Rackミドルウェアとして動作する1リクエスト毎に勝手に消える超簡易キャッシュストア

cache_by_request.rb

class CacheByRequest
  def self.read(key)
    if Thread.current[:cache_by_request]
      Thread.current[:cache_by_request].read(key)
    else
      raise "before CacheByRequest::Store initialization"
    end
  end

  def self.write(key, val)
    if Thread.current[:cache_by_request]
      Thread.current[:cache_by_request].write(key, val)
    else
      raise "before CacheByRequest::Store initialization"
    end
  end

  def self.with_stubbed
    Thread.current[:cache_by_request] = Store.new
    yield
  ensure
    Thread.current[:cache_by_request] = nil
  end

  def initialize(app)
    @app = app
  end

  def call(env)
    Thread.current[:cache_by_request] = Store.new
    @app.call(env)
  ensure
    Thread.current[:cache_by_request] = nil
  end

  class Store
    def initialize
      @data = HashWithIndifferentAccess.new
    end

    def read(key)
      @data[key]
    end

    def write(key, val)
      @data[key] = val
    end
  end
end