Build, Validate, Route, Authenticate, and Mock using OpenAPI definitions.

OpenAPI Backend is a Framework-agnostic middleware tool for building beautiful APIs with OpenAPI Specification.

Features

• Build APIs by describing them in OpenAPI specification
• Register handlers 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
• Register Auth / Security Handlers for OpenAPI Security Schemes to authorize API requests
• Auto-mock API responses using OpenAPI examples objects or JSON Schema definitions
• Built with TypeScript, types included
• Optimised runtime routing and validation. No generated code!
• OpenAPI 3.1 support

Documentation

New! OpenAPI Backend documentation is now found on openapistack.co

https://openapistack.co/docs/openapi-backend/intro

Quick Start

Full example projects included in the repo

npm install --save openapi-backend

1import OpenAPIBackend from 'openapi-backend';
2
3// create api with your definition file or object
4const api = new OpenAPIBackend({ definition: './petstore.yml' });
5
6// register your framework specific request handlers here
7api.register({
8  getPets: (c, req, res) => res.status(200).json({ result: 'ok' }),
9  getPetById: (c, req, res) => res.status(200).json({ result: 'ok' }),
10  validationFail: (c, req, res) => res.status(400).json({ err: c.validation.errors }),
11  notFound: (c, req, res) => res.status(404).json({ err: 'not found' }),
12});
13
14// initalize the backend
15api.init();

Express

1import express from 'express';
2
3const app = express();
4app.use(express.json());
5app.use((req, res) => api.handleRequest(req, req, res));
6app.listen(9000);

See full Express example

See full Express TypeScript example

AWS Serverless (Lambda)

1// API Gateway Proxy handler
2module.exports.handler = (event, context) =>
3  api.handleRequest(
4    {
5      method: event.httpMethod,
6      path: event.path,
7      query: event.queryStringParameters,
8      body: event.body,
9      headers: event.headers,
10    },
11    event,
12    context,
13  );

See full AWS SAM example

See full AWS CDK example

See full SST example

See full Serverless Framework example

Azure Function

1module.exports = (context, req) =>
2  api.handleRequest(
3    {
4      method: req.method,
5      path: req.params.path,
6      query: req.query,
7      body: req.body,
8      headers: req.headers,
9    },
10    context,
11    req,
12  );

See full Azure Function example

Fastify

1import fastify from 'fastify';
2
3fastify.route({
4  method: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'],
5  url: '/*',
6  handler: async (request, reply) =>
7    api.handleRequest(
8      {
9        method: request.method,
10        path: request.url,
11        body: request.body,
12        query: request.query,
13        headers: request.headers,
14      },
15      request,
16      reply,
17    ),
18});
19fastify.listen();

See full Fastify example

Hapi

1import Hapi from '@hapi/hapi';
2
3const server = new Hapi.Server({ host: '0.0.0.0', port: 9000 });
4server.route({
5  method: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'],
6  path: '/{path*}',
7  handler: (req, h) =>
8    api.handleRequest(
9      {
10        method: req.method,
11        path: req.path,
12        body: req.payload,
13        query: req.query,
14        headers: req.headers,
15      },
16      req,
17      h,
18    ),
19});
20server.start();

See full Hapi example

Koa

1import Koa from 'koa';
2import bodyparser from 'koa-bodyparser';
3
4const app = new Koa();
5
6app.use(bodyparser());
7app.use((ctx) =>
8  api.handleRequest(
9    ctx.request,
10    ctx,
11  ),
12);
13app.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.

1async function getPetByIdHandler(c, req, res) {
2  const id = c.request.params.id;
3  const pet = await pets.getPetById(id);
4  return res.status(200).json({ result: pet });
5}
6api.register('getPetById', getPetByIdHandler);
7// or
8api.register({
9  getPetById: getPetByIdHandler,
10});

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 above are Express-specific handler arguments.

Request validation

The easiest way to enable request validation in your API is to register a validationFail handler.

1function validationFailHandler(c, req, res) {
2  return res.status(400).json({ status: 400, err: c.validation.errors });
3}
4api.register('validationFail', validationFailHandler);

Once registered, 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 using validateResponse.

1api.register({
2  getPets: (c) => {
3    // when a postResponseHandler is registered, your operation handlers' return value gets passed to context.response
4    return [{ id: 1, name: 'Garfield' }];
5  },
6  postResponseHandler: (c, req, res) => {
7    const valid = c.api.validateResponse(c.response, c.operation);
8    if (valid.errors) {
9      // response validation failed
10      return res.status(502).json({ status: 502, err: valid.errors });
11    }
12    return res.status(200).json(c.response);
13  },
14});

It's also possible to validate the response headers using validateResponseHeaders.

1api.register({
2  getPets: (c) => {
3    // when a postResponseHandler is registered, your operation handlers' return value gets passed to context.response
4    return [{ id: 1, name: 'Garfield' }];
5  },
6  postResponseHandler: (c, req, res) => {
7    const valid = c.api.validateResponseHeaders(res.headers, c.operation, {
8      statusCode: res.statusCode,
9      setMatchType: 'exact',
10    });
11    if (valid.errors) {
12      // response validation failed
13      return res.status(502).json({ status: 502, err: valid.errors });
14    }
15    return res.status(200).json(c.response);
16  },
17});

Auth / Security Handlers

If your OpenAPI definition contains Security Schemes you can register security handlers to handle authorization for your API:

1components:
2  securitySchemes:
3  - ApiKey:
4      type: apiKey
5      in: header
6      name: x-api-key
7security:
8  - ApiKey: []

1api.registerSecurityHandler('ApiKey', (c) => {
2  const authorized = c.request.headers['x-api-key'] === 'SuperSecretPassword123';
3  // truthy return values are interpreted as auth success
4  // you can also add any auth information to the return value
5  return authorized;
6});

The authorization status and return values of each security handler can be accessed via the Context Object

You can also register an unauthorizedHandler to handle unauthorized requests.

1api.register('unauthorizedHandler', (c, req, res) => {
2  return res.status(401).json({ err: 'unauthorized' })
3});

See examples:

• API Key auth (express)
• JWT auth (express)

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:

1api.register('notImplemented', (c, req, res) => {
2  const { status, mock } = c.api.mockResponseForOperation(c.operation.operationId);
3  return res.status(status).json(mock);
4});

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

1paths:
2  '/pets':
3    get:
4      operationId: getPets
5      summary: List pets
6      responses:
7        200:
8          $ref: '#/components/responses/PetListWithExample'
9  '/pets/{id}':
10    get:
11      operationId: getPetById
12      summary: Get pet by its id
13      responses:
14        200:
15          $ref: '#/components/responses/PetResponseWithSchema'
16components:
17  responses:
18    PetListWithExample:
19      description: List of pets
20      content:
21        'application/json':
22          example:
23            - id: 1
24              name: Garfield
25            - id: 2
26              name: Odie
27    PetResponseWithSchema:
28      description: A single pet
29      content:
30        'application/json':
31          schema:
32            type: object
33            properties:
34              id:
35                type: integer
36                minimum: 1
37              name:
38                type: string
39                example: Garfield

The example above will yield:

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

See full Mock API example on Express

Commercial support

For assistance with integrating openapi-backend in your company, reach out at support@openapistack.co.

Contributing

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