Grape

Note: This is the master branch of Grape where we're trying to maintain things to be relatively stable. If you want to live on the edge, check out the frontier.

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.

Project Tracking

• Grape Google Group
• Grape Wiki

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 'v1', :using => :header, :vendor => 'twitter', :format => :json

  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

  resource :account do
    before{ authenticate! }

    get '/private' do
      "Congratulations, you found the secret!"
    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  /statuses/public_timeline(.json)
GET  /statuses/home_timeline(.json)
GET  /statuses/show/:id(.json)
POST /statuses/update(.json)

Versioning is handled with HTTP Accept head by default, but can be configures to use different strategies. For example, to request the above with a version, you would make the following request:

curl -H Accept=application/vnd.twitter-v1+json http://localhost:9292/statuses/public_timeline

By default, the first matching version is used when no Accept header is supplied. This behavior is similar to routing in Rails. To circumvent this default behaviour, one could use the :strict option. When this option is set to true, a 404 Not found error is returned when no correct Accept header is supplied.

Serialization takes place automatically.

Helpers

You can define helper methods that your endpoints can use with the helpers macro by either giving a block or a module:

module MyHelpers
  def say_hello(user)
    "hey there #{user.name}"
  end
end

class API < Grape::API
  # define helpers with a block
  helpers do
    def current_user
      User.find(params[:user_id])
    end
  end

  # or mix in a module
  helpers MyHelpers

  get '/hello' do
    # helpers available in your endpoint and filters
    say_hello(current_user)
  end
end

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

Grape can be told to rescue all exceptions and instead return them in text or json formats.

class Twitter::API < Grape::API
  rescue_from :all
end

You can also rescue specific exceptions.

class Twitter::API < Grape::API
  rescue_from ArgumentError, NotImplementedError
end

The error format can be specified using error_format. Available formats are :json and :txt (default).

class Twitter::API < Grape::API
  error_format :json
end

You can rescue all exceptions with a code block. The rack_response wrapper automatically sets the default error code and content-type.

class Twitter::API < Grape::API
  rescue_from :all do |e|
    rack_response({ :message => "rescued from #{e.class.name}" })
  end
end

You can also rescue specific exceptions with a code block and handle the Rack response at the lowest level.

class Twitter::API < Grape::API
  rescue_from :all do |e|
    Rack::Response.new([ e.message ], 500, { "Content-type" => "text/error" }).finish
  end
end

class Twitter::API < Grape::API
  rescue_from ArgumentError do |e|
    Rack::Response.new([ "ArgumentError: #{e.message}" ], 500)
  end
  rescue_from NotImplementedError do |e|
    Rack::Response.new([ "NotImplementedError: #{e.message}" ], 500)
  end
end

Writing Tests

You can test a Grape API with RSpec. Tests make HTTP requests, therefore they must go into the spec/request group. You may want your API code to go into app/api - you can match that layout under spec by adding the following in spec/spec_helper.rb.

RSpec.configure do |config|
  config.include RSpec::Rails::RequestExampleGroup, :type => :request, :example_group => {
    :file_path => /spec\/api/
  }
end

A simple RSpec API test makes a get request and parses the response.

require 'spec_helper'

describe Twitter::API do
  describe "GET /api/v1/statuses" do
    it "returns an empty array of statuses" do
      get "/api/v1/statuses"
      response.status.should == 200
      JSON.parse(response.body).should == []
    end
  end
end

Inspecting an API

Grape exposes arrays of API versions and compiled routes. Each route contains a route_prefix, route_version, route_namespace, route_method, route_path and route_params.

class TwitterAPI < Grape::API

  version 'v1'
  get "version" do
    api.version
  end

  version 'v2'
  namespace "ns" do
    get "version" do
      api.version
    end
  end
end

TwitterAPI::versions # yields [ 'v1', 'v2' ]
TwitterAPI::routes # yields an array of Grape::Route objects
TwitterAPI::routes[0].route_version # yields 'v1'

Grape also supports storing additional parameters with the route information. This can be useful for generating documentation. The optional hash that follows the API path may contain any number of keys and its values are also accessible via a dynamically-generated route_[name] function.

class StringAPI < Grape::API
  get "split/:string", { :params => [ "token" ], :optional_params => [ "limit" ] } do
    params[:string].split(params[:token], (params[:limit] || 0))
  end
end

StringAPI::routes[0].route_params # yields an array [ "string", "token" ]
StringAPI::routes[0].route_optional_params # yields an array [ "limit" ]

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.