# File lib/rack/runtime.rb, line 15
15:     def call(env)
16:       start_time = Time.now
17:       status, headers, body = @app.call(env)
18:       request_time = Time.now - start_time
19: 
20:       if !headers.has_key?(@header_name)
21:         headers[@header_name] = "%0.6f" % request_time
22:       end
23: 
24:       [status, headers, body]
25:     end