link.rb

class Link
  attr_reader :url

  def initialize(url)
    @url = url
  end

  def bad?
    return false if link.blank?
    (GlobalPreference.get('suspicious_words') + GlobalPreference.get('bad_words')).any? { |word| url =~ eval("/#{word.strip}/") }
  end

  def evil?
   return false if link.blank?
   hoptoad_message("Link to #{link} redirected more than #{self.class.retry_limit} times on message ##{self.id}") if limit == 0
   link = "http://" + link unless link.start_with?("http")
   begin
     response = Net::HTTP.get_response(URI.parse(link))
     case response
     when Net::HTTPSuccess, Net::HTTPOK
      bad?
     when Net::HTTPRedirection, HTTPMovedPermanently
       puts "Redirected to #{response['location']}"
       Link.new(response['location']).bad?
     end
    rescue
      false
    end
  end
end

link_checker.rb

module LinkChecker
  def self.included(base)
    base.class_eval do
      require 'net/http'
      require 'uri'
      
      before_save :_check_for_evil_links
      cattr_accessor :check_evil_links_on_attributes, :suspicious_callback, :retry_limit
    end

    base.extend ClassMethods
  end
  
  module ClassMethods
    
    def check_evil_links_on(options = {})
      options.assert_valid_keys :fields, :suspicious_callback, :retry_limit
      raise "You need to specify a suspicious callback on 'check_evil_links_on'" if options[:suspicious_callback].blank?
      self.check_evil_links_on_attributes = options[:fields].to_a.collect(&:to_s) & self.column_names
      self.suspicious_callback = options[:suspicious_callback].to_sym
      self.retry_limit = options[:retry_limit]
    end
    
  end
  
    protected 
    def _check_for_evil_links
      raw_data = self.class.check_evil_links_on_attributes.collect {|attr_name| self.send(attr_name.to_sym) if self.respond_to?(attr_name.to_sym)}.compact.join(" ")
      if links = raw_data.scan(/[a-z0-9]+(?:[\-\.]{1}[a-z0-9]+)*\.[a-z]{2,5}(?:(?::[0-9]{1,5})?\/[^\s]*)?/)
        if links.any? {|link| link_has_bad_words?(link) || link_is_evil?(link, self.class.retry_limit)}
          begin
            self.send(self.class.suspicious_callback.to_sym) #if self.respond_to?(self.class.suspicious_callback.to_sym)
          rescue
          end
        end
      end
    end
    
    def link_has_bad_words?(link = "")
      return false if link.blank?
     return (GlobalPreference.get('suspicious_words') + GlobalPreference.get('bad_words')).any? { |word| link =~ eval("/#{word.strip}/") }

    end
    
    def link_is_evil?(link = "", limit = 1)
      return false if link.blank?
      hoptoad_message("Link to #{link} redirected more than #{self.class.retry_limit} times on message ##{self.id}") if limit == 0
      link = "http://" + link unless link.start_with?("http")
      begin
        response = Net::HTTP.get_response(URI.parse(link))
        case response
        when Net::HTTPSuccess, Net::HTTPOK
          return link_has_bad_words?(link)
        when Net::HTTPRedirection, HTTPMovedPermanently
          puts "Redirected to #{response['location']}"
          return link_has_bad_words?(response['location'])
        else
        end
      rescue
        return false
      end
  end
end