accepts

What is accepts?

The 'accepts' npm package is a utility for content negotiation in Node.js. It allows a server to interpret the content types that a client can handle and respond with the most appropriate content type. It is commonly used in HTTP server frameworks like Express to simplify the process of determining what MIME types the client accepts in the 'Accept' HTTP header.

What are accepts's main functionalities?

Content Type Negotiation

This code demonstrates how to use the 'accepts' package to determine the best response content type based on the client's 'Accept' header. The server responds with either JSON, HTML, or plain text.

const accepts = require('accepts');
const http = require('http');

http.createServer(function (req, res) {
  var accept = accepts(req);
  var preferredType = accept.type(['json', 'html']);
  if (preferredType === 'json') {
    res.setHeader('Content-Type', 'application/json');
    res.end(JSON.stringify({ message: 'Hello, JSON!' }));
  } else if (preferredType === 'html') {
    res.setHeader('Content-Type', 'text/html');
    res.end('<p>Hello, HTML!</p>');
  } else {
    res.setHeader('Content-Type', 'text/plain');
    res.end('Hello, plain text!');
  }
}).listen(3000);

Language Negotiation

This code snippet shows how to use the 'accepts' package to determine the client's preferred language from the 'Accept-Language' header and respond accordingly.

const accepts = require('accepts');
const http = require('http');

http.createServer(function (req, res) {
  var accept = accepts(req);
  var preferredLanguage = accept.language(['en', 'es', 'fr']);
  res.end('Preferred language: ' + preferredLanguage);
}).listen(3000);

Encoding Negotiation

This example illustrates how to use the 'accepts' package to negotiate the content encoding that the client supports, such as 'gzip' or 'deflate'.

const accepts = require('accepts');
const http = require('http');

http.createServer(function (req, res) {
  var accept = accepts(req);
  var preferredEncoding = accept.encoding(['gzip', 'deflate']);
  res.end('Preferred encoding: ' + preferredEncoding);
}).listen(3000);

Charset Negotiation

This code sample demonstrates how to use the 'accepts' package to determine which charset the client prefers, such as 'utf-8' or 'iso-8859-1'.

const accepts = require('accepts');
const http = require('http');

http.createServer(function (req, res) {
  var accept = accepts(req);
  var preferredCharset = accept.charset(['utf-8', 'iso-8859-1']);
  res.end('Preferred charset: ' + preferredCharset);
}).listen(3000);

Other packages similar to accepts

negotiator

The 'negotiator' package is similar to 'accepts' and provides an HTTP content negotiation algorithm that is compliant with RFC 7231. It offers more detailed control over the negotiation process compared to 'accepts', but it might be more complex to use for simple scenarios.

negotiate

The 'negotiate' package is another alternative for content negotiation in Node.js. It is designed to be a simple and lightweight solution, but it may not be as feature-rich or widely used as 'accepts'.

README

accepts

Higher level content negotiation based on negotiator. Extracted from koa for general use.

In addition to negotiator, it allows:

• Allows types as an array or arguments list, ie (['text/html', 'application/json']) as well as ('text/html', 'application/json').
• Allows type shorthands such as json.
• Returns false when no types match
• Treats non-existent headers as *

Installation

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install accepts

API

var accepts = require('accepts')

accepts(req)

Create a new Accepts object for the given req.

.charset(charsets)

Return the first accepted charset. If nothing in charsets is accepted, then false is returned.

.charsets()

Return the charsets that the request accepts, in the order of the client's preference (most preferred first).

.encoding(encodings)

Return the first accepted encoding. If nothing in encodings is accepted, then false is returned.

.encodings()

Return the encodings that the request accepts, in the order of the client's preference (most preferred first).

.language(languages)

Return the first accepted language. If nothing in languages is accepted, then false is returned.

.languages()

Return the languages that the request accepts, in the order of the client's preference (most preferred first).

.type(types)

Return the first accepted type (and it is returned as the same text as what appears in the types array). If nothing in types is accepted, then false is returned.

The types array can contain full MIME types or file extensions. Any value that is not a full MIME type is passed to require('mime-types').lookup.

.types()

Return the types that the request accepts, in the order of the client's preference (most preferred first).

Examples

Simple type negotiation

This simple example shows how to use accepts to return a different typed respond body based on what the client wants to accept. The server lists it's preferences in order and will get back the best match between the client and server.

var accepts = require('accepts')
var http = require('http')

function app (req, res) {
  var accept = accepts(req)

  // the order of this list is significant; should be server preferred order
  switch (accept.type(['json', 'html'])) {
    case 'json':
      res.setHeader('Content-Type', 'application/json')
      res.write('{"hello":"world!"}')
      break
    case 'html':
      res.setHeader('Content-Type', 'text/html')
      res.write('<b>hello, world!</b>')
      break
    default:
      // the fallback is text/plain, so no need to specify it above
      res.setHeader('Content-Type', 'text/plain')
      res.write('hello, world!')
      break
  }

  res.end()
}

http.createServer(app).listen(3000)

You can test this out with the cURL program:

curl -I -H'Accept: text/html' http://localhost:3000/

License

MIT