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/**
* Expose `fresh()`.
*/
module.exports = fresh;
/**
* Check freshness of `req` and `res` headers.
*
* When the cache is "fresh" __true__ is returned,
* otherwise __false__ is returned to indicate that
* the cache is now stale.
*
* @param {Object} req
* @param {Object} res
* @return {Boolean}
* @api public
*/
function fresh(req, res) {
// defaults
var etagMatches = true;
var notModified = true;
// fields
var modifiedSince = req['if-modified-since'];
var noneMatch = req['if-none-match'];
var lastModified = res['last-modified'];
var etag = res['etag'];
var cc = req['cache-control'];
// unconditional request
if (!modifiedSince && !noneMatch) return false;
// check for no-cache cache request directive
if (cc && cc.indexOf('no-cache') !== -1) return false;
// parse if-none-match
if (noneMatch) noneMatch = noneMatch.split(/ *, */);
// if-none-match
if (noneMatch) etagMatches = ~noneMatch.indexOf(etag) || '*' == noneMatch[0];
// if-modified-since
if (modifiedSince) {
modifiedSince = new Date(modifiedSince);
lastModified = new Date(lastModified);
notModified = lastModified <= modifiedSince;
}
return !! (etagMatches && notModified);
}