read_raw_data_selection computed which chunks a selection intersects, threw
the answer away, decoded the entire dataset and picked elements out of it —
for contiguous layouts too. A 64x64 window of a 64 MB deflate dataset cost
105 ms, about half a full read; every selection cost the same whatever its
size.
New partial_read module: materialise only the selection's bounding box — the
overlapping rows of a contiguous dataset (straight from the file bytes) or the
overlapping chunks (only those are decompressed) — then run the existing
extractor over that buffer with the selection translated to the box origin, so
extraction semantics are exactly the full-read ones. It declines (falling back
to the old path) for All/None, compact/virtual/storage-less layouts, and boxes
covering more than half the dataset. That window now takes 0.39 ms, one row
2.7 ms, one column 5.2 ms.
Selections are validated against the dataset shape first. They were not: a
hyperslab past an edge came back padded with zeros and a point with an
out-of-range column wrapped into the next row, returning the wrong element
with no error. Now FormatError::SelectionOutOfBounds (also rank mismatch and
overlapping blocks); the facade's fill-aware path validates too.
Tests: equivalence against a reference extraction from a full read over 60
random hyperslabs/point lists per layout (contiguous, chunked, deflate) for
ranks 1-3. New read_harness bench binary with before/after in BENCHMARKS.md.
Co-Authored-By: Claude Fable 5.1 <[email protected]>
- Path resolution follows soft links in both old-style (symbol table, cache
type 2) and new-style (compact and dense Link message) groups: absolute and
relative targets, links to groups, links through links, with a depth limit
so a link cycle is NestingDepthExceeded rather than a hang. A dangling link
reports the target it could not find. Previously every soft link was
PathNotFound.
- An external link is FormatError::ExternalLinkUnsupported { filename,
object_path } instead of a misleading PathNotFound.
- Message 0x0007 (External Data Files) is now a known MessageType, and a
dataset carrying it is FormatError::ExternalDataFilesUnsupported. Such a
dataset has no data address in this file, so it would otherwise be read as
"never written" and answered with fill values — wrong data, no error.
- Dense link iteration is shared between hard-link listing and the new
symbolic-link lookup; entry listing behaviour is unchanged.
- h5py interop test for both libver settings.
Co-Authored-By: Claude Fable 5.1 <[email protected]>
A dataset created from a committed (named) datatype stores only a shared-
message reference to it. The facade parsed those reference bytes as the
datatype itself, producing `Time { size: 0 }` and unreadable data, and an
attribute using a committed datatype was silently dropped.
- shared_message::parse_shared_ref had the encoding wrong: it skipped six
reserved bytes for version 2 (only version 1 has them) and had the version 3
types inverted (1 is the SOHM heap, 2 is "committed, in another object
header"). Verified against h5py 3.16 / HDF5 2.0, which writes
`02 02 <address>` under both default and latest libver bounds. Resolution
now dispatches on which field the reference carries.
- New shared_message::message_data resolves a header message through the
indirection; the reader, lazy and mmap facades use it for datatype,
dataspace and filter-pipeline messages.
- AttributeMessage honours the v2/v3 flags (bit 0 datatype shared, bit 1
dataspace shared) via the new parse_in_file, used everywhere file data is
available. Parsing a shared attribute without file access is now
FormatError::UnresolvedSharedMessage instead of a garbage datatype.
- h5py interop test covering both libver settings.
Co-Authored-By: Claude Fable 5.1 <[email protected]>
