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The pre-insert MQTT probe added in 0.2.4.2 (b51598ea) had two bugs that
compounded on P1S firmware specifically:
1. Fixed 2-second sleep was too short. P1S broker + TLS handshake
routinely needs 3-5s to surface CONNACK on a cold MQTT session (same
firmware family with the documented "broker stops publishing but TCP
stays alive" quirk at bambu_mqtt.py:3181), so the probe falsely rejected
a printer that would have connected fine. H2C's broker is snappier and
cleared the 2s window without trouble — which is why the reporter's
H2C added without issue and only the P1S misbehaved.
2. client.disconnect() ran synchronously on the asyncio thread.
BambuMQTTClient.disconnect() ends in paho's loop_stop() which joins
the network thread; if that thread was still mid-TLS-handshake to the
slow P1S socket when teardown ran, the join blocked the asyncio thread
for as long as the handshake took to complete or fail. POST /printers
wedged, every other HTTP request queued behind it, Docker healthcheck
timed out — user-visible symptom: "the container hangs."
Fix:
- Replace the fixed sleep with a polling loop (8s budget, 200ms tick,
early-returns the moment state.connected flips True). Slow brokers
get the headroom they need; happy-path connects still finish in
~1-2s. Constants exposed as PROBE_TIMEOUT_SECONDS / PROBE_POLL_
INTERVAL_SECONDS class attributes so tests can dial them down.
- Move client.disconnect() to await asyncio.to_thread(...) so paho's
thread-join can never block the event loop.
The empty-card-report-prevention goal of the original probe stays
intact: a genuinely wrong access code still results in connected=False
after the 8s budget, the 400 with code=printer_connection_failed
still fires, the row is still never persisted.