chat server example using EM::Channel pub-sub, with simple tracing for teaching

em_chat_channel_server.rb

require 'eventmachine'
require 'socket'

class Client < EM::Connection
  include EM::P::LineText2

  HELP = "Server - Welcome to ghettochat. Use /nick to set your nick.\n"

  def initialize(global_channel)
    @global = global_channel
  end

  def post_init
    @port, @ip = Socket.unpack_sockaddr_in get_peername
    @name = "#{@ip}:#{@port}"

    @subscription = @global.subscribe(self, :on_global)

    global_broadcast "connected"
    send_data HELP
  end

  def unbind
    @global.unsubscribe(@subscription)
    global_broadcast "disconnected"
  end

  def receive_line(line)
    case line.strip
    when /^$/ # empty?
    when %r%^/nick (\w+)%
      @name = $1
    else
      global_broadcast line
    end
  end

  # new messages from the channel come in here from the subscription (based on
  # the EM::Callback args given to @global.subscribe)
  def on_global(message)
    send_data(message)
  end

  def global_broadcast(message)
    @global << "#{@name} - #{message}\n"
  end

  def inspect
    "#<#{self.class.name}:#{'0x%x' % object_id} #{@ip}:#{@port}>"
  end
end

def WithTracing(klass)
  Class.new(klass) do
    (instance_methods - Class.instance_methods).each do |m|
      eval <<-RUBY
      def #{m}(*a)
        arglist = a.map {|o| o.inspect }.join(', ')
        puts "\#{self.inspect}.#{m}(\#{arglist}\#{', &block' if block_given?})"
        super
      end
      RUBY
    end
  end
end

TracedClient = WithTracing(Client)

global_channel = EM::Channel.new

EM.run do
  trap(:INT) { EM.stop }
  EM.start_server('127.0.0.1', 9000, TracedClient, global_channel)
end