README.md

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## What is Grape?

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.

## Stable Release

You're reading the documentation for the next release of Grape, which should be 4.0.0.
The current stable release is [3.3.2](https://github.com/ruby-grape/grape/blob/v3.3.2/README.md).

## Project Resources

* [Grape Website](http://www.ruby-grape.org)
* [Documentation](http://www.rubydoc.info/gems/grape)
* Need help? [Open an Issue](https://github.com/ruby-grape/grape/issues)
* [Follow us on Twitter](https://twitter.com/grapeframework)

## Grape for Enterprise

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](https://tidelift.com/subscription/request-a-demo?utm_source=rubygems-grape&utm_medium=referral&utm_campaign=enterprise) for more details.

## Installation

Ruby 3.3 or newer is required.

Grape is available as a gem, to install it run:

    bundle add grape

## Basic Usage

Grape APIs are Rack applications that are created by subclassing `Grape::API`.
Below is a simple example showing some of the more common features of Grape in the context of recreating parts of the Twitter API.

```ruby
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
```

## Rails 7.1

Grape's [deprecator](https://api.rubyonrails.org/v7.1.0/classes/ActiveSupport/Deprecation.html) will be added to your application's deprecators [automatically](lib/grape/railtie.rb) as `:grape`, so that your application's configuration can be applied to it.

## Mounting

### All


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

```ruby
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.

### Rack

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

```ruby
run Twitter::API
```

(With pre-loading you can use)

```ruby
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.

### Alongside Sinatra (or other frameworks)

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

```ruby
# 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](https://www.rubydoc.info/gems/rack/Rack/Cascade). This may lead to undesirable behavior showing the [wrong 404 page from the wrong app](https://github.com/ruby-grape/grape/issues/1515).


### Rails

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`:

```ruby
mount Twitter::API => '/'
```
#### Zeitwerk
Rails's default autoloader is `Zeitwerk`. By default, it 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:

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

### 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.

```ruby
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.

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

Declarations as `before/after/rescue_from` can be placed before or after `mount`. In any case they will be inherited.

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

  rescue_from :all do
    error!({ "error" => "Internal Server Error" }, 500)
  end

  mount Twitter::Users
  mount Twitter::Search

  after do
    clean_cache!
  end

  rescue_from ZeroDivisionError do
    error!({ "error" => "Not found" }, 404)
  end
end
```

## Remounting

You can mount the same endpoints in two different locations.

```ruby
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`.

### Mount Configuration

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

```ruby
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:
```ruby
# 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 based on a `configuration`, you can use the helper `given`.

```ruby
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)


```ruby
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.

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

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

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

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

## Versioning

You have the option to provide various versions of your API by establishing a separate `Grape::API` class for each offered version and then integrating them into a primary `Grape::API` class. Ensure that newer versions are mounted before older ones. The default approach to versioning directs the request to the subsequent Rack middleware if a specific version is not found.

```ruby
require 'v1'
require 'v2'
require 'v3'
class App < Grape::API
  mount V3
  mount V2
  mount V1
end
```

To maintain the same endpoints from earlier API versions without rewriting them, you can indicate multiple versions within the previous API versions.

```ruby
class V1 < Grape::API
  version 'v1', 'v2', 'v3'

  get '/foo' do
    # your code for GET /foo
  end

  get '/other' do
    # your code for GET /other
  end
end

class V2 < Grape::API
  version 'v2', 'v3'

  get '/var' do
    # your code for GET /var
  end
end

class V3 < Grape::API
  version 'v3'

  get '/foo' do
    # your new code for GET /foo
  end
end
```

Using the example provided, the subsequent endpoints will be accessible across various versions:

```shell
GET /v1/foo
GET /v1/other
GET /v2/foo # => Same behavior as v1
GET /v2/other # => Same behavior as v1
GET /v2/var # => New endpoint not available in v1
GET /v3/foo # => Different behavior to v1 and v2
GET /v3/other # => Same behavior as v1 and v2
GET /v3/var # => Same behavior as v2
```

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`.

### Strategies

#### Path

```ruby
version 'v1', using: :path
```

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

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

#### Header

```ruby
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` header.

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

By default, the first matching version is used when no `Accept` header is supplied. This behavior is similar to routing in Rails. To circumvent this default behavior, one could use the `:strict` option. When this option is set to `true`, a `406 Not Acceptable` error is returned when no correct `Accept` header is supplied.

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.

Grape will evaluate the relative quality preference included in Accept headers and default to a quality of 1.0 when omitted. In the following example a Grape API that supports XML and JSON in that order will return JSON:

    curl -H "Accept: text/xml;q=0.8, application/json;q=0.9" localhost:1234/resource

#### Accept-Version Header

```ruby
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" http://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-Version` 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.

#### Param

```ruby
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 http://localhost:9292/statuses/public_timeline?apiver=v1

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

```ruby
version 'v1', using: :param, parameter: 'v'
```

    curl http://localhost:9292/statuses/public_timeline?v=v1


## Linting

You can check whether your API is in conformance with the [Rack's specification](https://github.com/rack/rack/blob/main/SPEC.rdoc) by calling `lint!` at the API level or through [configuration](#configuration).

```ruby
class Api < Grape::API
  lint!
end
```
```ruby
Grape.configure do |config|
  config.lint = true
end
```
```ruby
Grape.config.lint = true
```

### Bug in Rack::ETag under Rack 3.X
If you're using Rack 3.X and the `Rack::ETag` middleware (used by [Rails](https://guides.rubyonrails.org/rails_on_rack.html#inspecting-middleware-stack)), a [bug](https://github.com/rack/rack/pull/2324) related to linting has been fixed in [3.1.13](https://github.com/rack/rack/blob/v3.1.13/CHANGELOG.md#3113---2025-04-13) and [3.0.15](https://github.com/rack/rack/blob/v3.1.13/CHANGELOG.md#3015---2025-04-13) respectively.

## Describing Methods

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

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

```ruby
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']]
  default { code: 500, message: 'InvalidRequest', model: 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 the success response for this route.
* `failure`: (former http_codes) A definition of the used failure HTTP Codes and Entities.
* `default`: The definition and `Entity` used to present the default response for this route.
* `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][grape-swagger]

[grape-swagger]: https://github.com/ruby-grape/grape-swagger

## Configuration

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

* `param_builder`: Sets the [Parameter Builder](#parameters), 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

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

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

```ruby
Grape.configure do |config|
  config.param_builder = :hashie_mash
end
```

Available parameter builders are `:hash`, `:hash_with_indifferent_access`, and `:hashie_mash`.
See [params_builder](lib/grape/params_builder).

