Creating a Firefox Sidebar for Clearspace: Part I

It’s been embarassingly quiet on this blog of late, I apologize for all the delicious links, although a case could be made that blogs were originally nothing more than sharing links so maybe I shouldn’t be apologizing, but that’s a different blog post. Today I want to talk about the thing I’ve been working on at night, my non-day job if you will. A couple months ago I was reading all the hype about how JavaScript is going to take over the world and I’d been doing a lot of JavaScript during the day but I needed a project to get me through the night. Right about that time was when Twitter started taking off and I came across twitbin, which is a cool Firefox sidebar that shows you all of your friends tweets in a Firefox sidebar (the same sidebar that livehttpheaders and selenium IDE show up in), updated in real time. Like any good hacker, I wondered “how’d they do that” and started poking around the xpi file that you download to install Firefox extensions. Lo and behold, it’s JavaScript and HTML behind the scenes. Since Clearspace is one of those addictive, constantly updating, can’t get enough of it kind of applications (unlike Twitter you can actually use more than 140 characters! amazing!), I thought it would be both useful and potentially easy to create a sidebar for Clearspace, which brings me to this blog post.

I’m not sure where I started, but I’m pretty sure the first step wasn’t to create a plugin in Clearspace, I messed around for awhile with the technologies that go into creating a Firefox Extension: JavaScript, XUL (pronounced ‘zool’), install manifests, etc. I got a sample Firefox sidebar up and running that and spent way more time than I should have installing, viewing, uninstalling and restarting Firefox than I should have. I spent a lot of time digesting these sites:

I’ll discuss some of the things I ran into on the Firefox / JavaScript side in a second blog post: right now I want to talk about the Clearspace side of the plugin.

Eventually, I got to a place where I was comfortable enough with the Firefox side of things to creating the Clearspace part of the plugin. The content that is displayed in the sidebar is nothing more than plain HTML and CSS. If you install the Clearspace plugin you can actually view the content in any browser: go to http://example.com/clearspace/cf-view.jspa (replacing example.com with the host name of your installation). You’ll see that the content looks surprisingly similiar to the content that shows up on the the homepage of Clearspace, and in fact, it is the same content. The one difference between this page and other pages in Clearspace is that it never does a page reload. All the views (the login page, the settings page, the view page, etc.) are included in the resulting HTML, but hidden using CSS so that you only see one view at a time. When you click a button at the top of the page, two things usually happen: a) the current view is hidden using CSS and the new view is displayed using CSS and b) an AJAX request is sent out to a WebWork action that performs some action: logging you out, getting the updated content since your last time you viewed the page, saving your Clearfox settings, etc. This process might seem a little backwards: why not just work the same way a regular web page browsing session works where you click a link and your browser loads another page? It’s actually a limitation imposed by the Firefox extension model, so I won’t go into it here, but if you’re curious, you can do a search for ‘DOMContentLoaded firefox extension’.

So now that you (hopefully) understand how the client works, I’m going to assume that you won’t have any problems copying the ‘example’ plugin that Clearspace ships with and dive right into the pieces that are distinctive about the Clearspace part of the Clearfox plugin.

First, I needed to define the WebWork actions that Clearfox was going to use, which means I needed to create the xwork-plugin.xml file. The descriptor for the view that I mentioned earlier looks like this:

<action name="cf-view"
   class="com.jivesoftware.clearspace.plugin.clearfoxplugin.ViewAction">
   <result name="success">/plugins/clearfox/resources/view.ftl</result>
   <result name="update">/plugins/clearfox/resources/update.ftl</result>
</action>

That action is pretty standard: there are two possible results: the ‘success’ result shows the list of the 25 most recently updated pieces of content, the update result is used by an AJAX request to update the existing page with the n most recently updated pieces of content since the last refresh (which by default is invoked every 5 minute). The ViewAction class extends com.jivesoftware.community.action.MainAction, which is the WebWork action that handles the display of the homepage of Clearspace, so ViewAction simply invokes

super.execute();

to get the same content you’d get if you viewed the homepage. When the Clearfox plugin refreshes every 5 or so minutes it invokes the

public String doUpdate()

method, passing in the time (in milliseconds) that the last piece of content it has a record of was updated. It gets back a (presumably) shorter list of content that it then updates the view with.

