Calculating Chunk Bounds

[xloem]

Hi,

Is there documentation somewhere, or could somebody answer, how to calculate the bounds of a chunk around a non-aligned absolute data offset?

I'm trying to put together code to extract dataitems from ans104 bundles and other larger transactions, without downloading the entire data, knowing only an offset into the data.

What I have right now works, but it basically pings /chunk2/ repeatedly up until the offset, closing the connection after the 3
bytes of length are transferred. It's pretty slow. I understand most of the blocks are aligned to 256KiB, but that there are a handful of situations where this is not true, especially in very old transactions. What is the whole situation, including old transactions?

EDIT:
I've discerned this much: The offset of a tx, minus its size, plus 1, is the start of a chunk, and all chunks are 256KiB.