class Rack::CommonLogger

def log(env, status, response_headers, began_at)
  request = Rack::Request.new(env)
  length = extract_content_length(response_headers)
  msg = sprintf(FORMAT,
    request.ip || "-",
    request.get_header("REMOTE_USER") || "-",
    Time.now.strftime("%d/%b/%Y:%H:%M:%S %z"),
    request.request_method,
    request.script_name,
    request.path_info,
    request.query_string.empty? ? "" : "?#{request.query_string}",
    request.get_header(SERVER_PROTOCOL),
    status.to_s[0..3],
    length,
    Utils.clock_time - began_at)
  msg.gsub!(/[^[:print:]\n]/) { |c| sprintf("\\x%x", c.ord) }
  logger = @logger || request.get_header(RACK_ERRORS)
  # Standard library logger doesn't support write but it supports << which actually
  # calls to write on the log device without formatting
  if logger.respond_to?(:write)
    logger.write(msg)
  else
    logger << msg
  end
end