FEATURE: Make Discourse work offline with WorkboxJS (#7870)

app/assets/javascripts/discourse/initializers/register-service-worker.js.es6

@@ -9,9 +9,7 @@ export default {
     const isSupported = isSecured && "serviceWorker" in navigator;
 
     if (isSupported) {
-      const isApple = !!navigator.platform.match(/(Mac|iPhone|iPod|iPad)/i);
-
-      if (Discourse.ServiceWorkerURL && !isApple) {
+      if (Discourse.ServiceWorkerURL) {
         navigator.serviceWorker.getRegistrations().then(registrations => {
           for (let registration of registrations) {
             if (

app/assets/javascripts/discourse/lib/ajax.js.es6

@@ -140,7 +140,7 @@ export function ajax() {
     }
 
     if (args.type === "GET" && args.cache !== true) {
-      args.cache = false;
+      args.cache = true; // Disable JQuery cache busting param, which was created to deal with IE8
     }
 
     ajaxObj = $.ajax(Discourse.getURL(url), args);

app/assets/javascripts/service-worker.js.erb

@@ -1,117 +1,25 @@
 'use strict';
 
+importScripts("<%= ::UrlHelper.absolute("/javascripts/workbox/workbox-sw.js") %>");
 
-// Special offline and fetch interception is restricted to Android only
-// we have had a large amount of pain supporting this on Firefox / Safari
-// it is only strongly required on Android, when PWA gets better on iOS
-// we can unlock it there as well, for Desktop we can consider unlocking it
-// if we start supporting offline browsing for laptops
-if (/(android)/i.test(navigator.userAgent)) {
+workbox.setConfig({
+  modulePathPrefix: "<%= ::UrlHelper.absolute("/javascripts/workbox") %>"
+});
 
-  // Incrementing CACHE_VERSION will kick off the install event and force previously cached
-  // resources to be cached again.
-  const CACHE_VERSION = 1;
+const cacheVersion = "1";
 
-  const CURRENT_CACHES = {
-    offline: 'offline-v' + CACHE_VERSION
-  };
-
-  const OFFLINE_URL = 'offline.html';
-
-  const createCacheBustedRequest = function(url) {
-    var headers = new Headers({
-      'Discourse-Track-View': '0'
-    });
-
-    var request = new Request(url, {cache: 'reload', headers: headers});
-    // See https://fetch.spec.whatwg.org/#concept-request-mode
-    // This is not yet supported in Chrome as of M48, so we need to explicitly check to see
-    // if the cache: 'reload' option had any effect.
-    if ('cache' in request) {
-      return request;
-    }
-
-    // If {cache: 'reload'} didn't have any effect, append a cache-busting URL parameter instead.
-    var bustedUrl = new URL(url, self.location.href);
-    bustedUrl.search += (bustedUrl.search ? '&' : '') + 'cachebust=' + Date.now();
-    return new Request(bustedUrl, {headers: headers});
-  }
-
-  self.addEventListener('install', function(event) {
-    event.waitUntil(
-      // We can't use cache.add() here, since we want OFFLINE_URL to be the cache key, but
-      // the actual URL we end up requesting might include a cache-busting parameter.
-      fetch(createCacheBustedRequest(OFFLINE_URL)).then(function(response) {
-        return caches.open(CURRENT_CACHES.offline).then(function(cache) {
-          return cache.put(OFFLINE_URL, response);
-        });
-      }).then(function(cache) {
-        self.skipWaiting();
-      })
-    );
-  });
-
-  self.addEventListener('activate', function(event) {
-    // Delete all caches that aren't named in CURRENT_CACHES.
-    // While there is only one cache in this example, the same logic will handle the case where
-    // there are multiple versioned caches.
-    var expectedCacheNames = Object.keys(CURRENT_CACHES).map(function(key) {
-      return CURRENT_CACHES[key];
-    });
-
-    event.waitUntil(
-      caches.keys().then(function(cacheNames) {
-        return Promise.all(
-          cacheNames.map(function(cacheName) {
-            if (expectedCacheNames.indexOf(cacheName) === -1) {
-              // If this cache name isn't present in the array of "expected" cache names,
-              // then delete it.
-              return caches.delete(cacheName);
-            }
-          })
-        );
-      }).then(function() {
-        self.clients.claim()
-      })
-    );
-  });
-
-  self.addEventListener('fetch', function(event) {
-    // Bypass service workers if this is a url with a token param
-    if(/\?.*token/i.test(event.request.url)) {
-      return;
-    }
-    // We only want to call event.respondWith() if this is a navigation request
-    // for an HTML page.
-    // request.mode of 'navigate' is unfortunately not supported in Chrome
-    // versions older than 49, so we need to include a less precise fallback,
-    // which checks for a GET request with an Accept: text/html header.
-    if (event.request.mode === 'navigate' ||
-        (event.request.method === 'GET' &&
-         event.request.headers.get('accept').includes('text/html'))) {
-      event.respondWith(
-        fetch(event.request).catch(function(error) {
-          // The catch is only triggered if fetch() throws an exception, which will most likely
-          // happen due to the server being unreachable.
-          // If fetch() returns a valid HTTP response with an response code in the 4xx or 5xx
-          // range, the catch() will NOT be called. If you need custom handling for 4xx or 5xx
-          // errors, see https://github.com/GoogleChrome/samples/tree/gh-pages/service-worker/fallback-response
-          if (!navigator.onLine) {
-            return caches.match(OFFLINE_URL);
-          } else {
-            throw new Error(error);
-          }
-        })
-      );
-    }
-
-    // If our if() condition is false, then this fetch handler won't intercept the request.
-    // If there are any other fetch handlers registered, they will get a chance to call
-    // event.respondWith(). If no fetch handlers call event.respondWith(), the request will be
-    // handled by the browser as if there were no service worker involvement.
-  });
-
-}
+// Cache all GET requests, so Discourse can be used while offline
+workbox.routing.registerRoute(
+  new RegExp('.*?'), // Matches all, GET is implicit
+  new workbox.strategies.NetworkFirst({ // This will only use the cache when a network request fails
+    cacheName: "discourse-" + cacheVersion,
+    plugins: [
+      new workbox.expiration.Plugin({
+        maxAgeSeconds: 7* 24 * 60 * 60, // 7 days
+      }),
+    ],
+  })
+);
 
