• What is Grape?
• Stable Release
• Project Resources
• Grape for Enterprise
• Installation
• Basic Usage
• Mounting
  • All
  • Rack
  • ActiveRecord without Rails
    • Rails 4
    • Rails 5+
  • Alongside Sinatra (or other frameworks)
  • Rails
    • Rails < 5.2
    • Rails 6.0
  • Modules
• Remounting
  • Mount Configuration
• Versioning
  • Path
  • Header
  • Accept-Version Header
  • Param
• Describing Methods
• Configuration
• Parameters
  • Params Class
  • Declared
  • Include Parent Namespaces
  • Include Missing
• Parameter Validation and Coercion
  • Supported Parameter Types
  • Integer/Fixnum and Coercions
  • Custom Types and Coercions
  • Multipart File Parameters
  • First-Class JSON Types
  • Multiple Allowed Types
  • Validation of Nested Parameters
  • Dependent Parameters
  • Group Options
  • Renaming
  • Built-in Validators
    • allow_blank
    • values
    • except_values
    • same_as
    • regexp
    • mutually_exclusive
    • exactly_one_of
    • at_least_one_of
    • all_or_none_of
    • Nested mutually_exclusive, exactly_one_of, at_least_one_of, all_or_none_of
  • Namespace Validation and Coercion
  • Custom Validators
  • Validation Errors
  • I18n
  • Custom Validation messages
    • presence, allow_blank, values, regexp
    • same_as
    • all_or_none_of
    • mutually_exclusive
    • exactly_one_of
    • at_least_one_of
    • Coerce
    • With Lambdas
    • Pass symbols for i18n translations
    • Overriding Attribute Names
    • With Default
• Headers
  • Request
    • Header Case Handling
  • Response
• Routes
• Helpers
• Path Helpers
• Parameter Documentation
• Cookies
• HTTP Status Code
• Redirecting
• Recognizing Path
• Allowed Methods
• Raising Exceptions
  • Default Error HTTP Status Code
  • Handling 404
• Exception Handling
  • Rescuing exceptions inside namespaces
  • Unrescuable Exceptions
  • Exceptions that should be rescued explicitly
  • Rails 3.x
• Logging
• API Formats
  • JSONP
  • CORS
• Content-type
• API Data Formats
• JSON and XML Processors
• RESTful Model Representations
  • Grape Entities
  • Hypermedia and Roar
  • Rabl
  • Active Model Serializers
• Sending Raw or No Data
• Authentication
  • Basic and Digest Auth
  • Register custom middleware for authentication
• Describing and Inspecting an API
• Current Route and Endpoint
• Before, After and Finally
• Anchoring
• Using Custom Middleware
  • Grape Middleware
  • Rails Middleware
  • Remote IP
• Writing Tests
  • Writing Tests with Rack
    • RSpec
    • Airborne
    • MiniTest
  • Writing Tests with Rails
    • RSpec
    • MiniTest
  • Stubbing Helpers
• Reloading API Changes in Development
  • Reloading in Rack Applications
  • Reloading in Rails Applications
• Performance Monitoring
  • Active Support Instrumentation
    • endpoint_run.grape
    • endpoint_render.grape
    • endpoint_run_filters.grape
    • endpoint_run_validators.grape
    • format_response.grape
  • Monitoring Products
• Contributing to Grape
• Security
• License
• Copyright

Grape is a REST-like API 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.

You're reading the documentation for the next release of Grape, which should be 1.5.4. Please read UPGRADING when upgrading from a previous version. The current stable release is 1.5.3.

• Grape Website
• Documentation
• Need help? Try Grape Google Group or Gitter
• Follow us on Twitter

Available as part of the Tidelift Subscription.

The maintainers of Grape are working with Tidelift to deliver commercial support and maintenance. Save time, reduce risk, and improve code health, while paying the maintainers of Grape. Click here for more details.

In 2020, we plan to use the money towards gathering Grape contributors for dinner in New York City.

Ruby 2.4 or newer is required.

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.

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
    prefix :api

    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
      route_param :id do
        get do
          Status.find(params[:id])
        end
      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

By default Grape will compile the routes on the first route, it is possible to pre-load routes using the compile! method.

Twitter::API.compile!

This can be added to your config.ru (if using rackup), application.rb (if using rails), or any file that loads your server.

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

run Twitter::API

(With pre-loading you can use)

Twitter::API.compile!
run Twitter::API

And would respond to the following routes:

GET /api/statuses/public_timeline
GET /api/statuses/home_timeline
GET /api/statuses/:id
POST /api/statuses
PUT /api/statuses/:id
DELETE /api/statuses/:id

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

If you want to use ActiveRecord within Grape, you will need to make sure that ActiveRecord's connection pool is handled correctly.

The easiest way to achieve that is by using ActiveRecord's ConnectionManagement middleware in your config.ru before mounting Grape, e.g.:

use ActiveRecord::ConnectionAdapters::ConnectionManagement

Use otr-activerecord as follows:

use OTR::ActiveRecord::ConnectionManagement

If you wish to mount Grape alongside another Rack framework such as Sinatra, you can do so easily using Rack::Cascade:

# Example config.ru

require 'sinatra'
require 'grape'

class API < Grape::API
  get :hello do
    { hello: 'world' }
  end
end

class Web < Sinatra::Base
  get '/' do
    'Hello world.'
  end
end

use Rack::Session::Cookie
run Rack::Cascade.new [Web, API]

Note that order of loading apps using Rack::Cascade matters. The grape application must be last if you want to raise custom 404 errors from grape (such as error!('Not Found',404)). If the grape application is not last and returns 404 or 405 response, cascade utilizes that as a signal to try the next app. This may lead to undesirable behavior showing the wrong 404 page from the wrong app.

Place API files into app/api. Rails expects a subdirectory that matches the name of the Ruby module and a file name that matches the name of the class. In our example, the file name location and directory for Twitter::API should be app/api/twitter/api.rb.

Modify config/routes:

mount Twitter::API => '/'

Modify application.rb:

config.paths.add File.join('app', 'api'), glob: File.join('**', '*.rb')
config.autoload_paths += Dir[Rails.root.join('app', 'api', '*')]

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

For Rails versions greater than 6.0.0.beta2, Zeitwerk autoloader is the default for CRuby. By default Zeitwerk inflects api as Api instead of API. To make our example work, you need to uncomment the lines at the bottom of config/initializers/inflections.rb, and add API as an acronym:

ActiveSupport::Inflector.inflections(:en) do |inflect|
  inflect.acronym 'API'
end

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

Keep in mind such declarations as before/after/rescue_from must be placed before mount in a case where they should be inherited.

class Twitter::API < Grape::API
  before do
    header 'X-Base-Header', 'will be defined for all APIs that are mounted below'
  end

  mount Twitter::Users
  mount Twitter::Search
end

You can mount the same endpoints in two different locations.

class Voting::API < Grape::API
  namespace 'votes' do
    get do
      # Your logic
    end

    post do
      # Your logic
    end
  end
end

class Post::API < Grape::API
  mount Voting::API
end

class Comment::API < Grape::API
  mount Voting::API
end

Assuming that the post and comment endpoints are mounted in /posts and /comments, you should now be able to do get /posts/votes, post /posts/votes, get /comments/votes and post /comments/votes.

