exegesis-express

What is exegesis-express?

exegesis-express is an npm package that provides a framework for building APIs using OpenAPI (formerly known as Swagger) specifications. It integrates with Express.js to allow developers to define their API endpoints, request/response validation, and middleware based on OpenAPI definitions.

What are exegesis-express's main functionalities?

API Endpoint Definition

This code demonstrates how to set up an Express server with exegesis-express middleware to handle API endpoints defined in an OpenAPI specification file.

const express = require('express');
const exegesisExpress = require('exegesis-express');
const path = require('path');

async function createServer() {
  const app = express();

  const options = {
    controllers: path.resolve(__dirname, './controllers'),
  };

  const exegesisMiddleware = await exegesisExpress.middleware(path.resolve(__dirname, './openapi.yaml'), options);

  app.use(exegesisMiddleware);

  app.use((err, req, res, next) => {
    res.status(err.status || 500).json({ message: err.message });
  });

  return app;
}

createServer().then(app => {
  app.listen(3000, () => {
    console.log('Listening on port 3000');
  });
}).catch(err => {
  console.error(err.stack);
  process.exit(1);
});

Request/Response Validation

This code sample shows how to enable request and response validation in an Express server using exegesis-express. The `validateResponses` option ensures that responses conform to the OpenAPI specification.

const express = require('express');
const exegesisExpress = require('exegesis-express');
const path = require('path');

async function createServer() {
  const app = express();

  const options = {
    controllers: path.resolve(__dirname, './controllers'),
    validateResponses: true, // Enable response validation
  };

  const exegesisMiddleware = await exegesisExpress.middleware(path.resolve(__dirname, './openapi.yaml'), options);

  app.use(exegesisMiddleware);

  app.use((err, req, res, next) => {
    res.status(err.status || 500).json({ message: err.message });
  });

  return app;
}

createServer().then(app => {
  app.listen(3000, () => {
    console.log('Listening on port 3000');
  });
}).catch(err => {
  console.error(err.stack);
  process.exit(1);
});

Custom Middleware Integration

This code demonstrates how to integrate custom middleware into an Express server that uses exegesis-express. The custom middleware logs a message for each request.

const express = require('express');
const exegesisExpress = require('exegesis-express');
const path = require('path');

async function createServer() {
  const app = express();

  const options = {
    controllers: path.resolve(__dirname, './controllers'),
  };

  const exegesisMiddleware = await exegesisExpress.middleware(path.resolve(__dirname, './openapi.yaml'), options);

  app.use(exegesisMiddleware);

  // Custom middleware
  app.use((req, res, next) => {
    console.log('Custom middleware executed');
    next();
  });

  app.use((err, req, res, next) => {
    res.status(err.status || 500).json({ message: err.message });
  });

  return app;
}

createServer().then(app => {
  app.listen(3000, () => {
    console.log('Listening on port 3000');
  });
}).catch(err => {
  console.error(err.stack);
  process.exit(1);
});

Other packages similar to exegesis-express

swagger-express-middleware

swagger-express-middleware is a package that provides Express middleware for working with Swagger (OpenAPI) documents. It offers features like request validation, mock responses, and more. Compared to exegesis-express, it focuses more on Swagger 2.0 and provides a different set of utilities for handling API requests.

express-openapi-validator

express-openapi-validator is a package that validates API requests and responses against an OpenAPI 3 specification. It integrates with Express.js and provides features like request validation, response validation, and security handling. It is similar to exegesis-express but focuses more on validation and security aspects.

openapi-backend

openapi-backend is a package that helps build and manage backend services using OpenAPI definitions. It provides features like request validation, routing, and response validation. Unlike exegesis-express, it is framework-agnostic and can be used with various server frameworks, not just Express.

README

exegesis-express

exegesis

n. An explanation or critical interpretation of a text, especially an API definition document.

-- No dictionary ever

This library implements an Express middleware for OpenAPI 3.x.

Features

• Full support for OpenAPI 3.x.x (see issues tagged with conformance for areas which could use some improvement).
• Built in support for "application/json" and "application/x-www-form-urlencoded" requests
• Can use express body parser middlewares
• Response validation
• Authentication support
• Plugins allow easy extensibility
• Easy support for validating custom formats

Tutorial

Check out the tutorial here.

Usage

Calling exegesisExpress.middleware(openApiFile, options) will return a Promise which resolves to a connect/express middleware (alternatively you can call exegesisExpress.middleware(openApiFile, options, done), if callbacks are your thing).

openApiFile is either a path to your openapi.yaml or openapi.json file, or it can be a JSON object with the contents of your OpenAPI document. This should have the x-exegesis-controller extension defined on any paths you want to be able to access.

options can be anything you can pass to exegesis. At a minimum, you'll probably want to provide options.controllers, a path to where your controller modules can be found. If you have any security requirements defined, you'll also want to pass in some authenticators. To enable response validation, you'll want to provide a validation callback function via onResponseValidationError(). Exegesis's functionality can also be extended using plugins, which run on every request. Plugins let you add functionality like role base authorization, or CORS.

Where to put Exegesis-Express in your middleware stack

Exegesis-express should appear near the top of your middleware stack, before any body parsers. This is because exegesis will take care of parsing the body for you, and it can't do that if the body has already been read. If you put a body parser ahead of exegesis-express, exegesis will try to use req.body if it's there.

Servers section

OpenAPI 3.x lets you specify what servers your API is available on. For example:

servers:
  - url: '/api/v2'

By default, exegesis will take 'servers' into account when routing requests, so if you have the above servers section, and a path in your API called "/users", then exegesis will only match the route if the incoming requests has the URL "/api/v2/users".

If you have path templates in your servers, the variables will be available to your controllers via context.params.server.

If you specify the ignoreServers option, however, exegesis will ignore the servers section, an route purely based on your paths. This lets you do something like:

    const exegesisMiddleware = await exegesisExpress.middleware(
        path.resolve(__dirname, './openapi.yaml'),
        {ignorePaths: true}
    );
    app.use('/api/v2', exegesisMiddleware);

which means non-api paths will not even be sent to the exegesis middleware.

Example

import express from 'express';
import path from 'path';
import http from 'http';
import * as exegesisExpress from 'exegesis-express';

async function createServer() {
    // See https://github.com/exegesis-js/exegesis/blob/master/docs/Options.md
    const options = {
        controllers: path.resolve(__dirname, './controllers')
    };

    const exegesisMiddleware = await exegesisExpress.middleware(
        path.resolve(__dirname, './openapi.yaml'),
        options
    );

    const app = express();

    // If you have any body parsers, this should go before them.
    app.use(exegesisMiddleware);

    app.use((req, res) => {
        res.status(404).json({message: `Not found`});
    });

    app.use((err, req, res, next) => {
        res.status(500).json({message: `Internal error: ${err.message}`});
    });

    const server = http.createServer(app);
    server.listen(3000);
}

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Copyright 2018 Jason Walton