Grape

Grape is a REST-like API micro-framework for Ruby. It is built to complement existing web application frameworks such as Rails and Sinatra by providing a simple DSL to easily provide APIs. It has built-in support for common conventions such as multiple formats, subdomain/prefix restriction, and versioning.

Installation

Grape is available as a gem, to install it just install the gem:

gem install grape

Basic Usage

Grape APIs are Rack applications that are created by subclassing Grape::API. Below is a simple example showing some of the more common features of Grape in the context of recreating parts of the Twitter API.

class Twitter::API < Grape::API
  version '1'
  
  helpers do
    def current_user
      @current_user ||= User.authorize!(env)
    end
    
    def authenticate!
      error!('401 Unauthorized', 401) unless current_user
    end
  end
  
  resource :statuses do
    get :public_timeline do
      Tweet.limit(20)
    end
  
    get :home_timeline do
      authenticate!
      current_user.home_timeline
    end
    
    get '/show/:id' do
      Tweet.find(params[:id])
    end
    
    post :update do
      authenticate!
      Tweet.create(
        :user => current_user,
        :text => params[:status]
      )
    end
  end
end

This would create a Rack application that could be used like so (in a Rackup config.ru file):

run Twitter::API

And would respond to the following routes:

GET  /1/statuses/public_timeline(.json)
GET  /1/statuses/home_timeline(.json)
GET  /1/statuses/show/:id(.json)
POST /1/statuses/update(.json)

Serialization takes place automatically. For more detailed usage information, please visit the Grape Wiki.

Error Handling

The default behavior of Grape is to rescue all exceptions and to return a 403 status code with the exception's message in the response body.

It's possible to disable this behavior and pass exceptions further up the stack. This usually means displaying the web server's error page as a result.

class Twitter::API < Grape::API
  use Grape::Middleware::Error, :rescue => false
  ...
end

It's also common to change the error format to JSON.

class Twitter::API < Grape::API
  use Grape::Middleware::Error, :format => :json
  ...
end

Finally, you can specify your own error formatter. The following example returns a custom error message in the JSON format.

class Twitter::API < Grape::API
  use Grape::Middleware::Error, :format => :custom, :formatters = { lambda { |message| { :custom => "the error message was: #{message}" } }
  ...
end

Note on Patches/Pull Requests

• Fork the project.
• Make your feature addition or bug fix.
• Add tests for it. This is important so I don't break it in a future version unintentionally.
• Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)
• Send me a pull request. Bonus points for topic branches.

Copyright

Copyright (c) 2010 Michael Bleigh and Intridea, Inc. See LICENSE for details.