A message shared through the file's SOHM heap (H5Pset_shared_mesg_index)
is referenced by heap ID, which needs the SOHM table from the superblock
extension. Only message_data_with_sohm (used for fill values) loaded it;
resolve_shared_message passed no table, so a SOHM-shared datatype,
dataspace, filter pipeline or attribute failed with "invalid shared
message version: 2" and the dataset or attribute could not be read.
resolve_shared_message now loads the table when the reference carries a
heap ID.
Found while making attrs() tolerant: SOHM attributes turned from an
error into missing keys in the audit read matrix. With this fix all 36
SOHM cases there match h5py (datasets, fill values and attributes, every
shareable message type, libver earliest and latest).
Regression test: sohm_shared_messages_resolve (h5py writes files sharing
each message type on its own and all of them; values and attributes
checked).
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
A version-1 shared message reference is version, type, six reserved bytes
and then an old-style symbol table entry: link-name offset (length size),
object header address, cache type, reserved, scratch. We read the address
straight after the reserved bytes, i.e. the link-name offset, and the
committed datatype lookup failed with InvalidObjectHeaderVersion (the bytes
checked in tcompound.h5: name offset 0x10, then 0x590 = /type1). Datasets
of 1.4/1.6-era files that use a committed datatype were unreadable.
Skip the name offset. parse_shared_ref has no length size, so add
parse_shared_ref_sized and use it in every internal caller;
parse_shared_ref keeps its signature and assumes length size == offset
size. The old parse_v1_ref unit test encoded the wrong layout and now uses
the real bytes.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
dataset_fill_value treated a shared Fill Value message as "no fill
value", so unwritten storage of a dataset whose fill value lives in the
file's shared-message (SOHM) heap read as zeros rather than its fill
value. libhdf5 shares fill values whenever the file has a SOHM index for
them.
- fill_value::dataset_fill_value_in follows the reference (another object
header, or the SOHM heap); read_full_with_fill and the facade's
selection read use it.
- dataset_fill_value, which has no file to follow a reference into, now
returns UnresolvedSharedMessage for a shared message instead of None.
- shared_message::load_sohm_table / message_data_with_sohm load the SOHM
table from the superblock extension on demand.
- parse_sohm_table skipped each index's leading version byte, reading
every field one byte off; SOHM references could never resolve.
Fixture shared_fill_value.h5 (HDF5 2.0, gen_shared_fill.py): sohm_b read
[0,1,2,3,0,0,0,0] and now reads [0,1,2,3,-7,-7,-7,-7], as h5py does.
Co-Authored-By: Claude Opus 5.5 (1M context) <[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]>
osobh