674 lines
23 KiB
JavaScript
674 lines
23 KiB
JavaScript
'use strict';
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// rfc7231 6.1
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const statusCodeCacheableByDefault = new Set([
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200,
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203,
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204,
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206,
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300,
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301,
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404,
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405,
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410,
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414,
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501,
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]);
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// This implementation does not understand partial responses (206)
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const understoodStatuses = new Set([
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200,
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203,
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204,
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300,
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301,
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302,
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303,
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307,
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308,
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404,
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405,
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410,
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414,
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501,
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]);
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const errorStatusCodes = new Set([
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500,
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502,
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503,
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504,
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]);
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const hopByHopHeaders = {
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date: true, // included, because we add Age update Date
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connection: true,
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'keep-alive': true,
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'proxy-authenticate': true,
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'proxy-authorization': true,
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te: true,
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trailer: true,
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'transfer-encoding': true,
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upgrade: true,
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};
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const excludedFromRevalidationUpdate = {
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// Since the old body is reused, it doesn't make sense to change properties of the body
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'content-length': true,
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'content-encoding': true,
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'transfer-encoding': true,
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'content-range': true,
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};
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function toNumberOrZero(s) {
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const n = parseInt(s, 10);
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return isFinite(n) ? n : 0;
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}
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// RFC 5861
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function isErrorResponse(response) {
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// consider undefined response as faulty
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if(!response) {
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return true
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}
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return errorStatusCodes.has(response.status);
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}
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function parseCacheControl(header) {
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const cc = {};
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if (!header) return cc;
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// TODO: When there is more than one value present for a given directive (e.g., two Expires header fields, multiple Cache-Control: max-age directives),
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// the directive's value is considered invalid. Caches are encouraged to consider responses that have invalid freshness information to be stale
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const parts = header.trim().split(/\s*,\s*/); // TODO: lame parsing
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for (const part of parts) {
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const [k, v] = part.split(/\s*=\s*/, 2);
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cc[k] = v === undefined ? true : v.replace(/^"|"$/g, ''); // TODO: lame unquoting
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}
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return cc;
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}
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function formatCacheControl(cc) {
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let parts = [];
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for (const k in cc) {
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const v = cc[k];
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parts.push(v === true ? k : k + '=' + v);
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}
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if (!parts.length) {
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return undefined;
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}
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return parts.join(', ');
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}
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module.exports = class CachePolicy {
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constructor(
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req,
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res,
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{
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shared,
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cacheHeuristic,
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immutableMinTimeToLive,
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ignoreCargoCult,
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_fromObject,
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} = {}
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) {
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if (_fromObject) {
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this._fromObject(_fromObject);
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return;
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}
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if (!res || !res.headers) {
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throw Error('Response headers missing');
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}
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this._assertRequestHasHeaders(req);
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this._responseTime = this.now();
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this._isShared = shared !== false;
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this._cacheHeuristic =
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undefined !== cacheHeuristic ? cacheHeuristic : 0.1; // 10% matches IE
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this._immutableMinTtl =
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undefined !== immutableMinTimeToLive
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? immutableMinTimeToLive
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: 24 * 3600 * 1000;
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this._status = 'status' in res ? res.status : 200;
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this._resHeaders = res.headers;
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this._rescc = parseCacheControl(res.headers['cache-control']);
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this._method = 'method' in req ? req.method : 'GET';
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this._url = req.url;
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this._host = req.headers.host;
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this._noAuthorization = !req.headers.authorization;
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this._reqHeaders = res.headers.vary ? req.headers : null; // Don't keep all request headers if they won't be used
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this._reqcc = parseCacheControl(req.headers['cache-control']);
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// Assume that if someone uses legacy, non-standard uncecessary options they don't understand caching,
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// so there's no point stricly adhering to the blindly copy&pasted directives.
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if (
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ignoreCargoCult &&
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'pre-check' in this._rescc &&
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'post-check' in this._rescc
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) {
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delete this._rescc['pre-check'];
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delete this._rescc['post-check'];
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delete this._rescc['no-cache'];
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delete this._rescc['no-store'];
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delete this._rescc['must-revalidate'];
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this._resHeaders = Object.assign({}, this._resHeaders, {
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'cache-control': formatCacheControl(this._rescc),
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});
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delete this._resHeaders.expires;
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delete this._resHeaders.pragma;
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}
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// When the Cache-Control header field is not present in a request, caches MUST consider the no-cache request pragma-directive
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// as having the same effect as if "Cache-Control: no-cache" were present (see Section 5.2.1).
