Hide Notes 

Slide 1: How to take your Web Application Offline with Google Gears Dion Almaer ajaxian.com code.google.com
Slide 2: The Future of Web Apps • It will be hard to determine what is and isn’t a web app • The web will be everywhere • Mobile (iPhone) • Desktop • Widgets • TV • The browser will be fast
Slide 3: Why? “How often are you on a plane?” • Reliability • 1% of downtime can hurt at the wrong time • Performance • Local acceleration • Convenience • Not having to find a connection • You are offline more than you think!
Slide 4: Offline Web via Open Web • Why just solve this problem for Google? • Why not solve it for others? • Solution: Make it open source with a liberal license • New BSD
Slide 5: What is the philosophy? • One application, one URL • Seamless transitions between online and offline • Ability to use local data, even when online • Available to all users on all platforms • ... and a pony
Slide 6: What is the philosophy? Browser plugin: IE, Firefox, Safari (almost!)
Slide 7: What is the philosophy?
Slide 8: What is the philosophy? Do for offline what XMLHttpRequest did for web apps Ajax Libraries Dojo, jQuery, Prototype, GWT Gears Libraries Dojo Offline, GWT XMLHttpRequest Gears Open Web Open Web
Slide 9: Ajax Architecture
Slide 10: Offline Architecture • Read and write using local store • Changes are queued for later synchronization • Server communication is completely decoupled from UI actions, happens periodically whenever there is a connection
Slide 11: What are the pieces?
Slide 12: Database Embedded using SQLite Contributed Full Text Search var db = google.gears.factory.create('beta.database', '1.0'); db.open('database-demo'); db.execute('create table if not exists Demo (Phrase varchar(255), Timestamp int)'); db.execute('insert into Demo values (?, ?)', [phrase, currTime]); var rs = db.execute('select * from Demo order by Timestamp desc');
Slide 13: GearsDB Abstract over the API var bob = {id: 3, name: 'Bob', url: 'http://bob.com', description: 'whee'}; db.insertRow('person', bob); db.insertRow('person', bob, 'name = ?', ['Bob']); db.selectAll('select * from person', null, function(person) { document.getElementById('selectAll').innerHTML += ' ' + person.name; }); var person = db.selectRow('person', 'id = 1'); // update person.name = 'Harry'; db.updateRow('person', person); person = db.selectRow('person', 'id = 1'); // force person.name = 'Sally'; db.forceRow('person', person); person = db.selectRow('person', 'id = 1'); db.deleteRow('person', bob);
Slide 14: GearsORM Are we going to get a GearsHibernate? var Person = new GearsOrm.Model("Person", { firstName: GearsOrm.Fields.String({maxLength:25}), lastName: GearsOrm.Fields.String({maxLength:25}) }); GearsORM.Transaction(function() { new Person({name:"John"}).save(); new Person({name:"Doe"}).save(); }); Person.select("firstName = 'Uriel'"); Person.count("lastName = ?",["Katz"]) “While developing transaction support for GearsORM i had to write a test, in that test it execute 100 inserts and 100 updates, this test take about 15 seconds for the inserts and about 10 seconds for the updates without transactions,when using transactions for each set it takes about 377ms for the inserts and 200ms for the updates that is about 39 times faster!”
Slide 15: GearShift DB Migrations for Gears Gearshift.rules[1] = { // create the demo table up: function() { return this.e("CREATE TABLE demo_table ( id INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR(30), movie VARCHAR(30) )").success; }, down: function() { return this.e("DROP TABLE demo_table").success; } };
Slide 16: Database Tools
Slide 17: Alignment with AIR Ext.data.SqlDB “The APIs for AIR and Google Gears are nothing alike. In fact, AIR's SQLite database API is 100% asynchronous via events while Gears API is all synchronous with results coming immediately on execution. So Ext.data.SqlDB was created to abstract both of these APIs into a single API to access both.” NOTE: AIR beta 2 has added a synchronous API
Slide 18: Local Server A mini-web server that groks 200 and 304
Slide 19: ResourceStore Manually Capturing var pageFiles = [ location.pathname, 'gears_base.js', '../scripts/gears_db.js', ‘foo.html’ ]; try { localServer = google.gears.factory.create('beta.localserver', '1.0'); } catch (e) { alert('Could not create local server: ' + e.message); return; } var store = localServer.openStore(this.storeName) || localServer.createStore(this.storeName); store.capture(pageFiles, function(url, success, captureId) { console.log(url + ' capture ' + (success ? 'succeeded' : 'failed')); });
Slide 20: ManagedResourceStore Capture entire applications • List application resources in a separate • • • manifest Gears captures and updates the list atomically Gears auto-updates automatically on each view (within reason) Supports multiple users per application
Slide 21: ManagedResourceStore Sample Code var localserver = google.gears.factory.create('beta.localserver', '1.0'); var store = localserver.createManagedStore('mystore'); store.manifestUrl = 'http://myapp.com/offline-manifest.json'; store.checkForUpdates();
Slide 22: ManagedResourceStore JSON Me { // version of the manifest file format "betaManifestVersion": 1, // version of the set of resources described in this manifest file "version": "my_version_string", // optional // If the store specifies a requiredCookie, when a request would hit // an entry contained in the manifest except the requiredCookie is // not present, the local server responds with a redirect to this URL. "redirectUrl": "login.html", // URLs to be cached (URLs are given relative to the manifest URL) "entries": [ { "url": "main.html", "src": "main_offline.html" }, { "url": ".", "redirect": "main.html" }, { "url": "main.js" } { "url": "formHandler.html", "ignoreQuery": true }, ] }
Slide 23: Gears Manifest Generator Ruby Me json = Google::Gears::LocalServer::Manifest.new do |m| m.version = 'MyNewVer' m.add_entry({ :url => 'main.html', :src => 'foo.html' }) m.add_extra_info :to => 'main.html', :redirect => 'foo_redirect.html' m.find_entries :in => '.', :ignore => Google::Gears::LocalServer::Manifest::LEADING_PERIOD end
Slide 24: HTML 5 Offline in General <html application=”manifest-of-urls.txt”> <html application> “There’s a concept of an application cache. An application cache is a group of resources, the group being identified by a URI (which typically happens to resolve to a manifest). Resources in a cache are either top-level or not; top-level resources are those that are HTML or XML and when parsed with scripting disabled have with the value of the attribute pointing to the same URI as identifies the cache. When you visit a page you first check to see if you have that page in a cache as a known top-level page.”
