RFR: 8303920: Avoid calling out to python in DataDescriptorSignatureMissing test [v6]

[Eirik Bjorsnos]

On Sat, 11 Mar 2023 08:27:06 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> Please review this PR which brings  the DataDescriptorSignatureMissing test back to life.
>> 
>> This test currently calls out to Python to create a test vector ZIP with a Data Descriptor without the recommended but optional signature. The Python dependency has turned out to be very brittle, so the test is currently marked with `@ignore` 
>> 
>> The PR replaces Python callouts with directly creating the test vector ZIP in the test itself. We can then remove the `@ignore`tag and run this useful test automatically.
>
> Eirik Bjorsnos has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains eight additional commits since the last revision:
> 
>  - Merge branch 'master' into signature-less-data-descriptor
>  - Add assertNotNulls to catch unexpectedly missing entries
>  - Revert change to Google copyright line, add an Oracle copyright line instead.
>  - Use "Signatureless" consistently
>  - Remove reference to python in the @summary of DataDescriptorSignatureMissing
>  - Update copyright years
>  - Add method comments
>  - Instead of calling out to python, create a ZIP file and remove the data descriptor signature.

Since we strip 4 bytes from the first entry's data descriptor, we need to account for this by reducing the second CEN header's LOC offset by 4. Similarly, the END header's CEN offset also needs adjustment.

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PR Comment: https://git.openjdk.org/jdk/pull/12959#issuecomment-1508989195