Simple telnet bot example

telnet-example.c

/* telnet-example.c
 *
 * Copyright (c) 2015 Mittorn.  Use may be in whole
 * or in part in accordance to the General Public License (GPL).
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
*/

/*****************************************************************************/
/*** telnet-example.c													   ***/
/*****************************************************************************/

/**************************************************************************
*   This is a simple telnet chat utility. It connects to server and	
*	sends/reads lines. Useful for some routers configuration.
*	based on simple-client.c by Sean Walton and Macmillan Publishers
**************************************************************************/
#include <stdio.h>
#include <string.h>
#ifdef _WIN32
#include <winsock.h>
#pragma comment(lib,"wsock32.lib") //Winsock Library
#define close closesocket
#define errno 1
#define perror(x) fprintf(stderr, "%s: failed\n", x)
#else
#include <errno.h> // errno will not work on windows
#include <sys/socket.h>
#include <resolv.h>
#include <stdlib.h> // exit()
#endif
#define PORT_INT		23			  // telnet connection port
#define SERVER_ADDR	 "192.168.1.1"
#define MAXBUF		  1024

#define bzero(x,y) memset(x,0,y)

#ifdef WIN32
static int inet_aton(const char *cp, struct in_addr *inp)
{
	unsigned long addr;
	if (cp == 0 || inp == 0)
	{
		return -1;
	}
 
	addr = inet_addr(cp);
	if (addr == INADDR_NONE || addr == INADDR_ANY)
	{
		return -1;
	}
 
	inp->s_addr = addr;
	return -1;
}
#endif

int sockfd;

// read data until get string
void waitforstring(const char *s)
{
	int res, pos = 0;
	char buffer[MAXBUF];
	bzero(buffer, MAXBUF);
 	while(res = recv(sockfd, buffer + pos, sizeof(buffer) - pos, 0) > 0)
	{
		if(res > 0)
		{
			pos += res;
			buffer[MAXBUF-1] = 0;
			printf("%s", buffer + pos);
			if(strstr(buffer, s))
				return;
		}
	}
}

// send string
void sendstring(const char *s)
{
	int pos = 0, len = strlen(s);
	// Only small messages supported now,
	// need to improve this
	send(sockfd, s, len, 0);
}

int main()
{   
	struct sockaddr_in dest;
#ifdef _WIN32
	static WSADATA winsockdata;
	WSAStartup( MAKEWORD( 1, 1 ), &winsockdata );
#endif
	// Open socket
	if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0 )
	{
		perror("Create socket error");
		exit(errno);
	}

	// Initialize server address/port struct
	bzero(&dest, sizeof(dest));
	dest.sin_family = AF_INET;
	dest.sin_port = htons(PORT_INT);
	if ( inet_aton(SERVER_ADDR, &dest.sin_addr.s_addr) == 0 )
	{
		perror("Cannot understand \""SERVER_ADDR);
		exit(errno);
	}
#if 0 // if you wish to enable non-blocking mode, enable this
#ifdef WIN32
	unsigned long arg = 1;
	ioctlsocket(sockfd, FIONBIO, &arg);
#else
	int arg = fcntl(sockfd, F_GETFL, NULL);
	arg |= O_NONBLOCK;
	fcntl(sockfd, F_SETFL, arg);
#endif
#endif
	// Connect to server
	if ( connect(sockfd, (struct sockaddr*)&dest, sizeof(dest)) != 0 )
	{
		perror("connect");
		exit(errno);
	}

	// Example: login to router and replace route
	waitforstring("ogin: ");
	sendstring("admin\n");
	waitforstring("assword: ");
	sendstring("admin\n");
	waitforstring(">");
	sendstring("sh -c \"route del default;route add default ppp1\"\n");
	waitforstring(">");
	close(sockfd);
	return 0;
}