validate reserved names in Rails 3

reserved_name_validator.rb

# app/validators/reserved_name_validator.rb
class ReservedNameValidator < ActiveModel::EachValidator
  RESERVED_NAMES = %w{
    about account add admin api
    app apps archive archives auth
    blog
    config connect contact create
    delete direct_messages downloads
    edit email
    faq favorites feed feeds follow followers following
    help home
    invitations invite
    jobs
    login log-in log_in logout log-out log_out logs
    map maps
    oauth oauth_clients openid
    privacy
    register remove replies rss
    save search sessions settings
    signup sign-up sign_up signin sign-in sign_in signout sign-out sign_out
    sitemap ssl subscribe
    terms test trends
    unfollow unsubscribe url user
    widget widgets
    xfn xmpp
  }

  def validate_each(object, attribute, value)
    if RESERVED_NAMES.include?(value)
      object.errors[attribute] << (options[:message] || "is not a valid name")
    end
  end
end

# app/models/#{model}.rb
class User < ActiveRecord::Base
  validates :username, :reserved_name => true
end