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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);

}