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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](LICENSE)