safari

Google Gears is a fantastic browser plugin; it allows a developer to create applications that run while offline, syncing with a server when online. Two great examples of the power of that mechanism are Gmail (both the “desktop browser” and the mobile Android-version) and Mindmeister (only while in trial, for paying Mindmeister-accounts after that period). The problem with Gears however is that it’s a plugin and not a lot of people have it installed: only Chrome-users have it by default. And that’s where HTML5 comes in; one of the areas where the new spec offers vast improvements over html4/xhtml is the ability to take webapps offline by allowing a developer to store files for offline usage and to write data to a local, browser-embedded database. Both Safari 4 and Firefox 3.5 support these features, so maybe HTML5 makes Gears already redundant in those browsers with more to come?
I haven’t gotten around to experimenting with offline databases yet, but I did already look into offline files. At first sight, Gears Localserver and HTML5 Offline Webapps indeed seem very similar; your html-page points to a manifest-file which contains a list of assets (pages, images, css, js, …) that the browser has to store for offline usage. Easy enough, no?
To get a better feel of how offlining in HTML5 works, I decided to try to write a simple WordPress plugin to replace its ‘Gears Turbo’-option. Turbo (which you can find in the Options-menu) essentially stores 1Mb of files locally, to speed up delivery of the WP-admin pages. To make a long story short; my plugin didn’t work. For starters, by default requests for non-local data are blocked, but it’s easy enough to unblock network access by adding “NETWORK:*” (with a newline before the wildcard) to the manifest. But more fundamentally; HTML5 Offline Webapps not only stores the files specified in the manifest-file, but also every html-page which points to the manifest (see my test here). There’s no way you can exclude those “master entries” from being stored. So if pages are stored, that means they have to be static and that all dynamic parts should be handled by javascript (fetching data using ajax and updating your page with it). And that, my friends, is clearly not a use-case that is applicable to WordPress admin-pages.
So HTML5 Offline Webapps is no drop-in solution to speed up delivery of dynamic pages, you’ll still need Gears to take care of that (or rely on old-fashioned carefully configured expiry- and cache-headers). But, as Google proves with the iPhone-version of Gmail, Offline Webapps combined with a HTML5 offline database can work miracles if you use it the correct way.