You can configure remountable endpoints to change how they behave according to where they are mounted.

class Voting::API < Grape::API
  namespace 'votes' do
    desc "Vote for your #{configuration[:votable]}"
    get do
      # Your logic
    end
  end
end

class Post::API < Grape::API
  mount Voting::API, with: { votable: 'posts' }
end

class Comment::API < Grape::API
  mount Voting::API, with: { votable: 'comments' }
end

Note that if you're passing a hash as the first parameter to mount, you will need to explicitly put () around parameters:

# good
mount({ ::Some::Api => '/some/api' }, with: { condition: true })

# bad
mount ::Some::Api => '/some/api', with: { condition: true }

You can access configuration on the class (to use as dynamic attributes), inside blocks (like namespace)

If you want logic happening given on an configuration, you can use the helper given.

class ConditionalEndpoint::API < Grape::API
  given configuration[:some_setting] do
    get 'mount_this_endpoint_conditionally' do
      configuration[:configurable_response]
    end
  end
end

If you want a block of logic running every time an endpoint is mounted (within which you can access the configuration Hash)

class ConditionalEndpoint::API < Grape::API
  mounted do
    YourLogger.info "This API was mounted at: #{Time.now}"

    get configuration[:endpoint_name] do
      configuration[:configurable_response]
    end
  end
end

More complex results can be achieved by using mounted as an expression within which the configuration is already evaluated as a Hash.

class ExpressionEndpointAPI < Grape::API
  get(mounted { configuration[:route_name] || 'default_name' }) do
    # some logic
  end
end

class BasicAPI < Grape::API
  desc 'Statuses index' do
    params: mounted { configuration[:entity] || API::Entities::Status }.documentation
  end
  params do
    requires :all, using: mounted { configuration[:entity] || API::Entities::Status }.documentation
  end
  get '/statuses' do
    statuses = Status.all
    type = current_user.admin? ? :full : :default
    present statuses, with: mounted { configuration[:entity] || API::Entities::Status }, type: type
  end
end

class V1 < Grape::API
  version 'v1'
  mount BasicAPI, with: { entity: mounted { configuration[:entity] || API::Enitities::Status } }
end

class V2 < Grape::API
  version 'v2'
  mount BasicAPI, with: { entity: mounted { configuration[:entity] || API::Enitities::V2::Status } }
end

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

version 'v1', using: :path

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

curl https://localhost:9292/v1/statuses/public_timeline

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

Currently, Grape only supports versioned media types in the following format:

vnd.vendor-and-or-resource-v1234+format

Basically all tokens between the final - and the + will be interpreted as the version.

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

curl -H Accept:application/vnd.twitter-v1+json https://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.

When an invalid Accept header is supplied, a 406 Not Acceptable error is returned if the :cascade option is set to false. Otherwise a 404 Not Found error is returned by Rack if no other route matches.

version 'v1', using: :accept_version_header

Using this versioning strategy, clients should pass the desired version in the HTTP Accept-Version header.

curl -H "Accept-Version:v1" https://localhost:9292/statuses/public_timeline

By default, the first matching version is used when no Accept-Version 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 and the :cascade option is set to false. Otherwise a 404 Not Found error is returned by Rack if no other route matches.

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 https://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 https://localhost:9292/statuses/public_timeline?v=v1

You can add a description to API methods and namespaces. The description would be used by grape-swagger to generate swagger compliant documentation.

Note: Description block is only for documentation and won't affects API behavior.

desc 'Returns your public timeline.' do
  summary 'summary'
  detail 'more details'
  params  API::Entities::Status.documentation
  success API::Entities::Entity
  failure [[401, 'Unauthorized', 'Entities::Error']]
  named 'My named route'
  headers XAuthToken: {
            description: 'Validates your identity',
            required: true
          },
          XOptionalHeader: {
            description: 'Not really needed',
            required: false
          }
  hidden false
  deprecated false
  is_array true
  nickname 'nickname'
  produces ['application/json']
  consumes ['application/json']
  tags ['tag1', 'tag2']
end
get :public_timeline do
  Status.limit(20)
end

• detail: A more enhanced description
• params: Define parameters directly from an Entity
• success: (former entity) The Entity to be used to present by default this route
• failure: (former http_codes) A definition of the used failure HTTP Codes and Entities
• named: A helper to give a route a name and find it with this name in the documentation Hash
• headers: A definition of the used Headers
• Other options can be found in grape-swagger

Use Grape.configure to set up global settings at load time. Currently the configurable settings are:

• param_builder: Sets the Parameter Builder, defaults to Grape::Extensions::ActiveSupport::HashWithIndifferentAccess::ParamBuilder.

To change a setting value make sure that at some point during load time the following code runs

Grape.configure do |config|
  config.setting = value
end

For example, for the param_builder, the following code could run in an initializer:

Grape.configure do |config|
  config.param_builder = Grape::Extensions::Hashie::Mash::ParamBuilder
end

You can also configure a single API:

API.configure do |config|
  config[key] = value
end

This will be available inside the API with configuration, as if it were mount configuration.

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"}' 'https://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;type=image/jpg' https://localhost:9292/upload

The Grape endpoint:

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

In the case of conflict between either of:

• route string parameters
• GET, POST and PUT parameters
• the contents of the request body on POST and PUT

Route string parameters will have precedence.

By default parameters are available as ActiveSupport::HashWithIndifferentAccess. This can be changed to, for example, Ruby Hash or Hashie::Mash for the entire API.

class API < Grape::API
  include Grape::Extensions::Hashie::Mash::ParamBuilder

  params do
    optional :color, type: String
  end
  get do
    params.color # instead of params[:color]
  end

The class can also be overridden on individual parameter blocks using build_with as follows.

params do
  build_with Grape::Extensions::Hash::ParamBuilder
  optional :color, type: String
end

Or globally with the Configuration Grape.configure.param_builder.

In the example above, params["color"] will return nil since params is a plain Hash.

Available parameter builders are Grape::Extensions::Hash::ParamBuilder, Grape::Extensions::ActiveSupport::HashWithIndifferentAccess::ParamBuilder and Grape::Extensions::Hashie::Mash::ParamBuilder.

Grape allows you to access only the parameters that have been declared by your params block. It will:

• Filter out the params that have been passed, but are not allowed.
• Include any optional params that are declared but not passed.

Consider the following API endpoint:

format :json

post 'users/signup' do
  { 'declared_params' => declared(params) }
end

If you do not specify any parameters, declared will return an empty hash.

