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
import OpenAPIBackend from 'openapi-backend';
// create api with your definition file or object
const api = new OpenAPIBackend({ definition: './petstore.yml' });
// register your framework specific request handlers here
api.register({
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 TypeScript 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 Framework 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
Fastify
import fastify from 'fastify';
fastify.route({
method: ['GET', 'POST', 'PUT', 'PATCH', 'DELETE'],
url: '/*',
handler: async (request, reply) =>
api.handleRequest(
{
method: request.method,
path: request.url,
body: request.body,
query: request.query,
headers: request.headers,
},
request,
reply,
),
});
fastify.listen();Hapi
import Hapi from '@hapi/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();Koa
import Koa from 'koa';
import bodyparser from 'koa-bodyparser';
const app = new Koa();
app.use(bodyparser());
app.use((ctx) =>
api.handleRequest(
ctx.request,
ctx,
),
);
app.listen(9000);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);
// or
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 above are Express-specific handler arguments.
Request validation
The easiest way to enable request validation in your API is to register a validationFail
handler.
function validationFailHandler(c, req, res) {
return res.status(400).json({ status: 400, err: c.validation.errors });
}
api.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.
api.register({
getPets: (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);
},
});It's also possible to validate the response headers using validateResponseHeaders.
api.register({
getPets: (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.validateResponseHeaders(res.headers, c.operation, {
statusCode: res.statusCode,
setMatchType: 'exact',
});
if (valid.errors) {
// response validation failed
return res.status(502).json({ status: 502, err: valid.errors });
}
return res.status(200).json(c.response);
},
});Auth / Security Handlers
If your OpenAPI definition contains Security Schemes you can register security handlers to handle authorization for your API:
components:
securitySchemes:
- ApiKey:
type: apiKey
in: header
name: x-api-key
security:
- ApiKey: []api.registerSecurityHandler('ApiKey', (c) => {
const authorized = c.request.headers['x-api-key'] === 'SuperSecretPassword123';
// truthy return values are interpreted as auth success
// you can also add any auth information to the return value
return authorized;
});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.
api.register('unauthorizedHandler', (c, req, res) => {
return res.status(401).json({ err: 'unauthorized' })
});See examples:
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: GarfieldThe 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!