/*!
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* fresh
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* Copyright(c) 2012 TJ Holowaychuk
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* Copyright(c) 2016-2017 Douglas Christopher Wilson
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* MIT Licensed
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*/
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'use strict'
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/**
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* RegExp to check for no-cache token in Cache-Control.
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* @private
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*/
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var CACHE_CONTROL_NO_CACHE_REGEXP = /(?:^|,)\s*?no-cache\s*?(?:,|$)/
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/**
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* Module exports.
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* @public
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*/
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module.exports = fresh
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/**
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* Check freshness of the response using request and response headers.
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*
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* @param {Object} reqHeaders
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* @param {Object} resHeaders
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* @return {Boolean}
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* @public
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*/
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function fresh (reqHeaders, resHeaders) {
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// fields
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var modifiedSince = reqHeaders['if-modified-since']
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var noneMatch = reqHeaders['if-none-match']
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// unconditional request
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if (!modifiedSince && !noneMatch) {
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return false
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}
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// Always return stale when Cache-Control: no-cache
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// to support end-to-end reload requests
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// https://tools.ietf.org/html/rfc2616#section-14.9.4
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var cacheControl = reqHeaders['cache-control']
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if (cacheControl && CACHE_CONTROL_NO_CACHE_REGEXP.test(cacheControl)) {
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return false
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}
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// if-none-match
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if (noneMatch && noneMatch !== '*') {
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var etag = resHeaders['etag']
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if (!etag) {
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return false
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}
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var etagStale = true
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var matches = parseTokenList(noneMatch)
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for (var i = 0; i < matches.length; i++) {
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var match = matches[i]
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if (match === etag || match === 'W/' + etag || 'W/' + match === etag) {
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etagStale = false
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break
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}
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}
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if (etagStale) {
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return false
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}
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}
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// if-modified-since
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if (modifiedSince) {
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var lastModified = resHeaders['last-modified']
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var modifiedStale = !lastModified || !(parseHttpDate(lastModified) <= parseHttpDate(modifiedSince))
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if (modifiedStale) {
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return false
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}
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}
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return true
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}
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/**
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* Parse an HTTP Date into a number.
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*
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* @param {string} date
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* @private
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*/
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function parseHttpDate (date) {
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var timestamp = date && Date.parse(date)
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// istanbul ignore next: guard against date.js Date.parse patching
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return typeof timestamp === 'number'
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? timestamp
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: NaN
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}
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/**
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* Parse a HTTP token list.
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*
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* @param {string} str
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* @private
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*/
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function parseTokenList (str) {
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var end = 0
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var list = []
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var start = 0
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// gather tokens
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for (var i = 0, len = str.length; i < len; i++) {
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switch (str.charCodeAt(i)) {
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case 0x20: /* */
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if (start === end) {
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start = end = i + 1
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}
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break
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case 0x2c: /* , */
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list.push(str.substring(start, end))
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start = end = i + 1
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break
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default:
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end = i + 1
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break
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}
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}
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// final token
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list.push(str.substring(start, end))
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return list
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}
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