Oasis

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Introduction

Background

The OpenAPI Specification (OAS) defines a standard, programming language-agnostic interface description for REST APIs, which allows both humans and computers to discover and understand the capabilities of a service without requiring access to source code, additional documentation, or inspection of network traffic. When properly defined via OpenAPI, a consumer can understand and interact with the remote service with a minimal amount of implementation logic. Similar to what interface descriptions have done for lower-level programming, the OpenAPI Specification removes guesswork in calling a service.

Oasis is:

Base on Plug's implements, according to the OpenAPI Specification to generate server's router and the all well defined HTTP request handlers, since the OAS defines a detailed collection of data types by JSON Schema Specification, Oasis leverages this and focuses on the types conversion and validation to the parameters of the HTTP request.

  • Maintain an OpenAPI Specification document(in YAML or JSON) is the first priority
  • Generate the maintainable router and HTTP request handlers code by the defined document
  • In general, we do not need to manually write the OpenAPI definitions in Elixir
  • Simplify the REST APIs to convert types and validate the parameters of the HTTP request
  • More reference and communication to your REST APIs

Installation

Add oasis as a dependency to your mix.exs

def deps do
  [
    {:oasis, "~> 0.3"}
  ]
end

Implements to OAS

Oasis does not cover the full OpenAPI specification, so far the implements contain:

We also have some OpenAPI Specification Extensions defined for use, please see our Specification Extensions Guide.

How to use

Prepare YAML or JSON specification

First, write your API document refer the OpenAPI Specification(see reference for details), we build Oasis with the version 3.1.0 of the OAS, as usual, the common use case should be covered for the version 3.0.* of the OAS.

Here is a minimum specification for an example in YAML, we save it as "petstore-mini.yaml" in this tutorial.

openapi: "3.1.0"
info:
  title: Petstore Mini
paths:
  /pets:
    get:
      parameters:
        - name: tags
          in: query
          required: false
          schema:
            type: array
            items:
              type: string
        - name: limit
          in: query
          requried: false
          schema:
            type: integer
            format: int32
      response:
        '200':
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: '#/components/schemas/Pet'
    post:
      operationId: addPet
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/NewPet'
      response:
        '200':
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Pet'

  /pets/{id}:
    get:
      operationId: find pet by id
      parameters:
        - name: id
          in: path
          required: true
          schema:
            type: integer
            format: int64
      response:
        '200':
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Pet'
components:
  schemas:
    Pet:
      allOf:
        - $ref: '#/components/schemas/NewPet'
        - type: object
          required:
          - id
          properties:
            id:
              type: integer
              format: int64

    NewPet:
      type: object
      required:
        - name
      properties:
        name:
          type: string
        tag:
          type: string

Run mix task

And then we run the following mix task to generate the corresponding files:

mix oas.gen.plug --file path/to/petstore-mini.yaml

We will see these output:

Generates Router and Plug modules from OAS
* creating lib/oasis/gen/router.ex
* creating lib/oasis/gen/pre_find_pet_by_id.ex
* creating lib/oasis/gen/find_pet_by_id.ex
* creating lib/oasis/gen/pre_add_pet.ex
* creating lib/oasis/gen/add_pet.ex
* creating lib/oasis/gen/pre_get_pets.ex
* creating lib/oasis/gen/get_pets.ex

The arguments of oas.gen.plug mix task:

  • --file, required, the completed path to the specification file in YAML or JSON format.
  • --router, optional, the generated router's module alias, by default it is Router (the full module name is Oasis.Gen.Router by default), for example we set --router Hello.MyRouter meanwhile there is no other special name space defined, the final router module is Oasis.Gen.Hello.MyRouter in /lib/oasis/gen/hello/my_router.ex path.
  • --name-space, optional, the generated all modules' name space, by default it is Oasis.Gen, this argument will always override the name space from the input --file if any "x-oasis-name-space" field(s) defined.

Special instructions

Name Plug's handler

Refer the OAS, the operationId field of Operation Object is not required, but it should be unique among all operations described in the API if operationId field exists.

  • When use this field, Oasis will use it to construct the generated module alias and the file name of ".ex" file, e.g. see the above find_pet_by_id.ex file with Oasis.Gen.FindPetById module name.
  • When not use this filed, Oasis will combine the HTTP verb with the URL to generate the module alias and the file name of ".ex" file, e.g. see the above get_pets.ex file with Oasis.Gen.GetPets module name.

Generated code to folder

The generated codes are always put in the lib directory of your application root path, because they need to be integrated into your application in runtime.

