def getHTTPCachingHeaders(content, view_method, keywords, time=None):
    """ Update HTTP caching headers in REQUEST

        o 'content' is the content object being published.

        o 'view_method' is the name of the view being published

        o 'keywords' is a set of extra keywords modifying the view.

        o If 'time' is supplied, use it instead of the current time
          (for reliable testing).
        """
