OAPI Routing System

OAPI Routing System library is a middleware for express.js web servers aiming to simplify, secure and document APIs.

The goal is to define once and for all the API contract inside the code base, in a simple and reusable way. Then, use this definition to generate OpenAPI documentation and validate parameters automatically.

Example

Assuming your create the following route (route/hello-world.js):

export const endpoint = '/';
export const method = 'get';
export const summary = 'Salute the visitor by his / her name.';

export const query = {
    name: {
        $type: 'string',
        $description: 'The visitor\'s name',
        $example: 'Bob',
    },
};

export const responses = [{
    $code: 200,
    $contentType: 'text/plain',
    $description: 'A salutation message.',
    $example: 'Hello Bob!',
    $schema: 'string',
}];

export async function handler(req, res, cfg) {
    res.send(`Hellow ${req.query.name}!`);
}

The library will automatically generate the following OpenAPI documentation:

{
  "openapi": "3.0.0",
  "info": {
    "title": "hello-world",
    "description": "This is a minimal example of how to use the oapi-routing-system.",
    "version": "1.0.0"
  },
  "paths": {
    "/": {
      "get": {
        "summary": "Salute the visitor by his / her name.",
        "responses": {
          "200": {
            "description": "A salutation message.",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "string",
                  "example": "Hello Bob!"
                }
              }
            }
          }
        },
        "parameters": [
          {
            "name": "name",
            "description": "The visitor's name",
            "in": "query",
            "required": true,
            "schema": {
              "type": "string",
              "example": "Bob"
            }
          }
        ]
      }
    }
  }
}

If a visitor doesn't send a name as query parameter, the server will return an error. Same if the parameter is not a string (although, this seems quite impossible since a query parameter is necessarily a string - but you get the idea).

You can check the complete code with comments in example/hellow-world.

Usage

1. Create your routes, one per file, exporting the following parameters:

   • endpoint (string) - REQUIRED - the endpoint where to mount the route (example: /hellow-world).
   • method (string) - OPTIONAL - the HTTP method accepted by the endpoint (defaults to get).
   • summary (string) - OPTIONAL - a short summary of the route, try to limit yourself to one line (default to none).
   • description (string) - OPTIONAL - a longer explanation of the route, no length restriction (default to none).
   • parameters (object) - OPTIONAL - if you have path parameters (ex: /user/:id) the specification for these (see below how to structure it).
   • query (object) - OPTIONAL - specification if the query parameters accepted by the route (see examples on how to structure it).
   • body (object) - OPTIONAL - for the mothod accepting one, the request body specification (see examples on how to structure it).
   • responses (array) - REQUIRED - the different responses that may be returned by the route (see examples on how to structure it).
   • handler (function) - REQUIRED - the actual "busniess" function that read params and respond to the client. This function receives the usual req and res parameters from express.js, plus the configuration of the application (see below how this configuration is defined).

2. Import and instanciate a new oapi-routing-system instance:

   import { OApiRoutingSystem } from 'oapi-routing-system';
   
    // This is a dummy configuration for our routes
    // It can be anything and will be passed to each route handler untouched
    const configuration = {};
   
   // Initialize a new router, passing in the configuration reference.
   // This configuraiton object can then be used in any route handler.
   const crs = new OApiRoutingSystem(configuration);
   
   // Set the generic information about the API required by OpenAPI.
   // You may ommit this call for quick tests, but your OpenAPI json won't be strictly valid.
   await crs.defineOpenApiInfo(title, description, version);
   
   // Load routes from the file system assuming they are declared in `src/route` (using dynamic imports).
   await crs.loadFile('src/route/hellow-world.mjs');
   // You can also use `loadFile(path)` if you prefer to load them one by one
   // or `loadModule(name, module)` if you want to import the files statically.

3. Get the router and OpenAPI definition to use in your express server:

   import express from 'express';
   import swagger from 'swagger-ui-express';
   
   // Create an express server with JSON and urlencoded body parsers.
   const app = express();
   app.use(express.json());
   app.use(express.urlencoded({ extended: true }));
   
   // Get the final open-api description and serve it with you favourite UI (here, we use swagger-ui).
   const openapi = crs.getOpenApiAsJson();
   app.use('/swagger', swagger.serve);
   app.get('/swagger', swagger.setup(openapi));
   
   // Add our router to the express server.
   app.use(crs.getRouter());
   
   // Start the server.
   app.listen(port, () => console.log(`Server listening on port ${port}`));

4. While not really mandatory, it is strongly recomended to also setup a custom error handler for validation errors:

   import { ValidationError } from 'oapi-routing-system';
   
   // Add error management: OApiRoutingSystem will forward a ValidationError if a request is invalid.
   // Here, we return an HTTP 400 error in this case, with the descriptive message contained in the error.
   app.use((err, req, res, next) => {
       if (err instanceof ValidationError) {
           // Customize the response as you like.
           res.status(400).send(err.message);
       } else {
           next(err);
       }
   });