rack_middleware_example.rb

# Rack middleware example 

require 'rubygems'
require 'rack'

class MyRackMiddleware   
  def initialize(app)
    @app = app
  end
  
  def call(env)
    request = Rack::Request.new(env)
    if request.path =~ /params/
      [200,{"Content-Type" => "text/html"}, "#{request.params.inspect}"]
    else
      @app.call(env)
    end
  end  
end

if $0 == __FILE__
  require 'rack/contrib'
  
  log_file = File.open('rack_app.log',"a")

  app = Rack::Builder.app { 
    use Rack::CommonLogger, log_file
    use Rack::ShowExceptions
    use Rack::Lint
    use MyRackMiddleware  
    run Rack::NotFound.new('404.html') 
  }

  begin
    Rack::Handler::WEBrick.run app, :Port => 9292
  ensure
    log_file.close
  end
end


__END__

To run as a Rack application:
  $> ruby rack_app.rb

If you do not have the rack-contrib gem, install by:
  $> gem install rack-rack-contrib --source=http://gems.github.com/
    
See the output by typing the following into the browser
  http://localhost:9292/params?hello=world