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openapi-backend

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Readme

OpenAPI Backend

Build, Validate, Route, and Mock using OpenAPI specification. Framework-agnostic middleware tools for building APIs with the OpenAPI standard.

OpenAPI Backend sits nicely in between your framework and business logic. It handles routing, input validation and response mocking; using only standard OpenAPI specification.

Also see: openapi-frontend

Features

Build APIs by describing them in OpenAPI document specification and importing them via YAML or JSON files or just passing an object
Register handler functions for operationIds to route requests in your favourite Node.js backend
Use JSON Schema to validate API requests and/or responses. OpenAPI Backend uses the AJV library under the hood for performant validation
Mock API responses using OpenAPI examples objects or JSON Schema definitions
TypeScript types included

(Currently only OpenAPI v3.0.0+ is supported)

Documentation

See DOCS.md

Quick Start

Full example projects included in the repo

npm install --save openapi-backend

import OpenAPIBackend from 'openapi-backend';

const api = new OpenAPIBackend({
  definition: {
    openapi: '3.0.1',
    info: {
      title: 'My API',
      version: '1.0.0',
    },
    paths: {
      '/pets': {
        get: {
          operationId: 'getPets',
          responses: {
            200: { description: 'ok' },
          },
        },
      },
      '/pets/{id}': {
        get: {
          operationId: 'getPetById',
          responses: {
            200: { description: 'ok' },
          },
        },
        parameters: [
          {
            name: 'id',
            in: 'path',
            required: true,
            schema: {
              type: 'integer',
            },
          },
        ],
      },
    },
  },
  handlers: {
    // your platform specific request handlers here
    getPets: (c, req, res) => res.status(200).json({ result: 'ok' }),
    getPetById: (c, req, res) => res.status(200).json({ result: 'ok' }),
    validationFail: (c, req, res) => res.status(400).json({ err: c.validation.errors }),
    notFound: (c, req, res) => res.status(404).json({ err: 'not found' }),
  },
});

// initalize the backend
api.init();

Express

import express from 'express';

const app = express();
app.use(express.json());
app.use((req, res) => api.handleRequest(req, req, res));
app.listen(9000);

See full Express example

AWS Serverless (Lambda)

// API Gateway Proxy handler
module.exports.handler = (event, context) =>
  api.handleRequest(
    {
      method: event.httpMethod,
      path: event.path,
      query: event.queryStringParameters,
      body: event.body,
      headers: event.headers,
    },
    event,
    context,
  );

See full Serverless Lambda example

Azure Function

module.exports = (context, req) =>
  api.handleRequest(
    {
      method: req.method,
      path: req.params.path,
      query: req.query,
      body: req.body,
      headers: req.headers,
    },
    context,
    req,
  );

See full Azure Function example

Hapi

import Hapi from 'hapi';

const server = new Hapi.Server({ host: '0.0.0.0', port: 9000 });
server.route({
  method: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'],
  path: '/{path*}',
  handler: (req, h) =>
    api.handleRequest(
      {
        method: req.method,
        path: req.path,
        body: req.payload,
        query: req.query,
        headers: req.headers,
      },
      req,
      h,
    ),
});
server.start();

See full Hapi example

Koa

import Koa from 'koa';

const app = new Koa();
app.use((ctx) =>
  api.handleRequest(
    {
      method: ctx.request.method,
      path: ctx.request.path,
      body: ctx.request.body,
      query: ctx.request.query,
      headers: ctx.request.headers,
    },
    ctx,
  ),
);
app.listen(9000);

See full Koa example

Registering Handlers for Operations

Handlers are registered for operationIds found in the OpenAPI definitions. You can register handlers as shown above with new OpenAPIBackend() constructor opts, or using the register() method.

async function getPetByIdHandler(c, req, res) {
  const id = c.request.params.id;
  const pet = await pets.getPetById(id);
  return res.status(200).json({ result: pet });
}
api.register('getPetById', getPetByIdHandler);

Operation handlers are passed a special Context object as the first argument, which contains the parsed request, the matched API operation and input validation results. The other arguments in the example aboce are Express-specific handler arguments.

Request validation

You can enable request validation in your API by registering a validationFail handler.

function validationFailHandler(c, req, res) {
  return res.status(400).json({ status: 400, err: c.validation.errors });
}
api.register('validationFail', validationFailHandler);

This handler gets called if any JSON Schemas in either operation parameters (in: path, query, header, cookie) or requestPayload don't match the request.

The context object c gets a validation property with the validation result.

Response validation

OpenAPIBackend doesn't automatically perform response validation for your handlers, but you can register a postResponseHandler to add a response validation step.

api.register({
  getPet: (c) => {
    // when a postResponseHandler is registered, your operation handlers' return value gets passed to context.response
    return [{ id: 1, name: 'Garfield' }];
  },
  postResponseHandler: (c, req ,res) => {
    const valid = c.api.validateResponse(c.response, c.operation);    
    if (valid.errors) {
      // response validation failed
      return res.status(502).json({ status: 502, err: valid.errors });
    }
    return res.status(200).json(c.response);
  },
});

Mocking API responses

Mocking APIs just got really easy with OpenAPI Backend! Register a notImplemented handler and use mockResponseForOperation() to generate mock responses for operations with no custom handlers specified yet:

api.register('notImplemented', (c, req, res) => {
  const { status, mock } = c.api.mockResponseForOperation(c.operation.operationId);
  return res.status(status).json(mock);
});

OpenAPI Backend supports mocking responses using both OpenAPI example objects and JSON Schema:

paths:
  '/pets':
    get:
      operationId: getPets
      summary: List pets
      responses:
        200:
          $ref: '#/components/responses/PetListWithExample'
  '/pets/{id}':
    get:
      operationId: getPetById
      summary: Get pet by its id
      responses:
        200:
          $ref: '#/components/responses/PetResponseWithSchema'
components:
  responses:
    PetListWithExample:
      description: List of pets
      content:
        'application/json':
          example:
            - id: 1
              name: Garfield
            - id: 2
              name: Odie
    PetResponseWithSchema:
      description: A single pet
      content:
        'application/json':
          schema:
            type: object
            properties:
              id:
                type: integer
                minimum: 1
              name:
                type: string
                example: Garfield

The example above will yield:

api.mockResponseForOperation('getPets'); // => { status: 200, mock: [{ id: 1, name: 'Garfield' }, { id: 2, name: 'Odie' }]}
api.mockResponseForOperation('getPetById'); // => { status: 200, mock: { id: 1, name: 'Garfield' }}

See full Mock API example on Express

Contributing

OpenAPI Backend is Free and Open Source Software. Issues and pull requests are more than welcome!