code: def active?(url)
        # normalize the url
        url = URI(url)
  
        # session key
        key = key_for(url)
  
        return @sessions.has_key?(key)
      end
docs: Creates a new session cache.
  
   @param [Hash] options
     Configuration options.
  
   @option [Hash] :proxy (Spidr.proxy)
     Proxy options.
  
   @option [Integer] :open_timeout (Spidr.open_timeout)
     Optional open timeout.
  
   @option [Integer] :ssl_timeout (Spidr.ssl_timeout)
     Optional ssl timeout.
  
   @option [Integer] :read_timeout (Spidr.read_timeout)
     Optional read timeout.
  
   @option [Integer] :continue_timeout (Spidr.continue_timeout)
     Optional `Continue` timeout.
  
   @option [Integer] :keep_alive_timeout (Spidr.keep_alive_timeout)
     Optional `Keep-Alive` timeout.
  
   @since 0.6.0
  
  
   Determines if there is an active HTTP session for a given URL.
  
   @param [URI::HTTP, String] url
     The URL that represents a session.
  
   @return [Boolean]
     Specifies whether there is an active HTTP session.
  
   @since 0.2.3