Rack Middleware

config.ru

require 'poc'

use UrlEncodedParametersEliminator
run App.new

poc.rb

require 'rubygems'
require 'rack'
require 'ruby-debug'

class UrlEncodedParametersEliminator
  def initialize(app, param='test')
    @app   = app
    @param = param
  end

  def call(env)
    @env = env

    status, headers, body = @app.call(@env)

    if @env["REQUEST_METHOD"] == "GET" && request_uri.include?(@param)
      uri = request_uri.gsub(pattern, '')
      uri.sub!(/\?$/, '')

      response(status, headers, body, uri)
    else
      [status, headers, body]
    end
  end

  private

  def request_uri
    @request_uri ||= @env['REQUEST_URI']
  end

  def response(status, headers, body, uri)
    new_response = Rack::Response.new(body, status, headers)
    new_response.redirect(uri)
    new_response.finish
  end

  def pattern
    Regexp.new("&?#{@param}[^&]*&?")
  end
end

class App
  def call(env)
   [200, {'Content-Type' => 'text/plain'}, ['Hello Middleware']]
  end
end