#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"