What is Grape?

Grape is a REST-like API micro-framework for Ruby. It's built to 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.

Project Tracking

• Grape Google Group
• Grape Wiki

Stable Release

You're reading the documentation for the next release of Grape. The current stable release is 0.2.1.

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.

classTwitter::API < Grape::APIversion'v1',:using=>:header,:vendor=>'twitter'helpersdodefcurrent_user@current_user ||= User.authorize!(env)enddefauthenticate!error!('401 Unauthorized',401)unlesscurrent_userendendresource:statusesdodesc"Returns a public timeline."get:public_timelinedoTweet.limit(20)enddesc"Returns a personal timeline."get:home_timelinedoauthenticate!current_user.home_timelineenddesc"Returns a tweet."paramsdorequires:id,:type=>Integer,:desc=>"Tweet id."endget'/show/:id'doTweet.find(params[:id])enddesc"Creates a tweet."paramsdorequires:status,:type=>String,:desc=>"Your status."endpost:updatedoauthenticate!Tweet.create(:user=>current_user,:text=>params[:status])endendend

Mounting

Rack

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

runTwitter::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)

Rails

In a Rails application, modify config/routes:

mountTwitter::API=>"/"

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.

classTwitter::API < Grape::APImountTwitter::APIv1mountTwitter::APIv2end

Versioning

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

Header

version'v1',:using=>:header

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 404 Not found error is returned when no correct Accept header is supplied.

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

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/events?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/events?v=v1

Describing Methods

You can add a description to API methods and namespaces.

desc"Returns a reticulated spline."get"spline/:id"doSpline.find(params[:id])end

Parameters

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

getdoArticle.order(params[:sort_by])end

Parameters are also populated from the request body on POST and PUT for JSON and XML content-types.

The Request:

curl -d '{"some_key": "some_value"}' 'http://localhost:9292/json_endpoint' -H Content-Type:application/json -v

The Grape Endpoint:

post'/json_endpoint'doparams[:some_key]end

Parameter Validation and Coercion

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

paramsdorequires:id,type: Integeroptional:name,type: String,regexp: /^[a-z]+$/endget':id'do# params[:id] is an Integerend

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

Namespace Validation and Coercion

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

namespace:shelvesdoparamsdorequires:shelf_id,type: Integer,desc: "A shelf."endnamespace":shelf_id"dodesc"Retrieve a book from a shelf."paramsdorequires:book_id,type: Integer,desc: "A book."endget":book_id"do# params[:shelf_id] defines a shelf# params[:book_id] defines a bookendendend

Custom Validators

classdoit < Grape::Validations::Validatordefvalidate_param!(attr_name,params)unlessparams[attr_name] == 'im custom'throw:error,:status=>400,:message=>"#{attr_name}: is not custom!"endendend

paramsdorequires:name,:doit=>trueend

You can also create custom classes that take additional parameters

classLength < Grape::Validations::SingleOptionValidatordefvalidate_param!(attr_name,params)unlessparams[attr_name].length == @optionthrow:error,:status=>400,:message=>"#{attr_name}: must be #{@option} characters long"endendend

paramsdorequires:name,:length=>5end

Headers

Headers are available through the header helper or the env hash object.

getdocontent_type=header['Content-type']
...
end

getdoerror!'Unauthorized',401unlessenv['HTTP_SECRET_PASSWORD'] == 'swordfish'
...
end

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'/show/:id',:requirements=>{:id=>/[0-9]*/}doTweet.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:

moduleMyHelpersdefsay_hello(user)"hey there #{user.name}"endendclassAPI < Grape::API# define helpers with a blockhelpersdodefcurrent_userUser.find(params[:user_id])endend# or mix in a modulehelpersMyHelpersget'/hello'do# helpers available in your endpoint and filterssay_hello(current_user)endend

Cookies

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

classAPI < Grape::APIget'/counter'docookies[:counter] ||= 0cookies[:counter] += 1{:counter=>cookies[:counter]}enddelete'/counter'do{:result=>cookies.delete(:counter)}endend

To set more than value use hash-based syntax:

cookies[:counter]={:value=>0,:expires=>Time.tomorrow,:domain=>'.example.com',:path=>'/'}cookies[:counter][:value] +=1

Redirecting

You can redirect to a new url temporarily or permanently.

redirect"/new_url"

redirect"/new_url",:permanent=>true

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 instead return them in text or json formats.

classTwitter::API < Grape::APIrescue_from:allend

You can also rescue specific exceptions.

classTwitter::API < Grape::APIrescue_fromArgumentError,NotImplementedErrorend

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

classTwitter::API < Grape::APIerror_format:jsonend

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

classTwitter::API < Grape::APIrescue_from:alldo |e|
rack_response({:message=>"rescued from #{e.class.name}"})endend

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

classTwitter::API < Grape::APIrescue_from:alldo |e|
Rack::Response.new([e.message],500,{"Content-type"=>"text/error"}).finishendend

Or rescue specific exceptions.

classTwitter::API < Grape::APIrescue_fromArgumentErrordo |e|
Rack::Response.new(["ArgumentError: #{e.message}"],500)endrescue_fromNotImplementedErrordo |e|
Rack::Response.new(["NotImplementedError: #{e.message}"],500)endend

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.

classAPI < Grape::APIhelpersdodefloggerAPI.loggerendendget'/hello'dologger.info"someone said hello""hey there"endend

You can also set your own logger.

classMyLoggerdefwarning(message)puts"this is a warning: #{message}"endendclassAPI < Grape::APIloggerMyLogger.newhelpersdodefloggerAPI.loggerendendget'/hello'dologger.warning"someone said hello""hey there"endend

Content-Types

By default, Grape supports XML, JSON, Atom, RSS, and text content-types. Serialization takes place automatically.

