Tag Archives: extensions

The Review Board Extension Life-Cycle

According to the timeline, I’m still in the community-bonding period for GSoC.  Coding for my project is supposed to start sometime towards the end of May.

So I’m using the time to do the following:

  • Close as many small, easy tickets as I can for the  upcoming Review Board release.  I’ve already posted some patches for review.  More forthcoming.
  • Get to know the tools I’ll be using.  Review Board is hosted on Github, and I’m relatively new to the whole DVCS thing.  I’ve been figuring out how to use Git, how to post patches, merging, branching, etc.
  • Get to know the area I’ll be working in.  I’ve been figuring out how Django apps organize themselves.  I’ve also drawn up a map of the current state of the extension framework to help me visualize it.
  • Get to know the other developers working on Review Board.  I’ve been hanging out in the #reviewboard-soc FreeNode IRC channel.  Very nice, and helpful people to work with.
  • Develop a plan of attack for my project

And this last point is the one I want to talk about.

The Review Board Extension Life-Cycle

An extension isn’t just some isolated piece of code that gets crammed into an application.  When you’ve got multiple extensions already installed and running, installing and activating a new extension is like introducing a new animal into an ecosystem.  You have to make sure that your new animal plays nice with the others, and that, in the morning, there won’t be a pile of rotting corpses where your application used to be.

I may have gotten carried away with my metaphor.

So let’s look at what I’m envisioning as the life-cycle for a Review Board extension.  I’ll start right from the top.

Getting the Extension

Ideally, this will work as nicely as WordPress’s implementation:  a Review Board administrator is given a catalog of extensions to choose from within the Administrator interface, and one click later, the desired extensions are downloaded and ready to be installed.

For all you system administrators out there, that last idea might make your toes curl.  A Review Board administrator is not necessarily a system administrator, and the system administrator knows what he/she likes on their machine.  An application that can go and download other applications can be dangerous.  We have to ensure that the application that we’re downloading is the one we’re trying to download.  The last thing we need is some man-in-the-middle to do something cute and bork the code review machine.  And we want to ensure that the extension functions as advertised.  No hidden features.  No self-destruct mechanisms.  No back doors.

Do I have a plan for this part?  Well….no, not really.  I don’t imagine I’ll get that far – I consider it a little out of my scope.  So, for my project, I think it’ll satisfy if the system admin (or Review Board admin) can manually download the extension, decompress it, and place it where Review Board can work with it.  That other stuff can come later (and I’ll try to design so that it can come later easily).

Installing the Extension

Ok, so at this point, we’ve got our extension downloaded in a place where Review Board can see it.

So now what?

Now we need to install the extension.  To me, that means letting the extension put its roots into the RB install by creating database tables, preparing initial data, and generally doing everything to make conditions suitable for the extension to function.

When an extension install begins, I imagine it will consider the following questions (in no particular order):

  1. Do I (the extension) depend on other extensions to function?  If so, are those extensions present?  If not, let the user know so that they can go get them.
  2. Are there some extensions already installed that will conflict with me, or make me behave badly?  If so, let the user know so that they can either remove that conflict, or find an alternative extension.
  3. Is the user entirely aware of what I can do?  Make sure that my capabilities, limitations, and behavioural quirks are known to the user.

Once those 3 questions are answered, and everything is looking good for the install, the extension will create the database tables it needs (if any) in order to function.  If anything goes wrong during this process, the database changes will be rolled back, and the user will get a full read out about what went wrong.

If nothing goes wrong, the extension will be installed.  The user might then be asked to set some initial operating parameters for the extension.

Ok great – the extension is installed.  Now what?

Activating the Extension

For something that sounds so dramatic, the explanation about what happens is pretty short:  Review Board simply becomes aware that the extension is activated, and passes data through the necessary hooks in order for the extension to function properly.  Upon activation, the extension should do a quick double-check to ensure that all prerequisites for the extension have been met.  This is because we can’t trust users to activate an extension immediately after downloading them.

The Extension Runs

While it’s activated, the extension will probably react to various events that happen on Review Board.  Tables will be updated.  View methods will be run.  Templates will be rendered.

