express-negotiate-middleware

This middleware allows client to negotiate responses based on the accept or content-type headers allowing a single route to return multi-formats of data.

Features

• clients to accept multiple responses application/xhtml+xml;q=0.9,*/*;q=0.7,application/xml;q=0.8,text/html;q=1
• client to state which response they perfer with relative quality factor
• default handlers for fallback responses

Project Status

Installation

Requirements

• Node Version: 16+ (may work on older versions but not tested)
• Dependencies are listed in package.json

Install dependencies

npm install

Linting

Run the Static analiser:

npm run lint

Correct issues which can be automatically fixed:

npm run lint:fix

Testing

Full test suite:

npm test

Examples

Basic Example

In this example the server will have the abilty to return both html and JSON. The client will able to negation which gets returned.

Server

import express, { Request, Response } from 'express';
import { negotiate, NotAcceptable } from 'express-negotiate-middleware';

const jsonHandler = (_request: Request, response: Response): void => {
  response.json({ message: 'hello world' });
};

const htmlHandler = (_request: Request, response: Response): void => {
  response.send('<h1>hello world</h1>');
};

const application = express();

application.get('/', negotiate({ 'application/json': jsonHandler, 'text/html': htmlHandler }));

application.listen(8080);

Client

// ask the server for json
const jsonData = await fetch('http://localhost:8080/', {
    headers: {
      'Accept': 'application/json',
      'Content-Type': 'application/json'
    },
});
// ask the server for html
const htmlData = await fetch('http://localhost:8080/', {
    headers: {
      'Accept': 'text/html',
      'Content-Type': 'text/html'
    },
});

// prefer json by using q parameter
// q is usally between 0-1 higher numbers mean return this type first

const jsonData = await fetch('http://localhost:8080/', {
    headers: {
      'Accept': 'application/json;q=1,text/html',
    },
});

Default handlers

You can set a default handler that all requests fall into should a negatiation fails

application.get('/', negotiate({ 
    'application/json': jsonHandler, 
    'text/html': htmlHandler, 
    // if negation fails return json
    default: jsonHanlder 
}));

If there is no default handler then failed negatiations will throw NotAcceptable error

Handling errors

Creating a error handling middleware allows for all errors to be passed to next(error) and be handled in a single location

import express, { Request, Response } from 'express';
import { negotiate, NotAcceptable } from 'express-negotiate-middleware';

const jsonHandler = (_request: Request, response: Response): void => {
  response.json({ message: 'hello world' });
};

const htmlHandler = (_request: Request, response: Response): void => {
  response.send('<h1>hello world</h1>');
};

const application = express();

application.get('/', negotiate({ 'application/json': jsonHandler, 'text/html': htmlHandler }));

application.use((error: unknown, _request: Request, response: Response) => {
  if (error instanceof NotAcceptable) {
    response.status(error.statusCode).json({ error: error.message });
  } else {
    response.status(500).json(error);
  }
});

application.listen(8080);