Custom name space of generated modules

By default, the name space of the generated module is Oasis.Gen and its folder path is lib/oasis/gen, but we can custom it use these ways:

  1. As a final global definition when run oas.gen.plug mix task, input --name-space argument to set this, this argument always overrides all name space even we have some sections of document have special definition (via "x-oasis-name-space"), for example:
  mix oas.gen.plug --file path/to/petstore-mini.yaml --name-space My.Petstore
  Generates Router and Plug modules from OAS
  * creating lib/my/petstore/router.ex
  * creating lib/my/petstore/pre_find_pet_by_id.ex
  * creating lib/my/petstore/find_pet_by_id.ex
  * creating lib/my/petstore/pre_add_pet.ex
  * creating lib/my/petstore/add_pet.ex
  * creating lib/my/petstore/pre_get_pets.ex
  * creating lib/my/petstore/get_pets.ex

Now, we can see the generation folder path is lib/my/petstore, let's open the get_pets.ex file, the module name changed from Oasis.Gen.GetPets to My.Petstore.GetPets.

  1. Use "x-oasis-name-space" in the OAS's Operation Object, for example, add this newline x-oasis-name-space: Common.Api as below:
    paths:
      /pets:
        get:
          x-oasis-name-space: Common.Api
          parameters:
            - name: tags
              ...
        post:
          ...
      /pets/{id}:
        ...

Run again, please note this time no --name-space argument.

  mix oas.gen.plug --file path/to/petstore-mini.yaml
  Generates Router and Plug modules from OAS
  * creating lib/oasis/gen/router.ex
  * creating lib/oasis/gen/pre_find_pet_by_id.ex
  * creating lib/oasis/gen/find_pet_by_id.ex
  * creating lib/oasis/gen/pre_add_pet.ex
  * creating lib/oasis/gen/add_pet.ex
  * creating lib/common/api/pre_get_pets.ex
  * creating lib/common/api/get_pets.ex

We can see pre_get_pets.ex and get_pets.ex files are moved into the expected path, and their module names are Common.Api.GetPets and Common.Api.PreGetPets, other operations do not define any "x-oasis-name-space" field, so they still use the default one Oasis.Gen.

  1. Use "x-oasis-name-space" in the OAS's Paths Object, this use case as a global setting and can archive it in the document under the file version management, for example, add this newline x-oasis-name-space: Common.Api as below:
    paths:
      x-oasis-name-space: Common.Api
      /pets:
        get:
          parameters:
            - name: tags
              ...
        post:
          ...
      /pets/{id}:
        ...

Run again, please note this time no --name-space argument, and the GET operation of the "/pets" path is no "x-oasis-name-space" either.

  mix oas.gen.plug --file path/to/petstore-mini.yaml
  Generates Router and Plug modules from OAS
  * creating lib/common/api/router.ex
  * creating lib/common/api/pre_find_pet_by_id.ex
  * creating lib/common/api/find_pet_by_id.ex
  * creating lib/common/api/pre_add_pet.ex
  * creating lib/common/api/add_pet.ex
  * creating lib/common/api/pre_get_pets.ex
  * creating lib/common/api/get_pets.ex

We can see all generated files are moved into the expected path, and all modules' name start with Common.Api.

Summarize about the name space of generated module:

  1. The optional --name-space argument to the mix oas.gen.plug command line is in the highest priority to set the name space;

  2. We also can define "x-oasis-name-space" extension field in the specification document to make this archivable, please see here for details.

HTTP request handler files in pairs

The generated HTTP request handler files are named in pairs, one is pre_operation.ex, and another is operation.ex, the name beginning with pre_ file is in charge of converting and validating the parameters of each HTTP request definition, the content of this file will be updated according to the section of the document changes or Oasis upgrade in the future, so we CAN NOT write any business logic in this file; another file is only created in the first time of generation as long as this file does not exist, this is a common Plug module which is after the defined preprocessor by Plug's pipeline, we need to fill in business logic in here.

mix oas.gen.plug --file path/to/petstore-mini.yaml
Generates Router and Plug modules from OAS
* creating lib/oasis/gen/router.ex
* creating lib/oasis/gen/pre_find_pet_by_id.ex
* creating lib/oasis/gen/find_pet_by_id.ex
* creating lib/oasis/gen/pre_add_pet.ex
* creating lib/oasis/gen/add_pet.ex
* creating lib/oasis/gen/pre_get_pets.ex
* creating lib/oasis/gen/get_pets.ex

Integration

After the above generation, let's integrate it, assume the generated router is Oasis.Gen.Router, we can use it in the Plug's adapter like this:

Plug.Adapters.Cowboy.child_spec(
  scheme: :http,
  plug: Oasis.Gen.Router,
  options: [
    port: port
  ]
)

Or we can plug this router into the existence router module like this:

defmodule MyExistenceRouter do
  use Plug.Router

  plug(Oasis.Gen.Router)

  plug(:match)
  plug(:dispatch)

  # other

end

Please note that the added line of plug(Oasis.Gen.Router) is before the line of plug(:match).

TODO

  1. The Specification contains XML object is not supported so far.
  2. Make document more clear.
  3. There are still some details maybe not implement(or bug) from the OAS, please create an issue or a PR for tracking, thanks in advanced :)

Reference

  1. The official OpenAPI Specification v3: Github | Official Web Site
  2. JSON Schema Reference