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