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[platform-update-dev] How To Use Non-Plugin Feature Data


Hi There,

I have been building Eclipse features and update sites for a long time, and I still don't understand the <data> element of a feature.  I was hoping someone could explain this to me and how it is used with an update site.  I'll give you a scenario.

We have an install handler that allows for the installation of non-plugin files as part of a plugin/feature installation.  Currently we package these as JAR files included with various plugins and when our install handler sees one of these special JAR files when a plugin is installed, it inflates it to the right spot and stores reference counts in a simple file-based database so these files can be uninstalled when the plugin is later disabled/uninstalled.  It all works great but packaging the extra JAR file as part of our plugins cause me a lot of pain because it introduces a lot of external (and invisible) dependencies and plugin versioning can be hell.

So, I want to pull these JAR files out of the plugins entirely, and just "attach" them to the top-level features.  It looks like I can do that with the <data> element of a feature.  But I am having a hard time seeing how this is any different from just including a JAR file as part of your feature payload using the bin.includes part of build.properties.  Why is this extra <data> element needed and how does it help?  I mean, if I add a new data archive using the feature manifest editor, I can only choose from files in my feature anyway.  So how is this any different from just going to the Build tab of the feature manifest editor and checking it off there?  And if I do add it as a <data> element, do I need to include it in build.properties as well?  If I don't - it doesn't get deployed with my feature as part of the PDE build so I assume I have to do this, which seems to defeat the purpose of the feature (if it is there for what I think it is there for...).
But this brings me to my next problem.  We originally included these archives in the features simply by deploying them as another resource included in build.properties.  This caused massive issues with our update site however because our feature JAR's were quite large, and it seemed that when the update manager queried for updates to installed features it downloaded the entire feature JAR so it could unzip and read feature.xml, and this resulted in multiple megabytes of data being downloaded everytime the user checked for updates - which was totally unusable over a slow internet connection.  This was why we moved these files into the plugins and tweaked our install handler to begin with.

Anyway, assuming the <data> element of the feature is a way around the problem above (I assume that is one of the reasons it is there), how does this tie in to the <archive> element of the update site?  It looks to me from the docs that this allows you to supply external archives in subfolders of the features/ folder in the update site to the update manager, and it seems to suggest it is tied into the <data> element of the feature, but how?  If your feature can only specify <data> elements for files that are part of the feature, AND in order to deploy these files you need to include them in your feature's build.properties, AND since features are built and deployed as single JARs when you export an update site - well....I don't get it.

Can someone give me a working scenario on how to use these two concepts together?  Does it allow me to accomplish what I need to do here?

Thanks in advance,
Mark.
AMI Semiconductor - "Silicon Solutions for the Real World"
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