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What is Grape?

Grape is a REST-like API micro-framework for Ruby. It's designed to run on Rack or complement existing web application frameworks such as Rails and Sinatra by providing a simple DSL to easily develop RESTful APIs. It has built-in support for common conventions, including multiple formats, subdomain/prefix restriction, content negotiation, versioning and much more.

Build Status

Stable Release

You're reading the documentation for the next release of Grape, which should be 0.3.3. The current stable release is 0.3.2.

Project Tracking

Installation

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

gem install grape

If you're using Bundler, add the gem to Gemfile.

gem 'grape'

Run bundle install.

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.

module Twitter
  class 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

      desc "Return a public timeline."
      get :public_timeline do
        Status.limit(20)
      end

      desc "Return a personal timeline."
      get :home_timeline do
        authenticate!
        current_user.statuses.limit(20)
      end

      desc "Return a status."
      params do
        requires :id, :type => Integer, :desc => "Status id."
      end
      get ':id' do
        Status.find(params[:id])
      end

      desc "Create a status."
      params do
        requires :status, :type => String, :desc => "Your status."
      end
      post do
        authenticate!
        Status.create!({
          :user => current_user,
          :text => params[:status]
        })
      end

      desc "Update a status."
      params do
        requires :id, :type => String, :desc => "Status ID."
        requires :status, :type => String, :desc => "Your status."
      end
      put ':id' do
        authenticate!
        current_user.statuses.find(params[:id]).update({
          :user => current_user,
          :text => params[:status]
        })
      end

      desc "Delete a status."
      params do
        requires :id, :type => String, :desc => "Status ID."
      end
      delete ':id' do
        authenticate!
        current_user.statuses.find(params[:id]).destroy
      end

    end
  end
end

Mounting

Rack

The above sample creates a Rack application that can be run from a rackup config.ru file with rackup:

run Twitter::API

And would respond to the following routes:

GET /statuses/public_timeline(.json)
GET /statuses/home_timeline(.json)
GET /statuses/:id(.json)
POST /statuses(.json)
PUT /statuses/:id(.json)
DELETE /statuses/:id(.json)

Grape will also automatically respond to HEAD and OPTIONS for all GET, and just OPTIONS for all other routes.

Rails

Place API files into app/api and modify application.rb.

config.paths.add "app/api", :glob => "**/*.rb"
config.autoload_paths += Dir["#{Rails.root}/app/api/*"]

Modify config/routes:

mount Twitter::API => '/'

See below for additional code that enables reloading of API changes in development.

Modules

You can mount multiple API implementations inside another one. These don't have to be different versions, but may be components of the same API.

class Twitter::API < Grape::API
  mount Twitter::APIv1
  mount Twitter::APIv2
end

You can also mount on a path, which is similar to using prefix inside the mounted API itself.

class Twitter::API < Grape::API
  mount Twitter::APIv1 => '/v1'
end

Versioning

There are three strategies in which clients can reach your API's endpoints: :path, :header and :param. The default strategy is :path.

Path

version 'v1', :using => :path

Using this versioning strategy, clients should pass the desired version in the URL.

curl -H http://localhost:9292/v1/statuses/public_timeline

Header

version 'v1', :using => :header, :vendor => 'twitter'

Using this versioning strategy, clients should pass the desired version in the HTTP Accept head.

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 behavior, one could use the :strict option. When this option is set to true, a 406 Not Acceptable error is returned when no correct Accept header is supplied.

Param

version 'v1', :using => :param

Using this versioning strategy, clients should pass the desired version as a request parameter, either in the URL query string or in the request body.

curl -H http://localhost:9292/statuses/public_timeline?apiver=v1

The default name for the query parameter is 'apiver' but can be specified using the :parameter option.

version 'v1', :using => :param, :parameter => "v"
curl -H http://localhost:9292/statuses/public_timeline?v=v1

Describing Methods

You can add a description to API methods and namespaces.

desc "Returns your public timeline."
get :public_timeline do
  Status.limit(20)
end

Parameters

Request parameters are available through the params hash object. This includes GET, POST and PUT parameters, along with any named parameters you specify in your route strings.

get :public_timeline do
  Status.order(params[:sort_by])
end

Parameters are automatically populated from the request body on POST and PUT for form input, JSON and XML content-types.

The request:

curl -d '{"text": "140 characters"}' 'http://localhost:9292/statuses' -H Content-Type:application/json -v

The Grape endpoint:

post '/statuses' do
  Status.create!({ :text => params[:text] })
end

Multipart POSTs and PUTs are supported as well.