You can also configure a single API:

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

This will be available inside the API with `configuration`, as if it were [mount configuration](#mount-configuration).

## Parameters

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

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

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

The request:

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

The Grape endpoint:

```ruby
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' http://localhost:9292/upload
```

The Grape endpoint:

```ruby
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.

### Params Class

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

```ruby
class API < Grape::API
  build_with :hashie_mash

  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.

```ruby
params do
  build_with :hash
  optional :color, type: String
end
```

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

Available parameter builders are `:hash`, `:hash_with_indifferent_access`, and `:hashie_mash`.
See [params_builder](lib/grape/params_builder).

### Declared

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.
  * Perform any parameter renaming on the resulting hash.

Consider the following API endpoint:

````ruby
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**

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

**Response**

````json
{
  "declared_params": {}
}

````

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

````ruby
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**

````bash
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**

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

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

````ruby
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**

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

**Response**

````json
{
  "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.

### Include Parent Namespaces

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`.

````ruby
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**

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

**Response**

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

### Include Missing

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:

````ruby
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**

````bash
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**

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

**Response with include_missing:true**

````json
{
  "declared_params": {
    "user": {
      "first_name": "first name",
      "last_name": null
    }
  }
}
````

It also works on nested hashes:

````ruby
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**

````bash
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**

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

**Response with include_missing:true**

````json
{
  "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**

````bash
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**

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

### Evaluate Given

By default `declared(params)` will not evaluate `given` and return all parameters. Use `evaluate_given` to evaluate all `given` blocks and return only parameters that satisfy `given` conditions. Consider the following API:

````ruby
format :json

params do
  optional :child_id, type: Integer
  given :child_id do
    requires :father_id, type: Integer
  end
end

post 'child' do
  { 'declared_params' => declared(params, evaluate_given: true) }
end
````

**Request**

````bash
curl -X POST -H "Content-Type: application/json" localhost:9292/child -d '{"father_id": 1}'
````

**Response with evaluate_given:false**

````json
{
  "declared_params": {
    "child_id": null,
    "father_id": 1
  }
}
````

**Response with evaluate_given:true**

````json
{
  "declared_params": {
    "child_id": null
  }
}
````

It also works on nested hashes:

````ruby
format :json

params do
  requires :child, type: Hash do
    optional :child_id, type: Integer
    given :child_id do
      requires :father_id, type: Integer
    end
  end
end

post 'child' do
  { 'declared_params' => declared(params, evaluate_given: true) }
end
````

**Request**

````bash
curl -X POST -H "Content-Type: application/json" localhost:9292/child -d '{"child": {"father_id": 1}}'
````

**Response with evaluate_given:false**

````json
{
  "declared_params": {
    "child": {
      "child_id": null,
      "father_id": 1
    }
  }
}
````

**Response with evaluate_given:true**

````json
{
  "declared_params": {
    "child": {
      "child_id": null
    }
  }
}
````

### Parameter Precedence

Using `route_param` takes higher precedence over a regular parameter defined with same name:

```ruby
params do
  requires :foo, type: String
end
route_param :foo do
  get do
    { value: params[:foo] }
  end
end
```

**Request**

```bash
curl -X POST -H "Content-Type: application/json" localhost:9292/bar -d '{"foo": "baz"}'
```

**Response**

```json
{
  "value": "bar"
}
```

## Parameter Validation and Coercion

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

```ruby
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.

```ruby
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.

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

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

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

You can use the value of one parameter as the default value of some other parameter. In this case, if the `primary_color` parameter is not provided, it will have the same value as the `color` one. If both of them not provided, both of them will have `blue` value.

```ruby
params do
  optional :color, type: String, default: 'blue'
  optional :primary_color, type: String, default: -> (params) { params[:color] }
end
```

### Supported Parameter Types

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

### Custom Types and Coercions

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.

```ruby
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`.

```ruby
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`.

```ruby
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.

```ruby
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
```

### Multipart File Parameters

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

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

### First-Class `JSON` Types

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:

```ruby
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.

```ruby
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`.

### Multiple Allowed Types

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

```ruby
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`:

```ruby
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"]
```

### Multiple Hash Schemas with `oneof`

A Hash parameter that may take one of several different shapes can be declared with the `oneof:` option. Each variant is a `Proc` that uses the normal `params` DSL — so the full validator surface (`requires`, `optional`, `regexp:`, `values:`, `allow_blank:`, nested `Hash`/`Array`, etc.) is available inside.

```ruby
params do
  requires :value, type: Hash, oneof: [
    proc { requires :fixed_price, type: Float },
    proc do
      requires :time_unit, type: String
      requires :rate, type: Float
    end
  ]
end
post '/pricing' do
  params[:value]
end
```

Both of these requests succeed:

```bash
curl -d '{"value":{"fixed_price":100.0}}' -H 'Content-Type: application/json' /pricing
curl -d '{"value":{"time_unit":"hour","rate":50.0}}' -H 'Content-Type: application/json' /pricing
```

A request that doesn't match any variant returns `400` with `value does not match any of the allowed schemas`.

Variants are tried in declaration order; the first variant that validates without errors wins, and any coercions it performed (e.g. `"150.5"` → `150.5`) are applied to the request params. Nested hash structures inside variants work the same as elsewhere in Grape:

```ruby
params do
  requires :options, type: Hash, oneof: [
    proc do
      requires :form, type: Hash do
        requires :colour, type: String
        optional :size, type: Integer
      end
    end,
    proc do
      requires :api, type: Hash do
        requires :authenticated, type: Grape::API::Boolean
      end
    end
  ]
end
```

`oneof:` requires `type: Hash`. The variants array must be non-empty and each entry must be a `Proc`; violating either raises an `ArgumentError` at definition time.

### Validation of Nested Parameters

Parameters can be nested using `group` or by calling `requires` or `optional` with a block.
In the [above example](#parameter-validation-and-coercion), 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.

```ruby
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
```

### Dependent Parameters

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:

```ruby
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`:

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

You can rename parameters:

```ruby
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`.

### Group Options

Parameters options can be grouped. It can be useful if you want to extract common validation or types for several parameters.
Within these groups, individual parameters can extend or selectively override the common settings, allowing you to maintain the defaults at the group level while still applying parameter-specific rules where necessary.

