Service Worker Video Caching Sample

service-worker/prefetch-video/README.md

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+Service Worker Video Cache Sample
+===
+See https://googlechrome.github.io/samples/service-worker/prefetch-video/index.html for a live demo.
+
+Learn more at https://www.chromestatus.com/feature/6561526227927040

service-worker/prefetch-video/index.html

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+---
+feature_name: "Service Worker Sample: Cache Video"
+chrome_version: 52
+feature_id: 6561526227927040
+local_js_files: ['index.js', 'service-worker.js']
+---
+
+<video controls  poster="static/poster.jpg"
+  style="margin: 0 0 1em 0; max-width: 100%; width: 480px;">
+  <source src="static/gbike.webm" type="video/webm" />
+  <source src="static/gbike.mp4" type="video/mp4" />
+  <p>Your browser does not support the video element.</p>
+</video>
+
+<div id="currentSrc"></div>
+
+<h3>Background</h3>
+
+<p>This sample demonstrates basic service worker registration, in conjunction with pre-fetching a video and its poster image.</p>
+
+<p>Visit <code>chrome://inspect/#service-workers</code> and click on the "inspect" link below the registered service worker to view logging statements for the various actions the <code><a href="service-worker.js">service-worker.js</a></code> script is performing. Since most of the action takes place during the service worker's install handler, and that is only executed the very first time you visit this page (unless the service worker script changes), it can be helpful to inspect the logging in a <a href="https://support.google.com/chrome/answer/95464">Chrome Incognito window</a>.</p>
+
+<p>To try out caching, disconnect from your network then reload this page.</p>
+
+
+{% include js_snippet.html filename='index.js' title='index.js' %}
+{% include js_snippet.html filename='service-worker.js' displayonly=true title='service-worker.js' %}

service-worker/prefetch-video/index.js

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+// Helper function which returns a promise which resolves once the service worker registration
+// is past the "installing" state.
+function waitUntilInstalled(registration) {
+  return new Promise(function(resolve, reject) {
+    if (registration.installing) {
+      // If the current registration represents the "installing" service worker, then wait
+      // until the installation step (during which the resources are pre-fetched) completes
+      // to display the file list.
+      registration.installing.addEventListener('statechange', function(e) {
+        if (e.target.state === 'installed') {
+          resolve();
+        } else if (e.target.state === 'redundant') {
+          reject();
+        }
+      });
+    } else {
+      // Otherwise, if this isn't the "installing" service worker, then installation must have been
+      // completed during a previous visit to this page, and the resources are already pre-fetched.
+      // So we can show the list of files right away.
+      resolve();
+    }
+  });
+}
+
+if ('serviceWorker' in navigator) {
+  navigator.serviceWorker.register('./service-worker.js', {
+    scope: './'
+  })
+    .then(waitUntilInstalled)
+    // .then(showFilesList)
+    .catch(function(error) {
+      // Something went wrong during registration. The service-worker.js file
+      // might be unavailable or contain a syntax error.
+      document.querySelector('#status').textContent = error;
+    });
+} else {
+  // The current browser doesn't support service workers.
+  var aElement = document.createElement('a');
+  aElement.href =
+    'http://www.chromium.org/blink/serviceworker/service-worker-faq';
+  aElement.textContent =
+    'Service workers are not supported in the current browser.';
+  document.querySelector('#status').appendChild(aElement);
+}
+
+document.querySelector('video').onloadedmetadata = function() {
+  var fileName = this.currentSrc.replace(/^.*[\\\/]/, '');
+  document.querySelector('#currentSrc').textContent = 'Video src: ' + fileName;
+};

