In the AU and NZ moot I had good chances to talk with Dan and MartinD about a cunning plan to get a Gears-based offline moodle going.
When we disscussed architecture for the current moodle-on-a-stick (MoaS) based we also talked quite a bit about a Gears-based approach. At the time, it looked huge and risky. Google had just released GG, and was talking about upgrading Reader to use it.
So there many things stacked against it: Noone had seen Reader doing the offline thing yet, Gears had a somewhat restrictive license, and it seemed that we'd have to implement a significant chunk of Moodle as an AJAX application.
Things have changed between then and now. Google has made things much simpler now with a BSD license and Reader shows it can make the offline thing work very well.
Reimplementing Moodle as an AJAX app was still a big monster in my head until recently. But a volunteer approached me recently saying he could take a stab at it, and I thought "what would be the simplest thing that could possibly work?"
The answer was suprisingly simple: store the damn HTML, CSS and JS in the sqlite DB that Gears provides.
So from the course page, we can "go offline" by
- Storing the html+css in sqlite -
- Requesting a special 'manifest of resources that are ok to use offline' - published by the course-format page...
- Retrieving those offline resources. Initially, just mod/resource contents. Later we can extend this support to work with other modules.
- When we use the course homepage later while offline, we'll walk the DOM to show CSS blocks 'disabled' (by graying them out) and we will disable links to resources we cannot support offline.
- As the user browses the content we do have offline, the JS code keeps track of resources visited. Upon reconnection to the moodle site, we push back the collected logs to mdl_log(*)
- Other modules (mod/forum for example) can be supported with ob magic and/or more explicit/AJAXy use of JS.
* - we'll need to review the log handling code. So far we've never had "out-of-sequence" log entries, and this will introduce them for the first time. I'm sure there'll be a few gotchas there.
Hearing this, MartinD suggested that - as long as we go the "store html" way (supported with output buffering tricks if needed) then we can add the ability to produce a plain old zipfile with a course homepage + static resources. I think it's a good secondary goal to have -- though I'm not sure what limits we'll have with this.
Tony Anderson - the volunteer who sparked this - has been working on a proof-of-concept implementation. It currently uses Gears and GreaseMonkey, and requires a few manual tweaks. Unfortunately, I don't think that code can be merged directly - we will want to refine the approach to avoid GreaseMonkey and other inconveniences. My take is that we can either adapt it, or use it as a reference for a more moodlish implentation -- Tony is not a moodle dev, so he's not necessarily familiar with our odd style
Tony's code is here http://lists.laptop.org/pipermail/server-devel/2008-September/002101.html together with some discussion around it.
I also hear noises from Barcelona -- Ludo and Ruben may be able to get involved. This could start getting interesting.
Getting this from a PoC to something shippable will take a bit of work. Right now I still have a ton of work to do on other aspects of Moodle that are more urgent for OLPC, but I will find the time to work on this working with Tony, Ludo and Ruben. Sleeping is optional, right?
Once the urgent infrastructure stuff for olpc is sorted, I'll be keen on bringing this to completion -- at least of an initial stage.
