Re: Extensions Infrastructure Work

On Tue, Jun 21, 2011 at 5:11 PM, Jasper St. Pierre
<jstpierre mecheye net> wrote:
> Recap from last time:
> It seems like everything we discussed yesterday has gotten positive
> responses. If you have any ideas or concerns about this, please don't
> hesitate to ask.
> If you're curious, all the code that I demoed last time, including
> both the Stateful/Stateless approaches is indeed working. I've mainly
> been testing with the "Hello, World" extension, but I've hacked up the
> Places Menu and the Drive Menu extensions as well. Implementation is
> left as an exercise for the reader.
> The code to do all this magic is in two places[0][1]. Disclaimer: it's
> extremely messy. You have been warned. I don't want these in GNOME Git
> yet because I'm rebasing, squashing patches, and force pushing often.
> That should slow down soon, but right now it's my baby. When it's all
> grown up, I'll move it into GNOME GIt proper.
> Here's some technical details about what I went over last time:
> For those curious, the website's partner in crime is
> gnome-shell-extension-tool[2]. There's an option that runs a small
> HTTP server which the web site can talk to. The HTTP server is
> basically a dummy proxy so that the website can talk to DBus. Before
> this lands, I'll rewrite the HTTP server so it's not based on
> BaseHTTPServer and move it into its own script. Maybe I'll rewrite it
> in gjs+libsoup instead, because I'm not aware of any light-weight,
> solid HTTP servers in Python... I don't want to install Twisted on a
> user's desktop machine, even though I'd love to.
> For all intents and purposes, the mimetype handler approach is dead. I
> may work on it to be a fallback for browsers without the cross-domain
> headers (Firefox added it in 3.5, released in 2009. That *should* be
> good enough, right?), but it would be an "extra time" thing.
> If I can figure out why the Shell's webm recorder and the <video> tag
> in Firefox aren't cooperating, you may see a small demo video of what
> I've done so far. This includes uploading, installing, enabling, and
> disabling extensions, as well as a simple error prompt that allows
> users to see any errors caused by the extension. Excusing the ugly
> code, it's all working.

About that: I couldn't get the <video> tag to work, so I uploaded it to YouTube:

... and the raw 12MB WebM file if you want it:

> Onto the new stuff:
> == Versioning and upgrading ==
> Today I started working on versioning and upgrading Shell extensions.
> The idea is that each Extension has a corresponding Extension Version
> that's associated with one zipfile: whenever an author upload a new
> zipfile, there's a new extension version. This way, if an extension
> upgrade accidentally crashes the Shell, extension authors can
> blacklist a version, causing the Shell's update system to rollback to
> the last known version. Web administrators also have the power to
> blacklist the extension in case of malice.
> I'm not going to do an upgrade automatically. Instead, the user will
> get a simple notification telling him that extensions can be upgraded.
> Clicking on it will open the website, where he
> can upgrade at his leisure. The 'shell-version' fieldcannot lie: the
> field is present for the user's benefit. If the automatic upgrading
> system sees that the newer versions are incompatible with the Shell,
> it won't pop up the notification or allow the user to upgrade.
> If the upgrade crashes the shell and there has been a recent rollback,
> the Shell will rollback and try again.
> How will we do a seamless upgrade? WIth the new enable/disable
> approach that I talked about last time in use, upgrading an extension
> should be fairly simple, provided people are playing by the rules:
>  1. Disable the extension.
>  2. Delete all internal copies of extension data (the extension
> module, importer object, state object and metadata object).
>  3. Run a full GC.
>  4. Delete the old extension directory.
>  5. Install the new extension and enable it as normal.
> Steps 3 and 4 are the ones I'm concerned about.
>  Colin: if someone leaves some signals connected on a Shell object,
> will the extension itself not collected? Is there a weakref we can add
> so that signals *can* be collected? Consider this question valid for
> any "s/signal/?/" you can think of.
>  Extension authors: when this is implemented, you cannot create or
> depend on any files in your extension dir, otherwise this just won't
> work. The "helper" object I talked about last time is just some crazy
> way for extensions to do extension-related tasks. I might add a
> "getExtensionStorage()" method that returns a GFile with a storage
> directory carved out for you that
> persists between versions. For assets, I might add a
> "getExtensionDataDir()", which does the same thing. "createDBus()"
> might be another.
> This should take me a good week and a half to do. After that, I'll
> look at Shell recovery for when the Shell crashes due to an extension.
>  Jasper
> [0]
> [1]
> [2]

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