FileBuilder stored every chunk of an LZF or Blosc dataset through the
filter with filter mask 0. libhdf5 counts LZF and Blosc output no smaller
than the chunk as a failure of the optional filter and stores the chunk raw
with the filter's mask bit set. For an LZF chunk whose stream was exactly
the chunk's size, the first libhdf5 rewrite stored raw data at the same
size and kept our stale mask 0 in the index, and h5py could no longer read
the dataset.
precompress_chunks now runs chunks through compress_chunk_masked (as
FileEditor does since f7e2ab1), sequentially and on the parallel path, and
build_chunked_data_from_precompressed records each chunk's real mask in
every index the writer builds: single chunk (layout field), Fixed Array and
Extensible Array filtered elements, and version-2 B-tree type 11 records
(create_datasets_parallel goes through the same path). The writer builds
no version-1 B-tree or implicit index. PrecompressedChunks::chunks gains
the mask. Files whose chunks all compress are byte-identical.
Latent only in the unreleased LZF/Blosc writer (added 2026-09-26); no
tagged release writes either filter.
Tests:
- plugin_filters_interop skipped_optional_filters_are_masked_as_libhdf5_masks_them:
LZF, shuffle+LZF+fletcher32 and Blosc over random, compressible and
alternating chunks in every index; masks equal an h5py-written twin's;
h5py r+ rewrites and extends them; h5py, h5dump and our reader read
every value. Before: 20 of 24 datasets had masks other than h5py's, and
with that check disabled h5py failed to read the rewritten datasets
("filter returned failure during read").
- plugin_filters_interop files_whose_chunks_all_compress_are_unchanged:
pins the pre-fix bytes of five all-compressing files.
- chunked_write skipped_lzf_chunks_are_masked_in_every_index (fails before:
mask 0, want 2).
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