 const idleThresholdTime = 1000 * 10; // 10 seconds
 var lastAction = -1;

lib/tasks/javascript.rake

@@ -90,6 +90,26 @@ task 'javascript:update' do
     }, {
       # TODO: drop when we eventually drop IE11, this will land in iOS in version 13
       source: 'intersection-observer/intersection-observer.js'
+    }, {
+      source: 'workbox-sw/build/.',
+      destination: 'workbox',
+      public: true
+    }, {
+      source: 'workbox-routing/build/.',
+      destination: 'workbox',
+      public: true
+    }, {
+      source: 'workbox-core/build/.',
+      destination: 'workbox',
+      public: true
+    }, {
+      source: 'workbox-strategies/build/.',
+      destination: 'workbox',
+      public: true
+    }, {
+      source: 'workbox-expiration/build/.',
+      destination: 'workbox',
+      public: true
     }
   ]
 

package.json

@@ -30,7 +30,12 @@
     "mousetrap": "https://github.com/discourse/mousetrap#firefox-alt-key",
     "pikaday": "1.8.0",
     "resumablejs": "1.1.0",
-    "spectrum-colorpicker": "1.8.0"
+    "spectrum-colorpicker": "1.8.0",
+    "workbox-core": "^4.3.1",
+    "workbox-expiration": "^4.3.1",
+    "workbox-routing": "^4.3.1",
+    "workbox-strategies": "^4.3.1",
+    "workbox-sw": "^4.3.1"
   },
   "devDependencies": {
     "@arkweid/lefthook": "^0.5.6",

