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	# Open API Spex
	[![Build Status](https://travis-ci.com/open-api-spex/open_api_spex.svg?branch=master)](https://travis-ci.com/open-api-spex/open_api_spex)
	[![Hex.pm](https://img.shields.io/hexpm/v/open_api_spex.svg)](https://hex.pm/packages/open_api_spex)


	Leverage Open Api Specification 3 (swagger) to document, test, validate and explore your Plug and Phoenix APIs.

	- Generate and serve a JSON Open Api Spec document from your code
	- Use the spec to cast request params to well defined schema structs
	- Validate params against schemas, eliminate bad requests before they hit your controllers
	- Validate responses against schemas in tests, ensuring your docs are accurate and reliable
	- Explore the API interactively with with [SwaggerUI](https://swagger.io/swagger-ui/)

	Full documentation available on [hexdocs](https://hexdocs.pm/open_api_spex/)

	## Installation

	The package can be installed by adding `open_api_spex` to your list of dependencies in `mix.exs`:

	```elixir
	def deps do
	[
	{:open_api_spex, "~> 3.4"}
	]
	end
	```

	## Generate Spec

	Start by adding an `ApiSpec` module to your application to populate an `OpenApiSpex.OpenApi` struct.

	```elixir
	defmodule MyAppWeb.ApiSpec do
	alias OpenApiSpex.{OpenApi, Server, Info, Paths}
	alias MyAppWeb.{Endpoint, Router}
	@behaviour OpenApi

	@impl OpenApi
	def spec do
	%OpenApi{
	servers: [
	# Populate the Server info from a phoenix endpoint
	Server.from_endpoint(Endpoint)
	],
	info: %Info{
	title: "My App",
	version: "1.0"
	},
	# populate the paths from a phoenix router
	paths: Paths.from_router(Router)
	}
	\|> OpenApiSpex.resolve_schema_modules() # discover request/response schemas from path specs
	end
	end
	```

	For each plug (controller) that will handle api requests, add an `open_api_operation` callback.
	It will be passed the plug opts that were declared in the router, this will be the action for a phoenix controller. The callback populates an `OpenApiSpex.Operation` struct describing the plug/action.

	```elixir
	defmodule MyAppWeb.UserController do
	alias OpenApiSpex.Operation
	alias MyAppWeb.Schemas.UserResponse

	@spec open_api_operation(atom) :: Operation.t()
	def open_api_operation(action) do
	operation = String.to_existing_atom("#{action}_operation")
	apply(__MODULE__, operation, [])
	end

	@spec show_operation() :: Operation.t()
	def show_operation() do
	%Operation{
	tags: ["users"],
	summary: "Show user",
	description: "Show a user by ID",
	operationId: "UserController.show",
	parameters: [
	Operation.parameter(:id, :path, :integer, "User ID", example: 123, required: true)
	],
	responses: %{
	200 => Operation.response("User", "application/json", UserResponse)
	}
	}
	end

	# Controller's `show` action
	def show(conn, %{id: id}) do
	{:ok, user} = MyApp.Users.find_by_id(id)
	json(conn, 200, user)
	end

	# For examples of other action operations, see
	# https://github.com/open-api-spex/open_api_spex/blob/master/examples/phoenix_app/lib/phoenix_app_web/controllers/user_controller.ex
	end
	```

	Declare the JSON schemas for request/response bodies in a `Schemas` module:
	Each module should implement the `OpenApiSpex.Schema` behaviour.
	The only callback is `schema/0`, which should return an `OpenApiSpex.Schema` struct.
	You may optionally declare a struct, linked to the JSON schema through the `x-struct` extension property.
	See `OpenApiSpex.schema/1` macro for a convenient way to reduce some boilerplate.

	```elixir
	defmodule MyAppWeb.Schemas do
	alias OpenApiSpex.Schema

	defmodule User do
	OpenApiSpex.schema(%{
	title: "User",
	description: "A user of the app",
	type: :object,
	properties: %{
	id: %Schema{type: :integer, description: "User ID"},
	name: %Schema{type: :string, description: "User name", pattern: ~r/[a-zA-Z][a-zA-Z0-9_]+/},
	email: %Schema{type: :string, description: "Email address", format: :email},
	birthday: %Schema{type: :string, description: "Birth date", format: :date},
	inserted_at: %Schema{
	type: :string,
	description: "Creation timestamp",
	format: :"date-time"
	},
	updated_at: %Schema{type: :string, description: "Update timestamp", format: :"date-time"}
	},
	required: [:name, :email],
	example: %{
	"id" => 123,
	"name" => "Joe User",
	"email" => "joe@gmail.com",
	"birthday" => "1970-01-01T12:34:55Z",
	"inserted_at" => "2017-09-12T12:34:55Z",
	"updated_at" => "2017-09-13T10:11:12Z"
	}
	})
	end

	defmodule UserResponse do
	require OpenApiSpex

	OpenApiSpex.schema(%{
	title: "UserResponse",
	description: "Response schema for single user",
	type: :object,
	properties: %{
	data: User
	},
	example: %{
	"data" => %{
	"id" => 123,
	"name" => "Joe User",
	"email" => "joe@gmail.com",
	"birthday" => "1970-01-01T12:34:55Z",
	"inserted_at" => "2017-09-12T12:34:55Z",
	"updated_at" => "2017-09-13T10:11:12Z"
	}
	}
	})
	end
	end
	```

