openapi_first

openapi_first is a Ruby gem for request / response validation and contract-testing against an OpenAPI 3.0 or 3.1 API description. It makes an APIFirst workflow easy and reliable.

You can use openapi_first on production for request validation and in your tests to avoid API drift with it's request/response validation and coverage features.

Contents

• Rack Middlewares
  • Request validation
  • Response validation
• Contract testing
  • Coverage
  • Test assertions
• Manual use
• Framework integration
• Configuration
• Hooks
• Alternatives
• Development
  • Benchmarks
  • Contributing

Rack Middlewares

Request validation

The request validation middleware returns a 4xx if the request is invalid or not defined in the API description. It adds a request object to the current Rack environment at env[OpenapiFirst::REQUEST] with the request parameters parsed exactly as described in your API description plus access to meta information from your API description. See Manual use for more details about that object.

use OpenapiFirst::Middlewares::RequestValidation, 'openapi.yaml'

# Pass `raise_error: true` to raise an error if request is invalid:
use OpenapiFirst::Middlewares::RequestValidation, 'openapi.yaml', raise_error: true

Error responses

openapi_first produces a useful machine readable error response that can be customized. The default response looks like this. See also RFC 9457.

http-status: 400
content-type: "application/problem+json"

{
  "title": "Bad Request Body",
  "status": 400,
  "errors": [
    {
      "message": "value at `/data/name` is not a string",
      "pointer": "/data/name",
      "code": "string"
    },
    {
      "message": "number at `/data/numberOfLegs` is less than: 2",
      "pointer": "/data/numberOfLegs",
      "code": "minimum"
    },
    {
      "message": "object at `/data` is missing required properties: mandatory",
      "pointer": "/data",
      "code": "required"
    }
  ]
}

openapi_first offers a JSON:API error response by passing error_response: :jsonapi:

use OpenapiFirst::Middlewares::RequestValidation, 'openapi.yaml, error_response: :jsonapi'

See details of JSON:API error response

// http-status: 400
// content-type: "application/vnd.api+json"

{
  "errors": [
    {
      "status": "400",
      "source": {
        "pointer": "/data/name"
      },
      "title": "value at `/data/name` is not a string",
      "code": "string"
    },
    {
      "status": "400",
      "source": {
        "pointer": "/data/numberOfLegs"
      },
      "title": "number at `/data/numberOfLegs` is less than: 2",
      "code": "minimum"
    },
    {
      "status": "400",
      "source": {
        "pointer": "/data"
      },
      "title": "object at `/data` is missing required properties: mandatory",
      "code": "required"
    }
  ]
}

Custom error responses

You can build your own custom error response with error_response: MyCustomClass that implements OpenapiFirst::ErrorResponse. You can define custom error responses globally by including / implementing OpenapiFirst::ErrorResponse and register it via OpenapiFirst.register_error_response(my_name, MyCustomErrorResponse) and set error_response: my_name.

Response validation

This middleware raises an error by default if the response is not valid. This can be useful in a test or staging environment, especially if you are adopting OpenAPI for an existing implementation.

use OpenapiFirst::Middlewares::ResponseValidation, 'openapi.yaml' if ENV['RACK_ENV'] == 'test'

# Pass `raise_error: false` to not raise an error:
use OpenapiFirst::Middlewares::ResponseValidation, 'openapi.yaml', raise_error: false

If you are adopting OpenAPI you can use these options together with hooks to get notified about requests/responses that do match your API description.

Contract Testing

Here are two aspects of contract testing: Validation and Coverage

Validation

By validating requests and responses, you can avoid that your API implementation processes requests or returns responses that don't match your API description. You can use test assertions or rack middlewares or manual validation to validate requests and responses with openapi_first.

Coverage

To make sure your whole API description is implemented, openapi_first ships with a coverage feature.

Note

This is a brand new feature. ✨ Your feedback is very welcome.

This feature tracks all requests/responses that are validated via openapi_first and tells you about which request/responses are missing. Here is how to set it up with rack-test:

1. Register all OpenAPI documents to track coverage for. This should go at the top of your test helper file before loading your application code.

require 'openapi_first'
OpenapiFirst::Test.setup do |test|
  test.register('openapi/openapi.yaml')
  test.minimum_coverage = 100 # (Optional) Setting this will lead to an `exit 2` if coverage is below minimum
  test.skip_response_coverage { it.status == '500' } # (Optional) Skip certain responses
end

2. Add an app method to your tests, which wraps your application with silent request / response validation. This validates all requests/responses in your test run. (✷1)

def app
  OpenapiFirst::Test.app(MyApp)
end

3. Run your tests. The Coverage feature will tell you about missing request/responses.

Or you can generate a Module and include it in your rspec spec_helper.rb:

config.include OpenapiFirst::Test::Methods[MyApp], type: :request

(✷1): It does not matter what method of openapi_first you use to validate requests/responses. Instead of using OpenapiFirstTest.app to wrap your application, you could also use the middlewares or test assertion method, but you would have to do that for all requests/responses defined in your API description to make coverage work.