public/javascripts/workbox/workbox-expiration.dev.js

@@ -0,0 +1,652 @@
+this.workbox = this.workbox || {};
+this.workbox.expiration = (function (exports, DBWrapper_mjs, deleteDatabase_mjs, WorkboxError_mjs, assert_mjs, logger_mjs, cacheNames_mjs, getFriendlyURL_mjs, registerQuotaErrorCallback_mjs) {
+  'use strict';
+
+  try {
+    self['workbox:expiration:4.3.1'] && _();
+  } catch (e) {} // eslint-disable-line
+
+  /*
+    Copyright 2018 Google LLC
+
+    Use of this source code is governed by an MIT-style
+    license that can be found in the LICENSE file or at
+    https://opensource.org/licenses/MIT.
+  */
+  const DB_NAME = 'workbox-expiration';
+  const OBJECT_STORE_NAME = 'cache-entries';
+
+  const normalizeURL = unNormalizedUrl => {
+    const url = new URL(unNormalizedUrl, location);
+    url.hash = '';
+    return url.href;
+  };
+  /**
+   * Returns the timestamp model.
+   *
+   * @private
+   */
+
+
+  class CacheTimestampsModel {
+    /**
+     *
+     * @param {string} cacheName
+     *
+     * @private
+     */
+    constructor(cacheName) {
+      this._cacheName = cacheName;
+      this._db = new DBWrapper_mjs.DBWrapper(DB_NAME, 1, {
+        onupgradeneeded: event => this._handleUpgrade(event)
+      });
+    }
+    /**
+     * Should perform an upgrade of indexedDB.
+     *
+     * @param {Event} event
+     *
+     * @private
+     */
+
+
+    _handleUpgrade(event) {
+      const db = event.target.result; // TODO(philipwalton): EdgeHTML doesn't support arrays as a keyPath, so we
+      // have to use the `id` keyPath here and create our own values (a
+      // concatenation of `url + cacheName`) instead of simply using
+      // `keyPath: ['url', 'cacheName']`, which is supported in other browsers.
+
+      const objStore = db.createObjectStore(OBJECT_STORE_NAME, {
+        keyPath: 'id'
+      }); // TODO(philipwalton): once we don't have to support EdgeHTML, we can
+      // create a single index with the keyPath `['cacheName', 'timestamp']`
+      // instead of doing both these indexes.
+
+      objStore.createIndex('cacheName', 'cacheName', {
+        unique: false
+      });
+      objStore.createIndex('timestamp', 'timestamp', {
+        unique: false
+      }); // Previous versions of `workbox-expiration` used `this._cacheName`
+      // as the IDBDatabase name.
+
+      deleteDatabase_mjs.deleteDatabase(this._cacheName);
+    }
+    /**
+     * @param {string} url
+     * @param {number} timestamp
+     *
+     * @private
+     */
+
+
+    async setTimestamp(url, timestamp) {
+      url = normalizeURL(url);
+      await this._db.put(OBJECT_STORE_NAME, {
+        url,
+        timestamp,
+        cacheName: this._cacheName,
+        // Creating an ID from the URL and cache name won't be necessary once
+        // Edge switches to Chromium and all browsers we support work with
+        // array keyPaths.
+        id: this._getId(url)
+      });
+    }
+    /**
+     * Returns the timestamp stored for a given URL.
+     *
+     * @param {string} url
+     * @return {number}
+     *
+     * @private
+     */
+
+
+    async getTimestamp(url) {
+      const entry = await this._db.get(OBJECT_STORE_NAME, this._getId(url));
+      return entry.timestamp;
+    }
+    /**
+     * Iterates through all the entries in the object store (from newest to
+     * oldest) and removes entries once either `maxCount` is reached or the
+     * entry's timestamp is less than `minTimestamp`.
+     *
+     * @param {number} minTimestamp
+     * @param {number} maxCount
+     *
+     * @private
+     */
+
+
+    async expireEntries(minTimestamp, maxCount) {
+      const entriesToDelete = await this._db.transaction(OBJECT_STORE_NAME, 'readwrite', (txn, done) => {
+        const store = txn.objectStore(OBJECT_STORE_NAME);
+        const entriesToDelete = [];
+        let entriesNotDeletedCount = 0;
+
+        store.index('timestamp').openCursor(null, 'prev').onsuccess = ({
+          target
+        }) => {
+          const cursor = target.result;
+
+          if (cursor) {
+            const result = cursor.value; // TODO(philipwalton): once we can use a multi-key index, we
+            // won't have to check `cacheName` here.
+
+            if (result.cacheName === this._cacheName) {
+              // Delete an entry if it's older than the max age or
+              // if we already have the max number allowed.
+              if (minTimestamp && result.timestamp < minTimestamp || maxCount && entriesNotDeletedCount >= maxCount) {
+                // TODO(philipwalton): we should be able to delete the
+                // entry right here, but doing so causes an iteration
+                // bug in Safari stable (fixed in TP). Instead we can
+                // store the keys of the entries to delete, and then
+                // delete the separate transactions.
+                // https://github.com/GoogleChrome/workbox/issues/1978
+                // cursor.delete();
+                // We only need to return the URL, not the whole entry.
+                entriesToDelete.push(cursor.value);
+              } else {
+                entriesNotDeletedCount++;
+              }
+            }
+
+            cursor.continue();
+          } else {
+            done(entriesToDelete);
+          }
+        };
+      }); // TODO(philipwalton): once the Safari bug in the following issue is fixed,
+      // we should be able to remove this loop and do the entry deletion in the
+      // cursor loop above:
+      // https://github.com/GoogleChrome/workbox/issues/1978
+
+      const urlsDeleted = [];
+
+      for (const entry of entriesToDelete) {
+        await this._db.delete(OBJECT_STORE_NAME, entry.id);
+        urlsDeleted.push(entry.url);
+      }
+
+      return urlsDeleted;
+    }
+    /**
+     * Takes a URL and returns an ID that will be unique in the object store.
+     *
+     * @param {string} url
+     * @return {string}
+     *
+     * @private
+     */
+
+
+    _getId(url) {
+      // Creating an ID from the URL and cache name won't be necessary once
+      // Edge switches to Chromium and all browsers we support work with
+      // array keyPaths.
+      return this._cacheName + '|' + normalizeURL(url);
+    }
+
+  }
+
+  /*
+    Copyright 2018 Google LLC
+
+    Use of this source code is governed by an MIT-style
+    license that can be found in the LICENSE file or at
+    https://opensource.org/licenses/MIT.
+  */
+  /**
+   * The `CacheExpiration` class allows you define an expiration and / or
+   * limit on the number of responses stored in a
+   * [`Cache`](https://developer.mozilla.org/en-US/docs/Web/API/Cache).
+   *
+   * @memberof workbox.expiration
+   */
+
+  class CacheExpiration {
+    /**
+     * To construct a new CacheExpiration instance you must provide at least
+     * one of the `config` properties.
+     *
+     * @param {string} cacheName Name of the cache to apply restrictions to.
+     * @param {Object} config
+     * @param {number} [config.maxEntries] The maximum number of entries to cache.
+     * Entries used the least will be removed as the maximum is reached.
+     * @param {number} [config.maxAgeSeconds] The maximum age of an entry before
+     * it's treated as stale and removed.
+     */
+    constructor(cacheName, config = {}) {
+      {
+        assert_mjs.assert.isType(cacheName, 'string', {