The example below presents a typical case when parameters share common options.

```ruby
params do
  requires :first_name, type: String, regexp: /w+/, desc: 'First name', documentation: { in: 'body' }
  optional :middle_name, type: String, regexp: /w+/, desc: 'Middle name', documentation: { in: 'body', x: { nullable: true } }
  requires :last_name, type: String, regexp: /w+/, desc: 'Last name', documentation: { in: 'body' }
end
```

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

```ruby
params do
  with(type: String, regexp: /w+/, documentation: { in: 'body' }) do
    requires :first_name, desc: 'First name'
    optional :middle_name, desc: 'Middle name', documentation: { x: { nullable: true } }
    requires :last_name, desc: 'Last name'
  end
end
```

You can organize settings into layers using nested `with` blocks. Each layer can use, add to, or change the settings of the layer above it. This helps to keep complex parameters organized and consistent, while still allowing for specific customizations to be made.

```ruby
params do
  with(documentation: { in: 'body' }) do  # Applies documentation to all nested parameters
    with(type: String, regexp: /\w+/) do  # Applies type and validation to names
      requires :first_name, desc: 'First name'
      requires :last_name, desc: 'Last name'
    end
    optional :age, type: Integer, desc: 'Age', documentation: { x: { nullable: true } }  # Specific settings for 'age'
  end
end
```

### Renaming

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

```ruby
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 `declared(params)`.

### Built-in Validators

#### `allow_blank`

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.


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

#### `values`

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


```ruby
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?`).

```ruby
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 endless ranges are also supported with ActiveSupport >= 6.0, but they require that the type be provided.

```ruby
params do
  requires :minimum, type: Integer, values: 10..
  optional :maximum, type: Integer, values: ..10
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:

```ruby
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.

```ruby
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.

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

While Procs are convenient for single cases, consider using [Custom Validators](#custom-validators) in cases where a validation is used more than once.

When using `optional` together with `:values`, a missing key, a `nil` value, and any value that coerces to `nil` (such as `""` for `type: Symbol`) all pass validation — `optional` collapses "key may be absent" with "value may be nil". To reject blank values while still allowing the key to be absent, add `allow_blank: false`:

```ruby
params do
  optional :state, type: Symbol, values: [:active, :inactive], allow_blank: false
end
```

With `requires`, blank values are already rejected: `requires` enforces presence and `:values` rejects `nil`.

#### `except_values`

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.

```ruby
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
```

#### `same_as`

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

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

#### `length`

Parameters with types that support `#length` method can be restricted to have a specific length with the `:length` option.

The validator accepts `:min` or `:max` or both options or only `:is` to validate that the value of the parameter is within the given limits.

```ruby
params do
  requires :code, type: String, length: { is: 2 }
  requires :str, type: String, length: { min: 3 }
  requires :list, type: [Integer], length: { min: 3, max: 5 }
  requires :hash, type: Hash, length: { max: 5 }
end
```

#### `regexp`

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.

```ruby
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`.

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

#### `mutually_exclusive`

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

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

Multiple sets can be defined:

```ruby
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.

#### `exactly_one_of`

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

```ruby
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.

#### `at_least_one_of`

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

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

#### `all_or_none_of`

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

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

#### Nested `mutually_exclusive`, `exactly_one_of`, `at_least_one_of`, `all_or_none_of`

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

```ruby
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
```

### Namespace Validation and Coercion

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

```ruby
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`.

```ruby
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.

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

### Custom Validators

```ruby
class AlphaNumeric < Grape::Validations::Validators::Base
  def validate_param!(attr_name, params)
    return if params[attr_name].match?(/\A[[:alnum:]]+\z/)

    validation_error!(attr_name, 'must consist of alpha-numeric characters')
  end
end
```

```ruby
params do
  requires :text, alpha_numeric: true
end
```

You can also create custom classes that take parameters.

```ruby
class Length < Grape::Validations::Validators::Base
  def validate_param!(attr_name, params)
    return if params[attr_name].length <= @options

    validation_error!(attr_name, "must be at the most #{@options} characters long")
  end
end
```

```ruby
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.

```ruby
class Admin < Grape::Validations::Validators::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 @options
    # check if user is admin or not
    # as an example get a token from request and check if it's admin or not
    validation_error!(@attrs, 'Can not set admin-only field.') unless request.headers['X-Access-Token'] == 'admin'
  end
end
```

And use it in your endpoint definition as:

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

Each validator is instantiated once at route definition time and frozen. Any setup (option parsing, message building) should happen in `initialize`, not in `validate_param!` or `validate`.

#### Available helpers

The following protected/private helpers are available in any `Grape::Validations::Validators::Base` subclass:

| Helper | Description |
|---|---|
| `default_message_key(key)` | Class-level macro. Declares the default I18n key for `validation_error!`. A per-option `:message` override still takes precedence. |
| `validation_error!(attr_name_or_params, message = @exception_message)` | Raises `Grape::Exceptions::Validation`. Accepts a single attribute name or a pre-computed array of full param names. |
| `@options` | The validator option value, deep-frozen at initialization. |
| `@attrs` | Frozen array of attribute names this validator applies to. |
| `@scope` | The `ParamsScope` — use `@scope.full_name(attr_name)` for the fully-qualified param name. |
| `option_value` | Returns `@options[:value]` if present, otherwise `@options`. |
| `options_key?(key)` | Returns true if `@options` is a hash with a non-nil `key`. |
| `hash_like?(obj)` | Returns true if `obj` responds to `key?`. |
| `scrub(value)` | Returns `value` with invalid byte sequences scrubbed. |
| `translate(key, **opts)` | I18n lookup with `:en` fallback and `grape.errors.messages` scope. Called at request time to respect per-request locale. |

Use `default_message_key` for a fixed I18n key. The message is resolved once at route definition time via `message`, so a per-option `:message` override still wins:

```ruby
class SpecialValidator < Grape::Validations::Validators::Base
  default_message_key :special

  def validate_param!(attr_name, params)
    return if valid?(params[attr_name])

    validation_error!(attr_name)
  end
end
```

For interpolated messages that must respect per-request locale, call `translate` directly inside `validate_param!`:

```ruby
class SpecialValidator < Grape::Validations::Validators::Base
  def validate_param!(attr_name, params)
    return if valid?(params[attr_name])

    validation_error!(attr_name, translate(:special, min: 2, max: 10))
  end
end
```

### Validation Errors

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.

```ruby
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"]}]`.

```ruby
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`.
```ruby
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`.
```ruby
params do
  requires :beer, fail_fast: true
  requires :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.
```ruby
params do
  requires :blah, allow_blank: false, regexp: /blah/, fail_fast: true
end
```

### I18n

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](lib/grape/locale/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.