The request:

curl --form image_file=image.jpg http://localhost:9292/upload

The Grape endpoint:

post "upload" do
  # file in params[:image_file]
end

Parameter Validation and Coercion

You can define validations and coercion options for your parameters using a params block.

params do
  requires :id, type: Integer
  optional :text, type: String, regexp: /^[a-z]+$/
  group :media do
    requires :url
  end
end
put ':id' do
  # params[:id] is an Integer
end

When a type is specified an implicit validation is done after the coercion to ensure the output type is the one declared.

Parameters can be nested using group. In the above example, this means params[:media][:url] is required along with params[:id].

Namespace Validation and Coercion

Namespaces allow parameter definitions and apply to every method within the namespace.

namespace :statuses do
  params do
    requires :user_id, type: Integer, desc: "A user ID."
  end
  namespace ":user_id" do
    desc "Retrieve a user's status."
    params do
      requires :status_id, type: Integer, desc: "A status ID."
    end
    get ":status_id" do
      User.find(params[:user_id]).statuses.find(params[:status_id])
    end
  end
end

The namespace method has a number of aliases, including: group, resource, resources, and segment. Use whichever reads the best for your API.

Custom Validators

class AlphaNumeric < Grape::Validations::Validator
  def validate_param!(attr_name, params)
    unless params[attr_name] =~ /^[[:alnum:]]+$/
      throw :error, :status => 400, :message => "#{attr_name}: must consist of alpha-numeric characters"
    end
  end
end
params do
  requires :text, :alpha_numeric => true
end

You can also create custom classes that take parameters.

class Length < Grape::Validations::SingleOptionValidator
  def validate_param!(attr_name, params)
    unless params[attr_name].length <= @option
      throw :error, :status => 400, :message => "#{attr_name}: must be at the most #{@option} characters long"
    end
  end
end
params do
  requires :text, :length => 140
end

Validation Errors

When validation and coercion errors occur an exception of type Grape::Exceptions::ValidationError is raised. If the exception goes uncaught it will respond with a status of 400 and an error message. You can rescue a Grape::Exceptions::ValidationError and respond with a custom response.

rescue_from Grape::Exceptions::ValidationError do |e|
    Rack::Response.new({
        'status' => e.status,
        'message' => e.message,
        'param' => e.param
    }.to_json, e.status)
end

Headers

Request headers are available through the headers helper or from env in their original form.

get do
  error!('Unauthorized', 401) unless headers['Secret-Password'] == 'swordfish'
end
get do
  error!('Unauthorized', 401) unless env['HTTP_SECRET_PASSWORD'] == 'swordfish'
end

You can set a response header with header inside an API.

header "X-Robots-Tag", "noindex"

Routes

Optionally, you can define requirements for your named route parameters using regular expressions. The route will match only if all requirements are met.

get ':id', :requirements => { :id => /[0-9]*/ } do
  Status.find(params[:id])
end

Helpers

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

module StatusHelpers
  def user_info(user)
    "#{user} has statused #{user.statuses} status(s)"
  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 StatusHelpers

  get 'info' do
    # helpers available in your endpoint and filters
    user_info(current_user)
  end
end

Cookies

You can set, get and delete your cookies very simply using cookies method.

class API < Grape::API

  get 'status_count' do
    cookies[:status_count] ||= 0
    cookies[:status_count] += 1
    { :status_count => cookies[:status_count] }
  end

  delete 'status_count' do
    { :status_count => cookies.delete(:status_count) }
  end

end

Use a hash-based syntax to set more than one value.

cookies[:status_count] = {
    :value => 0,
    :expires => Time.tomorrow,
    :domain => '.twitter.com',
    :path => '/'
}

cookies[:status_count][:value] +=1

Delete a cookie with delete.

cookies.delete :status_count

Specify an optional path.

cookies.delete :status_count, :path => '/'

Redirecting

You can redirect to a new url temporarily (302) or permanently (301).

redirect "/statuses"
redirect "/statuses", :permanent => true

Allowed Methods

When you add a GET route for a resource, a route for the HEAD method will also be added automatically. You can disable this behavior with do_not_route_head!.

class API < Grape::API

  do_not_route_head!

  get '/example' do
    # only responds to GET
  end

end

When you add a route for a resource, a route for the OPTIONS method will also be added. The response to an OPTIONS request will include an "Allow" header listing the supported methods.

class API < Grape::API

  get '/rt_count' do
    { :rt_count => current_user.rt_count }
  end

  params do
    requires :value, :type => Integer, :desc => 'Value to add to the rt count.'
  end
  put '/rt_count' do
    current_user.rt_count += params[:value].to_i
    { :rt_count => current_user.rt_count }
  end

end
curl -v -X OPTIONS http://localhost:3000/rt_count

> OPTIONS /rt_count HTTP/1.1
>
< HTTP/1.1 204 No Content
< Allow: OPTIONS, GET, PUT

You can disable this behavior with do_not_route_options!.

