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/*!
* fresh
* Copyright(c) 2012 TJ Holowaychuk
* Copyright(c) 2016-2017 Douglas Christopher Wilson
* MIT Licensed
*/
'use strict'
/**
* RegExp to check for no-cache token in Cache-Control.
* @private
*/
var CACHE_CONTROL_NO_CACHE_REGEXP = /(?:^|,)\s*?no-cache\s*?(?:,|$)/
/**
* Simple expression to split token list.
* @private
*/
var TOKEN_LIST_REGEXP = / *, */
/**
* Module exports.
* @public
*/
module.exports = fresh
/**
* Check freshness of the response using request and response headers.
*
* @param {Object} reqHeaders
* @param {Object} resHeaders
* @return {Boolean}
* @public
*/
function fresh (reqHeaders, resHeaders) {
// fields
var modifiedSince = reqHeaders['if-modified-since']
var noneMatch = reqHeaders['if-none-match']
// unconditional request
if (!modifiedSince && !noneMatch) {
return false
}
// Always return stale when Cache-Control: no-cache
// to support end-to-end reload requests
// https://tools.ietf.org/html/rfc2616#section-14.9.4
var cacheControl = reqHeaders['cache-control']
if (cacheControl && CACHE_CONTROL_NO_CACHE_REGEXP.test(cacheControl)) {
return false
}
// if-none-match
if (noneMatch && noneMatch !== '*') {
var etag = resHeaders['etag']
var etagStale = !etag || noneMatch.split(TOKEN_LIST_REGEXP).every(function (match) {
return match !== etag && match !== 'W/' + etag && 'W/' + match !== etag
})
if (etagStale) {
return false
}
}
// if-modified-since
if (modifiedSince) {
var lastModified = resHeaders['last-modified']
var modifiedStale = !lastModified || Date.parse(lastModified) > Date.parse(modifiedSince)
if (modifiedStale) {
return false
}
}
return true
}
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