+          moduleName: 'workbox-expiration',
+          className: 'CacheExpiration',
+          funcName: 'constructor',
+          paramName: 'cacheName'
+        });
+
+        if (!(config.maxEntries || config.maxAgeSeconds)) {
+          throw new WorkboxError_mjs.WorkboxError('max-entries-or-age-required', {
+            moduleName: 'workbox-expiration',
+            className: 'CacheExpiration',
+            funcName: 'constructor'
+          });
+        }
+
+        if (config.maxEntries) {
+          assert_mjs.assert.isType(config.maxEntries, 'number', {
+            moduleName: 'workbox-expiration',
+            className: 'CacheExpiration',
+            funcName: 'constructor',
+            paramName: 'config.maxEntries'
+          }); // TODO: Assert is positive
+        }
+
+        if (config.maxAgeSeconds) {
+          assert_mjs.assert.isType(config.maxAgeSeconds, 'number', {
+            moduleName: 'workbox-expiration',
+            className: 'CacheExpiration',
+            funcName: 'constructor',
+            paramName: 'config.maxAgeSeconds'
+          }); // TODO: Assert is positive
+        }
+      }
+
+      this._isRunning = false;
+      this._rerunRequested = false;
+      this._maxEntries = config.maxEntries;
+      this._maxAgeSeconds = config.maxAgeSeconds;
+      this._cacheName = cacheName;
+      this._timestampModel = new CacheTimestampsModel(cacheName);
+    }
+    /**
+     * Expires entries for the given cache and given criteria.
+     */
+
+
+    async expireEntries() {
+      if (this._isRunning) {
+        this._rerunRequested = true;
+        return;
+      }
+
+      this._isRunning = true;
+      const minTimestamp = this._maxAgeSeconds ? Date.now() - this._maxAgeSeconds * 1000 : undefined;
+      const urlsExpired = await this._timestampModel.expireEntries(minTimestamp, this._maxEntries); // Delete URLs from the cache
+
+      const cache = await caches.open(this._cacheName);
+
+      for (const url of urlsExpired) {
+        await cache.delete(url);
+      }
+
+      {
+        if (urlsExpired.length > 0) {
+          logger_mjs.logger.groupCollapsed(`Expired ${urlsExpired.length} ` + `${urlsExpired.length === 1 ? 'entry' : 'entries'} and removed ` + `${urlsExpired.length === 1 ? 'it' : 'them'} from the ` + `'${this._cacheName}' cache.`);
+          logger_mjs.logger.log(`Expired the following ${urlsExpired.length === 1 ? 'URL' : 'URLs'}:`);
+          urlsExpired.forEach(url => logger_mjs.logger.log(`    ${url}`));
+          logger_mjs.logger.groupEnd();
+        } else {
+          logger_mjs.logger.debug(`Cache expiration ran and found no entries to remove.`);
+        }
+      }
+
+      this._isRunning = false;
+
+      if (this._rerunRequested) {
+        this._rerunRequested = false;
+        this.expireEntries();
+      }
+    }
+    /**
+     * Update the timestamp for the given URL. This ensures the when
+     * removing entries based on maximum entries, most recently used
+     * is accurate or when expiring, the timestamp is up-to-date.
+     *
+     * @param {string} url
+     */
+
+
+    async updateTimestamp(url) {
+      {
+        assert_mjs.assert.isType(url, 'string', {
+          moduleName: 'workbox-expiration',
+          className: 'CacheExpiration',
+          funcName: 'updateTimestamp',
+          paramName: 'url'
+        });
+      }
+
+      await this._timestampModel.setTimestamp(url, Date.now());
+    }
+    /**
+     * Can be used to check if a URL has expired or not before it's used.
+     *
+     * This requires a look up from IndexedDB, so can be slow.
+     *
+     * Note: This method will not remove the cached entry, call
+     * `expireEntries()` to remove indexedDB and Cache entries.
+     *
+     * @param {string} url
+     * @return {boolean}
+     */
+
+
+    async isURLExpired(url) {
+      {
+        if (!this._maxAgeSeconds) {
+          throw new WorkboxError_mjs.WorkboxError(`expired-test-without-max-age`, {
+            methodName: 'isURLExpired',
+            paramName: 'maxAgeSeconds'
+          });
+        }
+      }
+
+      const timestamp = await this._timestampModel.getTimestamp(url);
+      const expireOlderThan = Date.now() - this._maxAgeSeconds * 1000;
+      return timestamp < expireOlderThan;
+    }
+    /**
+     * Removes the IndexedDB object store used to keep track of cache expiration
+     * metadata.
+     */
+
+
+    async delete() {
+      // Make sure we don't attempt another rerun if we're called in the middle of
+      // a cache expiration.
+      this._rerunRequested = false;
+      await this._timestampModel.expireEntries(Infinity); // Expires all.
+    }
+
+  }
+
+  /*
+    Copyright 2018 Google LLC
+
+    Use of this source code is governed by an MIT-style
+    license that can be found in the LICENSE file or at
+    https://opensource.org/licenses/MIT.
+  */
+  /**
+   * This plugin can be used in the Workbox APIs to regularly enforce a
+   * limit on the age and / or the number of cached requests.
+   *
+   * Whenever a cached request is used or updated, this plugin will look
+   * at the used Cache and remove any old or extra requests.
+   *
+   * When using `maxAgeSeconds`, requests may be used *once* after expiring
+   * because the expiration clean up will not have occurred until *after* the
+   * cached request has been used. If the request has a "Date" header, then
+   * a light weight expiration check is performed and the request will not be
+   * used immediately.
+   *
+   * When using `maxEntries`, the entry least-recently requested will be removed from the cache first.
+   *
+   * @memberof workbox.expiration
+   */
+
+  class Plugin {
+    /**
+     * @param {Object} config
+     * @param {number} [config.maxEntries] The maximum number of entries to cache.
+     * Entries used the least will be removed as the maximum is reached.
+     * @param {number} [config.maxAgeSeconds] The maximum age of an entry before
+     * it's treated as stale and removed.
+     * @param {boolean} [config.purgeOnQuotaError] Whether to opt this cache in to
+     * automatic deletion if the available storage quota has been exceeded.
+     */
+    constructor(config = {}) {
+      {
+        if (!(config.maxEntries || config.maxAgeSeconds)) {
+          throw new WorkboxError_mjs.WorkboxError('max-entries-or-age-required', {
+            moduleName: 'workbox-expiration',
+            className: 'Plugin',
+            funcName: 'constructor'
+          });
+        }
+
+        if (config.maxEntries) {
+          assert_mjs.assert.isType(config.maxEntries, 'number', {
+            moduleName: 'workbox-expiration',
+            className: 'Plugin',
+            funcName: 'constructor',
+            paramName: 'config.maxEntries'
+          });
+        }
+
+        if (config.maxAgeSeconds) {
+          assert_mjs.assert.isType(config.maxAgeSeconds, 'number', {
+            moduleName: 'workbox-expiration',
+            className: 'Plugin',
+            funcName: 'constructor',
+            paramName: 'config.maxAgeSeconds'
+          });
+        }
+      }
+
+      this._config = config;
+      this._maxAgeSeconds = config.maxAgeSeconds;
+      this._cacheExpirations = new Map();
+
+      if (config.purgeOnQuotaError) {
+        registerQuotaErrorCallback_mjs.registerQuotaErrorCallback(() => this.deleteCacheAndMetadata());
