The chunk-size ceiling, measured on UM20147 with every size checked
byte-for-byte against a known-good download:
1024 / 2048 / 4096 / 8192 / 16384 -> served in full
32768 / 65535 -> SILENTLY CLAMPED to 16384
The clamp is the important part: a 32,768 B request returns 16,384 B of perfectly
good data and no error. Nothing in the response says it was truncated; the
length is the only signal.
THAT DICTATES HOW THE LOOP MUST BE WRITTEN. read_event_file() now tracks its
offset by BYTES RECEIVED rather than striding by chunk index. A fixed stride
would either fail on a clamp or skip the bytes it never collected; tracking what
actually arrived makes a clamp cost one extra request, and makes the loop
self-correcting against any short response -- precisely the failure mode that has
bitten the Series III side repeatedly.
Consequence of that change, recorded because it reverses an earlier decision: a
short chunk is NO LONGER AN ERROR. It used to raise, on the principle that a
silently short event is this codebase's recurring bug. But the device returns
short legitimately, and the real protection is the offset arithmetic plus the
final total-length check -- which still raises on a genuinely truncated event.
The test was rewritten rather than deleted, and says why.
CHUNK_SIZE = 16384. For UM20147's events: 4,796 B goes 5 requests -> 1,
30,230 B goes 30 -> 2, and 72,560 B goes 71 -> 5. Over cellular at ~0.65 s per
round trip that is ~46 s -> ~3.2 s on the large one.
Measured on one unit over USB, so THOR_CHUNK_SIZE = 1024 stays available and the
replay tests pin it -- reproducing THOR's exact traffic is one argument away, and
client.download_event()/get_event() take chunk_size for a link where large
responses are not surviving.
Full suite: 472 passed, 16 pre-existing failures unchanged.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ru8Lg9HkkYvX9VWWo65SmL
serversdownandClaude Opus 5
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