versionist

A plugin for versioning Rails 3 based RESTful APIs. Versionist supports three versioning strategies out of the box:

• Specifying version via an HTTP header
• Specifying version by prepending paths with a version slug
• Specifying version via a request parameter

A version of your API consists of:

• Namespaced controllers/routes
• Namespaced presenters
• Namespaced tests
• Documentation

Versionist includes Rails generators for generating new versions of your API as well as new components within an existing version.

Installation

Add the following dependency to your Rails 3 application's Gemfile file and run bundle install:

gem 'versionist'

Configuration

Versionist provides the method api_version that you use in your Rails 3 application's config/routes.rb file to constrain a collection of routes to a specific version of your API. The versioning strategy used by the collection of routes constrained by api_version is set by specifying either :header, :path, or :parameter (and their supporting values) in the configuration Hash passed to api_version. You configure the module namespace for your API version by specifying :module in the configuration Hash passed to api_version.

Versioning Strategies

HTTP Header

This strategy uses an HTTP header to request a specific version of your API.

Accept: application/vnd.mycompany.com; version=1,application/json
GET /foos

You configure the header to be inspected and the header value specifying the version in the configuration Hash passed to api_version.

Examples:

Content negotiation via the Accept header:

MyApi::Application.routes.draw do
  api_version(:module => "V1", :header => "Accept", :value => "application/vnd.mycompany.com; version=1") do
    match '/foos.(:format)' => 'foos#index', :via => :get
    match '/foos_no_format' => 'foos#index', :via => :get
    resources :bars
  end
end

Accept Header Gotcha

Please note: when your routes do not include an explicit format in the URL (i.e. match 'foos.(:format)' => foos#index), Rails inspects the Accept header to determine the requested format. Since an Accept header can have multiple values, Rails uses the first one present to determine the format. If your custom version header happens to be the first value in the Accept header, Rails would incorrectly try to interpret it as the format. If you use the Accept header, Versionist will move your custom version header (if found) to the end of the Accept header so as to not interfere with Rails' format resolution logic. This is the only case where Versionist will alter the incoming request.

Custom header:

MyApi::Application.routes.draw do
  api_version(:module => "V20120317", :header => "API-VERSION", :value => "v20120317") do
    match '/foos.(:format)' => 'foos#index', :via => :get
    match '/foos_no_format' => 'foos#index', :via => :get
    resources :bars
  end
end

Path

This strategy uses a URL path prefix to request a specific version of your API.

GET /v3/foos

You configure the path version prefix to be applied to the routes.

Example:

MyApi::Application.routes.draw do
  api_version(:module => "V3", :path => "/v3") do
    match '/foos.(:format)' => 'foos#index', :via => :get
    match '/foos_no_format' => 'foos#index', :via => :get
    resources :bars
  end
end

Request Parameter

This strategy uses a request parameter to request a specific version of your API.

GET /foos?version=v2

You configure the parameter name and value to be applied to the routes.

Example:

MyApi::Application.routes.draw do
  api_version(:module => "V2", :parameter => "version", :value => "v2") do
    match '/foos.(:format)' => 'foos#index', :via => :get
    match '/foos_no_format' => 'foos#index', :via => :get
    resources :bars
  end
end

Default Version

If a request is made to your API without specifying a specific version, by default a RoutingError (i.e. 404) will occur. You can optionally configure Versionist to return a specific version by default when none is specified. To specify that a version should be used as the default, include :default => true in the config hash passed to the api_version method.

Example.

MyApi::Application.routes.draw do
  api_version(:module => "V20120317", :header => "API-VERSION", :value => "v20120317", :default => true) do
    match '/foos.(:format)' => 'foos#index', :via => :get
    match '/foos_no_format' => 'foos#index', :via => :get
    resources :bars
  end
end

If you attempt to specify more than one default version, an error will be thrown at startup.

Rails Route :defaults Hash

The api_version method also supports Rails' :defaults hash (note that this is different than the :default key which controls the default API version described above). If a :defaults hash is passed to api_version, it will be applied to the collection of routes constrainted by api_version.

Example.

MyApi::Application.routes.draw do
  api_version(:module => "V20120317", :header => "API-VERSION", :value => "v20120317", :defaults => {:format => :json}, :default => true) do
    match '/foos.(:format)' => 'foos#index', :via => :get
    match '/foos_no_format' => 'foos#index', :via => :get
    resources :bars
  end
end

Version/Module Naming Convention Gotcha

Note that if your public facing version naming convention uses dots (i.e. v1.2.3), your module names cannot use dots, as you obviously cannot use dots in module names in Ruby. If you wish to simply replace dots with underscores, you'll need to use two underscores (i.e. __) in the module name passed to api_version to work around a quirk in Rails' inflector.