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if (
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res.headers['cache-control'] == null &&
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/no-cache/.test(res.headers.pragma)
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) {
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this._rescc['no-cache'] = true;
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}
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}
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now() {
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return Date.now();
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}
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storable() {
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// The "no-store" request directive indicates that a cache MUST NOT store any part of either this request or any response to it.
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return !!(
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!this._reqcc['no-store'] &&
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// A cache MUST NOT store a response to any request, unless:
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// The request method is understood by the cache and defined as being cacheable, and
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('GET' === this._method ||
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'HEAD' === this._method ||
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('POST' === this._method && this._hasExplicitExpiration())) &&
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// the response status code is understood by the cache, and
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understoodStatuses.has(this._status) &&
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// the "no-store" cache directive does not appear in request or response header fields, and
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!this._rescc['no-store'] &&
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// the "private" response directive does not appear in the response, if the cache is shared, and
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(!this._isShared || !this._rescc.private) &&
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// the Authorization header field does not appear in the request, if the cache is shared,
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(!this._isShared ||
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this._noAuthorization ||
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this._allowsStoringAuthenticated()) &&
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// the response either:
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// contains an Expires header field, or
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(this._resHeaders.expires ||
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// contains a max-age response directive, or
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// contains a s-maxage response directive and the cache is shared, or
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// contains a public response directive.
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this._rescc['max-age'] ||
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(this._isShared && this._rescc['s-maxage']) ||
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this._rescc.public ||
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// has a status code that is defined as cacheable by default
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statusCodeCacheableByDefault.has(this._status))
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);
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}
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_hasExplicitExpiration() {
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// 4.2.1 Calculating Freshness Lifetime
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return (
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(this._isShared && this._rescc['s-maxage']) ||
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this._rescc['max-age'] ||
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this._resHeaders.expires
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);
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}
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_assertRequestHasHeaders(req) {
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if (!req || !req.headers) {
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throw Error('Request headers missing');
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}
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}
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satisfiesWithoutRevalidation(req) {
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this._assertRequestHasHeaders(req);
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// When presented with a request, a cache MUST NOT reuse a stored response, unless:
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// the presented request does not contain the no-cache pragma (Section 5.4), nor the no-cache cache directive,
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// unless the stored response is successfully validated (Section 4.3), and
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const requestCC = parseCacheControl(req.headers['cache-control']);
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if (requestCC['no-cache'] || /no-cache/.test(req.headers.pragma)) {
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return false;
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}
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if (requestCC['max-age'] && this.age() > requestCC['max-age']) {
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return false;
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}
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if (
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requestCC['min-fresh'] &&
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this.timeToLive() < 1000 * requestCC['min-fresh']
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) {
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return false;
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}
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// the stored response is either:
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// fresh, or allowed to be served stale
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if (this.stale()) {
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const allowsStale =
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requestCC['max-stale'] &&
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!this._rescc['must-revalidate'] &&
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(true === requestCC['max-stale'] ||
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requestCC['max-stale'] > this.age() - this.maxAge());
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if (!allowsStale) {
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return false;
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}
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}
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return this._requestMatches(req, false);
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}
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_requestMatches(req, allowHeadMethod) {
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// The presented effective request URI and that of the stored response match, and
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return (
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(!this._url || this._url === req.url) &&
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this._host === req.headers.host &&
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// the request method associated with the stored response allows it to be used for the presented request, and
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(!req.method ||
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this._method === req.method ||
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(allowHeadMethod && 'HEAD' === req.method)) &&
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// selecting header fields nominated by the stored response (if any) match those presented, and
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this._varyMatches(req)
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);
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}
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_allowsStoringAuthenticated() {
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// following Cache-Control response directives (Section 5.2.2) have such an effect: must-revalidate, public, and s-maxage.