The login, logout and settings actions are all using in combination with AJAX and since none of them need to provide any data, they all return HTTP status code headers:

<action name="cf-login"
   class="com.jivesoftware.clearspace.plugin.clearfoxplugin.LoginAction">
   <result name="success" type="httpheader">
      <param name="status">200</param>
   </result>
   <result name="unauth" type="httpheader">
      <param name="status">401</param>
   </result>
</action>
<action name="cf-logout"
   class="com.jivesoftware.clearspace.plugin.clearfoxplugin.LogoutAction">
   <result name="success" type="httpheader">
   <param name="status">200</param>
   </result>
</action>
<action name="cf-settings"
   class="com.jivesoftware.clearspace.plugin.clearfoxplugin.SettingsAction">
   <result name="success" type="httpheader">
      <param name="status">200</param>
   </result>
</action>

The last action is used by the Firefox Extension framework to determine if the plugin (on the Firefox side) needs to be updated. The action descriptor looks like this:

<action name="cf-updater"
   class="com.jivesoftware.clearspace.plugin.clearfoxplugin.UpdaterAction">
   <result name="success">
      <param name="location">/plugins/clearfox/resources/updater.ftl</param>
      <param name="contentType">text/rdf</param>
   </result>
</action>

The one trick about this one is that the result sets an HTTP contentType header, which isn’t remarkable except that Clearspace uses Sitemesh, which attempts to decorate everything it can parse with a header and footer. The contentType header should be a hint to Sitemesh that you don’t want the result to be decorated / wrapped with a header and footer, but apparently the hint is to subtle for Sitemesh because it attempts to wrap the result of this action anyway, which leads to the second distinctive part of this plugin.

The way we bypass Sitemesh decoration in the core product is by modifying a file called templates.xml, which gives us the ability tell Sitemesh to exclude certain paths from being decorated. In Clearspace 1.7, which will be out in a couple weeks, plugins (which can’t modify templates.xml) will have the ability to tell Sitemesh about paths that they don’t want decorated. Hence the following entry in the plugin descriptor (always located at the root of plugin and named plugin.xml):

<sitemesh>
   <excludes>
      <pattern>/cf-updater.jsp*</pattern>
      </excludes>
</sitemesh>

Third, Another thing you may have noticed if you were following along with the source code (which is available from clearspace.jivesoftware.com) is that two of the action classes (ViewAction and LoginAction if you must know) are marked with the class annotation ‘AlwaysAllowAnonymous’. This annotation tells the Clearspace security interceptor that the anonymous users should be allowed to invoke the action without being logged in. This is probably a good place to remind you of one of the differences between Clearspace and ClearspaceX. Clearspace, by default, is configured to *require* users to login before they can see any content while ClearspaceX uses the opposite default: you only need to login (usually) if you want to post content. So back to the AlwaysAllowAnonymous annotation: it’s important mostly for the Clearspace (not ClearspaceX) implementations because you want to give people the ability to invoke the action and then the action itself handles the display of the login page in it’s own specific way. The RSS related actions in Clearspace work exactly the same way: they are all annotated with the AlwaysAllowAnonymous marker and then handle security via HTTP Basic Auth (Clearspace) or simply allow anonymous usage (ClearspaceX) because feed readers

Fourth, because the Firefox part of the plugin needs to be specific to your installation, all the Firefox plugin related files need to be zipped up to create the XPI file that your users will install into Firefox. The plugin framework gives you the ability to define a plugin class:

<class>com.jivesoftware.clearspace.plugin.clearfoxplugin.ClearFoxPlugin</class>

which implements com.jivesoftware.base.plugin.Plugin. The interface specifies a method:

public void initializePlugin(PluginManager manager, PluginMetaData pluginData);

which means that your plugin will get a chance to initialize itself. The Clearfox plugin uses this initialization hook to zip up the Firefox related files. The plugin is told where it lives:

public void initializePlugin(PluginManager manager, PluginMetaData metaData) {
   File pluginDir = metaData.getPluginDirectory();
   ... 

and then goes on to zip up the files located in the xpi directory of the plugin source.

So that’s that… if you got this far you probably don’t care, but I actually did a screencast of the whole thing that lives over here or you can check it out on blip.tv.

One thought on “Creating a Firefox Sidebar for Clearspace: Part I”

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>