Custom validators that inherit from `Grape::Validations::Validators::Base` have access to a `translate` helper (see `Grape::Util::Translation`) and should use it instead of calling `I18n` directly. It applies the same `:en` fallback as built-in validators, defaults `scope` to `'grape.errors.messages'`, and handles interpolation without needing `format`:

```ruby
# Good — scope defaults to 'grape.errors.messages', interpolation forwarded automatically
translate(:special, min: 2, max: 10)

# Bad — format is unnecessary and risks conflicting with I18n reserved keys
format I18n.t(:special, scope: 'grape.errors.messages'), min: 2, max: 10
```

Example custom validator using an interpolated i18n message:

```ruby
class SpecialValidator < Grape::Validations::Validators::Base
  def validate_param!(attr_name, params)
    return if valid?(params[attr_name])

    validation_error!(attr_name, translate(:special, min: 2, max: 10))
  end
end
```

### Custom Validation messages

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

#### `presence`, `allow_blank`, `values`, `regexp`

```ruby
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
```

#### `same_as`

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

#### `length`

```ruby
params do
  requires :code, type: String, length: { is: 2, message: 'code is expected to be exactly 2 characters long' }
  requires :str, type: String, length: { min: 5, message: 'str is expected to be at least 5 characters long' }
  requires :list, type: [Integer], length: { min: 2, max: 3, message: 'list is expected to have between 2 and 3 elements' }
end
```

#### `all_or_none_of`

```ruby
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
```

#### `mutually_exclusive`

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

#### `exactly_one_of`

```ruby
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
```

#### `at_least_one_of`

```ruby
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
```

#### `Coerce`

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

#### `With Lambdas`

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

#### `Pass symbols for i18n translations`

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

```ruby
params do
  requires :name, message: :name_required
end
```
```ruby
# en.yml

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

#### Overriding Attribute Names

You can also override attribute names.

```ruby
# 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'

#### With Default

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](lib/grape/locale/en.yml)

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

### Using `dry-validation` or `dry-schema`

As an alternative to the `params` DSL described above, you can use a schema or `dry-validation` contract to describe an endpoint's parameters. This can be especially useful if you use the above already in some other parts of your application. If not, you'll need to add `dry-validation` or `dry-schema` to your `Gemfile`.

Then call `contract` with a contract or schema defined previously:

```rb
CreateOrdersSchema = Dry::Schema.Params do
  required(:orders).array(:hash) do
    required(:name).filled(:string)
    optional(:volume).maybe(:integer, lt?: 9)
  end
end

# ...

contract CreateOrdersSchema
```

or with a block, using the [schema definition syntax](https://dry-rb.org/gems/dry-schema/1.13/#quick-start):

```rb
contract do
  required(:orders).array(:hash) do
    required(:name).filled(:string)
    optional(:volume).maybe(:integer, lt?: 9)
  end
end
```

The latter will define a coercing schema (`Dry::Schema.Params`). When using the former approach, it's up to you to decide whether the input will need coercing.

The `params` and `contract` declarations can also be used together in the same API, e.g. to describe different parts of a nested namespace for an endpoint.

## Headers

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

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

```ruby
get do
  error!('Unauthorized', 401) unless env['HTTP_SECRET_PASSWORD'] == 'swordfish'
end
```

#### Header Case Handling

The above example may have been requested as follows:

``` shell
curl -H "secret_PassWord: swordfish" ...
```

The header name will have been normalized for you.

- In the `header` helper names will be coerced into a downcased kebab case as `secret-password` if using Rack 3.
- In the `header` helper names will be coerced into a capitalized kebab case as `Secret-PassWord` if using Rack < 3.
- In the `env` collection they appear in all uppercase, in snake case, and prefixed with 'HTTP_' as `HTTP_SECRET_PASSWORD`

The header name will have been normalized per HTTP standards defined in [RFC2616 Section 4.2](https://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4.2) regardless of what is being sent by a client.

### Response

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

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

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

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

## Routes

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.

```ruby
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.

```ruby
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.

```ruby
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
```

## Helpers

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

```ruby
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`.

```ruby
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.

```ruby
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.

```ruby
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
```

## Path Helpers

If you need methods for generating paths inside your endpoints, please see the [grape-route-helpers](https://github.com/reprah/grape-route-helpers) gem.

## Parameter Documentation

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

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

If documentation isn't needed (for instance, it is an internal API), documentation can be disabled.

```ruby
class API < Grape::API
  do_not_document!

  # endpoints...
end
```

In this case, Grape won't create objects related to documentation which are retained in RAM forever.

## Cookies

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

```ruby
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.

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

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

Delete a cookie with `delete`.

```ruby
cookies.delete :status_count
```

Specify an optional path.

```ruby
cookies.delete :status_count, path: '/'
```

## HTTP Status Code

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

```ruby
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](http://www.rubydoc.info/github/rack/rack/Rack/Utils#HTTP_STATUS_CODES-constant)

```ruby
post do
  status :no_content
end
```

## Redirecting

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

```ruby
redirect '/statuses'
```

```ruby
redirect '/statuses', permanent: true
```

## Recognizing Path

You can recognize the endpoint matched with given path.

This API returns an instance of `Grape::Endpoint`.

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

API.recognize_path '/statuses'
```

Since version `2.1.0`, the `recognize_path` method takes into account the parameters type to determine which endpoint should match with given path.

```ruby
class Books < Grape::API
  resource :books do
    route_param :id, type: Integer do
      # GET /books/:id
      get do
        #...
      end
    end

    resource :share do
      # POST /books/share
      post do
      # ....
      end
    end
  end
end

API.recognize_path '/books/1' # => /books/:id
API.recognize_path '/books/share' # => /books/share
API.recognize_path '/books/other' # => nil
```


## Allowed Methods

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

``` ruby
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.

```ruby
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
```

``` shell
curl -v -X OPTIONS http://localhost:3000/rt_count

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

You can disable this behavior with `do_not_route_options!`.

If a request for a resource is made with an unsupported HTTP method, an HTTP 405 (Method Not Allowed) response will be returned. If the resource has `before` callbacks they will be executed, but no other callbacks will run.

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

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

## Raising Exceptions

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

```ruby
error! 'Access Denied', 401
```

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

```ruby
error! :not_found, 404
```

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

```ruby
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.

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

You can present documented errors with a Grape entity using the [grape-entity](https://github.com/ruby-grape/grape-entity) gem.

