src/vznnc.c

/*
 *  Copyright (C) 2014, Parallels, Inc. All rights reserved.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/* vzncc: VZ Nano NetCat, a trivial tool to either listen or connect to
 * a TCP port at localhost, and run a program with its input and output
 * redirected to the connected socket
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define FAIL 220
#define SELF "vznnc"

void usage(void) {
	fprintf(stderr, "Usage: " SELF " {l|c} PORT CMD [arg ...]\n");

	exit(1);
}

int main(int argc, char *argv[])
{
	int sockfd, connfd, port;
	socklen_t cl_len;
	struct sockaddr_in srv_addr = {}, cl_addr = {};
	int l = -1;
	int yes = 1;

	if (argc < 4)
		usage();

	if (strcmp(argv[1], "l") == 0)
		l = 1;
	else if (strcmp(argv[1], "c") == 0)
		l = 0;
	else
		usage();

	port = atoi(argv[2]);

	sockfd = socket(AF_INET, SOCK_STREAM, 0);
	if (sockfd < 0) {
		perror(SELF ": socket()");
		return FAIL;
	}

	if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int))) {
		perror(SELF ": setsockopt()");
		return FAIL;
	}

	srv_addr.sin_family = AF_INET;
	srv_addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
	srv_addr.sin_port = htons(port);

	if (l) { /* listen */
		if (bind(sockfd, (struct sockaddr *) &srv_addr,
					sizeof(srv_addr)) < 0) {
			perror(SELF ": bind()");
			return FAIL;
		}

		listen(sockfd, 0);

		cl_len = sizeof(cl_addr);
		connfd = accept(sockfd, (struct sockaddr *)&cl_addr, &cl_len);
		if (connfd < 0) {
			perror(SELF ": accept()");
			return FAIL;
		}
		close(sockfd);
	}
	else { /* connect */
		if (connect(sockfd, (struct sockaddr *)&srv_addr,
					sizeof(srv_addr)) < 0) {
			perror(SELF ": connect()");
			return FAIL;
		}
		connfd = sockfd;
	}

	close(0);
	close(1);
	dup2(connfd, 0);
	dup2(connfd, 1);
	close(connfd);

	execvp(argv[3], argv+3);

	perror(SELF ": execvp()");
	return 127;
}