Rack app for serving pre-generated GZip responses

config.ru

class StaticGZip
  DIRECTORY_INDEX = "index.html"
  attr_accessor :root_dir

  def initialize(root_dir)
    @root_dir = root_dir
  end

  def call(env)
    request = Rack::Request.new(env)
    
    file_path = File.join(File.dirname(__FILE__), root_dir, request.path)

    static_file = StaticFile.locate(file_path)
    static_file.to_response
  end

  class StaticFile
    attr_accessor :body

    def initialize(body)
      @body = body
    end

    def code
      200
    end

    def headers
      {}
    end

    def to_response
      [code, headers, [body]]
    end

    def self.locate(path)
      file_path = path.sub(/\/$/, "/#{DIRECTORY_INDEX}")

      [GZipFile, StaticFile, NullFile].each do |klass|
        file = klass.from_path(file_path)
        return file unless file.nil?
      end
    end

    def self.from_path(path)
      return unless File.exists?(path)
      body = File.read(path)
      self.new(body)
    end
  end

  class GZipFile < StaticFile
    def headers
      { 'Content-Encoding' => 'gzip' }
    end

    def self.from_path(path)
      super "#{path}.gz"
    end
  end

  class NullFile < StaticFile
    def initialize
    end

    def code
      404
    end

    def body
      "Not found"
    end

    def self.from_path(path)
      self.new
    end
  end
end

run StaticGZip.new("build")