Ruby SMTP to XMPP server/gateway

gistfile1.rb

require 'gserver'
require 'rubygems'
require 'xmpp4r'
require 'xmpp4r/roster'
require 'daemons'

JABBER_USER = 'service@domain.com'
JABBER_PASS = 'secret'
EMAIL_DOMAIN = 'domain.com'

class Array
  def ^(other)
   (self | other) - (self & other)
  end
end

# Based on code from here: http://snippets.dzone.com/posts/show/5152
class SMTPServer < GServer

  def serve(io)
    @rcpt = []
    @data_mode = false
    @email_message = ""
    puts "Connected"
    io.print "220 hello\r\n"
    loop do
      if IO.select([io], nil, nil, 0.1)
	      data = io.readpartial(4096)
	      puts ">>" + data
	      ok, op = process_line(data)
	      break unless ok
	      puts "<<" + op if op
	      io.print op if op
      end
      break if io.closed?
    end
    io.print "221 bye\r\n"
    io.close
    puts "Closed"
  end

  def process_line(line)
    if (@data_mode) && (line.chomp =~ /^\.$/)
      @email_message += line.gsub(/^\.(?:\r\n)$/, '')
      @data_mode = false
      send_message(@email_message)
      return true, "250 OK\r\n"
    elsif @data_mode
      @email_message += line
      return true, false
    elsif (line =~ /^(HELO|EHLO)/i)
      return true, "250 #{EMAIL_DOMAIN}\r\n"
    elsif (line =~ /^QUIT/i)
      return false, "bye\r\n"
    elsif (line =~ /^MAIL FROM\:/i)
      return true, "250 OK\r\n"
    elsif (line =~ /^RCPT TO\:/i)
      username = line.scan(/\:(?:<).*@(.*)\.#{EMAIL_DOMAIN}(?:>)/).flatten.first
      return true, "550 no such user here" unless username
      return true, "550 mailbox unavailable\r\n" unless @@online.include?(username.downcase)
      @rcpt |= [username]
      return true, "250 OK\r\n"
    elsif (line =~ /^DATA/i)
      @data_mode = true
      @email_message = ''
      return true, "354 Enter message, ending with \".\" on a line by itself\r\n"
    elsif (line =~ /^ONLINE/i)
      return true, "#{@@online.size} users online:\r\n  " + @@online.join("\r\n  ") + "\r\n"
    else
      return true, "500 ERROR\r\n"
    end
  end
  
  def send_message(email)
    @rcpt.each do |user|
      msg = Jabber::Message::new("#{user}@#{EMAIL_DOMAIN}", email)
      msg.type = :chat
      @@client.send(msg)
    end
  end
  
end

Daemons.run_proc('smtp.rb') do
  loop do
    @@client = Jabber::Client.new(Jabber::JID::new(JABBER_USER))
    @@client.connect
    @@client.auth(JABBER_PASS)
    @@client.send(Jabber::Presence.new.set_type(:available))

    @@client.add_message_callback do |m|
      if m.body =~ /The user '(.*)' was just created on node/
        puts "Requesting subscription to new user #{$1}"
        npres = Jabber::Presence.new.set_type(:subscribe).set_to($1)
        @@client.send(npres)
      end
    end

    roster = Jabber::Roster::Helper.new(@@client)
    roster.add_subscription_request_callback do |item,pres| 
      roster.accept_subscription(pres.from)

      puts "Requesting subscription to #{pres.from}"
      npres = Jabber::Presence.new.set_type(:subscribe).set_to(pres.from)
      @@client.send(npres)
    end

    @@online = []
    @@client.add_presence_callback do |old_presence, new_presence|
      unless old_presence.from.node == "service"
        @@online ^= [old_presence.from.node.downcase] if old_presence.type == :unavailable
        @@online |= [old_presence.from.node.downcase] unless old_presence.type
      end
    end

    a = SMTPServer.new(25, '0.0.0.0', 100)
    a.start
    a.join
  end
end