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