```ruby
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.

```ruby
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.

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

### Default Error HTTP Status Code

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

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

### Handling 404

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:

```ruby
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.

## Exception Handling

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

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

This mimics [default `rescue` behaviour](https://ruby-doc.org/core/StandardError.html) when an exception type is not provided.
Any other exception should be rescued explicitly, see [below](#exceptions-that-should-be-rescued-explicitly).

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.

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

If you want to customize the shape of grape exceptions returned to the user, to match your `:all` handler for example, you can pass a block to `rescue_from :grape_exceptions`.

```ruby
rescue_from :grape_exceptions do |e|
  error!(e, e.status)
end
```

You can also rescue specific exceptions.

```ruby
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.

```ruby
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. The formatter receives a `Grape::Exceptions::ErrorResponse` value object as `error:` plus three context kwargs — `env:`, `include_backtrace:`, `include_original_exception:`. Pull just the keys you need with `**` to ignore the rest:

```ruby
class Twitter::API < Grape::API
  error_formatter :txt, ->(error:, **) {
    "error #{error.status}: #{error.message} from #{error.backtrace}"
  }
end
```

You can also use a module or class.

```ruby
module CustomFormatter
  def self.call(error:, **)
    { status: error.status, message: error.message, backtrace: error.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.

```ruby
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.

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

#### Re-raising from inside a `rescue_from` block

A `rescue_from` block can re-raise an exception to invoke a different handler. This is useful for translating one exception class into another:

```ruby
class Twitter::API < Grape::API
  rescue_from Grape::Exceptions::ValidationErrors do |e|
    raise Api::Exceptions::InvalidValueError, e.full_messages
  end

  rescue_from Api::Exceptions::InvalidValueError do |e|
    error!({ errors: e.message }, 422)
  end
end
```

The first handler re-raises; the second handler runs against the new exception.

If the re-raised exception has no registered `rescue_from` and is a `Grape::Exceptions::Base` subclass, it is rendered through the default Grape error path (using its own `status` and `message`). Anything else — typos, `NoMethodError`, an unrelated `StandardError` — is treated as an internal error: it is exposed on `env['grape.exception']` for upstream Rack middleware to observe, and rendered to the API consumer as a generic `500 Internal Server Error`. This avoids leaking internal detail in the response body.

You can take control of the internal-error path by opting in with `rescue_from :internal_grape_exceptions`:

```ruby
class Twitter::API < Grape::API
  rescue_from :internal_grape_exceptions do |e|
    Sentry.capture_exception(e)
    error!({ message: 'Something went wrong' }, 500)
  end
end
```

When this handler is registered the framework hands the original exception to you, and you own the response shape and any logging. The framework deliberately does not log internal errors itself — it has no way to know your preferred format or destination.

A second raise inside the redispatched handler is not redispatched again — it goes straight to the framework's generic 500. This bounds the chain at one redispatch and prevents loops.

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

```ruby
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.

```ruby
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.

```ruby
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`).

```ruby
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.

```ruby
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`.

```ruby
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](https://guides.rubyonrails.org/action_controller_overview.html#rescue).

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

```ruby
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.

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

#### Rescuing exceptions inside namespaces

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

```ruby
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`.

#### Unrescuable Exceptions

`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.

#### Exceptions that should be rescued explicitly

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](https://ruby-doc.org/core/Exception.html).

## 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.

```ruby
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.

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

You can also set your own logger.

```ruby
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](https://github.com/aserafin/grape_logging) or [grape-middleware-logger](https://github.com/ridiculous/grape-middleware-logger) gems.

## API Formats

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.

```ruby
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`.

```ruby
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.

```ruby
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 calling `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.

```ruby
class Twitter::API < Grape::API
  post 'attachment' do
    filename = params[:file][:filename]
    content_type MIME::Types.type_for(filename)[0].to_s
    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.

```ruby
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.

```ruby
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.

```ruby
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`.

```ruby
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.

```ruby
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.

```ruby
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`
* `: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](https://github.com/rack) [here](https://github.com/rack/rack/blob/master/lib/rack/utils.rb#L567) will bypass serialization and the body entity - though there should be none - will not be modified.

### JSONP

Grape supports JSONP via [Rack::JSONP](https://github.com/rack/rack-contrib), part of the [rack-contrib](https://github.com/rack/rack-contrib) gem. Add `rack-contrib` to your `Gemfile`.

```ruby
require 'rack/contrib'

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

### CORS

Grape supports CORS via [Rack::CORS](https://github.com/cyu/rack-cors), part of the [rack-cors](https://github.com/cyu/rack-cors) gem. Add `rack-cors` to your `Gemfile`, then use the middleware in your config.ru file.

```ruby
require 'rack/cors'

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

run Twitter::API

```

## Content-type

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

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

## API Data Formats

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

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

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

```ruby
module CustomParser
  def self.call(object, env)
    { value: object.to_s }
  end
end
```

```ruby
content_type :txt, 'text/plain'
content_type :custom, 'text/custom'
parser :custom, CustomParser

put 'value' do
  params[:value]
end
```

You can invoke the above API as follows.

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

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']`.

## JSON and XML Processors

Grape uses `JSON` and `ActiveSupport::XmlMini` for JSON and XML parsing by default. It also detects and supports [multi_json](https://github.com/intridea/multi_json) and [multi_xml](https://github.com/sferik/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.

## RESTful Model Representations

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

### Grape Entities

Add the [grape-entity](https://github.com/ruby-grape/grape-entity) gem to your Gemfile.
Please refer to the [grape-entity documentation](https://github.com/ruby-grape/grape-entity/blob/master/README.md)
for more details.

The following example exposes statuses.

```ruby
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`.

```ruby
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.

```ruby
  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.

```ruby
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.

