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1# fresh
2
3[![NPM Version][npm-image]][npm-url]
4[![NPM Downloads][downloads-image]][downloads-url]
5[![Node.js Version][node-version-image]][node-version-url]
6[![Build Status][travis-image]][travis-url]
7[![Test Coverage][coveralls-image]][coveralls-url]
8
9HTTP response freshness testing
10
11## Installation
12
13This is a [Node.js](https://nodejs.org/en/) module available through the
14[npm registry](https://www.npmjs.com/). Installation is done using the
15[`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):
16
17```
18$ npm install fresh
19```
20
21## API
22
23<!-- eslint-disable no-unused-vars -->
24
25```js
26var fresh = require('fresh')
27```
28
29### fresh(reqHeaders, resHeaders)
30
31Check freshness of the response using request and response headers.
32
33When the response is still "fresh" in the client's cache `true` is
34returned, otherwise `false` is returned to indicate that the client
35cache is now stale and the full response should be sent.
36
37When a client sends the `Cache-Control: no-cache` request header to
38indicate an end-to-end reload request, this module will return `false`
39to make handling these requests transparent.
40
41## Known Issues
42
43This module is designed to only follow the HTTP specifications, not
44to work-around all kinda of client bugs (especially since this module
45typically does not recieve enough information to understand what the
46client actually is).
47
48There is a known issue that in certain versions of Safari, Safari
49will incorrectly make a request that allows this module to validate
50freshness of the resource even when Safari does not have a
51representation of the resource in the cache. The module
52[jumanji](https://www.npmjs.com/package/jumanji) can be used in
53an Express application to work-around this issue and also provides
54links to further reading on this Safari bug.
55
56## Example
57
58### API usage
59
60<!-- eslint-disable no-redeclare, no-undef -->
61
62```js
63var reqHeaders = { 'if-none-match': '"foo"' }
64var resHeaders = { 'etag': '"bar"' }
65fresh(reqHeaders, resHeaders)
66// => false
67
68var reqHeaders = { 'if-none-match': '"foo"' }
69var resHeaders = { 'etag': '"foo"' }
70fresh(reqHeaders, resHeaders)
71// => true
72```
73
74### Using with Node.js http server
75
76```js
77var fresh = require('fresh')
78var http = require('http')
79
80var server = http.createServer(function (req, res) {
81 // perform server logic
82 // ... including adding ETag / Last-Modified response headers
83
84 if (isFresh(req, res)) {
85 // client has a fresh copy of resource
86 res.statusCode = 304
87 res.end()
88 return
89 }
90
91 // send the resource
92 res.statusCode = 200
93 res.end('hello, world!')
94})
95
96function isFresh (req, res) {
97 return fresh(req.headers, {
98 'etag': res.getHeader('ETag'),
99 'last-modified': res.getHeader('Last-Modified')
100 })
101}
102
103server.listen(3000)
104```
105
106## License
107
108[MIT](LICENSE)
109
110[npm-image]: https://img.shields.io/npm/v/fresh.svg
111[npm-url]: https://npmjs.org/package/fresh
112[node-version-image]: https://img.shields.io/node/v/fresh.svg
113[node-version-url]: https://nodejs.org/en/
114[travis-image]: https://img.shields.io/travis/jshttp/fresh/master.svg
115[travis-url]: https://travis-ci.org/jshttp/fresh
116[coveralls-image]: https://img.shields.io/coveralls/jshttp/fresh/master.svg
117[coveralls-url]: https://coveralls.io/r/jshttp/fresh?branch=master
118[downloads-image]: https://img.shields.io/npm/dm/fresh.svg
119[downloads-url]: https://npmjs.org/package/fresh
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