Request

curl -X POST -H "Content-Type: application/json" localhost:9292/users/signup -d '{"user": {"first_name":"first name", "last_name": "last name"}}'

Response

{
  "declared_params": {}
}

Once we add parameters requirements, grape will start returning only the declared parameters.

format :json

params do
  optional :user, type: Hash do
    optional :first_name, type: String
    optional :last_name, type: String
  end
end

post 'users/signup' do
  { 'declared_params' => declared(params) }
end

Request

curl -X POST -H "Content-Type: application/json" localhost:9292/users/signup -d '{"user": {"first_name":"first name", "last_name": "last name", "random": "never shown"}}'

Response

{
  "declared_params": {
    "user": {
      "first_name": "first name",
      "last_name": "last name"
    }
  }
}

Missing params that are declared as type Hash or Array will be included.

format :json

params do
  optional :user, type: Hash do
    optional :first_name, type: String
    optional :last_name, type: String
  end
  optional :widgets, type: Array
end

post 'users/signup' do
  { 'declared_params' => declared(params) }
end

Request

curl -X POST -H "Content-Type: application/json" localhost:9292/users/signup -d '{}'

Response

{
  "declared_params": {
    "user": {
      "first_name": null,
      "last_name": null
    },
    "widgets": []
  }
}

The returned hash is an ActiveSupport::HashWithIndifferentAccess.

The #declared method is not available to before filters, as those are evaluated prior to parameter coercion.

By default declared(params) includes parameters that were defined in all parent namespaces. If you want to return only parameters from your current namespace, you can set include_parent_namespaces option to false.

format :json

namespace :parent do
  params do
    requires :parent_name, type: String
  end

  namespace ':parent_name' do
    params do
      requires :child_name, type: String
    end
    get ':child_name' do
      {
        'without_parent_namespaces' => declared(params, include_parent_namespaces: false),
        'with_parent_namespaces' => declared(params, include_parent_namespaces: true),
      }
    end
  end
end

Request

curl -X GET -H "Content-Type: application/json" localhost:9292/parent/foo/bar

Response

{
  "without_parent_namespaces": {
    "child_name": "bar"
  },
  "with_parent_namespaces": {
    "parent_name": "foo",
    "child_name": "bar"
  },
}

By default declared(params) includes parameters that have nil values. If you want to return only the parameters that are not nil, you can use the include_missing option. By default, include_missing is set to true. Consider the following API:

format :json

params do
  requires :user, type: Hash do
    requires :first_name, type: String
    optional :last_name, type: String
  end
end

post 'users/signup' do
  { 'declared_params' => declared(params, include_missing: false) }
end

Request

curl -X POST -H "Content-Type: application/json" localhost:9292/users/signup -d '{"user": {"first_name":"first name", "random": "never shown"}}'

Response with include_missing:false

{
  "declared_params": {
    "user": {
      "first_name": "first name"
    }
  }
}

Response with include_missing:true

{
  "declared_params": {
    "first_name": "first name",
    "last_name": null
  }
}

It also works on nested hashes:

format :json

params do
  requires :user, type: Hash do
    requires :first_name, type: String
    optional :last_name, type: String
    requires :address, type: Hash do
      requires :city, type: String
      optional :region, type: String
    end
  end
end

post 'users/signup' do
  { 'declared_params' => declared(params, include_missing: false) }
end

Request

curl -X POST -H "Content-Type: application/json" localhost:9292/users/signup -d '{"user": {"first_name":"first name", "random": "never shown", "address": { "city": "SF"}}}'

Response with include_missing:false

{
  "declared_params": {
    "user": {
      "first_name": "first name",
      "address": {
        "city": "SF"
      }
    }
  }
}

Response with include_missing:true

{
  "declared_params": {
    "user": {
      "first_name": "first name",
      "last_name": null,
      "address": {
        "city": "Zurich",
        "region": null
      }
    }
  }
}

Note that an attribute with a nil value is not considered missing and will also be returned when include_missing is set to false:

Request

curl -X POST -H "Content-Type: application/json" localhost:9292/users/signup -d '{"user": {"first_name":"first name", "last_name": null, "address": { "city": "SF"}}}'

Response with include_missing:false

{
  "declared_params": {
    "user": {
      "first_name": "first name",
      "last_name": null,
      "address": { "city": "SF"}
    }
  }
}

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[a-z]+\z/
  group :media, type: Hash do
    requires :url
  end
  optional :audio, type: Hash do
    requires :format, type: Symbol, values: [:mp3, :wav, :aac, :ogg], default: :mp3
  end
  mutually_exclusive :media, :audio
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.

Optional parameters can have a default value.

params do
  optional :color, type: String, default: 'blue'
  optional :random_number, type: Integer, default: -> { Random.rand(1..100) }
  optional :non_random_number, type: Integer, default:  Random.rand(1..100)
end

Default values are eagerly evaluated. Above :non_random_number will evaluate to the same number for each call to the endpoint of this params block. To have the default evaluate lazily with each request use a lambda, like :random_number above.

Note that default values will be passed through to any validation options specified. The following example will always fail if :color is not explicitly provided.

params do
  optional :color, type: String, default: 'blue', values: ['red', 'green']
end

The correct implementation is to ensure the default value passes all validations.

params do
  optional :color, type: String, default: 'blue', values: ['blue', 'red', 'green']
end

The following are all valid types, supported out of the box by Grape:

• Integer
• Float
• BigDecimal
• Numeric
• Date
• DateTime
• Time
• Boolean
• String
• Symbol
• Rack::Multipart::UploadedFile (alias File)
• JSON

Please be aware that the behavior differs between Ruby 2.4 and earlier versions. In Ruby 2.4, values consisting of numbers are converted to Integer, but in earlier versions it will be treated as Fixnum.

params do
  requires :integers, type: Hash do
    requires :int, coerce: Integer
  end
end
get '/int' do
  params[:integers][:int].class
end

...

get '/int' integers: { int: '45' }
  #=> Integer in ruby 2.4
  #=> Fixnum in earlier ruby versions

Aside from the default set of supported types listed above, any class can be used as a type as long as an explicit coercion method is supplied. If the type implements a class-level parse method, Grape will use it automatically. This method must take one string argument and return an instance of the correct type, or return an instance of Grape::Types::InvalidValue which optionally accepts a message to be returned in the response.

class Color
  attr_reader :value
  def initialize(color)
    @value = color
  end

  def self.parse(value)
    return new(value) if %w[blue red green]).include?(value)

    Grape::Types::InvalidValue.new('Unsupported color')
  end
end

params do
  requires :color, type: Color, default: Color.new('blue')
  requires :more_colors, type: Array[Color] # Collections work
  optional :unique_colors, type: Set[Color] # Duplicates discarded
end

get '/stuff' do
  # params[:color] is already a Color.
  params[:color].value
end

Alternatively, a custom coercion method may be supplied for any type of parameter using coerce_with. Any class or object may be given that implements a parse or call method, in that order of precedence. The method must accept a single string parameter, and the return value must match the given type.

params do
  requires :passwd, type: String, coerce_with: Base64.method(:decode64)
  requires :loud_color, type: Color, coerce_with: ->(c) { Color.parse(c.downcase) }

  requires :obj, type: Hash, coerce_with: JSON do
    requires :words, type: Array[String], coerce_with: ->(val) { val.split(/\s+/) }
    optional :time, type: Time, coerce_with: Chronic
  end
end

Note that, a nil value will call the custom coercion method, while a missing parameter will not.

