RFR: 8279283 - BufferedInputStream should override transferTo [v9]

[Markus KARG]

On Thu, 8 Sep 2022 06:32:59 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> The correctness of the actually written data is already checked in `checkTransferredContents`. I do not see what you win by replacing `ByteArrayInputStream` by `FileInputStream`. What additional risks do you cover, and what is so special about `FileInputStream` compared to any other `InputStream`? `FileInputStream::transferTo` is already checked by its own unit test.
>
>> Given that the implementation in this PR now calls the wrapped `InputStream`'s `transferTo` method, should we also include a test where the wrapped `InputStream` is a `FileInputStream` and the target `OutputStream` is a `FileOutputStream`, so that it exercises the `FileChannel#transferTo` code path and verifies the correct data is transferred?
> 
> Right, the implementation change means that the transferTo implementation of the wrapped input stream is used, or the base InputStream.transferTo is used. We should expect there is good test coverage of these implementations already but checking into that might find opportunities to expand those tests (not this PR of course).
> 
> For the new test to exercise the BIS.transferTo then I think it will need to test with a mark set, test when there are buffered bytes (read before transferTo), or when BIS has been extended.

Agreed that testing the non-empty-buffer (read-before-transferTo) and the mark-set cases (mark-before-transferTo), but still I do not see any need to take particularly `FileInputStream` into the boat; files only make the test run slower.

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PR: https://git.openjdk.org/jdk/pull/6935