config.ru

require 'pp'

class Middleware
  
  def initialize(app)
    @app = app
    
    puts "=-=-=- Initializing #{self.class}"
    pp app
  end
  
  def call(environment)
    puts "=-=-=- Calling #{self.class}"
  end
  
end

# Bold body
class FirstMiddleware < Middleware
  
  def call(environment)
    super
    
    status, headers, body = @app.call(environment)
    
    body = ["<b>#{body.first}</b>"]
    
    [ status, headers, body ]
  end
  
end

# Italic body
class SecondMiddleware < Middleware
  
  def call(environment)
    super
    
    status, headers, body = @app.call(environment)
    
    body = ["<i>#{body.first}</i>"]
    
    [ status, headers, body ]
  end
  
end

class Application
  
  def initialize
    puts "=-=-=- Initializing #{self.class}"
  end
  
  def call(environment)
    puts "=-=-=- Calling #{self.class}"
    
    [ 200, {}, ['Hello!'] ]
  end
  
end

use FirstMiddleware
use SecondMiddleware
run Application.new

gistfile1.txt

Puma starting in single mode...
* Version 2.8.1 (ruby 2.1.0-p0), codename: Sir Edmund Percival Hillary
* Min threads: 0, max threads: 16
* Environment: development
=-=-=- Initializing Application
=-=-=- Initializing SecondMiddleware
#<Application:0x000001013ef4e8>
=-=-=- Initializing FirstMiddleware
#<SecondMiddleware:0x000001013ef380 @app=#<Application:0x000001013ef4e8>>
* Listening on tcp://0.0.0.0:9292
Use Ctrl-C to stop

(in another terminal) $ curl http://localhost:9292

=-=-=- Calling FirstMiddleware
=-=-=- Calling SecondMiddleware
=-=-=- Calling Application
127.0.0.1 - - [08/Mar/2014 02:48:44] "GET / HTTP/1.1" 200 - 0.0006