Initial ServiceWorker CacheStorage API polyfill.

Source/modules/serviceworkers/polyfills/cacheStoragePolyfill.js

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// A simple, incomplete implementation of the CacheStorage API, intended to facilitate
+// end to end serviceworker testing.
+
+// See https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#cache-storage
+
+(function(global) {
+    var CacheStorage = function() {
+        this.cachesByName = {};
+    };
+
+    CacheStorage.prototype.get = function(key) {
+        if (this.cachesByName.hasOwnProperty(key)) {
+            return Promise.resolve(this.cachesByName[key]);

[jsbell, 2014/06/10 18:36:19]

Overall: this polyfill is doing all of the changes synchronously, then minting
promises.

This should be fine (and not observable), but once we make *any* part of this
async we'll want to make *all* methods async so that the microtasks are ordered
correctly. i.e. we'll want the `return new Promise(function(r,r) { ... do
everything here ... });` pattern, even though it's wordier.

[gavinp, 2014/06/10 20:03:08]

Aha, yes, good point. This way, when the user chains these operations using
.then(), ..., the operation is not executed until the correct time.

+        }
+        return Promise.reject('not found');
+    }
+
+    CacheStorage.prototype.has = function(key) {
+        if (this.cachesByName.hasOwnProperty(key)) {
+            return Promise.resolve(true);
+        }
+        return Promise.reject(false);

[jsbell, 2014/06/10 18:36:19]

Should resolve(false);

reject() should only be used when a synchronous API would raise an exception.

[gavinp, 2014/06/10 20:03:08]

Done.

+    }
+
+    // FIXME: Engage standardisation on removing this method from the spec.
+    CacheStorage.prototype.set = Promise.reject.bind(Promise, 'CacheStorage.prototype.set() not implemented.');
+
+    // FIXME: Engage standarisation on adding this method to the spec.

[jsbell, 2014/06/10 18:36:19]

typo: standar*d*isation

(Also, insert 's' vs. 'z' joke about UK vs. US English here.)

[gavinp, 2014/06/10 20:03:08]

Done. While I'm religious about US english in identifier names ("did that
function have colour or color?"), I'm not as good in comments.

+    CacheStorage.prototype.create = function(key) {
+        this.cachesByName[key] = new Cache();
+
+        return Promise.resolve();
+    }
+
+    // FIXME: Engage standarisation on adding this method to the spec.
+    CacheStorage.prototype.rename = function(fromKey, toKey) {
+        if (!this.cachesByName.hasOwnProperty(fromKey)) {
+            return Promise.reject('not found');
+        }
+        this.cachesByName[toKey] = this.cachesByName[fromKey];

[jsbell, 2014/06/10 18:36:19]

I assume it's intentional that no checking is done on cachesByName[toKey], i.e.
if it previously existed it is silently dropped?

[gavinp, 2014/06/10 20:03:08]

Yes. Akin to doing "set" followed by "delete."

+        delete this.cachesByName[fromKey];
+
+        return Promise.resolve();
+    }
+
+    CacheStorage.prototype.clear = function() {
+        this.cachesByName = {};
+
+        return Promise.resolve();
+    }
+
+    CacheStorage.prototype.delete = function(key) {
+        delete this.cachesByName[key];
+
+        return Promise.resolve();
+    }
+
+    CacheStorage.prototype.forEach = function(callback, thisArg) {
+        Object.keys(this.cachesByName).map(function(key) {
+            thisArg.callback(this.cachesByName[key], key, this);
+        });
+        return Promise.resolve();
+    }
+
+    // FIXME: Implement this.
+    CacheStorage.prototype.entries = Promise.reject.bind(Promise, 'CacheStorage.prototype.entries() not implemented.');
+
+    CacheStorage.prototype.keys = function() {
+        return Promise.resolve(this.cachesByName.keys());
+    }
+
+    CacheStorage.prototype.values = function() {
+        return Promise.resolve(Object.keys(this.cachesByName).map(function (key) {

[falken, 2014/06/10 18:36:12]

function space here

[gavinp, 2014/06/10 20:03:09]

Done.

+            return this.cachesByName[key];
+        }));
+    }
+
+    CacheStorage.prototype.size = function() {
+        return Promise.resolve(Object.keys(this.cachesByName).length);
+    }
+
+    CacheStorage.prototype.match = function(url, cacheName) {
+        this.get(cacheName).then(function (cache) {

[falken, 2014/06/10 18:36:12]

here too

[gavinp, 2014/06/10 20:03:08]

Done.

+            return cache.match(url);
+        });
+    }
+
+    global.CacheStorage = global.CacheStorage || CacheStorage;

[jsbell, 2014/06/10 18:36:19]

Intentional to expose constructor for this, in the simplified API case?

[gavinp, 2014/06/10 20:03:08]

Fair point, no real need. Done.

+    global.caches = global.caches || new CacheStorage();
+}(self));  // window or worker global scope.