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Re: [p2-dev] Pack200 and P2 rules headaches


Thomas Hallgren wrote on 05/07/2009 10:05:50 AM:
> Personally, I see this as a missing part of an otherwise good tool.
> Pack200 should have an option or something to control this. One way
> to overcome this deficiency is to check if a file is missing .class
> files and when that happens, change the magic. I've tried that, and
> it seems to work just fine.


Yes, it's really suprising that they would *default* to being incompatible with Java 5, but I guess that's what we're stuck with. On the other hand, there is very little value packing a JAR file that doesn't contain any class files, since the pack200 compression is strictly dealing with class file compression. In this case you're paying the deflate/inflate performance cost without any transfer improvement.

Hacking the magic seems a bit scary, in case there are any incompatible changes in the format we don't know about. A possible safer hack would be to check the magic and delete the packed file if the magic started with "CAFED00D/160" (gotta love those Java magic numbers). This would imply the file contains no class files (or pure Java 6 content, which I doubt is true for many Galileo bundles).