This document is not necessarily going to reflect the latest stable YAIL! The latest stable release's documentation is always at Nerdbucket.com.

Net::YAIL is a library built for dealing with IRC communications in Ruby. This is a project I've been building on and off since 2005 or so, based originally on the very messy initial release of IRCSocket (back when I first started, that was the only halfway-decent IRC lib I found). I've put a lot of time and effort into cleaning it up to make it better for my own uses, and now it's almost entirely my code.

Some credit should also be given to Ruby-IRC, as I stole its eventmap.yml file with very minor modifications.

This library may not be useful to everybody (or anybody other than myself, for that matter), and Ruby-IRC or another lib may work for your situation far better than this thing will, but the general design I built here has just felt more natural to me than the other libraries I've looked at since I started my project.

Need a slightly more complex example? For a separate project you can play with that relies on Net::YAIL, check out https://github.com/Nerdmaster/superloud (fair warning: this code is not even remotely appropriate!).

For the nitty-gritty, you can see all this stuff in the Net::YAIL docs page, as well as more complete documentation about the system. For a complete bot, check out the IRCBot source code as well as the various examples found in the github project or in the gem's examples directory. Below is just a very simple example:

require 'rubygems'
require 'net/yail'

irc = Net::YAIL.new(
  :address    => 'irc.someplace.co.uk',
  :username   => 'Frakking Bot',
  :realname   => 'John Botfrakker',
  :nicknames  => ['bot1', 'bot2', 'bot3']
)

# Register a proc callback
irc.on_welcome proc { |event| irc.join('#foo') }

# Register a block
irc.on_invite { |event| irc.join(event.channel) }

# Another way to register a block - note that this clobbers the prior callback
irc.set_callback(:incoming_invite) { |event| irc.join(event.channel) }

# Filter for all incoming pings so we can log them
irc.hearing_ping {|event| $stderr.puts event.inspect}

# Filter condition: if the message is a pm, ignore it by forcibly ending the event filter chain
irc.hearing_message(:if => {:pm? => true}) do |event|
  event.handle!
end

# Loops forever here until CTRL+C is hit.
irc.start_listening!

Now we've built a simple IRC listener that will connect to a (probably invalid) network, identify itself, and sit around waiting for the welcome message. After this has occurred, we join a channel. If invited to another channel, we will join it. We spit out info about all incoming PINGs.

YAIL is built with the concept of there being a single callback for any given event. Plugins can add functionality around an event via filters, but only the IRC client implementation should be writing callbacks. If you're building a bot or an IRC client, you should be handling events. If you're building a library that others will use and won't implement its own IRC handling, you should be primarily building filters.

When a callback is set, it overwrites any previous callback. This allows sane defaults to be set up if they make sense (such as responding to a PING with a PONG), but if the user decides to do so, he can easily overwrite those defaults.

Filters represent code that needs to be run before or after an event is handled. Filters running before an event can stop the event from triggering its callback, but this should be used only in very special cases (such as building a module to ignore events from specific users). Filters should be looked at as the hooks to be used when wanting to see an event, but shouldn't generally be the final callback of an event.

Callback and filter methods:

• set_callback(:xxx): Replaces the existing handler (if any) for the given event with the block or proc object passed in. Replace "xxx" with the callback name, such as :incoming_welcome, :outgoing_kick, etc. This is typically going to be used for incoming and custom events, but if you don't mind getting your hands dirty with raw IRC commands, you can also overwrite the outgoing handlers this way.
• before_filter(:xxx), after_filter(:xxx): These create a filter for any event, and as above take a proc object or a block. As many filters as desired may be created for an event. A before_filter() call could be used to actually modify the data that gets sent to the callback, while an after_filter() would make more sense for something like logging or gathering stats only for events that make it through the callback.

Shortcut methods make the common operations take a bit less typing, and are hopefully intuitive enough that you don't lose anything by using them. They are all used similarly to set_callback, before_filter, and after_filter, but with the event name as part of the method. They must be given a proc object or a block.