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return (
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this._rescc['must-revalidate'] ||
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this._rescc.public ||
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this._rescc['s-maxage']
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);
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}
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_varyMatches(req) {
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if (!this._resHeaders.vary) {
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return true;
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}
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// A Vary header field-value of "*" always fails to match
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if (this._resHeaders.vary === '*') {
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return false;
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}
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const fields = this._resHeaders.vary
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.trim()
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.toLowerCase()
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.split(/\s*,\s*/);
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for (const name of fields) {
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if (req.headers[name] !== this._reqHeaders[name]) return false;
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}
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return true;
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}
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_copyWithoutHopByHopHeaders(inHeaders) {
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const headers = {};
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for (const name in inHeaders) {
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if (hopByHopHeaders[name]) continue;
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headers[name] = inHeaders[name];
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}
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// 9.1. Connection
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if (inHeaders.connection) {
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const tokens = inHeaders.connection.trim().split(/\s*,\s*/);
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for (const name of tokens) {
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delete headers[name];
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}
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}
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if (headers.warning) {
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const warnings = headers.warning.split(/,/).filter(warning => {
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return !/^\s*1[0-9][0-9]/.test(warning);
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});
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if (!warnings.length) {
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delete headers.warning;
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} else {
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headers.warning = warnings.join(',').trim();
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}
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}
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return headers;
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}
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responseHeaders() {
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const headers = this._copyWithoutHopByHopHeaders(this._resHeaders);
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const age = this.age();
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// A cache SHOULD generate 113 warning if it heuristically chose a freshness
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// lifetime greater than 24 hours and the response's age is greater than 24 hours.
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if (
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age > 3600 * 24 &&
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!this._hasExplicitExpiration() &&
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this.maxAge() > 3600 * 24
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) {
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headers.warning =
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(headers.warning ? `${headers.warning}, ` : '') +
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'113 - "rfc7234 5.5.4"';
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}
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headers.age = `${Math.round(age)}`;
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headers.date = new Date(this.now()).toUTCString();
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return headers;
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}
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/**
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* Value of the Date response header or current time if Date was invalid
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* @return timestamp
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*/
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date() {
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const serverDate = Date.parse(this._resHeaders.date);
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if (isFinite(serverDate)) {
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return serverDate;
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}
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return this._responseTime;
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}
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/**
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* Value of the Age header, in seconds, updated for the current time.
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* May be fractional.
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*
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* @return Number
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*/
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age() {
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let age = this._ageValue();
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const residentTime = (this.now() - this._responseTime) / 1000;
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return age + residentTime;
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}
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_ageValue() {
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return toNumberOrZero(this._resHeaders.age);
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}
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/**
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* Value of applicable max-age (or heuristic equivalent) in seconds. This counts since response's `Date`.
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*
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* For an up-to-date value, see `timeToLive()`.
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*
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* @return Number
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*/
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maxAge() {
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if (!this.storable() || this._rescc['no-cache']) {
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return 0;
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}
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// Shared responses with cookies are cacheable according to the RFC, but IMHO it'd be unwise to do so by default
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// so this implementation requires explicit opt-in via public header
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if (
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this._isShared &&
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(this._resHeaders['set-cookie'] &&
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!this._rescc.public &&
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!this._rescc.immutable)
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) {
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return 0;
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}
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if (this._resHeaders.vary === '*') {
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return 0;
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}
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if (this._isShared) {
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if (this._rescc['proxy-revalidate']) {
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return 0;
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}
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// if a response includes the s-maxage directive, a shared cache recipient MUST ignore the Expires field.
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if (this._rescc['s-maxage']) {
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return toNumberOrZero(this._rescc['s-maxage']);
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}
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}
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// If a response includes a Cache-Control field with the max-age directive, a recipient MUST ignore the Expires field.
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if (this._rescc['max-age']) {
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return toNumberOrZero(this._rescc['max-age']);
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}
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const defaultMinTtl = this._rescc.immutable ? this._immutableMinTtl : 0;
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const serverDate = this.date();
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if (this._resHeaders.expires) {
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const expires = Date.parse(this._resHeaders.expires);
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// A cache recipient MUST interpret invalid date formats, especially the value "0", as representing a time in the past (i.e., "already expired").