Test assertions

openapi_first ships with a simple but powerful Test method to run request and response validation in your tests without using the middlewares. This is designed to be used with rack-test or Ruby on Rails integration tests or request specs.

Here is how to set it up for Rails integration tests:

Inside your test:

# test/integration/trips_api_test.rb
require 'test_helper'

class TripsApiTest < ActionDispatch::IntegrationTest
  include OpenapiFirst::Test::Methods

  test 'GET /trips' do
    get '/trips',
        params: { origin: 'efdbb9d1-02c2-4bc3-afb7-6788d8782b1e', destination: 'b2e783e1-c824-4d63-b37a-d8d698862f1d',
                  date: '2024-07-02T09:00:00Z' }

    assert_api_conform(status: 200)
    # assert_api_conform(status: 200, api: :v1) # Or this if you have multiple API descriptions
  end
end

Manual use

Load the API description:

require 'openapi_first'

definition = OpenapiFirst.load('openapi.yaml')

Validate request

validated_request = definition.validate_request(rack_request)

# Inspect the request and access parsed parameters
validated_request.valid?
validated_request.invalid?
validated_request.error # => Failure object or nil
validated_request.parsed_body # => The parsed request body (Hash)
validated_request.parsed_query # A Hash of query parameters that are defined in the API description, parsed exactly as described.
validated_request.parsed_path_parameters
validated_request.parsed_headers
validated_request.parsed_cookies
validated_request.parsed_params # Merged parsed path, query parameters and request body
# Access the Openapi 3 Operation Object Hash
validated_request.operation['x-foo']
validated_request.operation['operationId'] => "getStuff"
# or the whole request definition
validated_request.request_definition.path # => "/pets/{petId}"
validated_request.request_definition.operation_id # => "showPetById"

# Or you can raise an exception if validation fails:
definition.validate_request(rack_request, raise_error: true) # Raises OpenapiFirst::RequestInvalidError or OpenapiFirst::NotFoundError if request is invalid

Validate response

validated_response = definition.validate_response(rack_request, rack_response)

# Inspect the response and access parsed parameters and
validated_response.valid?
validated_response.invalid?
validated_response.error # => Failure object or nil
validated_response.status # => 200
validated_response.parsed_body
validated_response.parsed_headers

# Or you can raise an exception if validation fails:
definition.validate_response(rack_request,rack_response, raise_error: true) # Raises OpenapiFirst::ResponseInvalidError or OpenapiFirst::ResponseNotFoundError

Configuration

You can configure default options globally:

OpenapiFirst.configure do |config|
  # Specify which plugin is used to render error responses returned by the request validation middleware (defaults to :default)
  config.request_validation_error_response = :jsonapi
  # Configure if the request validation middleware should raise an exception (defaults to false)
  config.request_validation_raise_error = true
end

or configure per instance:

OpenapiFirst.load('openapi.yaml') do |config|
  config.request_validation_error_response = :jsonapi
end

Hooks

You can integrate your code at certain points during request/response validation via hooks.

Available hooks:

• after_request_validation
• after_response_validation
• after_request_parameter_property_validation
• after_request_body_property_validation

Setup per per instance:

OpenapiFirst.load('openapi.yaml') do |config|
  config.after_request_validation do |validated_request|
    validated_request.valid? # => true / false
  end
  config.after_response_validation do |validated_response, request|
    if validated_response.invalid?
      warn "#{request.request_method} #{request.path}: #{validated_response.error.message}"
    end
  end
end

Setup globally:

OpenapiFirst.configure do |config|
  config.after_request_parameter_property_validation do |data, property, property_schema|
    data[property] = Date.iso8601(data[property]) if property_schema['format'] == 'date'
  end
end

Framework integration

Using rack middlewares is supported in probably all Ruby web frameworks. If you are using Ruby on Rails for example, you can add the request validation middleware globally in config/application.rb or inside specific controllers.

The contract testing feature is designed to be used via rack-test, which should be compatible all Ruby web frameworks as well.

That aside, closer integration with specific frameworks like Sinatra, Hanami, Roda or Rails would be great. If you have ideas, pain points or PRs, please don't hesitate to share.

Alternatives

This gem was inspired by committee (Ruby) and Connexion (Python). Here is a feature comparison between openapi_first and committee.

Development

Run bin/setup to install dependencies.

See bundle exec rake to run the linter and the tests.

Run bundle exec rspec to run the tests only.

Benchmarks

Results

Run benchmarks:

cd benchmarks
bundle
bundle exec ruby benchmarks.rb

Contributing

If you have a question or an idea or found a bug, don't hesitate to create an issue on Github or Codeberg or say hi on Mastodon (ruby.social).

Pull requests are very welcome as well, of course. Feel free to create a "draft" pull request early on, even if your change is still work in progress. 🤗