Fix small reads of multi-part blobs

[DaveCTurner]

No description provided.

[elasticmachine]

Pinging @elastic/es-distributed (:Distributed/Snapshot/Restore)

[tlrx]

LGTM

Thanks David for catching and fixing this and sorry for this bug. I left a suggestion, feel free to use it or not.

[tlrx]

Thanks, I was able to reproduce and came with a similar fix.

For better readability I'd suggest to isolate single part case (and be paranoid about the length to read) from the multiple parts case, something like:

Suggested change

	endInPart - startInPart
	if (fileInfo.numberOfParts() == 1L) {
	return blobContainer.readBlob(fileInfo.partName(0L), position, Math.min(length, fileInfo.partBytes(0) - position));
	}
	final long startPart = getPartNumberForPosition(position);
	final long endPart = getPartNumberForPosition(position + length);
	return new SlicedInputStream(endPart - startPart + 1L) {
	@Override
	protected InputStream openSlice(long slice) throws IOException {
	final long currentPart = startPart + slice;
	final long startInPart = (currentPart == startPart) ? getRelativePositionInPart(position) : 0L;
	final long endInPart
	= (currentPart == endPart) ? getRelativePositionInPart(position + length) : getLengthOfPart(currentPart);
	return blobContainer.readBlob(fileInfo.partName(currentPart), startInPart, endInPart - startInPart
	);
	}
	};

[DaveCTurner]

Sure, sounds good, see 558e68a.