NIFI-9253 Corrected SSLSocketChannel.available() for TLSv1.3

[exceptionfactory]

Description of PR

NIFI-9253 Corrects SSLSocketChannel to avoid intermittent unit test and runtime failures related to TLSv1.3. The available() method implementation resulted in sporadic unit test failures for TLSv1.3 due to partial reads from the connected channel while attempting to determine available bytes. Partial reads produced incomplete TLS messages, causing AES-GCM decryption failures reported as Tag mismatch messages with SSLException.

The previous unit test used a loop for checking the available() bytes, causing intermittent failures. The updated unit test class includes separate methods with and without calls to available() in order to reproduce the potential problem. The corrected available() method in SSLSocketChannel avoids direct reads from the socket channel and instead returns the size of the application data buffer. This approach aligns with the documentation for InputStream.available(), which states that the method returns an estimate of the number of bytes that may be read, without blocking. Additional changes include refactoring and isolating the readChannel() and unwrap() methods in SSLSocketChannel for more streamlined handling of buffer underflow status.

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[joewitt]

local build is happy and github checks are happy. But i'm not sure I can give the code changes justice for a review. Anyone else available to look?

[exceptionfactory]

local build is happy and github checks are happy. But i'm not sure I can give the code changes justice for a review. Anyone else available to look?

Thanks for the feedback @joewitt!

@gresockj can you take a look at the changes based on reviewing previous updates to this class?

[gresockj]

I don't have any problems with the code changes, and I've run the unit tests several times, as well as verifying TLSv1.3 on PutTCP/ListenTCP and DistributedMapCacheClient. Since the problem has not surfaced, this is a +1 for me.

[pvillard31]

Merging based on @gresockj 's review and green builds.