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.

Raising Errors

You can raise errors explicitly.

error!("Access Denied", 401)

You can also return JSON formatted objects explicitly by raising error! and passing a hash instead of a message.

error!({ "error" => "unexpected error", "detail" => "missing widget" }, 500)

Exception Handling

By default Grape does not catch all unexpected exceptions. This means that the web server will handle the error and render the default error page as a result. It is possible to trap all exceptions by setting rescue_all_errors true instead. You may change the error format to JSON by using error_format :json and set the default error status to 200 with default_error_status 200. You may also include the complete backtrace of the exception with rescue_with_backtrace true either as text (for the :txt format) or as a :backtrace field in the json (for the :json format).

class Twitter::API < Grape::API
  rescue_all_errors true
  rescue_with_backtrace true
  error_format :json
  default_error_status 200

  # api methods
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.