If anything, ever, goes horribly wrong with an extension, the following will happen:

  1. A log entry will be written, dumping the error, and information about what the user was trying to do
  2. An error message will be displayed to the user, trying to tell them what exactly happened
  3. The extension (and its dependents) will be deactivated.  They will no longer react to events on Review Board.  Their tables will still be there, the settings will still, but the extension will be, in essence, asleep.  Dormant.  Non-reactive.

The administrator could try to reactivate the extension at this point.  They might try to contact the extension developer for support.

The Extension is Un-installed

If the user wants to rid themselves of an extension, they must first deactivate it.  This will put it (and its dependents) in the dormant state.  It just switches them off, nothing else.

Deactivated extensions can then be un-installed.  If the user chooses to un-install the extension, the extension database tables and settings will be wiped out.

The extension itself won’t be deleted though – at least, not within the scope of my project.  The extension files will need to be removed from Review Board manually.

At this point, any dependents that this uninstalled extension had will no longer be able to be activated.

Anyhow, that’s how I envision the life-cycle.  It’s my first go at it, so I’d love to hear some feedback if you have any.

Code Spelunking: Review Board Extensions

So this summer, I’m working on Review Board for the Google Summer of Code.

Until my GSoC acceptance, my romps into the code had been relatively shallow.  But with my proposal being given the green light, I’ve started doing more extensive explorations.

Review Board is built using the Django web framework.  I haven’t worked with Django before, but I have quite a bit of experience with Rails, so that should be an asset.  Using a web framework means having (relatively) predictable source code layout, and Review Board is no exception.

Djblets

At one point or another, the Review Board developers realized that a lot of their code wasn’t Review Board specific, and could be abstracted out into an external library.

That library is called Djblets.

Among other things, Djblets adds a DataGrid component for easy record sorting and pagination.  There are improvements to Django’s Authentication system.  Functions for easily displaying a user’s Gravatar.

And, low and behold, there is a branch of Djblets that provides classes and functions for giving a Django application an extension framework.  The classes are abstract enough so that, in your Django application, you can specify different types and behaviours for your Hooks.

Djblets -> Review Board

The Review Board extension branch takes these Djblets extension classes, and extends them into DashboardHooks, NavigationBarHooks, ReviewRequestDetailHooks…lots of different hooks.

So, Djblets creates the foundation abstractions.  Review Board makes these abstractions a little more specific.  And then an extension writer needs to instantiate and use these classes to design their extensions.  It sounds complicated, I know.

So Let’s Map It Out

When I start learning a new code base, I do a lot of drawing.  To me, getting to now a code base is like getting to know a city, and that means walking around it, and mapping it out.

So I’ve taken the liberty of mapping out the extension classes that I’ve found, and how they relate to one another.  Note that at the bottom of my map, a simple extension (RB Reports) is using some of those classes to hook itself into Review Board.  You can find this, and other extensions,here.

My map of the extension framework

Click here to check out my map of the current state of the extension framework

Now, before someone in the department starts complaining about my misuse of UML:  I’m not a UML guy.  I just wanted an easy piece of diagramming software, and the one that I found (Dia), did UML.  I just wanted something to draw boxes and lines. So please don’t freak out if you think I’m using the wrong symbols.

One symbol you might be wondering about is the blue quantum-flux-capacitor-implosion.

I’ll save that for a future post.

My GSoC Project: Review Board Extensions

If you didn’t already know, Review Board is an open-source web-based code review tool.  The MarkUs Team has been using Review Board for pre-commit code review for about a year now.  This has given the team a number of advantages:

  1. For a team that usually has a 4 month turnover, this allows us to quickly get new team members up to speed with how to contribute to MarkUs.  We review every change that they propose, and give them tips/guidance on how to make it fit in well with the application.  They learn, and the applications code stays healthy.
  2. We catch defects before they enter the code base.  Simple as that.
  3. We get a good sense of what other people are working on, and what is going on in the code.  Review Board has become a central conversation and learning hub for the developers on the MarkUs team.

So, the long and the short of it:  I like Review Board.  Review Board helps us write better code.  I want to make Review Board better.

So what am I proposing?

How to Avoid A Bloated Software Monster

You can never make some people happy.

No matter how decent your software is, someone will eventually come up to you and say:

Wow!  Your software would be perfect if only it had feature XYZ!  Sadly, because you don’t have feature XYZ, I can’t use it.  Please implement, k thx!