If a request for a resource is made with an unsupported HTTP method, an HTTP 405 (Method Not Allowed) response will be returned.

curl -X DELETE -v http://localhost:3000/rt_count/

> DELETE /rt_count/ HTTP/1.1
> Host: localhost:3000
>
< HTTP/1.1 405 Method Not Allowed
< Allow: OPTIONS, GET, PUT

Raising Exceptions

You can abort the execution of an API method by raising errors with error!.

error! "Access Denied", 401

You can also return JSON formatted objects 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 return them in the API format.

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 will match the request format. See "Content-Types" below.

Custom error formatters for existing and additional types can be defined with a proc.

class Twitter::API < Grape::API
  error_formatter :txt, lambda { |message, backtrace, options, env|
    "error: #{message} from #{backtrace}"
  }
end

You can also use a module or class.

module CustomFormatter
  def self.call(message, backtrace, options, env)
    { message: message, backtrace: backtrace }
  end
end

class Twitter::API < Grape::API
  error_formatter :custom, CustomFormatter
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

Or rescue specific exceptions.

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

Rails 3.x

When mounted inside Rails 3.x, errors like "404 Not Found" or "406 Not Acceptable" will likely be handled and rendered by Rails handlers. For instance, accessing a nonexistent route "/api/foo" raises a 404, which inside rails will ultimately be translated to an ActionController::RoutingError, which most likely will get rendered to a HTML error page.

Most APIs will enjoy avoiding Rails exceptions and have their own exceptions reaching the client. In that case, the :cascade option can be set to false on the versioning definition.

version 'v1', :using => :header, :vendor => 'twitter', :cascade => false

The :cascade option can also be used with the other versioning strategies (:param and :path).

Logging

Grape::API provides a logger method which by default will return an instance of the Logger class from Ruby's standard library.

To log messages from within an endpoint, you need to define a helper to make the logger available in the endpoint context.

class API < Grape::API
  helpers do
    def logger
      API.logger
    end
  end
  post '/statuses' do
    # ...
    logger.info "#{current_user} has statused"
  end
end

You can also set your own logger.

class MyLogger
  def warning(message)
    puts "this is a warning: #{message}"
  end
end

class API < Grape::API
  logger MyLogger.new
  helpers do
    def logger
      API.logger
    end
  end
  get '/statuses' do
    logger.warning "#{current_user} has statused"
  end
end

API Formats

By default, Grape supports XML, JSON, and TXT content-types. The default format is :txt.

Serialization takes place automatically. For example, you do not have to call to_json in each JSON API implementation.

Your API can declare which types to support by using content_type. Response format is determined by the request's extension, an explicit format parameter in the query string, or Accept header.

The following API will only respond to the JSON content-type and will not parse any other input than application/json, application/x-www-form-urlencoded, multipart/form-data, multipart/related and multipart/mixed. All other requests will fail with an HTTP 406 error code.

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

If you combine format with rescue_from :all, errors will be rendered using the same format. If you do not want this behavior, set the default error formatter with default_error_formatter.

class Twitter::API < Grape::API
  format :json
  content_type :txt, "text/plain"
  default_error_formatter :txt
end

Custom formatters for existing and additional types can be defined with a proc.

class Twitter::API < Grape::API
  content_type :xls, "application/vnd.ms-excel"
  formatter :xls, lambda { |object, env| object.to_xls }
end

You can also use a module or class.

module XlsFormatter
  def self.call(object, env)
    object.to_xls
  end
end

class Twitter::API < Grape::API
  content_type :xls, "application/vnd.ms-excel"
  formatter :xls, XlsFormatter
end

Built-in formats are the following.

  • :json: use object's to_json when available, otherwise call MultiJson.dump
  • :xml: use object's to_xml when available, usually via MultiXml, otherwise call to_s
  • :txt: use object's to_txt when available, otherwise to_s
  • :serializable_hash: use object's serializable_hash when available, otherwise fallback to :json

Use default_format to set the fallback format when the format could not be determined from the Accept header. See below for the order for choosing the API format.

