module ActionDispatch::Http::Cache::Request

def etag_matches?(etag) 

def etag_matches?(etag)
  if_none_match && if_none_match == etag
end

def fresh?(response)

supplied, both must match, or the request is not considered fresh.
If-Modified-Since and If-None-Match conditions. If both headers are
Check response freshness (Last-Modified and ETag) against request 
def fresh?(response)
  last_modified = if_modified_since
  etag          = if_none_match
  return false unless last_modified || etag
  success = true
  success &&= not_modified?(response.last_modified) if last_modified
  success &&= etag_matches?(response.etag) if etag
  success
end

def if_modified_since 

def if_modified_since
  if since = env['HTTP_IF_MODIFIED_SINCE']
    Time.rfc2822(since) rescue nil
  end
end

def if_none_match 

def if_none_match
  env['HTTP_IF_NONE_MATCH']
end

def not_modified?(modified_at) 

def not_modified?(modified_at)
  if_modified_since && modified_at && if_modified_since >= modified_at
end