module ActionDispatch::Http::Cache::Request

def etag_matches?(etag)
  if etag
    validators = if_none_match_etags
    validators.include?(etag) || validators.include?("*")
  end
end

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
  if since = get_header(HTTP_IF_MODIFIED_SINCE)
    Time.rfc2822(since) rescue nil
  end
end

def if_none_match
  get_header HTTP_IF_NONE_MATCH
end

def if_none_match_etags
  if_none_match ? if_none_match.split(",").each(&:strip!) : []
end

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