Hi, just a snippet to validate an url with Ruby on Rails.

class WebSite /^((http|https):\/\/)*[a-z0-9_-]{1,}\.*[a-z0-9_-]{1,}\.[a-z]{2,4}\/*$/i 
  def validate
    errors.add(:url, "unexistent") unless WebSite.existent_url?(:url)
  end

  def self.existent_url?(url)
    uri = URI.parse(url)
    http_conn = Net::HTTP.new(uri.host, uri.port)
    resp, data = http_conn.head("/" , nil)
    resp.code == "200"
  end
end