B2ND chunks were decoded whole, padding included, with up to 16x the HDF5
chunk size as their limit, so a crafted frame made each chunk allocate and
fill up to 16x the output (4 GiB for a 256 MiB HDF5 chunk). The padding is
the real bound (prod(ceil(c/b)*b) per chunk), but that can be 2^ndim times
the array, so it is no longer held at all:
- A Blosc2 chunk is now decoded block by block (decode_blocks), each block
handed to a sink as it is ready, with at most three blocks of scratch.
blosc2_decompress_chunk and plain frames still collect every block.
- reassemble places each B2ND block straight into the output and skips
blocks that are all padding (they are not decoded unless the delta
filter needs the first block). A frame's NaN chunks are handed over one
B2ND block at a time and its zero chunks cost nothing.
- A B2ND chunk must decode to exactly its padded size, its Blosc2 blocks
must be whole B2ND blocks no larger than the output, and a chunk may not
be larger than the array (hdf5-blosc2's chunk is the array), so a block
is never larger than the output.
Peak allocation for a 10-D array padded to 13x (NaN, repeated-value and
stored-block chunks) and for a 16x chunk was 4.5 MB and 17.8 MB for
315 KB and 1 MiB outputs before, and is now within the tests' bound.
Blosc2 files written by hdf5plugin in 9-D and 12-D, an 8 MiB single chunk,
1x1x1 and edge-chunk shapes still read exactly.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
