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node_modules/make-fetch-happen/lib/cache/policy.js

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+const CacheSemantics = require('http-cache-semantics')
+const Negotiator = require('negotiator')
+const ssri = require('ssri')
+
+// options passed to http-cache-semantics constructor
+const policyOptions = {
+  shared: false,
+  ignoreCargoCult: true,
+}
+
+// a fake empty response, used when only testing the
+// request for storability
+const emptyResponse = { status: 200, headers: {} }
+
+// returns a plain object representation of the Request
+const requestObject = (request) => {
+  const _obj = {
+    method: request.method,
+    url: request.url,
+    headers: {},
+    compress: request.compress,
+  }
+
+  request.headers.forEach((value, key) => {
+    _obj.headers[key] = value
+  })
+
+  return _obj
+}
+
+// returns a plain object representation of the Response
+const responseObject = (response) => {
+  const _obj = {
+    status: response.status,
+    headers: {},
+  }
+
+  response.headers.forEach((value, key) => {
+    _obj.headers[key] = value
+  })
+
+  return _obj
+}
+
+class CachePolicy {
+  constructor ({ entry, request, response, options }) {
+    this.entry = entry
+    this.request = requestObject(request)
+    this.response = responseObject(response)
+    this.options = options
+    this.policy = new CacheSemantics(this.request, this.response, policyOptions)
+
+    if (this.entry) {
+      // if we have an entry, copy the timestamp to the _responseTime
+      // this is necessary because the CacheSemantics constructor forces
+      // the value to Date.now() which means a policy created from a
+      // cache entry is likely to always identify itself as stale
+      this.policy._responseTime = this.entry.metadata.time
+    }
+  }
+
+  // static method to quickly determine if a request alone is storable
+  static storable (request, options) {
+    // no cachePath means no caching
+    if (!options.cachePath) {
+      return false
+    }
+
+    // user explicitly asked not to cache
+    if (options.cache === 'no-store') {
+      return false
+    }
+
+    // we only cache GET and HEAD requests
+    if (!['GET', 'HEAD'].includes(request.method)) {
+      return false
+    }
+
+    // otherwise, let http-cache-semantics make the decision
+    // based on the request's headers
+    const policy = new CacheSemantics(requestObject(request), emptyResponse, policyOptions)
+    return policy.storable()
+  }
+
+  // returns true if the policy satisfies the request
+  satisfies (request) {
+    const _req = requestObject(request)
+    if (this.request.headers.host !== _req.headers.host) {
+      return false
+    }
+
+    if (this.request.compress !== _req.compress) {
+      return false
+    }
+
+    const negotiatorA = new Negotiator(this.request)
+    const negotiatorB = new Negotiator(_req)
+
+    if (JSON.stringify(negotiatorA.mediaTypes()) !== JSON.stringify(negotiatorB.mediaTypes())) {
+      return false
+    }
+
+    if (JSON.stringify(negotiatorA.languages()) !== JSON.stringify(negotiatorB.languages())) {
+      return false
+    }
+
+    if (JSON.stringify(negotiatorA.encodings()) !== JSON.stringify(negotiatorB.encodings())) {
+      return false
+    }
+
+    if (this.options.integrity) {
+      return ssri.parse(this.options.integrity).match(this.entry.integrity)
+    }
+
+    return true
+  }
+
+  // returns true if the request and response allow caching
+  storable () {
+    return this.policy.storable()
+  }
+
+  // NOTE: this is a hack to avoid parsing the cache-control
+  // header ourselves, it returns true if the response's
+  // cache-control contains must-revalidate
+  get mustRevalidate () {
+    return !!this.policy._rescc['must-revalidate']
+  }
+
+  // returns true if the cached response requires revalidation
+  // for the given request
+  needsRevalidation (request) {
+    const _req = requestObject(request)
+    // force method to GET because we only cache GETs
+    // but can serve a HEAD from a cached GET
+    _req.method = 'GET'
+    return !this.policy.satisfiesWithoutRevalidation(_req)
+  }
+
+  responseHeaders () {
+    return this.policy.responseHeaders()
+  }
+
+  // returns a new object containing the appropriate headers
+  // to send a revalidation request
+  revalidationHeaders (request) {
+    const _req = requestObject(request)
+    return this.policy.revalidationHeaders(_req)
+  }
+
+  // returns true if the request/response was revalidated
+  // successfully. returns false if a new response was received
+  revalidated (request, response) {
+    const _req = requestObject(request)
+    const _res = responseObject(response)
+    const policy = this.policy.revalidatedPolicy(_req, _res)
+    return !policy.modified
+  }
+}
+
+module.exports = CachePolicy