class ActionController::Caching::Actions::ActionCachePath

def initialize(controller, options = {}, infer_extension = true)

request format.
expiring the cache - expire_action should expire the same files regardless of the
path & format. This is desirable when reading and writing the cache, but not when
If +infer_extension+ is true, the cache path extension is looked up from the request's 
def initialize(controller, options = {}, infer_extension = true)
  if infer_extension
    @extension = controller.params[:format]
    options.reverse_merge!(:format => @extension) if options.is_a?(Hash)
  end
  path = controller.url_for(options).split(%r{://}).last
  @path = normalize!(path)
end

def normalize!(path) 

def normalize!(path)
  path << 'index' if path[-1] == ?/
  path << ".#{extension}" if extension and !path.ends_with?(extension)
  URI.unescape(path)
end