Example of use of coerce_with with a lambda (a class with a parse method could also have been used) It will parse a string and return an Array of Integers, matching the Array[Integer] type.

params do
  requires :values, type: Array[Integer], coerce_with: ->(val) { val.split(/\s+/).map(&:to_i) }
end

Grape will assert that coerced values match the given type, and will reject the request if they do not. To override this behaviour, custom types may implement a parsed? method that should accept a single argument and return true if the value passes type validation.

class SecureUri
  def self.parse(value)
    URI.parse value
  end

  def self.parsed?(value)
    value.is_a? URI::HTTPS
  end
end

params do
  requires :secure_uri, type: SecureUri
end

Grape makes use of Rack::Request's built-in support for multipart file parameters. Such parameters can be declared with type: File:

params do
  requires :avatar, type: File
end
post '/' do
  params[:avatar][:filename] # => 'avatar.png'
  params[:avatar][:type] # => 'image/png'
  params[:avatar][:tempfile] # => #<File>
end

Grape supports complex parameters given as JSON-formatted strings using the special type: JSON declaration. JSON objects and arrays of objects are accepted equally, with nested validation rules applied to all objects in either case:

params do
  requires :json, type: JSON do
    requires :int, type: Integer, values: [1, 2, 3]
  end
end
get '/' do
  params[:json].inspect
end

client.get('/', json: '{"int":1}') # => "{:int=>1}"
client.get('/', json: '[{"int":"1"}]') # => "[{:int=>1}]"

client.get('/', json: '{"int":4}') # => HTTP 400
client.get('/', json: '[{"int":4}]') # => HTTP 400

Additionally type: Array[JSON] may be used, which explicitly marks the parameter as an array of objects. If a single object is supplied it will be wrapped.

params do
  requires :json, type: Array[JSON] do
    requires :int, type: Integer
  end
end
get '/' do
  params[:json].each { |obj| ... } # always works
end

For stricter control over the type of JSON structure which may be supplied, use type: Array, coerce_with: JSON or type: Hash, coerce_with: JSON.

Variant-type parameters can be declared using the types option rather than type:

params do
  requires :status_code, types: [Integer, String, Array[Integer, String]]
end
get '/' do
  params[:status_code].inspect
end

client.get('/', status_code: 'OK_GOOD') # => "OK_GOOD"
client.get('/', status_code: 300) # => 300
client.get('/', status_code: %w(404 NOT FOUND)) # => [404, "NOT", "FOUND"]

As a special case, variant-member-type collections may also be declared, by passing a Set or Array with more than one member to type:

params do
  requires :status_codes, type: Array[Integer,String]
end
get '/' do
  params[:status_codes].inspect
end

client.get('/', status_codes: %w(1 two)) # => [1, "two"]

Parameters can be nested using group or by calling requires or optional with a block. In the above example, this means params[:media][:url] is required along with params[:id], and params[:audio][:format] is required only if params[:audio] is present. With a block, group, requires and optional accept an additional option type which can be either Array or Hash, and defaults to Array. Depending on the value, the nested parameters will be treated either as values of a hash or as values of hashes in an array.

params do
  optional :preferences, type: Array do
    requires :key
    requires :value
  end

  requires :name, type: Hash do
    requires :first_name
    requires :last_name
  end
end

Suppose some of your parameters are only relevant if another parameter is given; Grape allows you to express this relationship through the given method in your parameters block, like so:

params do
  optional :shelf_id, type: Integer
  given :shelf_id do
    requires :bin_id, type: Integer
  end
end

In the example above Grape will use blank? to check whether the shelf_id param is present.

given also takes a Proc with custom code. Below, the param description is required only if the value of category is equal foo:

params do
  optional :category
  given category: ->(val) { val == 'foo' } do
    requires :description
  end
end

You can rename parameters:

params do
  optional :category, as: :type
  given type: ->(val) { val == 'foo' } do
    requires :description
  end
end

Note: param in given should be the renamed one. In the example, it should be type, not category.

Parameters options can be grouped. It can be useful if you want to extract common validation or types for several parameters. The example below presents a typical case when parameters share common options.

params do
  requires :first_name, type: String, regexp: /w+/, desc: 'First name'
  requires :middle_name, type: String, regexp: /w+/, desc: 'Middle name'
  requires :last_name, type: String, regexp: /w+/, desc: 'Last name'
end

Grape allows you to present the same logic through the with method in your parameters block, like so:

params do
  with(type: String, regexp: /w+/) do
    requires :first_name, desc: 'First name'
    requires :middle_name, desc: 'Middle name'
    requires :last_name, desc: 'Last name'
  end
end

You can rename parameters using as, which can be useful when refactoring existing APIs:

resource :users do
  params do
    requires :email_address, as: :email
    requires :password
  end
  post do
    User.create!(declared(params)) # User takes email and password
  end
end

The value passed to as will be the key when calling params or declared(params).

Parameters can be defined as allow_blank, ensuring that they contain a value. By default, requires only validates that a parameter was sent in the request, regardless its value. With allow_blank: false, empty values or whitespace only values are invalid.

allow_blank can be combined with both requires and optional. If the parameter is required, it has to contain a value. If it's optional, it's possible to not send it in the request, but if it's being sent, it has to have some value, and not an empty string/only whitespaces.

params do
  requires :username, allow_blank: false
  optional :first_name, allow_blank: false
end

Parameters can be restricted to a specific set of values with the :values option.

params do
  requires :status, type: Symbol, values: [:not_started, :processing, :done]
  optional :numbers, type: Array[Integer], default: 1, values: [1, 2, 3, 5, 8]
end

Supplying a range to the :values option ensures that the parameter is (or parameters are) included in that range (using Range#include?).

params do
  requires :latitude, type: Float, values: -90.0..+90.0
  requires :longitude, type: Float, values: -180.0..+180.0
  optional :letters, type: Array[String], values: 'a'..'z'
end

Note that both range endpoints have to be a #kind_of? your :type option (if you don't supply the :type option, it will be guessed to be equal to the class of the range's first endpoint). So the following is invalid:

params do
  requires :invalid1, type: Float, values: 0..10 # 0.kind_of?(Float) => false
  optional :invalid2, values: 0..10.0 # 10.0.kind_of?(0.class) => false
end

The :values option can also be supplied with a Proc, evaluated lazily with each request. If the Proc has arity zero (i.e. it takes no arguments) it is expected to return either a list or a range which will then be used to validate the parameter.

For example, given a status model you may want to restrict by hashtags that you have previously defined in the HashTag model.

params do
  requires :hashtag, type: String, values: -> { Hashtag.all.map(&:tag) }
end

Alternatively, a Proc with arity one (i.e. taking one argument) can be used to explicitly validate each parameter value. In that case, the Proc is expected to return a truthy value if the parameter value is valid. The parameter will be considered invalid if the Proc returns a falsy value or if it raises a StandardError.

params do
  requires :number, type: Integer, values: ->(v) { v.even? && v < 25 }
end

While Procs are convenient for single cases, consider using Custom Validators in cases where a validation is used more than once.

