simple rack mimddlewear

app.rb

require 'sinatra'

class MyApp < Sinatra::Base
    get '/hoge' do
      'Hello world!'
    end
end

config.ru

require './app'
require File.expand_path 'lib/my_rack_middleware', File.dirname(__FILE__)
use MyRackMiddleware
run MyApp

Gemfile

source "https://rubygems.org"

gem 'sinatra'

log.sh

tree -L 2
.
├── Gemfile
├── Gemfile.lock
├── app.rb
├── config.ru
├── lib
│   └── my_rack_middleware.rb
└── vendor
    └── bundle

bundle install

bundle exec rackup -p 4567

open http://localhost:4567

my_rack_middlewear.rb

# /lib/my_rack_middlewear.rb
class MyRackMiddleware
  def initialize(app)
    @app = app
  end

  def call(env)
    if env["PATH_INFO"] == '/hoge'
      status, headers, response = @app.call(env)
      status = 200
      response = ["hogehoge"]
      content_length = response.inject(0) do |sum, content|
        sum + content.bytesize
      end
      headers = { "Content-Type"           => "text/html;charset=utf-8",
                 "Content-Length"         => content_length.to_s,
                 "X-XSS-Protection"       => "1; mode=block",
                 "X-Content-Type-Options" => "nosniff",
                 "X-Frame-Options"        => "SAMEORIGIN"}
    else
      res = @app.call(env)
    end

    [status, headers, response]

  end
end