RFR: 8303866: Allow ZipInputStream.readEnd to parse small Zip64 ZIP files [v12]

[Alan Bateman]

On Wed, 10 Jan 2024 13:39:52 GMT, Eirik Bjørsnøs <eirbjo at openjdk.org> wrote:

>> ZipInputStream.readEnd currently assumes a Zip64 data descriptor if the number of compressed or uncompressed bytes read from the inflater is larger than the Zip64 magic value.
>> 
>> While the ZIP format  mandates that the data descriptor `SHOULD be stored in ZIP64 format (as 8 byte values) when a file's size exceeds 0xFFFFFFFF`, it also states that `ZIP64 format MAY be used regardless of the size of a file`. For such small entries, the above assumption does not hold.
>> 
>> This PR augments ZipInputStream.readEnd to also assume 8-byte sizes if the ZipEntry includes a Zip64 extra information field AND the 'compressed size' and 'uncompressed size' have the expected Zip64 "magic" value 0xFFFFFFFF. This brings ZipInputStream into alignment with the APPNOTE format spec:
>> 
>> 
>> When extracting, if the zip64 extended information extra 
>> field is present for the file the compressed and 
>> uncompressed sizes will be 8 byte values.
>> 
>> 
>> While small Zip64 files with 8-byte data descriptors are not commonly found in the wild, it is possible to create one using the Info-ZIP command line `-fd` flag:
>> 
>> `echo hello | zip -fd > hello.zip`
>> 
>> The PR also adds a test verifying that such a small Zip64 file can be parsed by ZipInputStream.
>
> Eirik Bjørsnøs has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Remove trailing whitespace
>  - Remove trailing whitespace

I was initially concerned about this change but I think it's okay. As you say, it expands set the set of ZIP file that can be read by ZipInputStream. I've added myself as reviewer to the CSR.

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PR Comment: https://git.openjdk.org/jdk/pull/12524#issuecomment-1892510671