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if (Number.isNaN(expires) || expires < serverDate) {
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return 0;
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}
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return Math.max(defaultMinTtl, (expires - serverDate) / 1000);
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}
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if (this._resHeaders['last-modified']) {
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const lastModified = Date.parse(this._resHeaders['last-modified']);
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if (isFinite(lastModified) && serverDate > lastModified) {
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return Math.max(
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defaultMinTtl,
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((serverDate - lastModified) / 1000) * this._cacheHeuristic
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);
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}
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}
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return defaultMinTtl;
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}
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timeToLive() {
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const age = this.maxAge() - this.age();
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const staleIfErrorAge = age + toNumberOrZero(this._rescc['stale-if-error']);
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const staleWhileRevalidateAge = age + toNumberOrZero(this._rescc['stale-while-revalidate']);
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return Math.max(0, age, staleIfErrorAge, staleWhileRevalidateAge) * 1000;
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}
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stale() {
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return this.maxAge() <= this.age();
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}
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_useStaleIfError() {
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return this.maxAge() + toNumberOrZero(this._rescc['stale-if-error']) > this.age();
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}
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useStaleWhileRevalidate() {
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return this.maxAge() + toNumberOrZero(this._rescc['stale-while-revalidate']) > this.age();
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}
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static fromObject(obj) {
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return new this(undefined, undefined, { _fromObject: obj });
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}
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_fromObject(obj) {
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if (this._responseTime) throw Error('Reinitialized');
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if (!obj || obj.v !== 1) throw Error('Invalid serialization');
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this._responseTime = obj.t;
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this._isShared = obj.sh;
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this._cacheHeuristic = obj.ch;
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this._immutableMinTtl =
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obj.imm !== undefined ? obj.imm : 24 * 3600 * 1000;
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this._status = obj.st;
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this._resHeaders = obj.resh;
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this._rescc = obj.rescc;
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this._method = obj.m;
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this._url = obj.u;
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this._host = obj.h;
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this._noAuthorization = obj.a;
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this._reqHeaders = obj.reqh;
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this._reqcc = obj.reqcc;
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}
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toObject() {
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return {
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v: 1,
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t: this._responseTime,
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sh: this._isShared,
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ch: this._cacheHeuristic,
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imm: this._immutableMinTtl,
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st: this._status,
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resh: this._resHeaders,
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rescc: this._rescc,
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m: this._method,
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u: this._url,
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h: this._host,
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a: this._noAuthorization,
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reqh: this._reqHeaders,
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reqcc: this._reqcc,
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};
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}
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/**
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* Headers for sending to the origin server to revalidate stale response.
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* Allows server to return 304 to allow reuse of the previous response.
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*
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* Hop by hop headers are always stripped.
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* Revalidation headers may be added or removed, depending on request.
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*/
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revalidationHeaders(incomingReq) {
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this._assertRequestHasHeaders(incomingReq);
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const headers = this._copyWithoutHopByHopHeaders(incomingReq.headers);
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// This implementation does not understand range requests
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delete headers['if-range'];
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if (!this._requestMatches(incomingReq, true) || !this.storable()) {
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// revalidation allowed via HEAD
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// not for the same resource, or wasn't allowed to be cached anyway
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delete headers['if-none-match'];
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delete headers['if-modified-since'];
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return headers;
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}
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/* MUST send that entity-tag in any cache validation request (using If-Match or If-None-Match) if an entity-tag has been provided by the origin server. */
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if (this._resHeaders.etag) {
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headers['if-none-match'] = headers['if-none-match']
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? `${headers['if-none-match']}, ${this._resHeaders.etag}`
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: this._resHeaders.etag;
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}
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// Clients MAY issue simple (non-subrange) GET requests with either weak validators or strong validators. Clients MUST NOT use weak validators in other forms of request.
|
|
const forbidsWeakValidators =
|
|
headers['accept-ranges'] ||
|
|
headers['if-match'] ||
|
|
headers['if-unmodified-since'] ||
|
|
(this._method && this._method != 'GET');
|
|
|
|
/* SHOULD send the Last-Modified value in non-subrange cache validation requests (using If-Modified-Since) if only a Last-Modified value has been provided by the origin server.
|
|
Note: This implementation does not understand partial responses (206) */
|
|
if (forbidsWeakValidators) {
|
|
delete headers['if-modified-since'];
|
|
|
|
if (headers['if-none-match']) {
|
|
const etags = headers['if-none-match']
|
|
.split(/,/)
|
|
.filter(etag => {
|
|
return !/^\s*W\//.test(etag);
|
|
});
|
|
if (!etags.length) {
|
|
delete headers['if-none-match'];
|
|
} else {
|
|
headers['if-none-match'] = etags.join(',').trim();
|
|
}
|
|
}
|
|
} else if (
|
|
this._resHeaders['last-modified'] &&
|
|
!headers['if-modified-since']
|
|
) {
|
|
headers['if-modified-since'] = this._resHeaders['last-modified'];
|
|
}
|
|
|
|
return headers;
|
|
}
|
|
|
|
/**
|
|
* Creates new CachePolicy with information combined from the previews response,
|
|
* and the new revalidation response.