For example, if your public facing version is v2.0.0 and you want to map this to the module V2_0_0, you would do the following in api_routes:

api_version(:module => "V2__0__0", :header => "Accept", :value => "application/vnd.mycompany.com; version=v2.0.0") do
  ...
end

If you use the generators provided Versionist (more below) simply pass the module name as is (without this double underscore hack) and Versionist will take care of this detail for you.

rails generate versionist:new_api_version v2.0.0 V2_0_0 header:Accept value:"application/vnd.mycompany.com; version=v2.0.0"
  route  api_version(:module => "V2__0__0", :header=>"Accept", :value=>"application/vnd.mycompany.com; version=v2.0.0") do
  end
  create  app/controllers/v2_0_0
  create  app/controllers/v2_0_0/base_controller.rb
  create  spec/controllers/v2_0_0
  create  spec/controllers/v2_0_0/base_controller_spec.rb
  create  app/presenters/v2_0_0
  create  app/presenters/v2_0_0/base_presenter.rb
  create  spec/presenters/v2_0_0
  create  spec/presenters/v2_0_0/base_presenter_spec.rb
  create  public/docs/v2.0.0
  create  public/docs/v2.0.0/index.html
  create  public/docs/v2.0.0/style.css


rails generate versionist:new_controller foos V2_0_0
  create  app/controllers/v2_0_0/foos_controller.rb
  create  spec/controllers/v2_0_0/foos_controller_spec.rb


rails generate versionist:new_presenter foos V2_0_0
  create  app/presenters/v2_0_0/foos_presenter.rb
  create  spec/presenters/v2_0_0/foos_presenter_spec.rb

Unfortunately this work-around currently only works in Rails 3.0 and 3.1, and does not work in Rails 3.2. See rails/rails#5849) and rails/rails#6105.

Don't shoot the messenger. :-)

Generators

Versionist comes with generators to facilitate creating new versions of your APIs and new components with an existing version. To see the available generators, simply run rails generate, and you will see the versionist generators under the versionist namespace.

The following generators are available:

versionist:new_api_version

creates the infrastructure for a new API version. This will create:

• A new controller namespace, base controller and test
• A new presenters namespace, base presenter and test
• A new documentation directory and base files

Usage

rails generate versionist:new_api_version <version> <module namespace> <versioning strategy options>

Example:

rails generate versionist:new_api_version v2 V2 header:Accept value:"application/vnd.mycompany.com; version=2"
  route  api_version(:module => "V2", :header=>"Accept", :value=>"application/vnd.mycompany.com; version=2") do
  end
  create  app/controllers/v2
  create  app/controllers/v2/base_controller.rb
  create  spec/controllers/v2
  create  spec/controllers/v2/base_controller_spec.rb
  create  spec/requests/v2
  create  spec/requests/v2/base_controller_spec.rb
  create  app/presenters/v2
  create  app/presenters/v2/base_presenter.rb
  create  spec/presenters/v2
  create  spec/presenters/v2/base_presenter_spec.rb
  create  public/docs/v2
  create  public/docs/v2/index.html
  create  public/docs/v2/style.css

versionist:new_controller

creates a new controller class with the given name under the given version module.

Usage

rails generate versionist:new_controller <name> <module namespace>

Example:

rails generate versionist:new_controller foos V2
  create  app/controllers/v2/foos_controller.rb
  create  spec/controllers/v2/foos_controller_spec.rb
  create  spec/requests/v2/foos_controller_spec.rb

versionist:new_presenter

creates a new presenter class with the given name under the given version module.

Usage

rails generate versionist:new_presenter <name> <module namespace>

Example:

rails generate versionist:new_presenter foos V2
  create  app/presenters/v2/foos_presenter.rb
  create  spec/presenters/v2/foos_presenter_spec.rb

versionist:copy_api_version

copies an existing API version to a new API version. This will do the following:

• Copy all existing routes in config/routes.rb from the old API version to routes for the new API version in config/routes.rb (see note below)
• Copy all existing controllers and tests from the old API version to the new API version
• Copy all existing presenters and tests from the old API version to the new API version
• Copy all documentation from the old API version to the new API version

Note: routes can only be copied with MRI Ruby 1.9 and above, as this feature relies on Ripper which is only available in stdlib in MRI Ruby 1.9 and above. Outside of routes copying, the other copy steps will work just fine in Ruby 1.8 and other non-MRI Ruby implementations.

Usage

rails generate versionist:copy_api_version <old version> <old module namespace> <new version> <new module namespace>

Example:

rails generate versionist:copy_api_version v2 V2 v3 V3
  route  api_version(:module => "V3", :header=>"Accept", :value=>"application/vnd.mycompany.com; version=3") do
  end
  Copying all files from app/controllers/v2 to app/controllers/v3
  Copying all files from spec/controllers/v2 to spec/controllers/v3
  Copying all files from app/presenters/v2 to app/presenters/v3
  Copying all files from spec/presenters/v2 to spec/presenters/v3
  Copying all files from public/docs/v2 to public/docs/v3