Fix DefaultDataBuffer#getNativeBuffer() to set correct limit

[injae-kim]

Closes gh-30967

Motivation

// DefaultDataBuffer
	public ByteBuffer getNativeBuffer() {
		this.byteBuffer.position(this.readPosition);
		this.byteBuffer.limit(readableByteCount()); // 👈 limit should be writePosition, not readableByteCount
		return this.byteBuffer;
	}

• We found that DefaultDataBuffer#getNativeBuffer set byteBuffer#limit as readableByteCount() incorrectly so fix to writePosition

Modification

• Fix DefaultDataBuffer#getNativeBuffer() to set correct limit as writePosition instead of readableByteCount()

Result

• Now DefaultDataBuffer#getNativeBuffer() return native bytebuffer with correct limit
• Close The method getNativeBuffer() in DefaultDataBuffer returns misconfigured ByteBuffer #30967

[injae-kim]

0  1  2  3  4  5  6  7  8  9
                     ^        ^
                   read     write

When readPosition: 7 and writePosition: 10,
Current getNativebuffer return bytebuffer with limit: 3 (readableByteCount(), writePos - readPos)

But I think we should set limit: 10 (writePos) correctly.

Like this commit, maybe we set redableByteCount() as length on bytebuffer's limit by mistake 😅

[injae-kim]

FYI) with current getNativeBuffer() logic, this test failed~!

[poutsma]

Thanks for supplying a PR. I decided to change the fix by returning a duplicate with independent position and limit, instead changing these on the buffer itself. This is arguably the way it should have been since 5fc1806.

[injae-kim]

Oh thank you for your additional polishing :)

I'm so happy that this is my first contribution(969d0bd) on spring-framework!
I'll continue to contribute by another PR 🚀