Set maxOutputLength correctly

[losipiuk]

Previously we were not accounting for bytesPreserved.
With recent check added to aircompressor code
(airlift/aircompressor@127b7f3)
it started manifesting as java.lang.IllegalArgumentException.

This is strictly validation fix. The passed array was not filled beyond
allocated size.

Description

fixes: #16541

Additional context and related issues

Release notes

( ) This is not user-visible or docs only and no release notes are required.
(x) Release notes are required, please propose a release note for me.
( ) Release notes are required, with the following suggested text:

# Section
* Fix some things. ({issue}`issuenumber`)

[losipiuk]

@arhimondr now clue how to test it though for now. The TestPagesSerde is not triggering errornous condition.

[losipiuk]

Actually code below:

System.arraycopy(
                        source.getSlice().byteArray(),
                        source.getSlice().byteArrayOffset() + source.getPosition(),
                        sink.getSlice().byteArray(),
                        sink.getSlice().byteArrayOffset() + bytesPreserved,
                        blockSize);

seems broken too. Do we know that blockSize will always fit in the targetSlice given some of the data is taken by bytesPreserved @arhimondr ?

[arhimondr]

int bufferSize = blockSizeInBytes
                        // to guarantee a single long can always be read entirely
                        + Long.BYTES;
                buffers[0] = new ReadBuffer(Slices.allocate(bufferSize))

The buffer size is allocated according to blockSize with an extra 8 bytes (one long) for carry-overs.

The carry over is guaranteed to never be higher than 8 bytes as this is the most what can be requested to be read in one shot.

[losipiuk]

👍

[losipiuk]

@arhimondr I tried to add regression test (attempt is here) but with no luck. I cannot trigger the code flow which results in check failure.
Unless you have some idea how to proceed with test lest merge it as is.

[losipiuk]

@arhimondr updated with test

[arhimondr]

Thanks. Great idea with constructing a specialized block encoder to cover the problematic code path. Love it!