```ruby
get '/users' do
  present { id: 10, name: :dgz }, with: Grape::Presenters::Presenter
end
````
The response will be

```ruby
{
  id:   10,
  name: 'dgz'
}
```

It has the same result with

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

### Hypermedia and Roar

You can use [Roar](https://github.com/apotonick/roar) to render HAL or Collection+JSON with the help of [grape-roar](https://github.com/ruby-grape/grape-roar), which defines a custom JSON formatter and enables presenting entities with Grape's `present` keyword.

### Rabl

You can use [Rabl](https://github.com/nesquena/rabl) templates with the help of the [grape-rabl](https://github.com/ruby-grape/grape-rabl) gem, which defines a custom Grape Rabl formatter.

### Active Model Serializers

You can use [Active Model Serializers](https://github.com/rails-api/active_model_serializers) serializers with the help of the [grape-active_model_serializers](https://github.com/jrhe/grape-active_model_serializers) gem, which defines a custom Grape AMS formatter.

## Sending Raw or No Data

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

```ruby
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`.

```ruby
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.

If you want to empty the body with an HTTP status code other than `204 No Content`, you can override the status code after specifying `body false` as follows

```ruby
class API < Grape::API
  get '/' do
    body false
    status 304
  end
end
```

You can also set the response to a file with `sendfile`. This works with the [Rack::Sendfile](https://www.rubydoc.info/gems/rack/Rack/Sendfile) middleware to optimally send the file through your web server software.

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

To stream a file in chunks use `stream`

```ruby
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.

```ruby
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
```

## Authentication

### Basic Auth

Grape has built-in Basic 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.

```ruby
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
```

### Register custom middleware for authentication

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:

```ruby

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](https://github.com/doorkeeper-gem/doorkeeper), [warden-oauth2](https://github.com/opperator/warden-oauth2) or [rack-oauth2](https://github.com/nov/rack-oauth2) for OAuth2 support.

You can access the controller params, headers, and helpers through the context with the `#context` method inside any auth middleware inherited from `Grape::Middleware::Auth::Base`.

## 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 `prefix`, `version`, `namespace`, `method` and `params`. You can add custom route settings to the route metadata with `route_setting`.

```ruby
class TwitterAPI < Grape::API
  version 'v1'
  desc 'Includes custom settings.'
  route_setting :custom, key: 'value'
  get do

  end
end
```

Examine the routes at runtime.

```ruby
TwitterAPI::versions # yields [ 'v1', 'v2' ]
TwitterAPI::routes # yields an array of Grape::Route objects
TwitterAPI::routes[0].version # => 'v1'
TwitterAPI::routes[0].description # => 'Includes custom settings.'
TwitterAPI::routes[0].settings[:custom] # => { key: 'value' }
```

Note that `Route#route_xyz` methods have been deprecated since 0.15.0 and removed since 2.0.1.

Please use `Route#xyz` instead.

Note that difference of `Route#options` and `Route#settings`.

The `options` can be referred from your route, it should be set by specifying key and value on verb methods such as `get`, `post` and `put`.
The `settings` can also be referred from your route, but it should be set by specifying key and value on `route_setting`.

## Current Route and Endpoint

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

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

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

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

## Before, After and Finally

Blocks can be executed before or after every API call, using `before`, `after`, `before_validation` and `after_validation`.
If the API fails the `after` call will not be triggered, if you need code to execute for sure use the `finally`.

Before and after callbacks execute in the following order:

1. `before`
2. `before_validation`
3. _validations_
4. `after_validation` (upon successful validation)
5. _the API call_ (upon successful validation)
6. `after` (upon successful validation and API call)
7. `finally` (always)

Steps 4, 5 and 6 only happen if validation succeeds.

If a request for a resource is made with an unsupported HTTP method (returning HTTP 405) only `before` callbacks will be executed.  The remaining callbacks will be bypassed.

If a request for a resource is made that triggers the built-in `OPTIONS` handler, only `before` and `after` callbacks will be executed.  The remaining callbacks will be bypassed.

For example, using a simple `before` block to set a header.

```ruby
before do
  header 'X-Robots-Tag', 'noindex'
end
```

You can ensure a block of code runs after every request (including failures) with `finally`:

```ruby
finally do
  # this code will run after every request (successful or failed)
end
```

**Namespaces**

Callbacks apply to each API call within and below the current namespace:

```ruby
class MyAPI < Grape::API
  get '/' do
    "root - #{@blah}"
  end

  namespace :foo do
    before do
      @blah = 'blah'
    end

    get '/' do
      "root - foo - #{@blah}"
    end

    namespace :bar do
      get '/' do
        "root - foo - bar - #{@blah}"
      end
    end
  end
end
```

The behavior is then:

```bash
GET /           # 'root - '
GET /foo        # 'root - foo - blah'
GET /foo/bar    # 'root - foo - bar - blah'
```

Params on a `namespace` (or whichever alias you are using) will also be available when using `before_validation` or `after_validation`:

```ruby
class MyAPI < Grape::API
  params do
    requires :blah, type: Integer
  end
  resource ':blah' do
    after_validation do
      # if we reach this point validations will have passed
      @blah = declared(params, include_missing: false)[:blah]
    end

    get '/' do
      @blah.class
    end
  end
end
```

The behavior is then:

```bash
GET /123        # 'Integer'
GET /foo        # 400 error - 'blah is invalid'
```

**Versioning**

When a callback is defined within a version block, it's only called for the routes defined in that block.

```ruby
class Test < Grape::API
  resource :foo do
    version 'v1', :using => :path do
      before do
        @output ||= 'v1-'
      end
      get '/' do
        @output += 'hello'
      end
    end

    version 'v2', :using => :path do
      before do
        @output ||= 'v2-'
      end
      get '/' do
        @output += 'hello'
      end
    end
  end
end
```

The behavior is then:

```bash
GET /foo/v1       # 'v1-hello'
GET /foo/v2       # 'v2-hello'
```

**Altering Responses**

Using `present` in any callback allows you to add data to a response:

```ruby
class MyAPI < Grape::API
  format :json

  after_validation do
    present :name, params[:name] if params[:name]
  end

  get '/greeting' do
    present :greeting, 'Hello!'
  end
end
```

The behavior is then:

```bash
GET /greeting              # {"greeting":"Hello!"}
GET /greeting?name=Alan    # {"name":"Alan","greeting":"Hello!"}
```

Instead of altering a response, you can also terminate and rewrite it from any callback using `error!`, including `after`. This will cause all subsequent steps in the process to not be called. **This includes the actual api call and any callbacks**

## 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 your API needs to get part of an URL, for instance:

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

    end
  end
end
```

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

## Instance Variables

You can use instance variables to pass information across the various stages of a request. An instance variable set within a `before` validator is accessible within the endpoint's code and can also be utilized within the `rescue_from` handler.

```ruby
class TwitterAPI < Grape::API
  before do
    @var = 1
  end

  get '/' do
    puts @var # => 1
    raise
  end

  rescue_from :all do
    puts @var # => 1
  end
end
```

The values of instance variables cannot be shared among various endpoints within the same API. This limitation arises due to Grape generating a new instance for each request made. Consequently, instance variables set within an endpoint during one request differ from those set during a subsequent request, as they exist within separate instances.

```ruby
class TwitterAPI < Grape::API
  get '/first' do
    @var = 1
    puts @var # => 1
  end

  get '/second' do
    puts @var # => nil
  end
end
```

## Using Custom Middleware

### Grape Middleware

You can make a custom middleware by using `Grape::Middleware::Base`.
It's inherited from some grape official middlewares in fact.