Slide 25: Worker Pool JavaScript needs threads after all? Brendan! WorkerPool Browser JavaScript Engine WorkerPool window, document no access
Slide 26: Worker Pool Run JavaScript in the background • Provides thread-like functionality to JavaScript • No more blocking the browser UI • Communication is via IPC, no shared state or threading primitives
Slide 27: Worker Pool Code function nextPrime(n) { // TODO: New top-secret prime-finding algorithm goes here. google.gears.workerPool.sendMessage(result); } var pool = google.gears.factory.create('beta.workerpool', '1.0'); pool.onmessage = function(message) { alert('next prime is: ' + message); } var worker = pool.createWorker(String(nextPrime) + '; nextPrime()');
Slide 28: Worker Pool Improved! • Cross-origin API allows Gears apps from different sites to work together • WorkerPool improvements: • createWorkerFromUrl() • onerror allows handling exceptions thrown by workers • New HttpRequest module allows fetching from WorkerPools • New Timer module allows timer events in WorkerPools • Implements the WhatWG Timer specification var timer = google.gears.factory.create("beta.timer", "1.0"); timer.setTimeout(function() { alert("Hello, from the future!"); },1000);
Slide 29: Why? How about Encryption dojox.sql("INSERT INTO CUSTOMERS VALUES (?, ?, ENCRYPT(?))", "Neuberg", "Brad", "555-34-8962")
Slide 30: The Digg Oracle
Slide 31: Full Text Search • Gears added FTS2 to SQLite • Create the database • Search the database db.execute('CREATE VIRTUAL TABLE recipe USING fts2(dish, ingredients)'); db.execute('SELECT dish FROM recipe WHERE recipe MATCH ?', ['tomatoes']); Fun queries: dish:stew tomatoes Find rows with 'stew' in the dish field, and 'tomatoes' in any field.
Slide 32: What didn’t you see here? Hint: Sync, sync, sync
Slide 33: Syncing is hard • Read only, small data • Read write, small data • Read only, huge data • Read write, huge data start simple, like Zoho Writer
Slide 34: Think about users and don’t make them think
Slide 35: Offline UI When to ask for user input?
Slide 36: Working with and without Gears We aren’t that arrogant! content = hasGears() ? new GearsBaseContent() : new CookieBaseContent();
Slide 37: Two Versions? Really? Only in the extreme { ‘url’: ‘main.html’, ‘src’: ‘main_offline.html’ }
Slide 38: Debugging is a Pain On the web? Duh. • Add Helper Code • To clear out the DB • Remove captured files • Disable the cache • Use Firebug / Lite
Slide 39: Debugging is a Pain On the web? Duh. GearsBaseContent.prototype.clearServer = function() { if (this.localServer.openStore(this.storeName)) { this.localServer.removeStore(this.storeName); this.store = null; } } GearsBaseContent.prototype.clearTables = function() { if (this.db) { this.db.run('delete from BaseQueries'); this.db.run('delete from BaseFeeds'); } displayQueries(); }
Slide 41: GWT and Gears try { db = new Database("database-demo"); db.execute("create table if not exists Demo (Phrase varchar(255), Timestamp int)"); } catch (GearsException e) { ... } button.addClickListener(new ClickListener() { public void onClick(Widget sender) { try { String phrase = input.getText(); if (phrase.length() > 0) { db.execute("insert into Demo values (?, ?)", new String[] { phrase, Integer.toString((int) System.currentTimeMillis())}); displayRecentPhrases(); } } catch (DatabaseException e) { Window.alert(e.toString()); } } });