Middleware that rewrites every image to be 'The Best Image on the Internet'

app.rb

require 'rubygems'
require 'sinatra'

Sinatra::Base.inline_templates = true

class App < Sinatra::Base

  get '/' do
    erb :index
  end

end

__END__

@@ index
<h1>Hello, World</h1>
<img src="/T3Zox.jpg" width="100" height="100" />

config.ru

require 'app'
require 'malcom_in_the_middleware'

use Malcom
run App

malcom_in_the_middleware.rb

class Malcom
  require 'nokogiri'

  def initialize(app)
    @app = app
  end

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

    static_dir = "http://thebestpictureontheinternet.com/"
    body = Nokogiri::HTML(body.first)

    body.css('img').each do |image|
      original = image.attributes.fetch('src').value
      original.gsub!(/^\//, '')
      image.attributes.fetch('src').value = "#{static_dir}#{original}"
    end

    headers['Content-Length'] = body.to_html.length.to_s

    [status, headers, body.to_html]
  end
end

rackup config.ru