openapi_first

OpenapiFirst helps to implement HTTP APIs based on an OpenAPI API description. It supports OpenAPI 3.0 and 3.1. It offers request and response validation and it ensures that your implementation follows exactly the API description.

Contents

• Manual use
  • Validate request
  • Validate response
• Rack Middlewares
  • Request validation
  • Response validation
• Test assertions
• Framework integration
• Configuration
• Hooks
• Alternatives
• Development
  • Benchmarks
  • Contributing

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

OpenapiFirst uses multi_json.

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 exaclty 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, spec: 'openapi.yaml'

Options

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 as well:

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

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.

readOnly / writeOnly properties

Request validation fails if request includes a property with readOnly: true.

Response validation fails if response body includes a property with writeOnly: true.

Response validation

This middleware is especially useful when testing. It raises an error by default if the response is not valid.

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

Options

Test assertions

openapi_first ships with a simple but powerful Test module 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:

# test_helper.rb
require 'openapi_first/test'
OpenapiFirst::Test.register('openapi/v1.openapi.yaml')

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)
  end
end

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 propert_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.

When running integration tests (or request specs when using rspec), it makes sense to add the response validation middleware to config/environments/test.rb:

config.middleware.use OpenapiFirst::Middlewares::ResponseValidation,
  spec: 'api/openapi.yaml'

That way you don't have to call specific test assertions to make sure your API matches the OpenAPI document. There is no need to run response validation on production if your test coverage is decent.

Alternatives

This gem was inspired by committe (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 or start a discussion.

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. 🤗