For example, you can write a middleware to log application exception.

```ruby
class LoggingError < Grape::Middleware::Base
  def after
    return unless @app_response && @app_response[0] == 500
    env['rack.logger'].error("Raised error on #{env['PATH_INFO']}")
  end
end
```

Your middleware can overwrite application response as follows, except error case.

```ruby
class Overwriter < Grape::Middleware::Base
  def after
    [200, { 'Content-Type' => 'text/plain' }, ['Overwritten.']]
  end
end
```

You can add your custom middleware with `use`, that push the middleware onto the stack, and you can also control where the middleware is inserted using `insert`, `insert_before` and `insert_after`.

```ruby
class CustomOverwriter < Grape::Middleware::Base
  def after
    [200, { 'Content-Type' => 'text/plain' }, [@options[:message]]]
  end
end


class API < Grape::API
  use Overwriter
  insert_before Overwriter, CustomOverwriter, message: 'Overwritten again.'
  insert 0, CustomOverwriter, message: 'Overwrites all other middleware.'

  get '/' do
  end
end
```

You can access the controller params, headers, and helpers through the context with the `#context` method inside any middleware inherited from `Grape::Middleware::Base`.

### Rails Middleware

Note that when you're using Grape mounted on Rails you don't have to use Rails middleware because it's already included into your middleware stack.
You only have to implement the helpers to access the specific `env` variable.

If you are using a custom application that is inherited from `Rails::Application` and need to insert a new middleware among the ones initiated via Rails, you will need to register it manually in your custom application class.

```ruby
class Company::Application < Rails::Application
  config.middleware.insert_before(Rack::Attack, Middleware::ApiLogger)
end
```

### Remote IP

By default you can access remote IP with `request.ip`. This is the remote IP address implemented by Rack. Sometimes it is desirable to get the remote IP [Rails-style](http://stackoverflow.com/questions/10997005/whats-the-difference-between-request-remote-ip-and-request-ip-in-rails) with `ActionDispatch::RemoteIp`.

Add `gem 'actionpack'` to your Gemfile and `require 'action_dispatch/middleware/remote_ip.rb'`. Use the middleware in your API and expose a `client_ip` helper. See [this documentation](http://api.rubyonrails.org/classes/ActionDispatch/RemoteIp.html) for additional options.

```ruby
class API < Grape::API
  use ActionDispatch::RemoteIp

  helpers do
    def client_ip
      env['action_dispatch.remote_ip'].to_s
    end
  end

  get :remote_ip do
    { ip: client_ip }
  end
end
```

## Writing Tests

### Writing Tests with Rack

Use `rack-test` and define your API as `app`.

#### RSpec

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

```ruby


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

  def app
    Twitter::API
  end

  context 'GET /api/statuses/public_timeline' do
    it 'returns an empty array of statuses' do
      get '/api/statuses/public_timeline'
      expect(last_response.status).to eq(200)
      expect(JSON.parse(last_response.body)).to eq []
    end
  end
  context 'GET /api/statuses/:id' do
    it 'returns a status by id' do
      status = Status.create!
      get "/api/statuses/#{status.id}"
      expect(last_response.body).to eq status.to_json
    end
  end
end
```

There's no standard way of sending arrays of objects via an HTTP GET, so POST JSON data and specify the correct content-type.

```ruby
describe Twitter::API do
  context 'POST /api/statuses' do
    it 'creates many statuses' do
      statuses = [{ text: '...' }, { text: '...'}]
      post '/api/statuses', statuses.to_json, 'CONTENT_TYPE' => 'application/json'
      expect(last_response.body).to eq 201
    end
  end
end
```

#### Airborne

You can test with other RSpec-based frameworks, including [Airborne](https://github.com/brooklynDev/airborne), which uses `rack-test` to make requests.

```ruby
require 'airborne'

Airborne.configure do |config|
  config.rack_app = Twitter::API
end

describe Twitter::API do
  context 'GET /api/statuses/:id' do
    it 'returns a status by id' do
      status = Status.create!
      get "/api/statuses/#{status.id}"
      expect_json(status.as_json)
    end
  end
end
```

#### MiniTest

```ruby
require 'test_helper'

class Twitter::APITest < MiniTest::Test
  include Rack::Test::Methods

  def app
    Twitter::API
  end

  def test_get_api_statuses_public_timeline_returns_an_empty_array_of_statuses
    get '/api/statuses/public_timeline'
    assert last_response.ok?
    assert_equal [], JSON.parse(last_response.body)
  end

  def test_get_api_statuses_id_returns_a_status_by_id
    status = Status.create!
    get "/api/statuses/#{status.id}"
    assert_equal status.to_json, last_response.body
  end
end
```

### Writing Tests with Rails

#### RSpec

```ruby
describe Twitter::API do
  context 'GET /api/statuses/public_timeline' do
    it 'returns an empty array of statuses' do
      get '/api/statuses/public_timeline'
      expect(response.status).to eq(200)
      expect(JSON.parse(response.body)).to eq []
    end
  end
  context 'GET /api/statuses/:id' do
    it 'returns a status by id' do
      status = Status.create!
      get "/api/statuses/#{status.id}"
      expect(response.body).to eq status.to_json
    end
  end
end
```

In Rails, HTTP request tests would go into the `spec/requests` 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/rails_helper.rb`.

```ruby
RSpec.configure do |config|
  config.include RSpec::Rails::RequestExampleGroup, type: :request, file_path: /spec\/api/
end
```

#### MiniTest

```ruby
class Twitter::APITest < ActiveSupport::TestCase
  include Rack::Test::Methods

  def app
    Rails.application
  end

  test 'GET /api/statuses/public_timeline returns an empty array of statuses' do
    get '/api/statuses/public_timeline'
    assert last_response.ok?
    assert_equal [], JSON.parse(last_response.body)
  end

  test 'GET /api/statuses/:id returns a status by id' do
    status = Status.create!
    get "/api/statuses/#{status.id}"
    assert_equal status.to_json, last_response.body
  end
end
```

### Stubbing Helpers

Because helpers are mixed in based on the context when an endpoint is defined, it can be difficult to stub or mock them for testing. `Grape::Endpoint.before_each` allows you to define behavior on the endpoint that will run before every request.

