RequestStore Documentation

Add request_store to your application's Gemfile to provide request-local storage that avoids the concurrency bugs associated with using Thread.current in threaded web servers like Puma or Thin.

gem 'request_store'

If you are not using Rails, you must manually include the RequestStore::Middleware in your Rack stack to ensure the store is cleared after each request.

use RequestStore::Middleware

While Rails 3+ applications are automatically configured via a Railtie, Rails 2.x applications require manual middleware configuration. Add the following to your config/environment.rb:

config.middleware.use RequestStore::Middleware

When used within a Rails application, RequestStore automatically configures itself via a Railtie. It inserts RequestStore::Middleware into the middleware stack to ensure the request-local storage is initialized and cleared correctly.

Specifically, it handles middleware placement based on the presence of ActionDispatch::RequestId (inserting after it) or falls back to inserting after Rack::MethodOverride. It also integrates with the Rails reloader (ActiveSupport::Reloader or ActionDispatch::Reloader) to call RequestStore.clear! during the reloading process, preventing data leakage between requests in development environments.

When using Rack::Test for testing, ensure the RequestStore::Middleware is included in your app definition so that storage is cleared between test requests.

# spec_helper.rb

def app
  Rack::Builder.new do
    use RequestStore::Middleware
    run MyApp
  end
end

Replace usage of Thread.current with RequestStore.store to ensure that data is local to the current request and is automatically cleared after the request completes. This prevents data from leaking between requests in threaded environments.

def index
  RequestStore.store[:foo] ||= 0
  RequestStore.store[:foo] += 1

  render :text => RequestStore.store[:foo]
end

The fetch method returns the stored value if it already exists. If no stored value exists, it executes the provided block, stores the result in the RequestStore, and returns it.

top_posts = RequestStore.fetch(:top_posts) do
  # code to obtain the top posts
end

The RequestStore module implements several methods that mirror the standard Ruby Hash API for interacting with the underlying storage:

• RequestStore.store: Returns the underlying hash object.
• RequestStore.store=(store): Replaces the entire store with a new hash.
• RequestStore.[](key) / RequestStore[]= (key, value): Standard bracket access for reading and writing.
• RequestStore.delete(key, &block): Removes a key from the store, optionally using a block to return a value.