Parameters can be restricted from having a specific set of values with the :except_values option.

The except_values validator behaves similarly to the values validator in that it accepts either an Array, a Range, or a Proc. Unlike the values validator, however, except_values only accepts Procs with arity zero.

params do
  requires :browser, except_values: [ 'ie6', 'ie7', 'ie8' ]
  requires :port, except_values: { value: 0..1024, message: 'is not allowed' }
  requires :hashtag, except_values: -> { Hashtag.FORBIDDEN_LIST }
end

A same_as option can be given to ensure that values of parameters match.

params do
  requires :password
  requires :password_confirmation, same_as: :password
end

Parameters can be restricted to match a specific regular expression with the :regexp option. If the value does not match the regular expression an error will be returned. Note that this is true for both requires and optional parameters.

params do
  requires :email, regexp: /.+@.+/
end

The validator will pass if the parameter was sent without value. To ensure that the parameter contains a value, use allow_blank: false.

params do
  requires :email, allow_blank: false, regexp: /.+@.+/
end

Parameters can be defined as mutually_exclusive, ensuring that they aren't present at the same time in a request.

params do
  optional :beer
  optional :wine
  mutually_exclusive :beer, :wine
end

Multiple sets can be defined:

params do
  optional :beer
  optional :wine
  mutually_exclusive :beer, :wine
  optional :scotch
  optional :aquavit
  mutually_exclusive :scotch, :aquavit
end

Warning: Never define mutually exclusive sets with any required params. Two mutually exclusive required params will mean params are never valid, thus making the endpoint useless. One required param mutually exclusive with an optional param will mean the latter is never valid.

Parameters can be defined as 'exactly_one_of', ensuring that exactly one parameter gets selected.

params do
  optional :beer
  optional :wine
  exactly_one_of :beer, :wine
end

Note that using :default with mutually_exclusive will cause multiple parameters to always have a default value and raise a Grape::Exceptions::Validation mutually exclusive exception.

Parameters can be defined as 'at_least_one_of', ensuring that at least one parameter gets selected.

params do
  optional :beer
  optional :wine
  optional :juice
  at_least_one_of :beer, :wine, :juice
end

Parameters can be defined as 'all_or_none_of', ensuring that all or none of parameters gets selected.

params do
  optional :beer
  optional :wine
  optional :juice
  all_or_none_of :beer, :wine, :juice
end

All of these methods can be used at any nested level.

params do
  requires :food, type: Hash do
    optional :meat
    optional :fish
    optional :rice
    at_least_one_of :meat, :fish, :rice
  end
  group :drink, type: Hash do
    optional :beer
    optional :wine
    optional :juice
    exactly_one_of :beer, :wine, :juice
  end
  optional :dessert, type: Hash do
    optional :cake
    optional :icecream
    mutually_exclusive :cake, :icecream
  end
  optional :recipe, type: Hash do
    optional :oil
    optional :meat
    all_or_none_of :oil, :meat
  end
end

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.

You can conveniently define a route parameter as a namespace using route_param.

namespace :statuses do
  route_param :id do
    desc 'Returns all replies for a status.'
    get 'replies' do
      Status.find(params[:id]).replies
    end
    desc 'Returns a status.'
    get do
      Status.find(params[:id])
    end
  end
end

You can also define a route parameter type by passing to route_param's options.

namespace :arithmetic do
  route_param :n, type: Integer do
    desc 'Returns in power'
    get 'power' do
      params[:n] ** params[:n]
    end
  end
end

class AlphaNumeric < Grape::Validations::Base
  def validate_param!(attr_name, params)
    unless params[attr_name] =~ /\A[[:alnum:]]+\z/
      fail Grape::Exceptions::Validation, params: [@scope.full_name(attr_name)], message: '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::Base
  def validate_param!(attr_name, params)
    unless params[attr_name].length <= @option
      fail Grape::Exceptions::Validation, params: [@scope.full_name(attr_name)], message: "must be at the most #{@option} characters long"
    end
  end
end

params do
  requires :text, length: 140
end

You can also create custom validation that use request to validate the attribute. For example if you want to have parameters that are available to only admins, you can do the following.

class Admin < Grape::Validations::Base
  def validate(request)
    # return if the param we are checking was not in request
    # @attrs is a list containing the attribute we are currently validating
    # in our sample case this method once will get called with
    # @attrs being [:admin_field] and once with @attrs being [:admin_false_field]
    return unless request.params.key?(@attrs.first)
    # check if admin flag is set to true
    return unless @option
    # check if user is admin or not
    # as an example get a token from request and check if it's admin or not
    fail Grape::Exceptions::Validation, params: @attrs, message: 'Can not set admin-only field.' unless request.headers['X-Access-Token'] == 'admin'
  end
end

And use it in your endpoint definition as:

params do
  optional :admin_field, type: String, admin: true
  optional :non_admin_field, type: String
  optional :admin_false_field, type: String, admin: false
end

Every validation will have its own instance of the validator, which means that the validator can have a state.

Validation and coercion errors are collected and an exception of type Grape::Exceptions::ValidationErrors is raised. If the exception goes uncaught it will respond with a status of 400 and an error message. The validation errors are grouped by parameter name and can be accessed via Grape::Exceptions::ValidationErrors#errors.

The default response from a Grape::Exceptions::ValidationErrors is a humanly readable string, such as "beer, wine are mutually exclusive", in the following example.

params do
  optional :beer
  optional :wine
  optional :juice
  exactly_one_of :beer, :wine, :juice
end

You can rescue a Grape::Exceptions::ValidationErrors and respond with a custom response or turn the response into well-formatted JSON for a JSON API that separates individual parameters and the corresponding error messages. The following rescue_from example produces [{"params":["beer","wine"],"messages":["are mutually exclusive"]}].

format :json
subject.rescue_from Grape::Exceptions::ValidationErrors do |e|
  error! e, 400
end

Grape::Exceptions::ValidationErrors#full_messages returns the validation messages as an array. Grape::Exceptions::ValidationErrors#message joins the messages to one string.

For responding with an array of validation messages, you can use Grape::Exceptions::ValidationErrors#full_messages.

format :json
subject.rescue_from Grape::Exceptions::ValidationErrors do |e|
  error!({ messages: e.full_messages }, 400)
end

Grape returns all validation and coercion errors found by default. To skip all subsequent validation checks when a specific param is found invalid, use fail_fast: true.

The following example will not check if :wine is present unless it finds :beer.

params do
  required :beer, fail_fast: true
  required :wine
end

The result of empty params would be a single Grape::Exceptions::ValidationErrors error.

Similarly, no regular expression test will be performed if :blah is blank in the following example.

params do
  required :blah, allow_blank: false, regexp: /blah/, fail_fast: true
end

Grape supports I18n for parameter-related error messages, but will fallback to English if translations for the default locale have not been provided. See en.yml for message keys.

In case your app enforces available locales only and :en is not included in your available locales, Grape cannot fall back to English and will return the translation key for the error message. To avoid this behaviour, either provide a translation for your default locale or add :en to your available locales.