service-worker/prefetch-video/service-worker.js

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+/*
+ Copyright 2014 Google Inc. All Rights Reserved.
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+ http://www.apache.org/licenses/LICENSE-2.0
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ */
+
+// While overkill for this specific sample in which there is only one cache,
+// this is one best practice that can be followed in general to keep track of
+// multiple caches used by a given service worker, and keep them all versioned.
+// It maps a shorthand identifier for a cache to a specific, versioned cache name.
+
+// Note that since global state is discarded in between service worker restarts, these
+// variables will be reinitialized each time the service worker handles an event, and you
+// should not attempt to change their values inside an event handler. (Treat them as constants.)
+
+// If at any point you want to force pages that use this service worker to start using a fresh
+// cache, then increment the CACHE_VERSION value. It will kick off the service worker update
+// flow and the old cache(s) will be purged as part of the activate event handler when the
+// updated service worker is activated.
+var CACHE_VERSION = 1;
+var CURRENT_CACHES = {
+  prefetch: 'prefetch-cache-v' + CACHE_VERSION
+};
+
+self.addEventListener('install', function(event) {
+  var now = Date.now();
+
+  var urlsToPrefetch = [
+    '/service-worker/prefetch-video/',
+    '/service-worker/prefetch-video/index.js',
+    '../../styles/main.css',
+    'static/video.mp4',
+    'static/video.webm',
+    'static/poster.jpg'];
+
+  // All of these logging statements should be visible via the "Inspect" interface
+  // for the relevant SW accessed via chrome://serviceworker-internals
+  console.log('Handling install event. Resources to prefetch:', urlsToPrefetch);
+
+  event.waitUntil(
+    caches.open(CURRENT_CACHES.prefetch).then(function(cache) {
+      var cachePromises = urlsToPrefetch.map(function(urlToPrefetch) {
+        // This constructs a new URL object using the service worker's script location as the base
+        // for relative URLs.
+        var url = new URL(urlToPrefetch, location.href);
+        // Append a cache-bust=TIMESTAMP URL parameter to each URL's query string.
+        // This is particularly important when precaching resources that are later used in the
+        // fetch handler as responses directly, without consulting the network (i.e. cache-first).
+        // If we were to get back a response from the HTTP browser cache for this precaching request
+        // then that stale response would be used indefinitely, or at least until the next time
+        // the service worker script changes triggering the install flow.
+        url.search += (url.search ? '&' : '?') + 'cache-bust=' + now;
+
+        // It's very important to use {mode: 'no-cors'} if there is any chance that
+        // the resources being fetched are served off of a server that doesn't support
+        // CORS (http://en.wikipedia.org/wiki/Cross-origin_resource_sharing).
+        // In this example, www.chromium.org doesn't support CORS, and the fetch()
+        // would fail if the default mode of 'cors' was used for the fetch() request.
+        // The drawback of hardcoding {mode: 'no-cors'} is that the response from all
+        // cross-origin hosts will always be opaque
+        // (https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#cross-origin-resources)
+        // and it is not possible to determine whether an opaque response represents a success or failure
+        // (https://github.com/whatwg/fetch/issues/14).
+        var request = new Request(url, {mode: 'no-cors'});
+        return fetch(request).then(function(response) {
+          if (response.status >= 400) {
+            throw new Error('request for ' + urlToPrefetch +
+              ' failed with status ' + response.statusText);
+          }
+
+          // Use the original URL without the cache-busting parameter as the key for cache.put().
+          return cache.put(urlToPrefetch, response);
+        }).catch(function(error) {
+          console.error('Not caching ' + urlToPrefetch + ' due to ' + error);
+        });
+      });
+
+      return Promise.all(cachePromises).then(function() {
+        console.log('Pre-fetching complete.');
+      });
+    }).catch(function(error) {
+      console.error('Pre-fetching failed:', error);
+    })
+    );
+});
+
+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.
+            console.log('Deleting out of date cache:', cacheName);
+            return caches.delete(cacheName);
+          }
+        })
+        );
+    })
+    );
+});
+
+self.addEventListener('fetch', function(event) {
+  console.log('Handling fetch event for', event.request.url);
+
+  if (event.request.headers.get('range')) {
+    var pos =
+    Number(/^bytes\=(\d+)\-$/g.exec(event.request.headers.get('range'))[1]);
+    console.log('Range request for', event.request.url,
+      ', starting position:', pos);
+    event.respondWith(
+      caches.open(CURRENT_CACHES.prefetch)
+      .then(function(cache) {
+        return cache.match(event.request.url);
+      }).then(function(res) {
+        if (!res) {
+          return fetch(event.request)
+          .then(res => {
+            return res.arrayBuffer();
+          });
+        }
+        return res.arrayBuffer();
+      }).then(function(ab) {
+        return new Response(
+          ab.slice(pos),
+          {
+            status: 206,
+            statusText: 'Partial Content',
+            headers: [
+              // ['Content-Type', 'video/webm'],
+              ['Content-Range', 'bytes ' + pos + '-' +
+                (ab.byteLength - 1) + '/' + ab.byteLength]]
+          });
+      }));
+  } else {
+    console.log('Non-range request for', event.request.url);
+    event.respondWith(
+    // caches.match() will look for a cache entry in all of the caches available to the service worker.
+    // It's an alternative to first opening a specific named cache and then matching on that.
+    caches.match(event.request).then(function(response) {
+      if (response) {
+        console.log('Found response in cache:', response);
+        return response;
+      }
+      console.log('No response found in cache. About to fetch from network...');
+      // event.request will always have the proper mode set ('cors, 'no-cors', etc.) so we don't
+      // have to hardcode 'no-cors' like we do when fetch()ing in the install handler.
+      return fetch(event.request).then(function(response) {
+        console.log('Response from network is:', response);
+
+        return response;
+      }).catch(function(error) {
+        // This catch() will handle exceptions thrown from the fetch() operation.
+        // Note that a HTTP error response (e.g. 404) will NOT trigger an exception.
+        // It will return a normal response object that has the appropriate error code set.
+        console.error('Fetching failed:', error);
+
+        throw error;
+      });
+    })
+    );
+  }
+});
+