vary

What is vary?

The vary npm package is a utility for manipulating the HTTP Vary header. It allows developers to programmatically append values to the Vary header of an HTTP response, ensuring that the correct header is constructed for proper handling of HTTP caching, content negotiation, and other mechanisms that might vary the response based on certain aspects of the request.

What are vary's main functionalities?

Appending to the Vary header

This feature allows you to append a field to the Vary header of an HTTP response. In the code sample, the 'User-Agent' field is added to the Vary header, indicating that the response may vary based on the 'User-Agent' header of the request.

"use strict";

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

http.createServer((req, res) => {
  vary(res, 'User-Agent');
  res.end('Response varies based on User-Agent header.');
}).listen(3000);

Appending multiple fields

This feature allows you to append multiple fields to the Vary header at once. In the code sample, both 'User-Agent' and 'Accept-Encoding' are added to the Vary header, indicating that the response may vary based on both of these request headers.

"use strict";

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

http.createServer((req, res) => {
  vary(res, 'User-Agent, Accept-Encoding');
  res.end('Response varies based on User-Agent and Accept-Encoding headers.');
}).listen(3000);

Other packages similar to vary

fresh

The 'fresh' package is an HTTP response freshness testing library that evaluates whether a response is still 'fresh' in the context of request and response headers. It is similar to 'vary' in that it deals with HTTP headers, but 'fresh' focuses on cache validation while 'vary' focuses on managing the Vary header.

negotiator

The 'negotiator' package is an HTTP content negotiation library that supports media types, charsets, encodings, languages, and more. It is similar to 'vary' in that it assists with content negotiation, but 'negotiator' provides a higher-level API for selecting the best response based on the client's request, whereas 'vary' is specifically for manipulating the Vary header.

README

vary

Manipulate the HTTP Vary header

Installation

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

$ npm install vary

API

var vary = require('vary')

vary(res, field)

Adds the given header field to the Vary response header of res. This can be a string of a single field, a string of a valid Vary header, or an array of multiple fields.

This will append the header if not already listed, otherwise leaves it listed in the current location.

// Append "Origin" to the Vary header of the response
vary(res, 'Origin')

vary.append(header, field)

Adds the given header field to the Vary response header string header. This can be a string of a single field, a string of a valid Vary header, or an array of multiple fields.

This will append the header if not already listed, otherwise leaves it listed in the current location. The new header string is returned.

// Get header string appending "Origin" to "Accept, User-Agent"
vary.append('Accept, User-Agent', 'Origin')

Examples

Updating the Vary header when content is based on it

var http = require('http')
var vary = require('vary')

http.createServer(function onRequest (req, res) {
  // about to user-agent sniff
  vary(res, 'User-Agent')

  var ua = req.headers['user-agent'] || ''
  var isMobile = /mobi|android|touch|mini/i.test(ua)

  // serve site, depending on isMobile
  res.setHeader('Content-Type', 'text/html')
  res.end('You are (probably) ' + (isMobile ? '' : 'not ') + 'a mobile user')
})

Testing

$ npm test

License

MIT