Grape supports custom validation messages for parameter-related and coerce-related error messages.

params do
  requires :name, values: { value: 1..10, message: 'not in range from 1 to 10' }, allow_blank: { value: false, message: 'cannot be blank' }, regexp: { value: /^[a-z]+$/, message: 'format is invalid' }, message: 'is required'
end

params do
  requires :password
  requires :password_confirmation, same_as: { value: :password, message: 'not match' }
end

params do
  optional :beer
  optional :wine
  optional :juice
  all_or_none_of :beer, :wine, :juice, message: "all params are required or none is required"
end

params do
  optional :beer
  optional :wine
  optional :juice
  mutually_exclusive :beer, :wine, :juice, message: "are mutually exclusive cannot pass both params"
end

params do
  optional :beer
  optional :wine
  optional :juice
  exactly_one_of :beer, :wine, :juice, message: { exactly_one: "are missing, exactly one parameter is required", mutual_exclusion: "are mutually exclusive, exactly one parameter is required" }
end

params do
  optional :beer
  optional :wine
  optional :juice
  at_least_one_of :beer, :wine, :juice, message: "are missing, please specify at least one param"
end

params do
  requires :int, type: { value: Integer, message: "type cast is invalid" }
end

params do
  requires :name, values: { value: -> { (1..10).to_a }, message: 'not in range from 1 to 10' }
end

You can pass a symbol if you want i18n translations for your custom validation messages.

params do
  requires :name, message: :name_required
end

# en.yml

en:
  grape:
    errors:
      format: ! '%{attributes} %{message}'
      messages:
        name_required: 'must be present'

You can also override attribute names.

# en.yml

en:
  grape:
    errors:
      format: ! '%{attributes} %{message}'
      messages:
        name_required: 'must be present'
      attributes:
        name: 'Oops! Name'

Will produce 'Oops! Name must be present'

You cannot set a custom message option for Default as it requires interpolation %{option1}: %{value1} is incompatible with %{option2}: %{value2}. You can change the default error message for Default by changing the incompatible_option_values message key inside en.yml

params do
  requires :name, values: { value: -> { (1..10).to_a }, message: 'not in range from 1 to 10' }, default: 5
end

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

The above example may have been requested as follows:

curl -H "secret_PassWord: swordfish" ...

The header name will have been normalized for you.

• In the header helper names will be coerced into a capitalized kebab case.
• In the env collection they appear in all uppercase, in snake case, and prefixed with 'HTTP_'.

The header name will have been normalized per HTTP standards defined in RFC2616 Section 4.2 regardless of what is being sent by a client.

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

header 'X-Robots-Tag', 'noindex'

When raising error!, pass additional headers as arguments. Additional headers will be merged with headers set before error! call.

error! 'Unauthorized', 401, 'X-Error-Detail' => 'Invalid token.'

To define routes you can use the route method or the shorthands for the HTTP verbs. To define a route that accepts any route set to :any. Parts of the path that are denoted with a colon will be interpreted as route parameters.

route :get, 'status' do
end

# is the same as

get 'status' do
end

# is the same as

get :status do
end

# is NOT the same as

get ':status' do # this makes params[:status] available
end

# This will make both params[:status_id] and params[:id] available

get 'statuses/:status_id/reviews/:id' do
end

To declare a namespace that prefixes all routes within, use the namespace method. group, resource, resources and segment are aliases to this method. Any endpoints within will share their parent context as well as any configuration done in the namespace context.

The route_param method is a convenient method for defining a parameter route segment. If you define a type, it will add a validation for this parameter.

route_param :id, type: Integer do
  get 'status' do
  end
end

# is the same as

namespace ':id' do
  params do
    requires :id, type: Integer
  end

  get 'status' do
  end
end

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

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

namespace :outer, requirements: { id: /[0-9]*/ } do
  get :id do
  end

  get ':id/edit' do
  end
end

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

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

module HttpCodesHelpers
  def unauthorized
    401
  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 an array of modules
  helpers StatusHelpers, HttpCodesHelpers

  before do
    error!('Access Denied', unauthorized) unless current_user
  end

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

You can define reusable params using helpers.

class API < Grape::API
  helpers do
    params :pagination do
      optional :page, type: Integer
      optional :per_page, type: Integer
    end
  end

  desc 'Get collection'
  params do
    use :pagination # aliases: includes, use_scope
  end
  get do
    Collection.page(params[:page]).per(params[:per_page])
  end
end

You can also define reusable params using shared helpers.

module SharedParams
  extend Grape::API::Helpers

  params :period do
    optional :start_date
    optional :end_date
  end

  params :pagination do
    optional :page, type: Integer
    optional :per_page, type: Integer
  end
end

class API < Grape::API
  helpers SharedParams

  desc 'Get collection.'
  params do
    use :period, :pagination
  end

  get do
    Collection
      .from(params[:start_date])
      .to(params[:end_date])
      .page(params[:page])
      .per(params[:per_page])
  end
end

Helpers support blocks that can help set default values. The following API can return a collection sorted by id or created_at in asc or desc order.

module SharedParams
  extend Grape::API::Helpers

  params :order do |options|
    optional :order_by, type: Symbol, values: options[:order_by], default: options[:default_order_by]
    optional :order, type: Symbol, values: %i(asc desc), default: options[:default_order]
  end
end

class API < Grape::API
  helpers SharedParams

  desc 'Get a sorted collection.'
  params do
    use :order, order_by: %i(id created_at), default_order_by: :created_at, default_order: :asc
  end

  get do
    Collection.send(params[:order], params[:order_by])
  end
end

If you need methods for generating paths inside your endpoints, please see the grape-route-helpers gem.

You can attach additional documentation to params using a documentation hash.

params do
  optional :first_name, type: String, documentation: { example: 'Jim' }
  requires :last_name, type: String, documentation: { example: 'Smith' }
end

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: '/'

By default Grape returns a 201 for POST-Requests, 204 for DELETE-Requests that don't return any content, and 200 status code for all other Requests. You can use status to query and set the actual HTTP Status Code

post do
  status 202

  if status == 200
     # do some thing
  end
end

You can also use one of status codes symbols that are provided by Rack utils

post do
  status :no_content
end

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

redirect '/statuses'

redirect '/statuses', permanent: true

You can recognize the endpoint matched with given path.

This API returns an instance of Grape::Endpoint.

class API < Grape::API
  get '/statuses' do
  end
end

API.recognize_path '/statuses'

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. If the resource has before and after callbacks they will be executed, but no other callbacks will run.

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 https://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. If the resource has before callbacks they will be executed, but no other callbacks will run.

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

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

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

error! 'Access Denied', 401

Anything that responds to #to_s can be given as a first argument to error!.

error! :not_found, 404

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)

You can set additional headers for the response. They will be merged with headers set before error! call.

error!('Something went wrong', 500, 'X-Error-Detail' => 'Invalid token.')