|
|
*
|
|
* Returns {policy, modified} where modified is a boolean indicating
|
|
* whether the response body has been modified, and old cached body can't be used.
|
|
*
|
|
* @return {Object} {policy: CachePolicy, modified: Boolean}
|
|
*/
|
|
revalidatedPolicy(request, response) {
|
|
this._assertRequestHasHeaders(request);
|
|
if(this._useStaleIfError() && isErrorResponse(response)) { // I consider the revalidation request unsuccessful
|
|
return {
|
|
modified: false,
|
|
matches: false,
|
|
policy: this,
|
|
};
|
|
}
|
|
if (!response || !response.headers) {
|
|
throw Error('Response headers missing');
|
|
}
|
|
|
|
// These aren't going to be supported exactly, since one CachePolicy object
|
|
// doesn't know about all the other cached objects.
|
|
let matches = false;
|
|
if (response.status !== undefined && response.status != 304) {
|
|
matches = false;
|
|
} else if (
|
|
response.headers.etag &&
|
|
!/^\s*W\//.test(response.headers.etag)
|
|
) {
|
|
// "All of the stored responses with the same strong validator are selected.
|
|
// If none of the stored responses contain the same strong validator,
|
|
// then the cache MUST NOT use the new response to update any stored responses."
|
|
matches =
|
|
this._resHeaders.etag &&
|
|
this._resHeaders.etag.replace(/^\s*W\//, '') ===
|
|
response.headers.etag;
|
|
} else if (this._resHeaders.etag && response.headers.etag) {
|
|
// "If the new response contains a weak validator and that validator corresponds
|
|
// to one of the cache's stored responses,
|
|
// then the most recent of those matching stored responses is selected for update."
|
|
matches =
|
|
this._resHeaders.etag.replace(/^\s*W\//, '') ===
|
|
response.headers.etag.replace(/^\s*W\//, '');
|
|
} else if (this._resHeaders['last-modified']) {
|
|
matches =
|
|
this._resHeaders['last-modified'] ===
|
|
response.headers['last-modified'];
|
|
} else {
|
|
// If the new response does not include any form of validator (such as in the case where
|
|
// a client generates an If-Modified-Since request from a source other than the Last-Modified
|
|
// response header field), and there is only one stored response, and that stored response also
|
|
// lacks a validator, then that stored response is selected for update.
|
|
if (
|
|
!this._resHeaders.etag &&
|
|
!this._resHeaders['last-modified'] &&
|
|
!response.headers.etag &&
|
|
!response.headers['last-modified']
|
|
) {
|
|
matches = true;
|
|
}
|
|
}
|
|
|
|
if (!matches) {
|
|
return {
|
|
policy: new this.constructor(request, response),
|
|
// Client receiving 304 without body, even if it's invalid/mismatched has no option
|
|
// but to reuse a cached body. We don't have a good way to tell clients to do
|
|
// error recovery in such case.
|
|
modified: response.status != 304,
|
|
matches: false,
|
|
};
|
|
}
|
|
|
|
// use other header fields provided in the 304 (Not Modified) response to replace all instances
|
|
// of the corresponding header fields in the stored response.
|
|
const headers = {};
|
|
for (const k in this._resHeaders) {
|
|
headers[k] =
|
|
k in response.headers && !excludedFromRevalidationUpdate[k]
|
|
? response.headers[k]
|
|
: this._resHeaders[k];
|
|
}
|
|
|
|
const newResponse = Object.assign({}, response, {
|
|
status: this._status,
|
|
method: this._method,
|
|
headers,
|
|
});
|
|
return {
|
|
policy: new this.constructor(request, newResponse, {
|
|
shared: this._isShared,
|
|
cacheHeuristic: this._cacheHeuristic,
|
|
immutableMinTimeToLive: this._immutableMinTtl,
|
|
}),
|
|
modified: false,
|
|
matches: true,
|
|
};
|
|
}
|
|
};
|