
#define recv(x,y,z,a) read(x,y,z)
#define send(x,y,z,a) write(x,y,z)
#define closesocket(s) close(s)
typedef int SOCKET;
#endif

#ifndef INADDR_NONE
#define INADDR_NONE 0xffffffff
#endif


struct client_t {
    int inuse;
    SOCKET csock, osock;
    time_t activity;
};

#define MAXCLIENTS 20
#define IDLETIMEOUT 300

int main(int argc, char *argv[])
{
    SOCKET lsock;
    char buf[4096];
    struct sockaddr_in laddr, oaddr;
    int i;
    FILE *flog = fopen("datapipe.log", "a");
    struct client_t clients[MAXCLIENTS];

#if defined(__WIN32__) || defined(WIN32) || defined(_WIN32)
    /* Winsock needs additional startup activities */
    WSADATA wsadata;

    WSAStartup(MAKEWORD(1, 1), &wsadata);
#endif


    /* check number of command line arguments */
    if (argc != 5) {
	fprintf(stderr,
		"Usage: %s localhost localport remotehost remoteport\n",
		argv[0]);
	return 30;
    }


    /* reset all of the client structures */
    for (i = 0; i < MAXCLIENTS; i++)
	clients[i].inuse = 0;


    /* determine the listener address and port */
    bzero(&laddr, sizeof(struct sockaddr_in));
    laddr.sin_family = AF_INET;
    laddr.sin_port = htons((unsigned short) atol(argv[2]));
    laddr.sin_addr.s_addr = inet_addr(argv[1]);
    if (!laddr.sin_port) {
	fprintf(stderr, "invalid listener port\n");
	return 20;
    }
    if (laddr.sin_addr.s_addr == INADDR_NONE) {
	struct hostent *n;

	if ((n = gethostbyname(argv[1])) == NULL) {
	    perror("gethostbyname");
	    return 20;
	}
	bcopy(n->h_addr, (char *) &laddr.sin_addr, n->h_length);
    }


    /* determine the outgoing address and port */
    bzero(&oaddr, sizeof(struct sockaddr_in));
    oaddr.sin_family = AF_INET;
    oaddr.sin_port = htons((unsigned short) atol(argv[4]));
    if (!oaddr.sin_port) {
	fprintf(stderr, "invalid target port\n");
	return 25;
    }
    oaddr.sin_addr.s_addr = inet_addr(argv[3]);
    if (oaddr.sin_addr.s_addr == INADDR_NONE) {
	struct hostent *n;

	if ((n = gethostbyname(argv[3])) == NULL) {
	    perror("gethostbyname");
	    return 25;
	}
	bcopy(n->h_addr, (char *) &oaddr.sin_addr, n->h_length);
    }


    /* create the listener socket */
    if ((lsock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
	perror("socket");
	return 20;
    }
    if (bind(lsock, (struct sockaddr *) &laddr, sizeof(laddr))) {
	perror("bind");
	return 20;
    }
    if (listen(lsock, 5)) {
	perror("listen");
	return 20;
    }


    /* change the port in the listener struct to zero, since we will
     * use it for binding to outgoing local sockets in the future. */
    laddr.sin_port = htons(0);


    /* fork off into the background. */
#if !defined(__WIN32__) && !defined(WIN32) && !defined(_WIN32)
    if ((i = fork()) == -1) {
	perror("fork");
	return 20;
    }
    if (i > 0)
	return 0;
    setsid();
#endif

    /* main polling loop. */
    while (1) {
	fd_set fdsr;
	int maxsock;
	struct timeval tv = { 1, 0 };
	time_t now = time(NULL);

	/* build the list of sockets to check. */
	FD_ZERO(&fdsr);
	FD_SET(lsock, &fdsr);
	maxsock = (int) lsock;
	for (i = 0; i < MAXCLIENTS; i++)
	    if (clients[i].inuse) {
		FD_SET(clients[i].csock, &fdsr);
		if ((int) clients[i].csock > maxsock)
		    maxsock = (int) clients[i].csock;
		FD_SET(clients[i].osock, &fdsr);
		if ((int) clients[i].osock > maxsock)
		    maxsock = (int) clients[i].osock;
	    }
	if (select(maxsock + 1, &fdsr, NULL, NULL, &tv) < 0) {
	    return 30;
	}


	/* check if there are new connections to accept. */
	if (FD_ISSET(lsock, &fdsr)) {
	    SOCKET csock = accept(lsock, NULL, 0);

	    for (i = 0; i < MAXCLIENTS; i++)
		if (!clients[i].inuse)
		    break;
	    if (i < MAXCLIENTS) {
		/* connect a socket to the outgoing host/port */
		SOCKET osock;

		if ((osock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
		    perror("socket");
		    closesocket(csock);
		} else
		    if (bind
			(osock, (struct sockaddr *) &laddr,
			 sizeof(laddr))) {
		    perror("bind");
		    closesocket(csock);
		    closesocket(osock);
		} else
		    if (connect
			(osock, (struct sockaddr *) &oaddr,
			 sizeof(oaddr))) {
		    perror("connect");
		    closesocket(csock);
		    closesocket(osock);
		} else {
		    clients[i].osock = osock;
		    clients[i].csock = csock;
		    clients[i].activity = now;
		    clients[i].inuse = 1;
		}
	    } else {
		fprintf(stderr, "too many clients\n");
		closesocket(csock);
	    }
	}


	/* service any client connections that have waiting data. */
	for (i = 0; i < MAXCLIENTS; i++) {
	    int nbyt, closeneeded = 0;

	    if (!clients[i].inuse) {
		continue;
	    } else if (FD_ISSET(clients[i].csock, &fdsr)) {
		if ((nbyt =
		     recv(clients[i].csock, buf, sizeof(buf), 0)) <= 0
		    || send(clients[i].osock, buf, nbyt, 0) <= 0)
		    closeneeded = 1;
		else {
		    clients[i].activity = now;
		    fprintf(flog, "%s", buf);
		    fflush(flog);
		    bzero(buf, sizeof(buf));
		}
	    } else if (FD_ISSET(clients[i].osock, &fdsr)) {
		if ((nbyt =
		     recv(clients[i].osock, buf, sizeof(buf), 0)) <= 0
		    || send(clients[i].csock, buf, nbyt, 0) <= 0)
		    closeneeded = 1;
		else {
		    clients[i].activity = now;
		    fprintf(flog, "%s", buf);
		    fflush(flog);
		    bzero(buf, sizeof(buf));
		}
	    } else if (now - clients[i].activity > IDLETIMEOUT) {
		closeneeded = 1;
	    }
	    if (closeneeded) {
		closesocket(clients[i].csock);
		closesocket(clients[i].osock);
		clients[i].inuse = 0;
	    }
	}

    }
    fclose(flog);
    return 0;
}