config.ru

require 'rack'

class RemoveBadWords
  BAD_WORDS = %w(emacs).freeze

  def initialize(app)
    @app = app
  end

  def call(env)
    req = Rack::Request.new(env)
    remove_bad_words!(req)
    @app.call(env)
  end

  private

  def remove_bad_words!(req)
    req.params.each do |k,v|
      if BAD_WORDS.include?(v)
        puts " Deleting 💩 #{v}💩"
        req.delete_param(k)
      end
    end
  end
end

class UpcaseAllTheThings
  def initialize(app)
    @app = app
  end

  def call(env)
    req = Rack::Request.new(env)
    req.params.each do |k,v|
      puts "Upcasing #{v} -> #{v.upcase}"
      req.update_param(k, v.upcase)
    end
    @app.call(env)
  end
end

app = Rack::Builder.new do
  use UpcaseAllTheThings
  use RemoveBadWords
  run proc { |env| ['200', {'Content-Type' => 'text/html'}, ["Params: #{Rack::Request.new(env).params}"]] }
end
run app