+      }
+    }
+    /**
+     * A simple helper method to return a CacheExpiration instance for a given
+     * cache name.
+     *
+     * @param {string} cacheName
+     * @return {CacheExpiration}
+     *
+     * @private
+     */
+
+
+    _getCacheExpiration(cacheName) {
+      if (cacheName === cacheNames_mjs.cacheNames.getRuntimeName()) {
+        throw new WorkboxError_mjs.WorkboxError('expire-custom-caches-only');
+      }
+
+      let cacheExpiration = this._cacheExpirations.get(cacheName);
+
+      if (!cacheExpiration) {
+        cacheExpiration = new CacheExpiration(cacheName, this._config);
+
+        this._cacheExpirations.set(cacheName, cacheExpiration);
+      }
+
+      return cacheExpiration;
+    }
+    /**
+     * A "lifecycle" callback that will be triggered automatically by the
+     * `workbox.strategies` handlers when a `Response` is about to be returned
+     * from a [Cache](https://developer.mozilla.org/en-US/docs/Web/API/Cache) to
+     * the handler. It allows the `Response` to be inspected for freshness and
+     * prevents it from being used if the `Response`'s `Date` header value is
+     * older than the configured `maxAgeSeconds`.
+     *
+     * @param {Object} options
+     * @param {string} options.cacheName Name of the cache the response is in.
+     * @param {Response} options.cachedResponse The `Response` object that's been
+     *     read from a cache and whose freshness should be checked.
+     * @return {Response} Either the `cachedResponse`, if it's
+     *     fresh, or `null` if the `Response` is older than `maxAgeSeconds`.
+     *
+     * @private
+     */
+
+
+    cachedResponseWillBeUsed({
+      event,
+      request,
+      cacheName,
+      cachedResponse
+    }) {
+      if (!cachedResponse) {
+        return null;
+      }
+
+      let isFresh = this._isResponseDateFresh(cachedResponse); // Expire entries to ensure that even if the expiration date has
+      // expired, it'll only be used once.
+
+
+      const cacheExpiration = this._getCacheExpiration(cacheName);
+
+      cacheExpiration.expireEntries(); // Update the metadata for the request URL to the current timestamp,
+      // but don't `await` it as we don't want to block the response.
+
+      const updateTimestampDone = cacheExpiration.updateTimestamp(request.url);
+
+      if (event) {
+        try {
+          event.waitUntil(updateTimestampDone);
+        } catch (error) {
+          {
+            logger_mjs.logger.warn(`Unable to ensure service worker stays alive when ` + `updating cache entry for '${getFriendlyURL_mjs.getFriendlyURL(event.request.url)}'.`);
+          }
+        }
+      }
+
+      return isFresh ? cachedResponse : null;
+    }
+    /**
+     * @param {Response} cachedResponse
+     * @return {boolean}
+     *
+     * @private
+     */
+
+
+    _isResponseDateFresh(cachedResponse) {
+      if (!this._maxAgeSeconds) {
+        // We aren't expiring by age, so return true, it's fresh
+        return true;
+      } // Check if the 'date' header will suffice a quick expiration check.
+      // See https://github.com/GoogleChromeLabs/sw-toolbox/issues/164 for
+      // discussion.
+
+
+      const dateHeaderTimestamp = this._getDateHeaderTimestamp(cachedResponse);
+
+      if (dateHeaderTimestamp === null) {
+        // Unable to parse date, so assume it's fresh.
+        return true;
+      } // If we have a valid headerTime, then our response is fresh iff the
+      // headerTime plus maxAgeSeconds is greater than the current time.
+
+
+      const now = Date.now();
+      return dateHeaderTimestamp >= now - this._maxAgeSeconds * 1000;
+    }
+    /**
+     * This method will extract the data header and parse it into a useful
+     * value.
+     *
+     * @param {Response} cachedResponse
+     * @return {number}
+     *
+     * @private
+     */
+
+
+    _getDateHeaderTimestamp(cachedResponse) {
+      if (!cachedResponse.headers.has('date')) {
+        return null;
+      }
+
+      const dateHeader = cachedResponse.headers.get('date');
+      const parsedDate = new Date(dateHeader);
+      const headerTime = parsedDate.getTime(); // If the Date header was invalid for some reason, parsedDate.getTime()
+      // will return NaN.
+
+      if (isNaN(headerTime)) {
+        return null;
+      }
+
+      return headerTime;
+    }
+    /**
+     * A "lifecycle" callback that will be triggered automatically by the
+     * `workbox.strategies` handlers when an entry is added to a cache.
+     *
+     * @param {Object} options
+     * @param {string} options.cacheName Name of the cache that was updated.
+     * @param {string} options.request The Request for the cached entry.
+     *
+     * @private
+     */
+
+
+    async cacheDidUpdate({
+      cacheName,
+      request
+    }) {
+      {
+        assert_mjs.assert.isType(cacheName, 'string', {
+          moduleName: 'workbox-expiration',
+          className: 'Plugin',
+          funcName: 'cacheDidUpdate',
+          paramName: 'cacheName'
+        });
+        assert_mjs.assert.isInstance(request, Request, {
+          moduleName: 'workbox-expiration',
+          className: 'Plugin',
+          funcName: 'cacheDidUpdate',
+          paramName: 'request'
+        });
+      }
+
+      const cacheExpiration = this._getCacheExpiration(cacheName);
+
+      await cacheExpiration.updateTimestamp(request.url);
+      await cacheExpiration.expireEntries();
+    }
+    /**
+     * This is a helper method that performs two operations:
+     *
+     * - Deletes *all* the underlying Cache instances associated with this plugin
+     * instance, by calling caches.delete() on your behalf.
+     * - Deletes the metadata from IndexedDB used to keep track of expiration
+     * details for each Cache instance.
+     *
+     * When using cache expiration, calling this method is preferable to calling
+     * `caches.delete()` directly, since this will ensure that the IndexedDB
+     * metadata is also cleanly removed and open IndexedDB instances are deleted.
+     *
+     * Note that if you're *not* using cache expiration for a given cache, calling
+     * `caches.delete()` and passing in the cache's name should be sufficient.
+     * There is no Workbox-specific method needed for cleanup in that case.
+     */
+
+
+    async deleteCacheAndMetadata() {
+      // Do this one at a time instead of all at once via `Promise.all()` to
+      // reduce the chance of inconsistency if a promise rejects.
+      for (const [cacheName, cacheExpiration] of this._cacheExpirations) {
+        await caches.delete(cacheName);
+        await cacheExpiration.delete();
+      } // Reset this._cacheExpirations to its initial state.
+
+
+      this._cacheExpirations = new Map();
+    }
+
+  }
+
+  /*
+    Copyright 2018 Google LLC
+
+    Use of this source code is governed by an MIT-style
+    license that can be found in the LICENSE file or at
+    https://opensource.org/licenses/MIT.
+  */
+
+  exports.CacheExpiration = CacheExpiration;
+  exports.Plugin = Plugin;
+
+  return exports;
+
+}({}, workbox.core._private, workbox.core._private, workbox.core._private, workbox.core._private, workbox.core._private, workbox.core._private, workbox.core._private, workbox.core));
+//# sourceMappingURL=workbox-expiration.dev.js.map

