Coding an Internet Relay Chat Bot in C++
----------------------------------------

by Eric Marcarelli <eric@cprogrammingcentral.com>

INTRODUCTION

     About a month ago I decided I was going to write a bot in C++. This was
no new idea - I'd wanted to do this for months - but I finally decided I 
was going to. I already knew a bit about IRC protocol, so I read Beej's 
socket programming guide, wrote a few simple test programs and assumed I was
good to go. How wrong could I be. I thought I'd done it all right, but it 
would not respound to PINGS. I searched the internet for a simple example
but found none. I hope this document will fill that void.

     I wrote a bot called tobby, which had a small set of commands, read 
froma config file, and executed simple scripts. Tobby is dead now, but what
I learned working on it will be put to good use here. I'm not going to 
teach you how to program sockets, or how to use the IRC protocol, I'll 
assume you've read up on them already. What I will show you is how to put 
the peices together and write a bot that connects to IRC, accepts input,
and replies. 

Before continuing:

Sockets Guide - http://www.ecst.csuchico.edu/~beej/guide/net/
IRC Protocol  - http://www.isi.edu/in-notes/rfc1459.txt

Can you do it without reading them? Probably, and although I'd probably 
try it, I don't recommend you do.

THE CODE

     The code in this guide is compiled with g++ in Linux. If you want
to use windows, and you know how to use winsock, converting the code 
probably wont be a big issue. But I don't feel like making two versions, 
sorry.

THE PLAN

     It's always good to start with a plan. (3/4 readers have now skipped
down to the example and started to play with it) We will be making a bot
called SimpleBot, who will

* Connect to IRC
* Join a channel
* Wait for someone to say "hello"
* Reply by saying "bye!" and quiting

sound interesting? Not really. But you need to start small. To keep things
simple the bot's nickname, the server, the channel, and everything else
will just be hard-coded in. 

HERE IT IS

Ok, ok, enough talk. Time for the code. It's all one big working example,
filled with comments. It's the easiest way to do it, I think.

/*

SimpleBot 
a simple IRC bot

*/

#include <iostream>
#include <errno.h>
#include <cstring>
#include <netdb.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>

using namespace std;

// substr is a clone of PHP's substr that I wrote

char *substr (const char *str, int start, int end) {
char *sub = new char[strlen(str)];
start -=1 ;

for(int i = 0;start<end;i += 1) {
        sub[i] = str[start];
        start += 1;
}
sub[end] = '\0';

return sub;
}

int main() {

struct hostent *he;
struct sockaddr_in their_addr; 
int sockfd;
char msg[512];
char buffer[512];
int length;
int stay = 1;

cout << "SimpleBot" << endl << "A Simple IRC Bot" << endl;

// Connect the socket to the server, if you read Beej's Guide a 
// lot of this will look fimiliar.

if ((he=gethostbyname("irc.quickstrike.org")) == NULL) {  
	perror("gethostbyname");
	exit(1);
}

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
	perror("socket");
	exit(1);
}

their_addr.sin_family = AF_INET;    
their_addr.sin_port = htons(6667);  
their_addr.sin_addr = *((struct in_addr *)he->h_addr);
memset(&(their_addr.sin_zero), '\0', 8); 

if (connect(sockfd, (struct sockaddr *)&their_addr, sizeof(struct sockaddr)) == -1) {
	perror("connect");
	exit(1);
}

// Time to register with USER and NICK

strcpy(msg,"USER simple simple simple :SimpleBot Example\r\nNICK SimpleIRC\r\n");

if (send(sockfd, msg, strlen(msg), 0) == -1) {
	perror("send");
}

// Ok, now comes the fun part. Before you are able to do anything
// else you need to reply to a ping with a pong. Since we want
// to be able to respond again next time we get pinged, we'll
// start the loop here.

while (stay) {
// get info from the server, put it in buffer
if ((length=recv(sockfd, buffer, 511, 0)) == -1) {
	perror("recv");
	exit(1);
}
buffer[length] = '\0';

// Go through buffer looking for ping, or other messages. 

for (int i = 0; buffer[i] != '\0'; i += 1) {

// do we have "PING"?
if (strncmp(substr(buffer,i,i+4),"PING",4) == 0) {
	// reply to ping with pong, also joining #testchan
	sprintf(msg, "PONG %s\r\njoin :#testchan\r\n",substr(buffer,i+6,i+13));
	
	if (send(sockfd, msg, strlen(msg), 0) == -1) {
		perror("send");
	}	
}
// do we have a "hello"?
// note: in a real bot you would definatly want to extract the 
// user's message and work with that.
if (strncmp(substr(buffer,i,i+5),"hello",5) == 0) {
	// send bye! to #testchan, then quit
	strcpy(msg, "PRIVMSG #testchan :bye!\r\nQUIT\r\n");
	
	if (send(sockfd, msg, strlen(msg), 0) == -1) {
		perror("send");
	}	
	
	stay = 0; // leave our while()
}

}

}

close(sockfd);

return 0;
}


Well there you have it, a simple bot that connects to IRC and accepts 
input. I hope you learned something. Good luck on your bot!