RFR: 8320971: Use BufferedInputStream.buf directly when param of implTransferTo() is trusted [v13]

[Sergey Tsypanov]

On Wed, 13 Dec 2023 16:46:16 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>>> It doesn't make sense here to add a new package com.sun.io for a single method class. This PR does not need to introduce any new classes at this point. I think this PR needs to focus solely on BIS.
>> 
>> So you actually prefer copy-and-paste and duplicated code?
>> 
>>> On the surface, transferTo reads to EOF so there are no more bytes to read from the underlying stream or byte[]. Adding a "growing file" and it breaks assumptions. So it's an important discussion point in this topic.
>> 
>> I still do not see what this has to do with the *actual* changes proposed by this PR. Can you please provide an example in what situation the *actual* changes proposed by this PR will fail in that case, while the original code will succeed?
>
>> > It doesn't make sense here to add a new package com.sun.io for a single method class. This PR does not need to introduce any new classes at this point. I think this PR needs to focus solely on BIS.
>> 
>> So you actually prefer copy-and-paste and duplicated code?
> 
> It's not important at this time, the starting point is to decide if BIS.transferTo should be changed or not. It does shared some concerns with BAIS but the set of concerns for both is not identical.

> the underlying byte[] can outlive the BAIS object

I guess this is true only for target OutputStreams incorporating another one or OutputStreams deliberately made malicious. For classes enumerated in IOStreams this is not a case, I think.

>  For BIS, transferTo may return a positive value more than once because the underlying stream is growing

As of this I don't understand how it affects the change. The JavaDoc of InputStream.transferTo() explicitly says that the method ` Reads all bytes from this input stream and writes the bytes to the given output stream` and I guess all the data is read only once

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PR Review Comment: https://git.openjdk.org/jdk/pull/16879#discussion_r1425794463