public/javascripts/workbox/workbox-expiration.prod.js

@@ -0,0 +1,2 @@
+this.workbox=this.workbox||{},this.workbox.expiration=function(t,e,s,i,a,n){"use strict";try{self["workbox:expiration:4.3.1"]&&_()}catch(t){}const h="workbox-expiration",c="cache-entries",r=t=>{const e=new URL(t,location);return e.hash="",e.href};class o{constructor(t){this.t=t,this.s=new e.DBWrapper(h,1,{onupgradeneeded:t=>this.i(t)})}i(t){const e=t.target.result.createObjectStore(c,{keyPath:"id"});e.createIndex("cacheName","cacheName",{unique:!1}),e.createIndex("timestamp","timestamp",{unique:!1}),s.deleteDatabase(this.t)}async setTimestamp(t,e){t=r(t),await this.s.put(c,{url:t,timestamp:e,cacheName:this.t,id:this.h(t)})}async getTimestamp(t){return(await this.s.get(c,this.h(t))).timestamp}async expireEntries(t,e){const s=await this.s.transaction(c,"readwrite",(s,i)=>{const a=s.objectStore(c),n=[];let h=0;a.index("timestamp").openCursor(null,"prev").onsuccess=(({target:s})=>{const a=s.result;if(a){const s=a.value;s.cacheName===this.t&&(t&&s.timestamp<t||e&&h>=e?n.push(a.value):h++),a.continue()}else i(n)})}),i=[];for(const t of s)await this.s.delete(c,t.id),i.push(t.url);return i}h(t){return this.t+"|"+r(t)}}class u{constructor(t,e={}){this.o=!1,this.u=!1,this.l=e.maxEntries,this.p=e.maxAgeSeconds,this.t=t,this.m=new o(t)}async expireEntries(){if(this.o)return void(this.u=!0);this.o=!0;const t=this.p?Date.now()-1e3*this.p:void 0,e=await this.m.expireEntries(t,this.l),s=await caches.open(this.t);for(const t of e)await s.delete(t);this.o=!1,this.u&&(this.u=!1,this.expireEntries())}async updateTimestamp(t){await this.m.setTimestamp(t,Date.now())}async isURLExpired(t){return await this.m.getTimestamp(t)<Date.now()-1e3*this.p}async delete(){this.u=!1,await this.m.expireEntries(1/0)}}return t.CacheExpiration=u,t.Plugin=class{constructor(t={}){this.D=t,this.p=t.maxAgeSeconds,this.g=new Map,t.purgeOnQuotaError&&n.registerQuotaErrorCallback(()=>this.deleteCacheAndMetadata())}k(t){if(t===a.cacheNames.getRuntimeName())throw new i.WorkboxError("expire-custom-caches-only");let e=this.g.get(t);return e||(e=new u(t,this.D),this.g.set(t,e)),e}cachedResponseWillBeUsed({event:t,request:e,cacheName:s,cachedResponse:i}){if(!i)return null;let a=this.N(i);const n=this.k(s);n.expireEntries();const h=n.updateTimestamp(e.url);if(t)try{t.waitUntil(h)}catch(t){}return a?i:null}N(t){if(!this.p)return!0;const e=this._(t);return null===e||e>=Date.now()-1e3*this.p}_(t){if(!t.headers.has("date"))return null;const e=t.headers.get("date"),s=new Date(e).getTime();return isNaN(s)?null:s}async cacheDidUpdate({cacheName:t,request:e}){const s=this.k(t);await s.updateTimestamp(e.url),await s.expireEntries()}async deleteCacheAndMetadata(){for(const[t,e]of this.g)await caches.delete(t),await e.delete();this.g=new Map}},t}({},workbox.core._private,workbox.core._private,workbox.core._private,workbox.core._private,workbox.core);
+//# sourceMappingURL=workbox-expiration.prod.js.map

public/javascripts/workbox/workbox-routing.prod.js

@@ -0,0 +1,2 @@
+this.workbox=this.workbox||{},this.workbox.routing=function(t,e,r){"use strict";try{self["workbox:routing:4.3.1"]&&_()}catch(t){}const s="GET",n=t=>t&&"object"==typeof t?t:{handle:t};class o{constructor(t,e,r){this.handler=n(e),this.match=t,this.method=r||s}}class i extends o{constructor(t,{whitelist:e=[/./],blacklist:r=[]}={}){super(t=>this.t(t),t),this.s=e,this.o=r}t({url:t,request:e}){if("navigate"!==e.mode)return!1;const r=t.pathname+t.search;for(const t of this.o)if(t.test(r))return!1;return!!this.s.some(t=>t.test(r))}}class u extends o{constructor(t,e,r){super(({url:e})=>{const r=t.exec(e.href);return r?e.origin!==location.origin&&0!==r.index?null:r.slice(1):null},e,r)}}class c{constructor(){this.i=new Map}get routes(){return this.i}addFetchListener(){self.addEventListener("fetch",t=>{const{request:e}=t,r=this.handleRequest({request:e,event:t});r&&t.respondWith(r)})}addCacheListener(){self.addEventListener("message",async t=>{if(t.data&&"CACHE_URLS"===t.data.type){const{payload:e}=t.data,r=Promise.all(e.urlsToCache.map(t=>{"string"==typeof t&&(t=[t]);const e=new Request(...t);return this.handleRequest({request:e})}));t.waitUntil(r),t.ports&&t.ports[0]&&(await r,t.ports[0].postMessage(!0))}})}handleRequest({request:t,event:e}){const r=new URL(t.url,location);if(!r.protocol.startsWith("http"))return;let s,{params:n,route:o}=this.findMatchingRoute({url:r,request:t,event:e}),i=o&&o.handler;if(!i&&this.u&&(i=this.u),i){try{s=i.handle({url:r,request:t,event:e,params:n})}catch(t){s=Promise.reject(t)}return s&&this.h&&(s=s.catch(t=>this.h.handle({url:r,event:e,err:t}))),s}}findMatchingRoute({url:t,request:e,event:r}){const s=this.i.get(e.method)||[];for(const n of s){let s,o=n.match({url:t,request:e,event:r});if(o)return Array.isArray(o)&&o.length>0?s=o:o.constructor===Object&&Object.keys(o).length>0&&(s=o),{route:n,params:s}}return{}}setDefaultHandler(t){this.u=n(t)}setCatchHandler(t){this.h=n(t)}registerRoute(t){this.i.has(t.method)||this.i.set(t.method,[]),this.i.get(t.method).push(t)}unregisterRoute(t){if(!this.i.has(t.method))throw new r.WorkboxError("unregister-route-but-not-found-with-method",{method:t.method});const e=this.i.get(t.method).indexOf(t);if(!(e>-1))throw new r.WorkboxError("unregister-route-route-not-registered");this.i.get(t.method).splice(e,1)}}let a;const h=()=>(a||((a=new c).addFetchListener(),a.addCacheListener()),a);return t.NavigationRoute=i,t.RegExpRoute=u,t.registerNavigationRoute=((t,r={})=>{const s=e.cacheNames.getPrecacheName(r.cacheName),n=new i(async()=>{try{const e=await caches.match(t,{cacheName:s});if(e)return e;throw new Error(`The cache ${s} did not have an entry for `+`${t}.`)}catch(e){return fetch(t)}},{whitelist:r.whitelist,blacklist:r.blacklist});return h().registerRoute(n),n}),t.registerRoute=((t,e,s="GET")=>{let n;if("string"==typeof t){const r=new URL(t,location);n=new o(({url:t})=>t.href===r.href,e,s)}else if(t instanceof RegExp)n=new u(t,e,s);else if("function"==typeof t)n=new o(t,e,s);else{if(!(t instanceof o))throw new r.WorkboxError("unsupported-route-type",{moduleName:"workbox-routing",funcName:"registerRoute",paramName:"capture"});n=t}return h().registerRoute(n),n}),t.Route=o,t.Router=c,t.setCatchHandler=(t=>{h().setCatchHandler(t)}),t.setDefaultHandler=(t=>{h().setDefaultHandler(t)}),t}({},workbox.core._private,workbox.core._private);
+//# sourceMappingURL=workbox-routing.prod.js.map

