RFR: 8341957: Add test for URLClassLoader loading invalid class with mismatching CRC32

[Jaikiran Pai]

On Fri, 11 Oct 2024 11:46:40 GMT, Eirik Bjørsnøs <eirbjo at openjdk.org> wrote:

> Please review this PR which adds test coverage for the case where `URLClassLoader.defineClass` fails with a `ClassFormatError` _and_ the CRC32 checksum of the class file byte array did not match the CRC32 value stated in the JAR file's CEN header.
> 
> In such cases, an `IOException` with the message _"CRC error while extracting entry from JAR file"_ is added as a suppressed exception to the `ClassFormatError`.
> 
> Adding a test documents this unspecified, but long-standing behavior.
> 
> For good measure, the test also covers the existing behavior of the module system class loader. Since the module system does not add similar suppressed exception on a CRC32 mismatch, this test mostly serves the purpose of documentation. 
> 
> The test is parameterized, as such it covers all eight combinations of {URLClassLoader/module class loader, valid/invalid class data, valid/invalid CRC checksum}.
> 
> Should any of the class loaders change behavior in the future (with or without intent), this test will notice and may need to be updated to document the new behavior. Otherwise, it will catch unintended regressions.
> 
> Testing: This is a test-only enhancement PR, no existing tests are updated.

Hello Eirik, from what I can see, the fact that a `ClassFormatError` thrown from `URLClassLoader` has a suppressed exception and that the suppressed exception would contain CRC failure related exception message is merely an implementation detail (which should be free to change any time). I think asserting this internal detail through a test case isn't necessary.

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PR Comment: https://git.openjdk.org/jdk/pull/21469#issuecomment-2408854972