RFR: 8279800: isAssignableFrom checks in AlgorithmParametersSpi.engineGetParameterSpec appear to be backwards

[Weijun Wang]

On Wed, 12 Jan 2022 06:08:29 GMT, Xue-Lei Andrew Fan <xuelei at openjdk.org> wrote:

>> Change the order so parent class is at the left.
>
> src/java.base/share/classes/com/sun/crypto/provider/BlockCipherParamsCore.java line 111:
> 
>> 109:     <T extends AlgorithmParameterSpec> T getParameterSpec(Class<T> paramSpec)
>> 110:         throws InvalidParameterSpecException {
>> 111:         if (paramSpec.isAssignableFrom(IvParameterSpec.class)) {
> 
> The call to cast() is confusing.   But if the paramSpec is AlgorithmParameterSpec.class or Object.class, what's the expected behavior?  There are potential casting exception, I guess.  Maybe, a exactly class matching could be better.

If so, then the `if` block will be true and the spec object is casted to your specified class (`AlgorithmParameterSpec.class` or `Object.class`) and it always succeeds.

This is exactly what I want to achieve. In fact, this bug and the other `getInstance(oid)` bug have the same root. I was trying to decode an algorithm identifier from its encoding. First, the encoding of the algorithm is in OID so `AlgorithmParameters.getInstance()` must support OID. Second, I want to get the spec from the parameters without knowing the algorithm name and the child `AlgorithmParametersSpec` class type, so `AlgorithmParameters::getParameterSpec` must support `AlgorithmParameterSpec.class` as the argument.

Otherwise, the program needs to know name and parameter spec type on all supported algorithms.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7037