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

The order for choosing the format is the following.

  • Use the file extension, if specified. If the file is .json, choose the JSON format.
  • Use the value of the format parameter in the query string, if specified.
  • Use the format set by the format option, if specified.
  • Attempt to find an acceptable format from the Accept header.
  • Use the default format, if specified by the default_format option.
  • Default to :txt.

JSONP

Grape suports JSONP via Rack::JSONP, part of the rack-contrib gem. Add rack-contrib to your Gemfile.

require 'rack/contrib'

class API < Grape::API
  use Rack::JSONP
  format :json
  get '/' do
    'Hello World'
  end
end

CORS

Grape supports CORS via Rack::CORS, part of the rack-cors gem. Add rack-cors to your Gemfile.

require 'rack/cors'

class API < Grape::API
  use Rack::Cors do
    allow do
      origins '*'
      resource '*', :headers => :any, :methods => :get
    end
  end
  format :json
  get '/' do
    'Hello World'
  end
end

Content-type

Content-type is set by the formatter. You can override the content-type of the response at runtime by setting the Content-Type header.

class API < Grape::API
  get '/home_timeline_js' do
    content_type "application/javascript"
    "var statuses = ...;"
  end
end

API Data Formats

Grape accepts and parses input data sent with the POST and PUT methods as described in the Parameters section above. It also supports custom data formats. You must declare additional content-types via content_type and optionally supply a parser via parser unless a parser is already available within Grape to enable a custom format. Such a parser can be a function or a class.

With a parser, parsed data is available "as-is" in env['api.request.body']. Without a parser, data is available "as-is" and in env['api.request.input'].

The following example is a trivial parser that will assign any input with the "text/custom" content-type to :value. The parameter will be available via params[:value] inside the API call.

module CustomParser
  def self.call(object, env)
    { :value => object.to_s }
  end
end
content_type :txt, "text/plain"
content_type :custom, "text/custom"
parser :custom, CustomParser

put "value" do
  params[:value]
end

You can invoke the above API as follows.

curl -X PUT -d 'data' 'http://localhost:9292/value' -H Content-Type:text/custom -v

RESTful Model Representations

Grape supports a range of ways to present your data with some help from a generic present method, which accepts two arguments: the object to be presented and the options associated with it. The options hash may include :with, which defines the entity to expose.

Grape Entities

Add the grape-entity gem to your Gemfile. Please refer to the grape-entity documentation for more details.

The following example exposes statuses.

module API

  module Entities
    class Status < Grape::Entity
      expose :user_name
      expose :text, :documentation => { :type => "string", :desc => "Status update text." }
      expose :ip, :if => { :type => :full }
      expose :user_type, user_id, :if => lambda{ |status, options| status.user.public? }
      expose :digest { |status, options| Digest::MD5.hexdigest(status.txt) }
      expose :replies, :using => API::Status, :as => :replies
    end
  end

  class Statuses < Grape::API
    version 'v1'

    desc 'Statuses index', {
      :object_fields => API::Entities::Status.documentation
    }
    get '/statuses' do
      statuses = Status.all
      type = current_user.admin? ? :full : :default
      present statuses, with: API::Entities::Status, :type => type
    end
  end
end

In addition to separately organizing entities, it may be useful to put them as namespaced classes underneath the model they represent.

class Status
  def entity
    Status.new(self)
  end

  class Entity < Grape::Entity
    expose :text, :user_id
  end
end

If you organize your entities this way, Grape will automatically detect the Entity class and use it to present your models. In this example, if you added present Status.new to your endpoint, Grape will automatically detect that there is a Status::Entity class and use that as the representative entity. This can still be overridden by using the :with option or an explicit represents call.

Hypermedia

You can use any Hypermedia representer, including Roar. Roar renders JSON and works with the built-in Grape JSON formatter. Add Roar::Representer::JSON into your models or call to_json explicitly in your API implementation.

Rabl

You can use Rabl templates with the help of the grape-rabl gem, which defines a custom Grape Rabl formatter.

Authentication

Basic and Digest Auth

Grape has built-in Basic and Digest authentication.

http_basic do |username, password|
  # verify user's password here
  { 'test' => 'password1' }[username] == password
end
http_digest({ :realm => 'Test Api', :opaque => 'app secret' }) do |username|
  # lookup the user's password here
  { 'user1' => 'password1' }[username]
end

Use warden-oauth2 or rack-oauth2 for OAuth2 support.