You can present documented errors with a Grape entity using the the grape-entity gem.

module API
  class Error < Grape::Entity
    expose :code
    expose :message
  end
end

The following example specifies the entity to use in the http_codes definition.

desc 'My Route' do
 failure [[408, 'Unauthorized', API::Error]]
end
error!({ message: 'Unauthorized' }, 408)

The following example specifies the presented entity explicitly in the error message.

desc 'My Route' do
 failure [[408, 'Unauthorized']]
end
error!({ message: 'Unauthorized', with: API::Error }, 408)

By default Grape returns a 500 status code from error!. You can change this with default_error_status.

class API < Grape::API
  default_error_status 400
  get '/example' do
    error! 'This should have http status code 400'
  end
end

For Grape to handle all the 404s for your API, it can be useful to use a catch-all. In its simplest form, it can be like:

route :any, '*path' do
  error! # or something else
end

It is very crucial to define this endpoint at the very end of your API, as it literally accepts every request.

Grape can be told to rescue all StandardError exceptions and return them in the API format.

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

This mimics default rescue behaviour when an exception type is not provided. Any other exception should be rescued explicitly, see below.

Grape can also rescue from all exceptions and still use the built-in exception handing. This will give the same behavior as rescue_from :all with the addition that Grape will use the exception handling defined by all Exception classes that inherit Grape::Exceptions::Base.

The intent of this setting is to provide a simple way to cover the most common exceptions and return any unexpected exceptions in the API format.

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

You can also rescue specific exceptions.

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

In this case UserDefinedError must be inherited from StandardError.

Notice that you could combine these two approaches (rescuing custom errors takes precedence). For example, it's useful for handling all exceptions except Grape validation errors.

class Twitter::API < Grape::API
  rescue_from Grape::Exceptions::ValidationErrors do |e|
    error!(e, 400)
  end

  rescue_from :all
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, ->(message, backtrace, options, env, original_exception) {
    "error: #{message} from #{backtrace}"
  }
end

You can also use a module or class.

module CustomFormatter
  def self.call(message, backtrace, options, env, original_exception)
    { 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 error! wrapper automatically sets the default error code and content-type.

class Twitter::API < Grape::API
  rescue_from :all do |e|
    error!("rescued from #{e.class.name}")
  end
end

Optionally, you can set the format, status code and headers.

class Twitter::API < Grape::API
  format :json
  rescue_from :all do |e|
    error!({ error: 'Server error.' }, 500, { 'Content-Type' => 'text/error' })
  end
end

You can also rescue all 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' })
  end
end

Or rescue specific exceptions.

class Twitter::API < Grape::API
  rescue_from ArgumentError do |e|
    error!("ArgumentError: #{e.message}")
  end

  rescue_from NoMethodError do |e|
    error!("NoMethodError: #{e.message}")
  end
end

By default, rescue_from will rescue the exceptions listed and all their subclasses.

Assume you have the following exception classes defined.

module APIErrors
  class ParentError < StandardError; end
  class ChildError < ParentError; end
end

Then the following rescue_from clause will rescue exceptions of type APIErrors::ParentError and its subclasses (in this case APIErrors::ChildError).

rescue_from APIErrors::ParentError do |e|
    error!({
      error: "#{e.class} error",
      message: e.message
    }, e.status)
end

To only rescue the base exception class, set rescue_subclasses: false. The code below will rescue exceptions of type RuntimeError but not its subclasses.

rescue_from RuntimeError, rescue_subclasses: false do |e|
    error!({
      status: e.status,
      message: e.message,
      errors: e.errors
    }, e.status)
end

Helpers are also available inside rescue_from.

class Twitter::API < Grape::API
  format :json
  helpers do
    def server_error!
      error!({ error: 'Server error.' }, 500, { 'Content-Type' => 'text/error' })
    end
  end

  rescue_from :all do |e|
    server_error!
  end
end

The rescue_from handler must return a Rack::Response object, call error!, or raise an exception (either the original exception or another custom one). The exception raised in rescue_from will be handled outside Grape. For example, if you mount Grape in Rails, the exception will be handle by Rails Action Controller.

Alternately, use the with option in rescue_from to specify a method or a proc.

class Twitter::API < Grape::API
  format :json
  helpers do
    def server_error!
      error!({ error: 'Server error.' }, 500, { 'Content-Type' => 'text/error' })
    end
  end

  rescue_from :all,          with: :server_error!
  rescue_from ArgumentError, with: -> { Rack::Response.new('rescued with a method', 400) }
end

Inside the rescue_from block, the environment of the original controller method(.self receiver) is accessible through the #context method.

class Twitter::API < Grape::API
  rescue_from :all do |e|
    user_id = context.params[:user_id]
    error!("error for #{user_id}")
  end
end

You could put rescue_from clauses inside a namespace and they will take precedence over ones defined in the root scope:

class Twitter::API < Grape::API
  rescue_from ArgumentError do |e|
    error!("outer")
  end

  namespace :statuses do
    rescue_from ArgumentError do |e|
      error!("inner")
    end
    get do
      raise ArgumentError.new
    end
  end
end

Here 'inner' will be result of handling occurred ArgumentError.

Grape::Exceptions::InvalidVersionHeader, which is raised when the version in the request header doesn't match the currently evaluated version for the endpoint, will never be rescued from a rescue_from block (even a rescue_from :all) This is because Grape relies on Rack to catch that error and try the next versioned-route for cases where there exist identical Grape endpoints with different versions.

Any exception that is not subclass of StandardError should be rescued explicitly. Usually it is not a case for an application logic as such errors point to problems in Ruby runtime. This is following standard recommendations for exceptions handling.

When mounted inside containers, such as Rails 3.x, errors such as "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 preventing downstream handlers from handling errors. You may set the :cascade option to false for the entire API or separately on specific version definitions, which will remove the X-Cascade: true header from API responses.

cascade false

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

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

To change the logger level.

class API < Grape::API
  self.logger.level = Logger::INFO
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

For similar to Rails request logging try the grape_logging or grape-middleware-logger gems.

Your API can declare which content-types to support by using content_type. If you do not specify any, Grape will support XML, JSON, BINARY, and TXT content-types. The default format is :txt; you can change this with default_format. Essentially, the two APIs below are equivalent.

class Twitter::API < Grape::API
  # no content_type declarations, so Grape uses the defaults
end

class Twitter::API < Grape::API
  # the following declarations are equivalent to the defaults

  content_type :xml, 'application/xml'
  content_type :json, 'application/json'
  content_type :binary, 'application/octet-stream'
  content_type :txt, 'text/plain'

  default_format :txt
end

If you declare any content_type whatsoever, the Grape defaults will be overridden. For example, the following API will only support the :xml and :rss content-types, but not :txt, :json, or :binary. Importantly, this means the :txt default format is not supported! So, make sure to set a new default_format.

class Twitter::API < Grape::API
  content_type :xml, 'application/xml'
  content_type :rss, 'application/xml+rss'

  default_format :xml
end

Serialization takes place automatically. For example, you do not have to call to_json in each JSON API endpoint implementation. The response format (and thus the automatic serialization) is determined in the following order:

• 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.

