LambdaOpenApi

This gem is a light weight DSL that works with rspec to allow developers to generate an OpenAPI (swagger) file based an AWS Lambda invoked by API Gateway. It works by writing a simple unit test for your lambda's code. When the test is executed, the input event and returned response are captured and used to build an OpenAPI file.

Installation

Add to your gem file:

group :test do
  gem 'rspec'
  gem 'lambda_open_api'
end

Create an initializer file to configure the gem.

LambdaOpenApi.configure do |config|
  config.file_name = "open_api.json"
  config.title = "My Example Api"
  config.description = "About this api"
  config.version = "1"
  config.host = "https://my_example_api.com"
  config.schemes = ["https"]
  config.consumes = ["application/json"] 
  config.produces = ["application/json"]
end

Include the gem in your spec hepler file spec/spec_helper.rb or any file that gets loaded before rspec is ran.

require "lambda_open_api"

RSpec.configure do |config|
  # ...
  # the rest of your normal config
  #...
end

That's it!

Usage

Let's say we have a lmabda that looks something like this.

require_relative '../spec_helper'

class MyLambda
  def self.process(event:, context: {})
    body = JSON.parse(event["body"])

    # do something useful

    {
      statusCode: 200,
      body: { message: "processed", name: body["name"], email: body["email"] }
    }
  end
end

We can write a spec file like this:

RSpec.describe MyLambda do

  resource "Users" do

    get "users/{id}" do
      path_summery "Some very high level details"
      path_description "Some more details about this path"

      example_case "200" do
        parameter({id: 1})

        event_body({
          name: "Timbo Baggins",
          email: "tbaggings@hotmail.com"
        }.to_json)

        event_headers({
          "Api-Key" => "the_api_key"
        })

        run_example do
          expect(lambda_response[:body]).to eq({:message => "processed", :email=>"tbaggings@hotmail.com", :name=>"Timbo Baggins"})
          expect(lambda_response[:statusCode]).to eq(200)
        end
      end
    end

  end
end

Run rspec

rspec

An Open Api file will be generated and saved that looks like this:

{
  "swagger": "2.0",
  "info": {
    "title": "My Example Api",
    "description": "About this api",
    "version": "1"
  },
  "host": "https://my_example.com",
  "schemes": [
    "https"
  ],
  "consumes": [
    "application/json"
  ],
  "produces": [
    "application/json"
  ],
  "paths": {
    "users/{id}": {
      "get": {
        "tags": [
          "Users"
        ],
        "summary": "Some very high level details",
        "description": "Some more details about this path",
        "consumes": [
          "application/json"
        ],
        "produces": [
          "application/json"
        ],
        "parameters": [
          {
            "name": "id",
            "in": "path",
            "description": "",
            "required": true,
            "type": "integer"
          },
          {
            "name": "body",
            "in": "body",
            "description": "",
            "required": false,
            "schema": {
              "description": "",
              "type": "object",
              "properties": {
                "name": {
                  "type": "string"
                },
                "email": {
                  "type": "string"
                }
              },
              "required": [

              ]
            }
          }
        ],
        "responses": {
          "200": {
            "examples": {
              "application/json": {
                "statusCode": 200,
                "body": {
                  "message": "processed",
                  "name": "Timbo Baggins",
                  "email": "tbaggings@hotmail.com"
                }
              }
            }
          }
        }
      }
    }
  }
}

From https://editor-next.swagger.io/

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/Timothyjb/lambda_open_api.

License

The gem is available as open source under the terms of the MIT License.