public/javascripts/workbox/workbox-strategies.prod.js

@@ -0,0 +1,2 @@
+this.workbox=this.workbox||{},this.workbox.strategies=function(e,t,s,n,r){"use strict";try{self["workbox:strategies:4.3.1"]&&_()}catch(e){}class i{constructor(e={}){this.t=t.cacheNames.getRuntimeName(e.cacheName),this.s=e.plugins||[],this.i=e.fetchOptions||null,this.h=e.matchOptions||null}async handle({event:e,request:t}){return this.makeRequest({event:e,request:t||e.request})}async makeRequest({event:e,request:t}){"string"==typeof t&&(t=new Request(t));let n,i=await s.cacheWrapper.match({cacheName:this.t,request:t,event:e,matchOptions:this.h,plugins:this.s});if(!i)try{i=await this.u(t,e)}catch(e){n=e}if(!i)throw new r.WorkboxError("no-response",{url:t.url,error:n});return i}async u(e,t){const r=await n.fetchWrapper.fetch({request:e,event:t,fetchOptions:this.i,plugins:this.s}),i=r.clone(),h=s.cacheWrapper.put({cacheName:this.t,request:e,response:i,event:t,plugins:this.s});if(t)try{t.waitUntil(h)}catch(e){}return r}}class h{constructor(e={}){this.t=t.cacheNames.getRuntimeName(e.cacheName),this.s=e.plugins||[],this.h=e.matchOptions||null}async handle({event:e,request:t}){return this.makeRequest({event:e,request:t||e.request})}async makeRequest({event:e,request:t}){"string"==typeof t&&(t=new Request(t));const n=await s.cacheWrapper.match({cacheName:this.t,request:t,event:e,matchOptions:this.h,plugins:this.s});if(!n)throw new r.WorkboxError("no-response",{url:t.url});return n}}const u={cacheWillUpdate:({response:e})=>200===e.status||0===e.status?e:null};class a{constructor(e={}){if(this.t=t.cacheNames.getRuntimeName(e.cacheName),e.plugins){let t=e.plugins.some(e=>!!e.cacheWillUpdate);this.s=t?e.plugins:[u,...e.plugins]}else this.s=[u];this.o=e.networkTimeoutSeconds,this.i=e.fetchOptions||null,this.h=e.matchOptions||null}async handle({event:e,request:t}){return this.makeRequest({event:e,request:t||e.request})}async makeRequest({event:e,request:t}){const s=[];"string"==typeof t&&(t=new Request(t));const n=[];let i;if(this.o){const{id:r,promise:h}=this.l({request:t,event:e,logs:s});i=r,n.push(h)}const h=this.q({timeoutId:i,request:t,event:e,logs:s});n.push(h);let u=await Promise.race(n);if(u||(u=await h),!u)throw new r.WorkboxError("no-response",{url:t.url});return u}l({request:e,logs:t,event:s}){let n;return{promise:new Promise(t=>{n=setTimeout(async()=>{t(await this.p({request:e,event:s}))},1e3*this.o)}),id:n}}async q({timeoutId:e,request:t,logs:r,event:i}){let h,u;try{u=await n.fetchWrapper.fetch({request:t,event:i,fetchOptions:this.i,plugins:this.s})}catch(e){h=e}if(e&&clearTimeout(e),h||!u)u=await this.p({request:t,event:i});else{const e=u.clone(),n=s.cacheWrapper.put({cacheName:this.t,request:t,response:e,event:i,plugins:this.s});if(i)try{i.waitUntil(n)}catch(e){}}return u}p({event:e,request:t}){return s.cacheWrapper.match({cacheName:this.t,request:t,event:e,matchOptions:this.h,plugins:this.s})}}class c{constructor(e={}){this.t=t.cacheNames.getRuntimeName(e.cacheName),this.s=e.plugins||[],this.i=e.fetchOptions||null}async handle({event:e,request:t}){return this.makeRequest({event:e,request:t||e.request})}async makeRequest({event:e,request:t}){let s,i;"string"==typeof t&&(t=new Request(t));try{i=await n.fetchWrapper.fetch({request:t,event:e,fetchOptions:this.i,plugins:this.s})}catch(e){s=e}if(!i)throw new r.WorkboxError("no-response",{url:t.url,error:s});return i}}class o{constructor(e={}){if(this.t=t.cacheNames.getRuntimeName(e.cacheName),this.s=e.plugins||[],e.plugins){let t=e.plugins.some(e=>!!e.cacheWillUpdate);this.s=t?e.plugins:[u,...e.plugins]}else this.s=[u];this.i=e.fetchOptions||null,this.h=e.matchOptions||null}async handle({event:e,request:t}){return this.makeRequest({event:e,request:t||e.request})}async makeRequest({event:e,request:t}){"string"==typeof t&&(t=new Request(t));const n=this.u({request:t,event:e});let i,h=await s.cacheWrapper.match({cacheName:this.t,request:t,event:e,matchOptions:this.h,plugins:this.s});if(h){if(e)try{e.waitUntil(n)}catch(i){}}else try{h=await n}catch(e){i=e}if(!h)throw new r.WorkboxError("no-response",{url:t.url,error:i});return h}async u({request:e,event:t}){const r=await n.fetchWrapper.fetch({request:e,event:t,fetchOptions:this.i,plugins:this.s}),i=s.cacheWrapper.put({cacheName:this.t,request:e,response:r.clone(),event:t,plugins:this.s});if(t)try{t.waitUntil(i)}catch(e){}return r}}const l={cacheFirst:i,cacheOnly:h,networkFirst:a,networkOnly:c,staleWhileRevalidate:o},q=e=>{const t=l[e];return e=>new t(e)},w=q("cacheFirst"),p=q("cacheOnly"),v=q("networkFirst"),y=q("networkOnly"),m=q("staleWhileRevalidate");return e.CacheFirst=i,e.CacheOnly=h,e.NetworkFirst=a,e.NetworkOnly=c,e.StaleWhileRevalidate=o,e.cacheFirst=w,e.cacheOnly=p,e.networkFirst=v,e.networkOnly=y,e.staleWhileRevalidate=m,e}({},workbox.core._private,workbox.core._private,workbox.core._private,workbox.core._private);
+//# sourceMappingURL=workbox-strategies.prod.js.map