For example, consider the following API.

class MultipleFormatAPI < Grape::API
  content_type :xml, 'application/xml'
  content_type :json, 'application/json'

  default_format :json

  get :hello do
    { hello: 'world' }
  end
end

• GET /hello (with an Accept: */* header) does not have an extension or a format parameter, so it will respond with JSON (the default format).
• GET /hello.xml has a recognized extension, so it will respond with XML.
• GET /hello?format=xml has a recognized format parameter, so it will respond with XML.
• GET /hello.xml?format=json has a recognized extension (which takes precedence over the format parameter), so it will respond with XML.
• GET /hello.xls (with an Accept: */* header) has an extension, but that extension is not recognized, so it will respond with JSON (the default format).
• GET /hello.xls with an Accept: application/xml header has an unrecognized extension, but the Accept header corresponds to a recognized format, so it will respond with XML.
• GET /hello.xls with an Accept: text/plain header has an unrecognized extension and an unrecognized Accept header, so it will respond with JSON (the default format).

You can override this process explicitly by specifying env['api.format'] in the API itself. For example, the following API will let you upload arbitrary files and return their contents as an attachment with the correct MIME type.

class Twitter::API < Grape::API
  post 'attachment' do
    filename = params[:file][:filename]
    content_type MIME::Types.type_for(filename)[0].to_s
    env['api.format'] = :binary # there's no formatter for :binary, data will be returned "as is"
    header 'Content-Disposition', "attachment; filename*=UTF-8''#{CGI.escape(filename)}"
    params[:file][:tempfile].read
  end
end

You can have your API only respond to a single format with format. If you use this, the API will not respond to file extensions other than specified in format. For example, consider the following API.

class SingleFormatAPI < Grape::API
  format :json

  get :hello do
    { hello: 'world' }
  end
end

• GET /hello will respond with JSON.
• GET /hello.json will respond with JSON.
• GET /hello.xml, GET /hello.foobar, or any other extension will respond with an HTTP 404 error code.
• GET /hello?format=xml will respond with an HTTP 406 error code, because the XML format specified by the request parameter is not supported.
• GET /hello with an Accept: application/xml header will still respond with JSON, since it could not negotiate a recognized content-type from the headers and JSON is the effective default.

The formats apply to parsing, too. 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

When the content-type is omitted, Grape will return a 406 error code unless default_format is specified. The following API will try to parse any data without a content-type using a JSON parser.

class Twitter::API < Grape::API
  format :json
  default_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, ->(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 formatters 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
• :binary: data will be returned "as is"

If a body is present in a request to an API, with a Content-Type header value that is of an unsupported type a "415 Unsupported Media Type" error code will be returned by Grape.

Response statuses that indicate no content as defined by Rack here will bypass serialization and the body entity - though there should be none - will not be modified.

Grape supports 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

Grape supports CORS via Rack::CORS, part of the rack-cors gem. Add rack-cors to your Gemfile, then use the middleware in your config.ru file.

require 'rack/cors'

use Rack::Cors do
  allow do
    origins '*'
    resource '*', headers: :any, methods: :get
  end
end

run Twitter::API

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

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' 'https://localhost:9292/value' -H Content-Type:text/custom -v

You can disable parsing for a content-type with nil. For example, parser :json, nil will disable JSON parsing altogether. The request data is then available as-is in env['api.request.body'].

Grape uses JSON and ActiveSupport::XmlMini for JSON and XML parsing by default. It also detects and supports multi_json and multi_xml. Adding those gems to your Gemfile and requiring them will enable them and allow you to swap the JSON and XML back-ends.

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.

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: ->(status, options) { status.user.public? }
      expose :digest do |status, options|
        Digest::MD5.hexdigest(status.txt)
      end
      expose :replies, using: API::Status, as: :replies
    end
  end

  class Statuses < Grape::API
    version 'v1'

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

You can use entity documentation directly in the params block with using: Entity.documentation.

module API
  class Statuses < Grape::API
    version 'v1'

    desc 'Create a status'
    params do
      requires :all, except: [:ip], using: API::Entities::Status.documentation.except(:id)
    end
    post '/status' do
      Status.create! params
    end
  end
end

You can present with multiple entities using an optional Symbol argument.

  get '/statuses' do
    statuses = Status.all.page(1).per(20)
    present :total_page, 10
    present :per_page, 20
    present :statuses, statuses, with: API::Entities::Status
  end

The response will be

  {
    total_page: 10,
    per_page: 20,
    statuses: []
  }

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
    Entity.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.

You can present hash with Grape::Presenters::Presenter to keep things consistent.

get '/users' do
  present { id: 10, name: :dgz }, with: Grape::Presenters::Presenter
end

The response will be

{
  id:   10,
  name: 'dgz'
}

It has the same result with

get '/users' do
  present :id, 10
  present :name, :dgz
end

You can use Roar to render HAL or Collection+JSON with the help of grape-roar, which defines a custom JSON formatter and enables presenting entities with Grape's present keyword.

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

You can use Active Model Serializers serializers with the help of the grape-active_model_serializers gem, which defines a custom Grape AMS formatter.

In general, use the binary format to send raw data.

class API < Grape::API
  get '/file' do
    content_type 'application/octet-stream'
    File.binread 'file.bin'
  end
end

You can set the response body explicitly with body.

class API < Grape::API
  get '/' do
    content_type 'text/plain'
    body 'Hello World'
    # return value ignored
  end
end

Use body false to return 204 No Content without any data or content-type.

You can also set the response to a file with sendfile. This works with the Rack::Sendfile middleware to optimally send the file through your web server software.

class API < Grape::API
  get '/' do
    sendfile '/path/to/file'
  end
end

To stream a file in chunks use stream

class API < Grape::API
  get '/' do
    stream '/path/to/file'
  end
end

If you want to stream non-file data use the stream method and a Stream object. This is an object that responds to each and yields for each chunk to send to the client. Each chunk will be sent as it is yielded instead of waiting for all of the content to be available.

class MyStream
  def each
    yield 'part 1'
    yield 'part 2'
    yield 'part 3'
  end
end

class API < Grape::API
  get '/' do
    stream MyStream.new
  end
end

Grape has built-in Basic and Digest authentication (the given block is executed in the context of the current Endpoint). Authentication applies to the current namespace and any children, but not parents.

http_basic do |username, password|
  # verify user's password here
  # IMPORTANT: make sure you use a comparison method which isn't prone to a timing attack
end

http_digest({ realm: 'Test Api', opaque: 'app secret' }) do |username|
  # lookup the user's password here
end

Grape can use custom Middleware for authentication. How to implement these Middleware have a look at Rack::Auth::Basic or similar implementations.

For registering a Middleware you need the following options:

• label - the name for your authenticator to use it later
• MiddlewareClass - the MiddlewareClass to use for authentication
• option_lookup_proc - A Proc with one Argument to lookup the options at runtime (return value is an Array as Parameter for the Middleware).

Example:

Grape::Middleware::Auth::Strategies.add(:my_auth, AuthMiddleware, ->(options) { [options[:realm]] } )


auth :my_auth, { realm: 'Test Api'} do |credentials|
  # lookup the user's password here
  { 'user1' => 'password1' }[username]
end

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