	For more examples of schema definitions, see the [sample Phoenix app](https://github.com/open-api-spex/open_api_spex/blob/master/examples/phoenix_app/lib/phoenix_app_web/schemas.ex)

	Now you can create a mix task to write the swagger file to disk:

	```elixir
	defmodule Mix.Tasks.MyApp.OpenApiSpec do
	def run([output_file]) do
	json =
	MyAppWeb.ApiSpec.spec()
	\|> Jason.encode!(pretty: true)

	:ok = File.write!(output_file, json)
	end
	end
	```

	Generate the file with: `mix myapp.openapispec spec.json`

	## Serve Spec

	To serve the API spec from your application, first add the `OpenApiSpex.Plug.PutApiSpec` plug somewhere in the pipeline.

	```elixir
	pipeline :api do
	plug OpenApiSpex.Plug.PutApiSpec, module: MyAppWeb.ApiSpec
	end
	```

	Now the spec will be available for use in downstream plugs.
	The `OpenApiSpex.Plug.RenderSpec` plug will render the spec as JSON:

	```elixir
	scope "/api" do
	pipe_through :api
	resources "/users", MyAppWeb.UserController, only: [:create, :index, :show]
	get "/openapi", OpenApiSpex.Plug.RenderSpec, []
	end
	```

	## Serve Swagger UI

	Once your API spec is available through a route, the `OpenApiSpex.Plug.SwaggerUI` plug can be used to serve a SwaggerUI interface. The `path:` plug option must be supplied to give the path to the API spec.

	All JavaScript and CSS assets are sourced from cdnjs.cloudflare.com, rather than vendoring into this package.

	```elixir
	scope "/" do
	pipe_through :browser # Use the default browser stack

	get "/", MyAppWeb.PageController, :index
	get "/swaggerui", OpenApiSpex.Plug.SwaggerUI, path: "/api/openapi"
	end

	scope "/api" do
	pipe_through :api

	resources "/users", MyAppWeb.UserController, only: [:create, :index, :show]
	get "/openapi", OpenApiSpex.Plug.RenderSpec, []
	end
	```

	## Validating and Casting Params

	OpenApiSpex can automatically validate requests before they reach the controller action function. Or if you prefer,
	you can explicitly call on OpenApiSpex to cast and validate the params within the controller action. This section
	describes the former.

	First, the `plug OpenApiSpex.Plug.PutApiSpec` needs to be called in the Router, as described above.

	Add the `OpenApiSpex.Plug.CastAndValidate` plug to a controller to validate request parameters, and to cast to Elixir types defined by the operation schema.

	```elixir
	plug OpenApiSpex.Plug.CastAndValidate
	```

	The `operation_id` can be inferred when used from a Phoenix controller from the contents of `conn.private`.

	```elixir
	defmodule MyAppWeb.UserController do
	use MyAppWeb, :controller
	alias OpenApiSpex.Operation
	alias MyAppWeb.Schemas.{User, UserRequest, UserResponse}

	plug OpenApiSpex.Plug.CastAndValidate

	def open_api_operation(action) do
	apply(__MODULE__, :"#{action}_operation", [])
	end

	def create_operation do
	import Operation
	%Operation{
	tags: ["users"],
	summary: "Create user",
	description: "Create a user",
	operationId: "UserController.create",
	parameters: [
	parameter(:id, :query, :integer, "user ID")
	],
	requestBody: request_body("The user attributes", "application/json", UserRequest),
	responses: %{
	201 => response("User", "application/json", UserResponse)
	}
	}
	end

	def create(conn = %{body_params: %UserRequest{user: %User{name: name, email: email, birthday: birthday = %Date{}}}}, %{id: id}) do
	# conn.body_params cast to UserRequest struct
	# conn.params.id cast to integer
	end
	end
	```

	Now the client will receive a 422 response whenever the request fails to meet the validation rules from the api spec.

	The response body will include the validation error message:

	```json
	{
	"errors": [
	{
	"message": "Invalid format. Expected :date",
	"source": {
	"pointer": "/data/birthday"
	},
	"title": "Invalid value"
	}
	]
	}
	```

	See also `OpenApiSpex.cast_and_validate/3` and `OpenApiSpex.Cast.cast/3` for more examples outside of a `plug` pipeline.

	## Validate Examples

	As schemas evolve, you may want to confirm that the examples given match the schemas.
	Use the `OpenApiSpex.Test.Assertions` module to assert on schema validations.

	```elixir
	use ExUnit.Case
	import OpenApiSpex.Test.Assertions

	test "UsersResponse example matches schema" do
	api_spec = MyAppWeb.ApiSpec.spec()
	schema = MyAppWeb.Schemas.UsersResponse.schema()
	assert_schema(schema.example, "UsersResponse", api_spec)
	end
	```

	## Validate Responses

	API responses can be tested against schemas using `OpenApiSpex.Test.Assertions` also:

	```elixir
	use MyAppWeb.ConnCase
	import OpenApiSpex.Test.Assertions

	test "UserController produces a UsersResponse", %{conn: conn} do
	api_spec = MyAppWeb.ApiSpec.spec()
	json =
	conn
	\|> get(user_path(conn, :index))
	\|> json_response(200)

	assert_schema(json, "UsersResponse", api_spec)
	end
	```

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