MqttSubscriptionManager is the P1 plain-MQTT ingest path: it holds the authored
RawPath → MqttTagDefinition table behind the shared EquipmentTagRefResolver,
establishes one SUBSCRIBE per distinct authored topic, and turns each inbound
message into a LastValueCache update plus an OnDataChange notification.
Load-bearing choices, each pinned by a falsified test:
- The published reference IS the RawPath (def.Name), never the topic and never
the TagConfig blob — DriverHostActor's dual-namespace fan-out is RawPath-keyed,
so any other key passes every unit test and delivers nothing in production.
- One message fans out to EVERY tag on its topic; several tags routinely share a
topic with different jsonPaths, and stopping at the first match silently starves
the rest.
- An unauthored topic raises nothing: MQTT ingest never auto-provisions.
- Wildcard-authored topics (accepted by the parser, warned at deploy) match via
MQTTnet's own MqttTopicFilterComparer, so '+'/'#' behave as a broker would.
Concrete topics stay a single lookup; the wildcard scan runs only when one exists.
- Retained seeds are honoured natively on MQTT 5.0 (retain handling) AND filtered
client-side on the retain flag, because 3.1.1 brokers always replay.
- Nothing throws on MQTTnet's dispatcher thread: a malformed payload degrades that
tag (BadDecodingError / BadTypeMismatch), and a throwing OnDataChange subscriber
is contained without starving the tags behind it.
- The manager issues the FIRST subscribe itself — Reconnected deliberately does not
fire after the initial ConnectAsync.
- Reconnect re-subscribe: total failure THROWS (MqttConnection then tears the
session down and retries under backoff, rather than serving a connected-but-deaf
driver); a partial SUBACK rejection degrades only the denied refs, because
retrying forever over one ACL-denied topic would take every tag dark.
MqttConnection gains a MessageReceived observer (fired on the dispatcher, throwing
observers contained) and a bounded SubscribeAsync under its own linked-CTS deadline
— deliberately not MqttClientOptions.Timeout, which already governs every MQTTnet
op. A refused filter is an outcome, not an exception; only the SUBSCRIBE itself
failing throws. Classify() is parameterised by operation name (messages unchanged
for connect).
JSONPath is a documented subset ($, $.a.b, $['a'], $.a[0]); filters/slices/
recursive descent report a miss rather than pulling in a JSONPath package for an
expression form that selects a set where a tag needs one scalar.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Joseph Doherty
d421487bcd