And so you either have to politely say “no”, and lose that user, or say “yes”, and add feature XYZ to the application.  And for users out there who don’t need, or don’t care about feature XYZ, that new feature just becomes a distraction and adds no value.  Make this happen a bunch of times, and you’ve got yourself a bloated mutha for a piece of software.

And we don’t want a bloated piece of software.  But we do want to make our users happy, and provide feature XYZ for them if they want it.

So what’s the solution?  We provide an extension framework (which is also sometimes called a plug-in architecture).

An extension framework allows developers to easily expand a piece of software to do new things.  So, if a user wants feature XYZ, we (or someone else) just creates and make available an extension that implements the feature.  The user installs the extension, activates it, and bam – our user is happy as a clam with their new feature.

And if we make it super-easy to develop them, third-party developers can write new, wonderful, interesting extensions to do things that…well, we wouldn’t have considered in the first place. It’s a new place for innovation.  What’s that old cliché?

If you build it [the plug-in framework], they will come [the third-party developers who write awesome things]

And the developers do come.  Just look at Firefox add-ons or WordPress plugins.  Entire ecosystems of extensions, doing things that the original developers would probably have never dreamed of doing on their own.  Hell, I’ve even written a Firefox add-on. And users love customizing their Firefox / WordPress with those extensions.  It adds value.

So we get wins all over the place:

  • Our user gets their feature
  • The software gets more attractive because it’s flexible and customizable
  • The original software developers get to focus on the core piece of software, and let the third-party developers focus on the fringe features

And this is where I think I can help Review Board.

(Before I go on, if you’re interested, here’s another article on the how and the why of plug-in architectures)

Review Board Extensions

So if you look at the Review Board Wiki, or glance at the mailing lists you see numerous requests from users for new features, for example:

It would be nice if the review board had a “next comment” button that is always available to click, or had a collapse/expand button. This would make it easier to see other people’s comments in cases like this.

…

It will be nice to have post-commit support. Instead of every post-commit review being a separate URL, if we could setup default rules for post-commit reviews to update an existing review providing the diff-between-diff features, it would be very useful.

The Review Board developers could smell the threat of bloated feature-creep from a mile away.  So, in a separate branch, they began working on integrating an extension framework into Review Board.

The extension branch, however, has been gathering dust, while the developers focus on more critical patches and releases.

My GSoC proposal is to finish off a draft of the extension framework, document it, and build a very simple extension for it.  My simple extension will allow me to record basic statistics about Review Board reviewers – for example, how long they spend on a particular review, their inspection rate, etc.

Having been a project lead MarkUs for so long, it’s going to be a good experience to be back on “the bottom” – to be the new developer who doesn’t entirely have a sense of the application code yet.  It’s going to be good to go code spelunking again.  I’ve done some preliminary explorations, and it’s reminding me of my first experiences with MarkUs.  Like a submarine using its sonar, I’m slowly getting a sense of the code terrain.

I’ll let you know what my first few sweeps find.

ReviewBoard Extensions: A State of Affairs

One of my potential research experiments involves augmenting ReviewBoard, and so, I’ve been studying the ReviewBoard code.

I want to give ReviewBoard the ability to record certain statistics – for example, the number of defects in a review request, number of defects found per reviewer, defect density, inspection rate, etc…

It turns out I’m not the only one who wants this to happen.  Check out this thread.

So it turns out that the devs building ReviewBoard are planning on integrating an extension framework.  Theoretically, users could then write their own extensions to customize ReviewBoard as they see fit.  Think WordPress plugins, but for a code review tool.  Neat.

According to the above link:

A lot of this [extension framework] already exists in a private development branch, and it will be one of our primary focuses as soon as 1.0 goes out.

However, I found the following quote from a relatively recent mailing list message:

[with regards to the extensions framework]…We have to finish building it, testing
it, getting other features we have planned into the release, and performing
the release. So, we’re looking at a year or more. But I don’t see how we’d
get the functionality you want short-term.

Hrmph.  My thinking:  maybe I can help them with it, and we can crank this puppy out sooner.

