fresh

What is fresh?

The 'fresh' npm package is a HTTP response freshness testing library. It is used to determine whether the response is still 'fresh' in the context of HTTP caching. It checks the request and response headers to decide if the response should be re-used or if a new one needs to be generated.

What are fresh's main functionalities?

Freshness Checking

This feature allows you to check if the HTTP response is still fresh by comparing the request and response headers. If the function returns true, the response is considered fresh.

const fresh = require('fresh');

const reqHeaders = { 'if-none-match': 'some-etag' };
const resHeaders = { 'etag': 'some-etag' };

const isFresh = fresh(reqHeaders, resHeaders);
console.log(isFresh); // true or false

Other packages similar to fresh

etag

The 'etag' package is used to generate HTTP ETags, which are typically used in HTTP headers to determine change in content at a given URL. While 'fresh' is used to check the freshness of responses, 'etag' helps in generating the identifiers that 'fresh' would use for its comparisons.

cache-control

The 'cache-control' package is used for parsing and formatting HTTP 'Cache-Control' headers. Unlike 'fresh', which checks for response freshness, 'cache-control' is more focused on providing utilities for working with the 'Cache-Control' header directly.

README

fresh

HTTP response freshness testing

Installation

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

$ npm install fresh

API

var fresh = require('fresh')

fresh(reqHeaders, resHeaders)

Check freshness of the response using request and response headers.

When the response is still "fresh" in the client's cache true is returned, otherwise false is returned to indicate that the client cache is now stale and the full response should be sent.

When a client sends the Cache-Control: no-cache request header to indicate an end-to-end reload request, this module will return false to make handling these requests transparent.

Known Issues

This module is designed to only follow the HTTP specifications, not to work-around all kinda of client bugs (especially since this module typically does not recieve enough information to understand what the client actually is).

There is a known issue that in certain versions of Safari, Safari will incorrectly make a request that allows this module to validate freshness of the resource even when Safari does not have a representation of the resource in the cache. The module jumanji can be used in an Express application to work-around this issue and also provides links to further reading on this Safari bug.

Example

API usage

var reqHeaders = { 'if-none-match': '"foo"' }
var resHeaders = { 'etag': '"bar"' }
fresh(reqHeaders, resHeaders)
// => false

var reqHeaders = { 'if-none-match': '"foo"' }
var resHeaders = { 'etag': '"foo"' }
fresh(reqHeaders, resHeaders)
// => true

Using with Node.js http server

var fresh = require('fresh')
var http = require('http')

var server = http.createServer(function (req, res) {
  // perform server logic
  // ... including adding ETag / Last-Modified response headers

  if (isFresh(req, res)) {
    // client has a fresh copy of resource
    res.statusCode = 304
    res.end()
    return
  }

  // send the resource
  res.statusCode = 200
  res.end('hello, world!')
})

function isFresh (req, res) {
  return fresh(req.headers, {
    'etag': res.getHeader('ETag'),
    'last-modified': res.getHeader('Last-Modified')
  })
}

server.listen(3000)

License

MIT