Describing and Inspecting an API

Grape routes can be reflected at runtime. This can notably be useful for generating documentation.

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. The description and the optional hash that follows the API path may contain any number of keys and its values are also accessible via dynamically-generated route_[name] functions.

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

Current Route and Endpoint

It's possible to retrieve the information about the current route from within an API call with route.

class MyAPI < Grape::API
  desc "Returns a description of a parameter."
  params do
    requires :id, :type => Integer, :desc => "Identity."
  end
  get "params/:id" do
    route.route_params[params[:id]] # yields the parameter description
  end
end

The current endpoint responding to the request is self within the API block or env['api.endpoint'] elsewhere. The endpoint has some interesting properties, such as source which gives you access to the original code block of the API implementation. This can be particularly useful for building a logger middleware.

class ApiLogger < Grape::Middleware::Base
  def before
    file = env['api.endpoint'].source.source_location[0]
    line = env['api.endpoint'].source.source_location[1]
    logger.debug "[api] #{file}:#{line}"
  end
end

Before and After

Execute a block before or after every API call with before and after.

before do
  header "X-Robots-Tag", "noindex"
end

Anchoring

Grape by default anchors all request paths, which means that the request URL should match from start to end to match, otherwise a 404 Not Found is returned. However, this is sometimes not what you want, because it is not always known upfront what can be expected from the call. This is because Rack-mount by default anchors requests to match from the start to the end, or not at all. Rails solves this problem by using a :anchor => false option in your routes. In Grape this option can be used as well when a method is defined.

For instance when you're API needs to get part of an URL, for instance:

class TwitterAPI < Grape::API
  namespace :statuses do
    get '/(*:status)', :anchor => false do

    end
  end
end

This will match all paths starting with '/statuses/'. There is one caveat though: the params[:status] parameter only holds the first part of the request url. Luckily this can be circumvented by using the described above syntax for path specification and using the PATH_INFO Rack environment variable, using env["PATH_INFO"]. This will hold everything that comes after the '/statuses/' part.

Writing Tests

You can test a Grape API with RSpec by making HTTP requests and examining the response.

Writing Tests with Rack

Use rack-test and define your API as app.

require 'spec_helper'

describe Twitter::API do
  include Rack::Test::Methods

  def app
    Twitter::API
  end

  describe Twitter::API do
    describe "GET /api/v1/statuses" do
      it "returns an empty array of statuses" do
        get "/api/v1/statuses"
        last_response.status.should == 200
        JSON.parse(last_response.body).should == []
      end
    end
    describe "GET /api/v1/statuses/:id" do
      it "returns a status by id" do
        status = Status.create!
        get "/api/v1/statuses/#{status.id}"
        last_response.body.should == status.to_json
      end
    end
  end
end

Writing Tests with Rails

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
  describe "GET /api/v1/statuses/:id" do
    it "returns a status by id" do
      status = Status.create!
      get "/api/v1/statuses/#{status.id}"
      response.body.should == status.to_json
    end
  end
end

In Rails, HTTP request tests would 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

Reloading API Changes in Development

Rails 3.x

Add API paths to config/application.rb.

# Auto-load API and its subdirectories
config.paths.add "app/api", :glob => "**/*.rb"
config.autoload_paths += Dir["#{Rails.root}/app/api/*"]

Create config/initializers/reload_api.rb.

if Rails.env.development?
  api_files = Dir["#{Rails.root}/app/api/**/*.rb"]
  api_reloader = ActiveSupport::FileUpdateChecker.new(api_files) do
    Rails.application.reload_routes!
  end
  ActionDispatch::Callbacks.to_prepare do
    api_reloader.execute_if_updated
  end
end

See StackOverflow #3282655 for more information.

Performance Monitoring

Grape integrates with NewRelic via the newrelic-grape gem.

Contributing to Grape

Grape is work of dozens of contributors. You're encouraged to submit pull requests, propose features and discuss issues.

  • Fork the project
  • Write tests for your new feature or a test that reproduces a bug
  • Implement your feature or make a bug fix
  • Add a line to CHANGELOG.md describing your change
  • Commit, push and make a pull request. Bonus points for topic branches.

License

MIT License. See LICENSE for details.

Copyright

Copyright (c) 2010-2012 Michael Bleigh, and Intridea, Inc.