Building an IRC Server from Scratch with Ruby and em-irc

Introduction

In this blog post, we’ll walk through the steps of creating an Internet Relay Chat (IRC) server using the Ruby programming language. IRC is a protocol for real-time communication over the internet, and is often used for chat rooms and online communities.

Prerequisites

Before we get started, you’ll need to have a few things installed on your machine:

• Ruby: You’ll need to have Ruby installed on your machine to follow along with this tutorial. If you don’t already have Ruby installed, you can download it from the official website (https://www.ruby-lang.org/en/downloads/) or use a package manager like Homebrew (for macOS) or apt-get (for Linux).
• Bundler: We’ll be using Bundler to manage our dependencies, so you’ll need to have it installed as well. You can install it by running gem install bundler on the command line.

Step 1: Set up the project

First, let’s create a new directory for our project and navigate to it in the terminal. We’ll call our project “irc-server”:

$ mkdir irc-server
$ cd irc-server

Next, let’s create a Gemfile to manage our dependencies. This file will specify the libraries we need for our project, and Bundler will handle installing them for us.

Create a new file called Gemfile in the irc-server directory and add the following contents:

source "https://rubygems.org"

gem "eventmachine"
gem "em-irc"

The eventmachine and em-irc gems will provide us with the necessary tools to build our IRC server.

Step 2: Write the server code

Now that we have our dependencies set up, let’s start building the actual server. Create a new file called server.rb in the irc-server directory and add the following code:

# Load the necessary libraries
require "eventmachine"
require "em-irc"

# Define the server hostname and port
HOSTNAME = "localhost"
PORT = 6667

# Create a new instance of the IRC server
EventMachine.run do
  # Set up the connection
  EventMachine::IRC::Server.new do
    # Set the hostname and port
    hostname HOSTNAME
    port PORT

    # When a client connects...
    on :connect do |client|
      puts "Client #{client.inspect} connected"
    end

    # When a client disconnects...
    on :disconnect do |client|
      puts "Client #{client.inspect} disconnected"
    end

    # When a client sends a message...
    on :privmsg do |client, message|
      puts "Client #{client.inspect} sent message: #{message}"
    end
  end
end

This code sets up a new instance of an IRC server using the EventMachine and em-irc libraries. It listens for connections on the specified hostname and port (in this case, localhost and 6667), and logs messages when a client connects, disconnects, or sends a message.

Step 3: Start the server

To start the server, simply run the server.rb file from the command line:

$ ruby server.rb

You should see a message in the terminal indicating that the server is listening on the specified hostname and port.

Now that the server is running, you can connect to it using an IRC client. Some popular IRC clients include mIRC (for Windows) and HexChat (for macOS and Linux).

To connect to the server using an IRC client, simply enter the hostname and port (in this case, localhost and 6667) in the client’s connection settings. Once connected, you should be able to join channels and start chatting with other users.

Relaying chat messages

To relay chat messages using em-irc and Ruby, you can use the on :privmsg event to listen for messages from clients and the send_raw method to send messages to clients.

Here’s an example of how you can implement channels in your IRC server:

# Load the necessary libraries
require "eventmachine"
require "em-irc"

# Define the server hostname and port
HOSTNAME = "localhost"
PORT = 6667

# Create a new instance of the IRC server
EventMachine.run do
  # Set up the connection
  EventMachine::IRC::Server.new do
    # Set the hostname and port
    hostname HOSTNAME
    port PORT

    # When a client connects...
    on :connect do |client|
      puts "Client #{client.inspect} connected"
    end

    # When a client disconnects...
    on :disconnect do |client|
      puts "Client #{client.inspect} disconnected"
    end

    # When a client sends a message...
    on :privmsg do |client, message|
      # Split the message into command and parameters
      command, *params = message.split(" ")

      # If the command is "JOIN"
      if command == "JOIN"
        # Get the channel name
        channel = params[0]

        # Join the channel
        client.send_raw("JOIN #{channel}")
With these basic building blocks, you can start building your own custom IRC server and chat application.
        # Send a message to the channel announcing the client's presence
        client.send_raw("PRIVMSG #{channel} :#{client.nick} has joined the channel")
      # If the command is "PRIVMSG"
      elsif command == "PRIVMSG"
        # Get the target (either a channel or a user) and the message
        target, message = params[0], params[1..-1].join(" ")

        # Relay the message to the target
        client.send_raw("PRIVMSG #{target} :#{message}")
      end
    end
  end
end

In this code, we listen for messages from clients using the on :privmsg event. If the message is a JOIN command, we add the client to the specified channel and send a message announcing their presence. If the message is a PRIVMSG command, we relay the message to the specified target (either a channel or a user).

Conclusion

In this tutorial, we learned how to create an IRC server using Ruby and the eventmachine and em-irc libraries. We set up the project, wrote the server code, and started the server, and were able to connect to it using an IRC client. With these basic building blocks, you can build more advanced features such as channel moderation, user lists, and more.