So where is this private branch?  It actually took a little bit of detective work…

Detective Work

I started by looking at the ReviewBoard repo on Github, which I assumed that the extensions branch would fork from.

I was right – check out the fork network.  There’s a branch helpfully labeled “extensions” forked by davidt, one of the ReviewBoard devs.

Two observations:

  1. This fork hasn’t been updated in about a month
  2. The extensions stuff references stuff from Djblets which doesn’t exist in the Djblets master branch

So I perform the same exercise – I glance at the Djblets fork network, and see the handily named “extensions” fork that is in davidt’s git repo.  Nice.

Ok, so those are the forks/branches that I’m going to grab.

A Fluke

So, funny story:  I was able to get this “extension” version of ReviewBoard working on my work machine.  But it was by a complete fluke – this extension version of Djblets is actually missing some pieces.  The only reason it worked for me was because I accidentally ran with the master checkout of Djblets first.  This errored out, and also generated a bunch of compiled Python.  I then switched to the extensions branch, which left the compiled Python behind.  The compiled Python filled all of the missing pieces that are in the extensions branch of Djblets, and so it ran.

For a guy who is pretty new to both Git and Django, I found that problem pretty frustrating to track down.  Especially when I started writing up the checkout instructions… big thanks to Zuzel for her invaluable (and patient) Django guidance.

Anyhow, if you’re interested in the steps to failure, here they are…

Setting Up (for failure)

I’m running Ubuntu Karmic.  I have Git installed.

  1. First of all, this document is invaluable
  2. Check out django_evolution from SVN to some local directory
  3. Put path to django-evolution into PYTHONPATH (export PYTHONPATH=$PYTHONPATH:/…/django-evolution-read-only/)
  4. Get Python Setuptools (sudo apt-get install python-setuptools)
  5. With easy_install, get nose, paramiko, recaptcha-client, Sphinx (sudo easy_install nose paramiko recaptcha-client sphinx)
  6. Clone original master Djblets repo (git clone git://github.com/djblets/djblets.git) and CD into djblets directory
  7. Add davidt’s remote Djblets branch (git remote add davidt git://github.com/davidt/djblets.git)
  8. Fetch davidt’s repo  (git fetch davidt)
  9. Track davidt’s extension branch for djblets (git branch extensions davidt/extensions)
  10. In djblets root dir, type:  sudo python setup.py develop
  11. This should install Django too.  The ReviewBoard install doc says to install from Subversion, but this will do for now.
  12. Clone ReviewBoard git repo (git clone git://github.com/reviewboard/reviewboard.git) and Cd into it
  13. Add davidt’s remote Reviewboard branch (git remote add davidt git://github.com/davidt/reviewboard.git)
  14. Fetch davidt’s repo  (git fetch davidt)
  15. Track davidt’s extensions branch of reviewboard (git branch extensions davidt/extensions)
  16. Switch to extensions branch (git checkout extensions)
  17. So reviewboard/reviewboard/extensions should have stuff in it.
  18. python ./contrib/internal/prepare-dev.py
  19. Manually create the directory reviewboard/reviewboard/htdocs/media/ext.  ReviewBoard expects it and will complain if it isn’t there.
  20. Run ./contrib/internal/devserver.sh
  21. Go to localhost:8080

If you’re like me, you’ll see an error about “no module named urls”.  This is because the extension branch of Djblets is missing urls.py in its djblets/log directory.  As you can see, urls.py exists in the master Djblets branch.

So I’ve accidentally got it running.  But this version of ReviewBoard I’ve created is like Frankenstein’s monster – it’s a sad, stitched together monstrosity that should probably never see the light of day.

I tried to merge the master branch of Djblets and ReviewBoard into the extensions branch, and then realized that I had no idea what I was doing.  The last guy you want doing a merge is a guy who doesn’t know what he’s doing.

So that’s where I stand with it.  Kind of a sad affair, really.  I’ve posted on the ReviewBoard developer mailing list asking for some guidance, but all is quiet so far.

In the meantime, I’ll continue studying the code when I can.  The extensions stuff is actually pretty far along, in my opinion – but what do I know, I’ve never built one.  I’ll also take a peek at some other examples of extension frameworks to see what I can learn about implementation (that’s right – I’m talking about you, WordPress).

I’ll let you know what I find.

