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VB.NET IRC Client
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by Jakash3
March 05, 2010

After building my first irc bot, I wish to make a tutorial on making a program
to: connect to an irc server, join a channel, and send and receive channel
comments. The process involves creating a socket and using it to connect to
the server. Once connected, it will send and receive messages from the server
which it will parse and output to the screen.

Before we start this tutorial, I assume that you know the common irc commands
and you have been in an irc chat before, and also that you VB.NET. We will be
making a VB.NET Console Application. In the source code we will first need to
define the essential variables that will hold data for bot to use and act upon,
including a variable for the socket object:

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Dim sock As System.Net.Sockets.Socket
Dim ircserver As String
Dim port As Integer
Dim Channel As String
Dim nick As String

'The following objects are for manipulating the console IN and OUT streams
Dim cout As System.IO.TextWriter = Console.Out
Dim cin As System.IO.TextReader = Console.In
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Next, we will prompt the user to enter in information for these variables in
order to specify the irc server, port, and channel to connect to as well as
their nick name to use.

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Sub Main()
cout.WriteLine("My IRC Bot")
cout.Write(vbNewLine)
cout.Write("Server name: ")
ircserver = cin.ReadLine
cout.Write("Port number: ")
port = cin.ReadLine
cout.Write("Channel: ")
channel = cin.ReadLine
cout.Write("Nickname: ")
nick = cin.ReadLine
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Now we initialize and connect the socket:

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Dim ipHostInfo As System.Net.IPHostEntry = System.Net.Dns.GetHostEntry(ircserver)
Dim EP As New System.Net.IPEndPoint(ipHostInfo.AddressList(0), port)
sock = New System.Net.Sockets.Socket(EP.Address.AddressFamily, Net.Sockets.SocketType.Stream, Net.Sockets.ProtocolType.Tcp)
sock.Connect(ircserver, port)
---------------------------------------

Once we connect to an irc server with a socket, it is a rule that you send at
least the NICK and USER commands to the server. This is where you register
and identify yourself as a new user, after that I will give myself a nickname
and set my mode status to +B which means Bot:

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send("NICK " & nick)
send("USER " & nick & " 0 * :REALNAMEHERE")
send("JOIN " & channel)
send("MODE " & nick & " +B")
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These lines of code will use the send() Sub-procedure to send data to the
server. Here.s what that Sub looks like:

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Sub send(ByVal msg As String)
msg &= vbCr & vbLf
Dim data() As Byte = System.Text.ASCIIEncoding.UTF8.GetBytes(msg)
sock.send(data, msg.length, socketflags.none)
End Sub
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The send sub will first take the argument and append a carriage return and
linefeed at the end of the string because irc servers separate each message
sent to it by CrLf. Then it will chop that string into a byte array filled
with each character of that string and use that as an argument to the send
method for the socket to send that data to the server.

Next we will make a loop to have the socket query to receive data from the
server for as long as the socket is still connected:

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While sock.connected = True
Dim mail As String = recv()
cout.WriteLine(mail)
End While
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recv() function will receive a packet of 4096 bytes in length from the server
as seen here:

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Function recv() As String
Dim data(4096) As Byte
sock.Receive(data, 4096, SocketFlags.None)
Dim mail As String = System.Text.ASCIIEncoding.UTF8.GetString(data)
If mail.Contains(" ") Then
If mail.Substring(0, 4) = "PING" Then
Dim pserv As String = mail.Substring(mail.IndexOf(":"), mail.Length - mail.IndexOf(":"))
pserv = pserv.TrimEnd(Chr(0))
mail = "PING from " & pserv & vbNewLine & "PONG to " & pserv
send("PONG " & pserv)
ElseIf mail.Substring(mail.IndexOf(" ") + 1, 7) = "PRIVMSG" Then
Dim tmparr() As String = Nothing
mail = mail.Remove(0, 1)
tmparr = mail.Split("!")
rnick = tmparr(0)
tmparr = mail.Split(":")
rmsg = tmparr(1)
mail = "msg: " & rnick & ">" & rmsg
End If
End If
mail = mail.TrimEnd(Chr(0))
mail = mail.Remove(mail.LastIndexOf(vbLf), 1)
mail = mail.Remove(mail.LastIndexOf(vbCr), 1)
Return mail
End Function
---------------------------------------

Now when it receives data from the server the messages we care about the most
are the ones that show up on an irc client and the ping requests from the
server to check if the client (us) is still active and online. When the server
sends a ping request, then we must send a pong message back. When a ping
request is sent from a irc server it comes in this format:

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PING :sender
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Where sender is the name of the server who sent the ping request. If a client
gets this message from the server then it must reply back with this message:

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PONG :receiver
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Where receiver is the name of the server to send the pong reply back to. Well
that.s part of what the function does after receiving the packet from the
server and converting it to a string. It first analyzes the packet first to
see if it.s a ping request and sends a pong reply back to the sender (which is
found by extracting the name of the server from the ping message) if it is.
Another common type of message that the server sends is the PRIVMSG message.
Which means that a user made a comment either to the channel on irc or to you

as a private message. The syntax is:

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:nick!realname PRIVMSG receiver :msg
---------------------------------------

Where nick is the nickname of the user sending the message, realname is the
realname or addresss of that user, receiver is the name of another user or a
channel to send the message to, and msg is the message to send. If the
receiver is a channel, then all users will see that message; Otherwise only
the user of the username specified on this message will receive that msg. What
makes it easier for programs is that the nick and realname are separated by !
and the message is prefixed with :.

Well after all that, if for some reason the While loop breaks and the socket is
disconnected, then it will issue the socket.close method and Return from the
main sub.

Now since we already know how to send and receive messages to irc servers now
you can make you own irc client or bot to process those messages and make
replies.
To send a message just use the PRIVMSG command:

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PRIVMSG receiver :msg
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receiver could be the name of a user or a channel. Remember to prefix the
channel with #

For more commands on the irc client protocol read this:
http://www.mirc.com/help/rfc2812.txt

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