More support for offset and length in methods operating on byte arrays

[Pavel Rappo]

Yes, overloads that accepted both source and destination ByteBuffer were there at some point, but then were removed:

commit 591834e28d482ea6a375ab215958e1635a7b111d
Author: Xueming Shen <sherman at openjdk.org>
Date:   Tue Dec 3 17:44:31 2013 -0800

    8028397: Undo the lenient MIME BASE64 decoder support change (JDK-8025003) and remove methods de/encode(buf, buf)

    Updated the spec and implementation as requested

    Reviewed-by: alanb

Let me paste the respective JBS description here for readers convenience:

The change set for "lenient mime decoder" support change (JDK-8025003) does not meet the requirement needed by the submitter and there is different understanding and opinion of what the "lenient" should be for the Base64 decoder. Given we are in late stage of the release. The decision is to back out the change and leave the functionality for future releases.

Also during the discussion, it became clear that the decode/encode(ByteBuffer, ByteBuffer) method pair are insufficient to support the requested de/encoding continuation functionality ("underflow" handling, in charset coder's term). Given the the most usage of these pair is for the channel read/writing, it appears it might be more useful/desired to provide a pair of wrap(readable/writableByteChannel) methods stead. While the wrap(channel) methods are under development, it does not appear it will make jdk8. For jdk8 we have decided to remove the decode/encode(Buffer, Buffer).

> On 14 Dec 2023, at 20:24, Pavel Rappo <pavel.rappo at oracle.com> wrote:
> 
> Upon a closer look, switching to ByteBuffer would only get you 50% towards where you want to be: the resulting ByteBuffer, whether encoded or decoded, is *allocated* by the respective methods and then returned as a result rather than accepted by those methods as a parameter.
> 
>> On 14 Dec 2023, at 19:57, Pavel Rappo <pavel.rappo at oracle.com> wrote:
>> 
>> 
>> 
>>> On 14 Dec 2023, at 06:10, Magnus <magnus.eriksson at gmail.com> wrote:
>>> 
>>> In the java libraries there are many methods that operate on byte arrays that do not allow you to specify offset and length for the relevant data instead forcing you to copy the relevant part to new arrays before using the methods reducing performance - I am for instance struggling with this in java.util.Base64 where the Encoders and Decoders lack a length parameter (also an offset would have been great even though I don't need that in my case).
>> 
>> Re: java.util.Base64. Encoder and Decoder also seem to be able to work with ByteBuffer. If you have an array, you can cheaply create a ByteBuffer wrapper around that array. The now-backing array would be read or written though from the specific position and up to the specific limit. Would that help?
>> 
>> -Pavel
>> 
>