Making my First Firefox Extension…in 90 Minutes

It’s a race.

I’m going to attempt to create a simple Firefox extension that will display the DOM ID of an element that my mouse cursor is hovering over in the status bar.

There are probably a ton of Firefox extensions that will do that already, but I want to give it a shot as a project.

It’s 3:30PM right now, and I want to try to get this done by 5:00PM.  I’m going to be using Ubuntu 8.04, gEdit, and Google to get me started.

And I’m going to record my progress here in this blog post.

Note: After I’m done, I’m going to edit my sporadic notes so that they make more sense.  So if you’re wondering just how I managed to stay so cool, calm, and collected in my prose under such time pressure, and why the publish date on this article is after 5PM, now you know.

3:35PM:

Gonna start with Google:  “building a firefox extension”

Ok, found an article about how to create a Firefox extension.

Apparently, the first thing I want to do is try setting up a development profile in Firefox.

3:41PM

Finished setting up my dev profile by opening up FF with this command:

firefox -no-remote -P

Then created a profile called “Development”.  After that, I typed “about:config” in the URL bar, and changed some settings as instructed on this site.

3:49PM

According to that last article, I can create a skeleton Extension project using this site.  Done – calling the project DOM ID Displayer

3:53PM

Installed this Extension – apparently, it’ll be some help.  Will let me reload Firefox’s chrome  shtuff without restarting the browser each time.  Useful.

3:55PM

Found this article on making a status bar extension in XUL.  Easy as pie.

4:05PM

Ok, I’ve coded something in XUL that should display a new panel in the status bar.

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet href="chrome://domiddisplayer/skin/overlay.css" type="text/css"?>
<!DOCTYPE overlay SYSTEM "chrome://domiddisplayer/locale/domiddisplayer.dtd">

<overlay id="domiddisplayer-overlay" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
<script src="overlay.js"/>

<!-- Firefox -->
<statusbar id="status-bar">
  <statusbarpanel id="domiddisplayer" label="Hello, World!" tooltiptext="Dom ID Displayer" />
</statusbar>
</overlay>

I put that in the “overlay.js” file in my ~/Experiments/Extensions/domidinspector/content folder that was created using that Wizard from 3:49.

Now, to get this thing to run in my Development profile, I create a symbolic link to it in the Development profile’s extensions directory

ln -s ~/Projects/Experiments/Extensions/domidinspector ~/.mozilla/firefox/nzuzbdpz.Development/extensions/domiddisplayer@mike.conley

Open Firefox with Development profile:

firefox -P Development &

4:16PM

Looks like I can access and relabel the XULElement that I’ve ID’d as “domiddisplayer” using this:

domiddisplayer.updateDisplay = function(event) {
var dom_element_id = event.relatedTarget.id;
document.getElementById('domiddisplayer').setAttribute('label', dom_element_id);
}

Cool – I can now change my text in the Firefox status window.  Now I just need to capture any time a mouse moves over a DOM element….yikes, that might be tricky.

4:33PM

Been tinkering with this as a way of putting a mouseover event listener on everything in the window:

window.addEventListener("mouseover", function(e) {
  domiddisplayer.updateDisplay(e);
}, false);

4:35PM

Seems to only be capturing mouseover/mouseout events on Chrome elements – so I can get the ID’s of the statusbar, etc.  These are XUL Elements, not the DOM elements of a web page…

So I’m close.

4:44PM

This page is super helpful…

Apparently, I need to wait for the content of the page to load before I can attach observers to all of its sub-elements.  Makes total sense.

So, in my domiddisplayer.onLoad function, I write this:

var appcontent = document.getElementById("appcontent");
if(appcontent)
  appcontent.addEventListener("DOMContentLoaded", domiddisplayer.onPageLoad, true);

And now, I create a function called onPageLoad, which looks like this:

domiddisplayer.onPageLoad = function(aEvent) {
//Runs when the page is loaded
  window.content.document.addEventListener("mouseover",
  function(e) {
    domiddisplayer.updateDisplay(e);
  }, false);
}

5:03PM

Done.  I’m over time, but I’ve finished a (relatively) working extension.

Here, it’s a mess, but you can download the whole thing right here if you want to tinker with what I did.

Download domiddisplayer.zip