Final-review fixes for Plan 2 (fit-rewriter). Every failure mode below now
surfaces as FitFormatError so Plan 3 can classify invalid FIT input as a
non-retryable activity error (spec 10.4).
- Range-check numeric values against the field's declared size before
struct.pack, so an oversized serial number or a 1-byte product field
raises FitFormatError instead of leaking a raw struct.error.
- Reject zero-size field definitions during parsing. A zero-size
device_info field 0 read back as device_index == 0 via
int.from_bytes(b"", ...), which could have let a paired sensor be
rewritten as an Edge 1030 Plus (spec 10.2).
- Add DeviceFieldValue.is_creator so callers can tell the creator
device_info record from sensor records instead of silently keeping
whichever record appeared last.
- Implement the missing spec 10.4 post-patch step: read the patched
buffer back and verify file_id 1/2/8 and creator device_info 2/4/27
hold the target values. A field that could not be written (e.g. a
product_name field too small for the target string) now fails the whole
conversion rather than producing a silent partial patch. Verification
runs before the output is written, so a half-rewritten file never lands
on disk.
- Use the field's actual endianness in _read_field_value's fallback path.
- Add curated re-exports in app/fit/__init__.py for Plan 3.
- Document _iter_data_fields' caller invariant (validate the container
first; end_offset is not clamped).
- Extend the preservation fixture with a product_name string field so the
zero-filling string write path is covered by the byte-preservation
proof, and test convert_fit_device against a 12-byte header.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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