Decodes Sparkplug-B wire bytes into a driver-side projection (SparkplugPayload /
SparkplugMetric / SparkplugValueKind) for the Task 21 ingest state machine.
- Never throws, for ANY input. It sits on MQTTnet's shared dispatcher thread, so
an escaping exception would stall delivery for every subscription on the
connection, not one tag. Garbage, truncation, zero-length, a valid protobuf of
another schema and an over-nested Template all resolve to a verdict.
- Zero-length input is INVALID, not "a payload with no metrics" — protobuf would
parse it as all-defaults, and that is how a truncated-to-nothing body gets
mistaken for a well-formed one.
- Explicit presence throughout (Has{Seq,Name,Alias,Datatype,Timestamp}), never a
zero-check: an NBIRTH legitimately carries seq = 0, and every DATA metric after
a birth carries an alias with no name and no datatype.
- Values are projected RAW, boxed, with the value oneof reported as an explicit
ValueKind — Absent / Null / Scalar / Unsupported all mean different things and
three of them carry a null value. DataSet/Template/extension decode as
Unsupported (v1 scope) rather than throwing or silently vanishing.
- ReinterpretSigned() undoes Sparkplug's two's-complement-in-an-unsigned-field
encoding of Int8/16/32/64. Kept out of decode because a DATA metric carries no
datatype — only the consumer, holding the birth's alias table, knows which
applies. Skipping it publishes 4294967254 for a tag whose value is -42.
- Datatype is carried as the generated Org.Eclipse.Tahu.Protobuf.DataType; the
SparkplugDataType map is Task 17's and is applied downstream (Task 21).
Golden vectors: nbirth.bin (seq=0, named/aliased catalog, a negative Int32, an
is_null metric, a DataSet metric) + ndata.bin (alias-only metrics, no name, no
datatype) are hand-built by SparkplugGoldenPayloads, committed, and pinned by a
drift guard that rebuilds and byte-compares them on every run — plus a test that
they actually reach the output directory, since a missing copy item is invisible
in source.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
MQTT has no discovery protocol, so the AdminUI address picker learns the topic
space the only way there is: subscribe to the wildcard and accumulate what
arrives. MqttBrowseSession serves that observation as a segment tree (split on
'/'); MqttDriverBrowser opens it with a distinct "{clientId}-browse-{guid8}"
identity under a 5-30 s clamped budget.
Browsing publishes NOTHING - the load-bearing safety property, since the picker
runs against a live plant broker. Every outbound message must route through the
single PublishAsync seam that counts into PublishCountForTest; P2's operator-
triggered Sparkplug rebirth is the one intended exception. Sparkplug mode fails
fast rather than serving a raw spBv1.0 topic tree that looks like a metric tree.
Deviation from the plan's ref list: the project also references .Driver so the
browse CONNECT reuses MqttConnection.BuildClientOptions (TLS posture, CA-pin
chain validator, credentials). A second copy would be a security divergence.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Joseph Doherty