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a rack dynamic routing platform
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Circuit is in heavy development and reorganization at the moment. We are planning to have this API and change stabilized in the 0.4.0 release. 0.4.0 and future releases will include deprecation warning and a 0.4.0-stable branch in GitHub.





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Anyone is welcome to contribute to circuit. Just fork us on GitHub and send a pull request when you are ready.

Please ensure the following compatibility requirements are met.

<<< docs/

A common discussion ensues.

Q: But why would someone need database powered Rack::Builder?

Response: The rack ecosystem doesn't have a good way to handle dynamic http routing. Circuit meets the needs of dynamic routing while preserving the functionality that Rack provides.

Comment: That seems really... slow.

Response: A valid point, but circuit isn't for every codebase. If you need dynamic routing (i.e. using splat routing methods followed by a database lookup), you are going to see similar performance to circuits backends. Along with that, circuit provides a number of useful features that far outweigh performance costs.

Comment: this isn't very Railsy

Response: In practice, codebases that use circuit to solve dynamic routing are more railsy.
Let me explain:

If you are constructing an application in Rails that requires dynamic user specified slugs, you probably have this line uncommented from your routes:

# yuck.
match '/*', to: 'site#proxy'

Say you are creating a CMS using this line. This means that that one action will handle all requests that don't match the rest of your routes definition. Immediately this might seem like a good idea, but it will inevitably lead to a very expensive Rails action that handles a large number of requests on the site.

Circuit will allow you to remove this line and use middlewares to route requests to different controllers (even rack applications), and control this logic via the backend of your choice. Routes can be extended with their specified behaviors, allowing even more control over requests than rails provides out of the box.

{Circuit::Behavior Behaviors} allow you to do change your middleware stack dynamically on a per-request/route basis (via the backend), enabling your dynamic routes to add middleware, modify the rack request object, and even change your downstream app. Using {Circuit::Middleware::Rewriter} in a behavior, you can easily reroute downstream requests to "standard-issue" rails controllers by simply rewriting the incoming path of the request.

A mapping graph to route rack requests.


Rackup-based behaviors.

Circuit uses behaviors to extend a requests functionality in the rack stack. Behaviors are written and stored in circuit-rackup files (.cru). The difference between a normal rackup file and a circuit-rackup file is that a circuit-rackup file does not have to have a run declaration; this makes circuit-rackup files only partially rackup compliant. Below is an example of a behavior that renders an ok response (this is a fully-compliant rackup file; however, we still use the .cru extension for the behavior):

# app/behaviors/render_ok.cru

run proc {|env| [200, {'Content-Type' => 'text/plain'}, ['OK']] }

Now that you have your behavior, you need to setup your {Circuit::Storage::Sites::Model Site} model:

# app/models/site.rb

class Site
  include Circuit::Storage::Sites::MongoidStore::Site
  has_one :root, :class_name => "Node"

and your {Circuit::Storage::Nodes::Model Node} model:

# app/models/node.rb

class Node
  include Circuit::Storage::Nodes::MongoidStore::Node
  belongs_to :site, :inverse_of => :root

Then create your site:

$ > @site = "", aliases: [""])
$ >
$ => true

and your root node with your RenderOk behavior:

$ > @node = @site, slug: nil, behavior_klass: "RenderOk")
$ >
$ => true
$ > @node.root? # the nil slug and defined site indicates the root
$ => true
$ > @node.behavior
$ => RenderOk
$ > @node.behavior.class
$ => Module
$ > @node.behavior.included_modules
$ => [Circuit::Behavior]

Now when the root of your site is accessed, the RenderOk behavior will be run.

Behaviors are loaded into memory during application initialization. Any modifications to behaviors will require restarting your application.

Also, remember that Circuit is not ActionPack-dependent. Only Rack, ActiveModel, and ActiveSupport are dependencies. This means that, from a Rails-perspective, Circuit's work ends before the Rails router takes over, so Circuit does not replace the Rails router. Although, it is theoretically possible to use the run method in a Behavior to directly run a specific controller and action and bypass the remainder of the Rails middleware stack entirely (including the Rails router).


One useful middleware baked into circuit is the Rewriter. The idea of this middleware is to use circuit routing to route to dynamic content you have associated in you routing tree.

# app/behaviors/page.cru

use Circuit::Middleware::Rewriter do |request|
      content_id =
      ["", "/contents/#{content_id}"]

and the corresponding downstream Rails routing file:

# config/routes.rb

Rails.application.routes.draw do
  resources :contents

In the above example, we are assuming you have created a model that has a content object associated to it. By doing this we have now created a small CMS.

Multi-Backend support

Circuit provides support for different backends to power this map tree. Currently, the gem includes a Mongoid backend and a memory backend. Each backend is how Circuit is constructed to interface with your persisted routing tree. Backends are ActiveModel based.

Currently, Backends are ActiveModel backed and within them they define the model that the router interacts with. We are discussing the idea of separating the backends from the model (to drop the ActiveModel dependency).

This is where circuit needs your help! We would love to see backends for many common ODM's. Our hit-list includes:

  • Mongoid
  • Memory
  • Yaml
  • Redis
  • ActiveRecord
  • RiakClient/Ripple

We will entertain pull requests from other commonly used libraries.

<<< docs/