osobhandClaude Opus 5.5 57e938c438 fix(format): honour unknown-message flags the way libhdf5 does ...

The object header parser failed on an unknown message with flag bit 3
set and ignored bit 7. Per the spec, bit 3 means "fail if unknown and
the file is opened for writing" and bit 7 "fail if unknown, always".
The parser only reads, so it now ignores bit 3 (as libhdf5 does for a
read-only open) and refuses bit 7, in v1 headers, v2 headers and their
continuation chunks.

On libhdf5's conformance file tbogus.h5 (added as a fixture) we used to
refuse Dataset2 and open Dataset3; we now match libhdf5: Dataset1, 2, 4
and 5 open, Dataset3 is refused.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

2026-09-25 21:14:30 -05:00

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