public/javascripts/workbox/workbox-sw.js

@@ -0,0 +1,2 @@
+!function(){"use strict";try{self["workbox:sw:4.3.1"]&&_()}catch(t){}const t="https://storage.googleapis.com/workbox-cdn/releases/4.3.1",e={backgroundSync:"background-sync",broadcastUpdate:"broadcast-update",cacheableResponse:"cacheable-response",core:"core",expiration:"expiration",googleAnalytics:"offline-ga",navigationPreload:"navigation-preload",precaching:"precaching",rangeRequests:"range-requests",routing:"routing",strategies:"strategies",streams:"streams"};self.workbox=new class{constructor(){return this.v={},this.t={debug:"localhost"===self.location.hostname,modulePathPrefix:null,modulePathCb:null},this.s=this.t.debug?"dev":"prod",this.o=!1,new Proxy(this,{get(t,s){if(t[s])return t[s];const o=e[s];return o&&t.loadModule(`workbox-${o}`),t[s]}})}setConfig(t={}){if(this.o)throw new Error("Config must be set before accessing workbox.* modules");Object.assign(this.t,t),this.s=this.t.debug?"dev":"prod"}loadModule(t){const e=this.i(t);try{importScripts(e),this.o=!0}catch(s){throw console.error(`Unable to import module '${t}' from '${e}'.`),s}}i(e){if(this.t.modulePathCb)return this.t.modulePathCb(e,this.t.debug);let s=[t];const o=`${e}.${this.s}.js`,r=this.t.modulePathPrefix;return r&&""===(s=r.split("/"))[s.length-1]&&s.splice(s.length-1,1),s.push(o),s.join("/")}}}();
+//# sourceMappingURL=workbox-sw.js.map

yarn.lock

@@ -2584,6 +2584,37 @@ wordwrap@~1.0.0:
   resolved "https://registry.yarnpkg.com/wordwrap/-/wordwrap-1.0.0.tgz#27584810891456a4171c8d0226441ade90cbcaeb"
   integrity sha1-J1hIEIkUVqQXHI0CJkQa3pDLyus=
 
+workbox-core@^4.3.1:
+  version "4.3.1"
+  resolved "https://registry.yarnpkg.com/workbox-core/-/workbox-core-4.3.1.tgz#005d2c6a06a171437afd6ca2904a5727ecd73be6"
+  integrity sha512-I3C9jlLmMKPxAC1t0ExCq+QoAMd0vAAHULEgRZ7kieCdUd919n53WC0AfvokHNwqRhGn+tIIj7vcb5duCjs2Kg==
+
+workbox-expiration@^4.3.1:
+  version "4.3.1"
+  resolved "https://registry.yarnpkg.com/workbox-expiration/-/workbox-expiration-4.3.1.tgz#d790433562029e56837f341d7f553c4a78ebe921"
+  integrity sha512-vsJLhgQsQouv9m0rpbXubT5jw0jMQdjpkum0uT+d9tTwhXcEZks7qLfQ9dGSaufTD2eimxbUOJfWLbNQpIDMPw==
+  dependencies:
+    workbox-core "^4.3.1"
+
+workbox-routing@^4.3.1:
+  version "4.3.1"
+  resolved "https://registry.yarnpkg.com/workbox-routing/-/workbox-routing-4.3.1.tgz#a675841af623e0bb0c67ce4ed8e724ac0bed0cda"
+  integrity sha512-FkbtrODA4Imsi0p7TW9u9MXuQ5P4pVs1sWHK4dJMMChVROsbEltuE79fBoIk/BCztvOJ7yUpErMKa4z3uQLX+g==
+  dependencies:
+    workbox-core "^4.3.1"
+
+workbox-strategies@^4.3.1:
+  version "4.3.1"
+  resolved "https://registry.yarnpkg.com/workbox-strategies/-/workbox-strategies-4.3.1.tgz#d2be03c4ef214c115e1ab29c9c759c9fe3e9e646"
+  integrity sha512-F/+E57BmVG8dX6dCCopBlkDvvhg/zj6VDs0PigYwSN23L8hseSRwljrceU2WzTvk/+BSYICsWmRq5qHS2UYzhw==
+  dependencies:
+    workbox-core "^4.3.1"
+
+workbox-sw@^4.3.1:
+  version "4.3.1"
+  resolved "https://registry.yarnpkg.com/workbox-sw/-/workbox-sw-4.3.1.tgz#df69e395c479ef4d14499372bcd84c0f5e246164"
+  integrity sha512-0jXdusCL2uC5gM3yYFT6QMBzKfBr2XTk0g5TPAV4y8IZDyVNDyj1a8uSXy3/XrvkVTmQvLN4O5k3JawGReXr9w==
+
 wrappy@1:
   version "1.0.2"
   resolved "https://registry.yarnpkg.com/wrappy/-/wrappy-1.0.2.tgz#b5243d8f3ec1aa35f1364605bc0d1036e30ab69f"