module Roda::RodaPlugins::Caching::RequestMethods

def last_modified(time)

with a 412 status.
before than the time specified, immediately returns a response
If the current request includes an If-Unmodified-Since header that is

with a 304 status.
equal or later than the time specified, immediately returns a response
If the current request includes an If-Modified-Since header that is

The +time+ argument should be a Time instance.
Set the last modified time of the resource using the Last-Modified header. 
def last_modified(time)
  return unless time
  res = response
  e = env
  res[RodaResponseHeaders::LAST_MODIFIED] = time.httpdate
  return if e['HTTP_IF_NONE_MATCH']
  status = res.status
  if (!status || status == 200) && (ims = time_from_header(e['HTTP_IF_MODIFIED_SINCE'])) && ims >= time.to_i
    res.status = 304
    halt
  end
  if (!status || (status >= 200 && status < 300) || status == 412) && (ius = time_from_header(e['HTTP_IF_UNMODIFIED_SINCE'])) && ius < time.to_i
    res.status = 412
    halt
  end
end