Your API can declare additional types to support. Response format is determined by the request's extension or Accept header.

classTwitter::API < Grape::APIcontent_type:xls,"application/vnd.ms-excel"end

You can also set the default format. 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 format, if specified by the format option.
• Attempt to find an acceptable format from the Accept header.
• Use the default format, if specified by the default_format option.
• Default to :txt otherwise.

classTwitter::API < Grape::APIformat:jsondefault_format:jsonend

You can override the content-type by setting the Content-Type header.

classAPI < Grape::APIget'/script'docontent_type"application/javascript""var x = 1;"endend

Reusable Responses with Entities

Entities are a reusable means for converting Ruby objects to API responses. Entities can be used to conditionally include fields, nest other entities, and build ever larger responses, using inheritance.

Defining Entities

Entities inherit from Grape::Entity, and define a simple DSL. Exposures can use runtime options to determine which fields should be visible, these options are available to :if, :unless, and :proc. The option keys :version and :collection will always be defined. The :version key is defined as api.version. The :collection key is boolean, and defined as true if the object presented is an array.

• expose SYMBOLS
  • define a list of fields which will always be exposed
• expose SYMBOLS, HASH
  • HASH keys include :if, :unless, :proc, :as, :using, :format_with, :documentation
    • :if and :unless accept hashes (passed during runtime) or procs (arguments are object and options)
• expose SYMBOL, {:format_with => :formatter}
  • expose a value, formatting it first
  • :format_with can only be applied to one exposure at a time
• expose SYMBOL, {:as => "alias"}
  • Expose a value, changing its hash key from SYMBOL to alias
  • :as can only be applied to one exposure at a time
• expose SYMBOL BLOCK
  • block arguments are object and options
  • expose the value returned by the block
  • block can only be applied to one exposure at a time

moduleAPImoduleEntitiesclassUser < Grape::Entityexpose:first_name,:last_nameexpose:field,:documentation=>{:type=>"string",:desc=>"words go here"}expose:email,:if=>{:type=>:full}expose:user_type,user_id,:if=>lambda{|user,options| user.confirmed?}expose(:name){|user,options| [user.first_name,user.last_name].join(' ')}expose:latest_status,:using=>API::Status,:as=>:statusendendendmoduleAPImoduleEntitiesclassUserDetailed < API::Entities::Userexpose:account_idendendend

Using Entities

Once an entity is defined, it can be used within endpoints, by calling #present. The #present method accepts two arguments, the object to be presented and the options associated with it. The options hash must always include :with, which defines the entity to expose.

If the entity includes documentation it can be included in an endpoint's description.

moduleAPIclassUsers < Grape::APIversion'v1'desc'User index',{:object_fields=>API::Entities::User.documentation}get'/users'do@users=User.alltype=current_user.admin? ? :full : :defaultpresent@users,with: API::Entities::User,:type=>typeendendend

Caveats

Entities with duplicate exposure names and conditions will silently overwrite one another. In the following example, when object#check equals "foo", only afield will be exposed. However, when object#check equals "bar" both bfield and foo will be exposed.

moduleAPImoduleEntitiesclassUser < Grape::Entityexpose:afield,:foo,:if=>lambda{|object,options| object.check=="foo"}expose:bfield,:foo,:if=>lambda{|object,options| object.check=="bar"}endendend

This can be problematic, when you have mixed collections. Using #respond_to? is safer.

moduleAPImoduleEntitiesclassUser < Grape::Entityexpose:afield,:if=>lambda{|object,options| object.check=="foo"}expose:bfield,:if=>lambda{|object,options| object.check=="bar"}expose:foo,:if=>lambda{object,options| object.respond_to?(:foo)}endendend

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 objectsTwitterAPI::routes[0].route_version# yields 'v1'TwitterAPI::routes[0].route_description# etc.

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

classMyAPI < Grape::APIdesc"Returns a description of a parameter."paramsdorequires:id,:type=>Integer,:desc=>"Identity."endget"params/:id"doroute.route_params[params[:id]]# yields the parameter descriptionendend

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:

classUrlAPI < Grape::APInamespace:urlsdoget'/(*:url)',:anchor=>falsedosome_dataendendend

This will match all paths starting with '/urls/'. There is one caveat though: the params[:url] 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 '/urls/' 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'describeTwitter::APIdoincludeRack::Test::MethodsdefappTwitter::APIenddescribeTwitter::APIdodescribe"GET /api/v1/statuses"doit"returns an empty array of statuses"doget"/api/v1/statuses"last_response.status.should == 200JSON.parse(response.body).should == []endenddescribe"GET /api/v1/statuses/:id"doit"returns a status by id"dostatus=Status.create!get"/api/v1/statuses/#{status.id}"last_response.body.should == status.to_jsonendendendend

Writing Tests with Rails

require'spec_helper'describeTwitter::APIdodescribe"GET /api/v1/statuses"doit"returns an empty array of statuses"doget"/api/v1/statuses"response.status.should == 200JSON.parse(response.body).should == []endenddescribe"GET /api/v1/statuses/:id"doit"returns a status by id"dostatus=Status.create!get"/api/v1/statuses/#{status.id}"resonse.body.should == status.to_jsonendendend

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.configuredo |config|
config.includeRSpec::Rails::RequestExampleGroup,:type=>:request,:example_group=>{:file_path=>/spec\/api/}end

Note on Patches/Pull Requests

• Fork the project
• Write tests for your new feature or a test that reproduces a bug
• Implement your feature or make a bug fix
• Do not mess with Rakefile, version or history
• Commit, push and make a pull request. Bonus points for topical branches.

License

MIT License. See LICENSE for details.

Copyright

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