This feature is provided by `Grape::Testing`, a standalone module intended for test environments only. Add it to your test helper:

```ruby
require 'grape/testing'
```

Then use it in your tests:

```ruby
describe 'an endpoint that needs helpers stubbed' do
  before do
    Grape::Endpoint.before_each do |endpoint|
      allow(endpoint).to receive(:helper_name).and_return('desired_value')
    end
  end

  after do
    Grape::Endpoint.reset_before_each
  end

  it 'stubs the helper' do

  end
end
```

## Reloading API Changes in Development

### Reloading in Rack Applications

Use [grape-reload](https://github.com/AlexYankee/grape-reload).

### Reloading in Rails Applications

#### Rails 7+ (Zeitwerk)

Rails 7+ uses [Zeitwerk](https://github.com/fxn/zeitwerk) as the default autoloader, which automatically handles reloading of code in development mode without any additional configuration.

If your API files are in `app/api`, Zeitwerk will automatically autoload and reload them. No additional configuration is needed.

If you encounter issues with reloading, ensure that:

1. Your API files follow Zeitwerk naming conventions (file names should match class names).
2. The `config.enable_reloading` is set to `true` in `config/environments/development.rb` (this is the default).

For troubleshooting autoloading issues, have a look at the [Rails documentation](https://guides.rubyonrails.org/autoloading_and_reloading_constants.html#troubleshooting).

See the [Rails Autoloading and Reloading Constants guide](https://guides.rubyonrails.org/autoloading_and_reloading_constants.html) for more information.

#### Rails 6 and Earlier

For Rails versions before 7, you need to configure reloading manually.

Add API paths to `config/application.rb`.

```ruby
# Auto-load API and its subdirectories
config.paths.add File.join('app', 'api'), glob: File.join('**', '*.rb')
config.autoload_paths += Dir[Rails.root.join('app', 'api', '*')]
```

Create `config/initializers/reload_api.rb`.

```ruby
if Rails.env.development?
  ActiveSupport::Dependencies.explicitly_unloadable_constants << 'Twitter::API'

  api_files = Dir[Rails.root.join('app', 'api', '**', '*.rb')]
  api_reloader = ActiveSupport::FileUpdateChecker.new(api_files) do
    Rails.application.reload_routes!
  end
  ActiveSupport::Reloader.to_prepare do
    api_reloader.execute_if_updated
  end
end
```

See [StackOverflow #3282655](http://stackoverflow.com/questions/3282655/ruby-on-rails-3-reload-lib-directory-for-each-request/4368838#4368838) for more information.

## Performance Monitoring

### Active Support Instrumentation

Grape has built-in support for [ActiveSupport::Notifications](http://api.rubyonrails.org/classes/ActiveSupport/Notifications.html) which provides simple hook points to instrument key parts of your application.


#### Hook Points

The following hook points are currently supported:

##### endpoint_run.grape

The main execution of an endpoint, includes filters and rendering.

* *endpoint* - The endpoint instance

##### endpoint_render.grape

The execution of the main content block of the endpoint.

* *endpoint* - The endpoint instance

##### endpoint_run_filters.grape

* *endpoint* - The endpoint instance
* *filters* - The filters being executed
* *type* - The type of filters (before, before_validation, after_validation, after)

##### endpoint_run_validators.grape

The execution of validators.

* *endpoint* - The endpoint instance
* *validators* - The validators being executed
* *request* - The request being validated

##### format_response.grape

Serialization or template rendering.

* *env* - The request environment
* *formatter* - The formatter object (e.g., `Grape::Formatter::Json`)

See the [ActiveSupport::Notifications documentation](http://api.rubyonrails.org/classes/ActiveSupport/Notifications.html) for information on how to subscribe to these events.

#### Subscribe to Hooks

Once subscribed to the instrumentation, you can intercept the events reported above.

```ruby
ActiveSupport::Notifications.subscribe(/<api_path>/) do |name, start, finish, id, payload|
  # your code to intercept the notification
end
```

The request data, the API’s internal data, and the response can be retrieved from the payload.

You can use `payload.fetch(:endpoint)` or directly `payload[:endpoint]`.

The `:endpoint` contains the data currently being processed, and access to attributes such as `body`, `request`, `params`, `headers`, `cookies` and `response_cookies`

For example, `payload[:endpoint].body` provides the current state of the response.

```ruby
ActiveSupport::Notifications.subscribe(/v1/) do |name, start, finish, id, payload|
  hook_record = {
    hook: name
    status: payload[:env]&.dig("api.endpoint")&.status
    format: payload[:env]&.dig("api.format")
    body: payload[:endpoint]&.body
    duration: (finish - start) * 1000
  }
  # your code to save the notification
end
```

### Monitoring Products

Grape integrates with following third-party tools:

* **New Relic** - [built-in support](https://docs.newrelic.com/docs/agents/ruby-agent/frameworks/grape-instrumentation) from v3.10.0 of the official [newrelic_rpm](https://github.com/newrelic/rpm) gem, also [newrelic-grape](https://github.com/xinminlabs/newrelic-grape) gem
* **Librato Metrics** - [grape-librato](https://github.com/seanmoon/grape-librato) gem
* **Rails Performance** - [rails_performance](https://github.com/igorkasyanchuk/rails_performance) gem
* **[Skylight](https://www.skylight.io/)** - [skylight](https://github.com/skylightio/skylight-ruby) gem, [documentation](https://docs.skylight.io/grape/)
* **[AppSignal](https://www.appsignal.com)** - [appsignal-ruby](https://github.com/appsignal/appsignal-ruby) gem, [documentation](http://docs.appsignal.com/getting-started/supported-frameworks.html#grape)
* **[ElasticAPM](https://www.elastic.co/products/apm)** - [elastic-apm](https://github.com/elastic/apm-agent-ruby) gem, [documentation](https://www.elastic.co/guide/en/apm/agent/ruby/3.x/getting-started-rack.html#getting-started-grape)
* **[Datadog APM](https://docs.datadoghq.com/tracing/)** - [ddtrace](https://github.com/datadog/dd-trace-rb) gem, [documentation](https://docs.datadoghq.com/tracing/setup_overview/setup/ruby/#grape)

## Contributing to Grape

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

See [CONTRIBUTING](CONTRIBUTING.md).

## Security

See [SECURITY](SECURITY.md) for details.

## License

MIT License. See [LICENSE](LICENSE) for details.

## Copyright

Copyright (c) 2010-2020 Michael Bleigh, Intridea Inc. and Contributors.