• on_xxx: Sets a callback for an incoming event, so on_join will be the same as calling set_callback(:incoming_join)
• hearing_xxx: Creates a before-filter on incoming event xxx. This is the same as calling before_filter(:incoming_xxx)
• heard_xxx: Creates an after-filter on incoming event xxx. This is the same as calling after_filter(:incoming_xxx)
• saying_xxx: Creates a before-filter on outgoing event xxx. This is the same as calling before_filter(:outgoing_xxx)
• said_xxx: Creates an after-filter on outgoing event xxx. This is the same as calling after_filter(:outgoing_xxx)

For some situations, you want your filter to only be called if a certain condition is met. Enter conditional filtering! By using this exciting feature, you can set up handlers and callbacks which only trigger when certain conditions are met. Be warned, though, this can get confusing....

Conditions can be added to any filter method, but should never be used on the callback, since there can be only one. To add a filter, you simply supply a hash with a key of either :if or :unless, and a value which is either another hash of conditions, or a proc.

If a proc is sent, it will be a method that is called and passed the event object. If the proc returns true, an :if condition is met and un :unless condition is not met. If a condition is not met, the filter is skipped entirely.

If a hash is sent, each key is expected to be an attribute on the event object. It's similar to a lambda where you return true if each attribute equals the value in the hash. For instance, :if => {:message => "food", :nick => "Simon"} is the same as :if => lambda {|e| e.message == "food" && e.nick == "Simon"}.

Example (very simple) filter conditions:

###
# NOTE: These were swiped from tests - "hearing_food", "not_hearing_bad", and "heard_nothing" are all lambda functions
###

# If the message looks like "food", the handler will be hit
@irc.hearing_msg(hearing_food, :if => lambda {|e| e.message =~ /food/})

# Unless the message looks like "bad", the handler will be hit
@irc.hearing_msg(not_hearing_bad, :unless => lambda {|e| e.message =~ /bad/})

# If the message is completely empty, this handler will be hit
@irc.heard_msg(heard_nothing, :if => {:message => ""})

# Multiple handler conditions are "ANDed" - that is they must all be true for the :if to succeed or the :unless to
# fail.  We do a block here instead of a proc to see how it looks.
@irc.heard_msg(:if => {:message => "bah", :pm? => true}) do
  # Message was "bah" and a pm!
end

• Allows event callbacks to be specified very easily for all known IRC events, and in all cases, one can choose to override the default handling mechanisms. Generally speaking, it's best to be sure you know what you're doing when you decide to change how PING is responded to, but the capability is there.
• Allows handling outgoing messages, such as when privmsg is called. You can filter data before it's sent out, log statistics after it's sent, or even customize the raw socket output. This is one feature I didn't see anywhere else.
• Threads for input and output are persistent. This is a feature, not a bug. Some may hate this approach, but I'm a total n00b to threads, and it seemed like the way to go, having thread loops responsible for their own piece of the library. I'd love input here if anybody can tell me why this is a bad idea....
• Unlimited before- and after-callback filters allow for building a modular framework on top of YAIL.
• There is now only ONE callback per event as of YAIL 1.5 (2.0 will actually remove the code supporting the "legacy" event system). This is a bit more constrictive than some libraries, but makes it a lot more clear what is the definitive handler of an event versus what provides functionality separate from said handler. For simple bots, this should actually be easier to use.
• Easy to build a simple bot without subclassing anything. One gripe I had with IRCSocket was that it was painful to do anything without subclassing and overriding methods. No need here.
• Lots of built-in reporting comes free by subclassing IRCBot, but is no longer required otherwise.
• Built-in PRIVMSG buffering! You can of course choose to not buffer, but by default you cannot send more than one message to a given target (user or channel) more than once per second. Additionally, this buffering method is ideal for a bot that's trying to be chatty on two channels at once, because buffering is per-target, so queing up 20 lines on ##foo doesn't mean waiting 20 seconds to spit data out to ##bar. The one caveat here is that if your app is trying to talk to too many targets at once, the buffering still won't save you from a flood-related server kick. If this is a problem for others, I'll look into building an even more awesome buffering system.
• The included IRCBot is a great starting point for building your own bot, but if you want something even simpler, just look at Net::YAIL's documentation for the most basic working examples.

I still have a lot to do, though. The output API is definitely not fully fleshed out. I believe that the library is also missing a lot for people who just have a different approach than me, since this was purely designed for my own benefit, and then released almost exclusively to piss off the people whose work I stole to get where I'm at today. (Just kiddin', Pope)

This code is released under the MIT license. I hear it's all the rage with the kids these days.