#151 Rack Middleware

Mar 02, 2009 | 12 minutes | Tools, Rails 2.3, Rack

Rack middleware is a way to filter a request and response coming into your application. In this episode I show how to modify the response body using middleware.

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Special thanks to Josh Peek for answering some questions I had on this topic.

Update: making the code below thread safe by duplicating self on call.

Note: as wldock and remi pointed out in the comments, it is important to change the headers["Content-Length"] value to reflect the new body length. See their comments for details.

          bash
        
rake middleware

          lib/response_timer.rb
        
class ResponseTimer
  def initialize(app, message = "Response Time")
    @app = app
    @message = message
  end
  
  def call(env)
    dup._call(env)
  end
  
  def _call(env)
    @start = Time.now
    @status, @headers, @response = @app.call(env)
    @stop = Time.now
    [@status, @headers, self]
  end
  
  def each(&block)
    block.call("<!-- #{@message}: #{@stop - @start} -->\n") if @headers["Content-Type"].include? "text/html"
    @response.each(&block)
  end
end

          config/environment.rb
        
config.middleware.use "ResponseTimer", "Load Time"